Science · Textbook solutions

Acids, Bases and Salts

Every textbook question in book order, plus the board's past questions. · 43 questions

Introduction

1 q

Question

Practice · 1

IT 2.1 Q1 $You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?$

2.1 Understanding the Chemical Properties of Acids and Bases

3 q

Questions

Practice · 3

IT 2.2 Q1 $Why should curd and sour substances not be kept in brass and copper vessels?$
IT 2.2 Q2 $Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?$
IT 2.2 Q3 $Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.$

2.2 What do all Acids and all Bases have in Common?

6 q

Questions

Practice · 6

IT 2.3 Q1 $Why do HCl, HNO₃, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?$
IT 2.3 Q2 $Why does an aqueous solution of an acid conduct electricity?$
IT 2.3 Q3 $Why does dry HCl gas not change the colour of the dry litmus paper?$
IT 2.3 Q4 $While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?$
IT 2.3 Q5 $How is the concentration of hydronium ions (H₃O⁺) affected when a solution of an acid is diluted?$
IT 2.3 Q6 $How is the concentration of hydroxide ions (OH⁻) affected when excess base is dissolved in a solution of sodium hydroxide?$

2.3 How Strong are Acid or Base Solutions?

4 q

Questions

Practice · 4

IT 2.4 Q1 $You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?$
IT 2.4 Q2 $What effect does the concentration of H⁺(aq) ions have on the nature of the solution?$
IT 2.4 Q3 $Do basic solutions also have H⁺(aq) ions? If yes, then why are these basic?$
IT 2.4 Q4 $Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?$

2.4 More about Salts

5 q

Questions

Practice · 5

IT 2.5 Q1 $What is the common name of the compound CaOCl₂?$
IT 2.5 Q2 $Name the substance which on treatment with chlorine yields bleaching powder.$
IT 2.5 Q3 $Name the sodium compound which is used for softening hard water.$
IT 2.5 Q4 $What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.$
IT 2.5 Q5 $Write an equation to show the reaction between Plaster of Paris and water.$

Exercises

24 q

Ex 2 Q1 $A solution turns red litmus blue, its pH is likely to be$
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Ex 2 Q2 $A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains$
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Ex 2 Q3 $10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount HCl solution (the same solution as before) required to neutralise it will be$
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Ex 2 Q4 $Which one of the following types of medicines is used for treating indigestion?$
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Ex 2 Q5 (a) $Write word equations and then balanced equations for the reaction taking place when — dilute sulphuric acid reacts with zinc granules.$
Ex 2 Q5 (b) $Write word equations and then balanced equations for the reaction taking place when — dilute hydrochloric acid reacts with magnesium ribbon.$
Ex 2 Q5 (c) $Write word equations and then balanced equations for the reaction taking place when — dilute sulphuric acid reacts with aluminium powder.$
Ex 2 Q5 (d) $Write word equations and then balanced equations for the reaction taking place when — dilute hydrochloric acid reacts with iron filings.$
Ex 2 Q6 $Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.$
Ex 2 Q7 $Why does distilled water not conduct electricity, whereas rain water does?$
Ex 2 Q8 $Why do acids not show acidic behaviour in the absence of water?$
Ex 2 Q9 (a) $Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is neutral?$
Ex 2 Q9 (b) $Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is strongly alkaline?$
Ex 2 Q9 (c) $Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is strongly acidic?$
Ex 2 Q9 (d) $Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is weakly acidic?$
Ex 2 Q9 (e) $Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is weakly alkaline?$
Ex 2 Q9 $Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Arrange the pH in increasing order of hydrogen-ion concentration.$
Ex 2 Q10 $Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH₃COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?$
Ex 2 Q11 $Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.$
Ex 2 Q12 (a) $A milkman adds a very small amount of baking soda to fresh milk. Why does he shift the pH of the fresh milk from 6 to slightly alkaline?$
Ex 2 Q12 (b) $A milkman adds a very small amount of baking soda to fresh milk. Why does this milk take a long time to set as curd?$
Ex 2 Q13 $Plaster of Paris should be stored in a moisture-proof container. Explain why?$
Ex 2 Q14 $What is a neutralisation reaction? Give two examples.$
Ex 2 Q15 $Give two important uses of washing soda and baking soda.$

What the board has asked from this chapter

Questions per paper · 63 papers · 2023 to 2026

2026

40 q

18 $To a small amount of copper oxide in a beaker, when we add dilute hydrochloric acid slowly with stirring, the change in the colour of the solution is due to the formation of :$
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Chemical Properties of Acids and Bases
17 $Tomato is a natural source of which acid ?$
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pH Scale and its Importance
17 $Tamarind is a natural source of which acid ?$
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Chemical Properties of Acids and Bases
18 $Which one of the following can be used as an acid-base indicator by a visually impaired (blind) student ?$
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Chemical Properties of Acids and Bases
18 $A metal carbonate reacts with a solution X which forms a salt, water and a gas Y. What are X and Y ?$
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Reactions with Metals and Carbonates
18 $Which of the following compounds is used for removing permanent hardness of water ?$
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Common Salt and Chemicals from It
18 $Rain water is called ‘acid rain’ when its :$
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pH Scale and its Importance
22 $In which case/cases will the bulb glow considering that all other connections of electric circuit are complete and working ?$
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Chemical Properties of Acids and Bases
19 $In the following diagram, if acetic acid of same concentration is taken in place of dilute sulphuric acid, then$
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Reactions with Metals and Carbonates
19 $An aqueous solution turns red litmus blue. Excess addition of which of the following solution would reverse the change ?$
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Neutralisation and Salt Formation

\mathrm{NaCl}

Option	Salt	Acid used	Base used	Nature of Salt
(A)	$\mathrm{NaCl}$	$\mathrm{HCl}$	$\mathrm{NaOH}$	Basic
(B)	$\mathrm{Na_2CO_3}$	$\mathrm{H_2CO_3}$	$\mathrm{NaOH}$	Neutral
(C)	$\mathrm{Na_2SO_4}$	$\mathrm{H_2SO_4}$	$\mathrm{NaOH}$	Acidic
(D)	$\mathrm{CH_3COONa}$	$\mathrm{CH_3COOH}$	$\mathrm{NaOH}$	Basic

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Neutralisation and Salt Formation

23 $\mathrm{NaOH}$
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Reactions with Metals and Carbonates
21 $The pH of the gastric juices released during digestion is :$
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pH Scale and its Importance
22 $Baking powder is a mixture of :$
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Common Salt and Chemicals from It
22 $Four solutions, namely fructose, ethanol, hydrochloric acid and sodium hydroxide filled in four separate beakers are connected one by one in an electric circuit with a bulb. The solutions in which the bulb will glow when current is passed are :$
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Chemical Properties of Acids and Bases
22 $The natural sources of oxalic acid, lactic acid and methanoic acid respectively are :$
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Chemical Properties of Acids and Bases
23 $Which one of the following chemicals is used in soda-acid fire-extinguishers ?$
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Common Salt and Chemicals from It
23 $How will you protect yourself from the heat generated while diluting a concentrated acid ?$
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Chemical Properties of Acids and Bases
27 (a) $\mathrm{HCl}$
Chemical Properties of Acids and Bases
25 $Define the following terms : (i) Olfactory indicator (ii) Water of crystallization$
Chemical Properties of Acids and Bases
25 $How is a universal indicator obtained ? How is the wide range of pH of solution tested by it ?$
pH Scale and its Importance
25 $Write the balanced chemical equation for the preparation of : (a) Sodium hydroxide by electrolysis of brine solution (b) Sodium carbonate$
Common Salt and Chemicals from It
25 $How is tooth decay related to pH ? How can it be prevented ?$
pH Scale and its Importance
25 $Write the preparation of Baking soda. How does it help in making cakes soft and spongy ?$
Common Salt and Chemicals from It
25 $Write the balanced chemical equations involved in the preparation of (a) Bleaching powder (b) Baking soda$
Common Salt and Chemicals from It
25 $(a) A compound ‘A’ is used in soda-lime fire-extinguisher and decomposes on heating to form compound ‘B’. Compound ‘B’ is used for removing permanent hardness of water. Identify ‘A’ and ‘B’. (b) Write chemical formula of Plaster of Paris. At what temperature gypsum is heated to obtain Plaster of Paris ?$
Common Salt and Chemicals from It
27 (b) $\mathrm{NaOH}$
Common Salt and Chemicals from It
25 $Why does one feels pain and irritation when stung by honey-bee ? Rubbing of baking soda on the stung area gives relief. How ?$
pH Scale and its Importance
27 (a) $Explain chlor-alkali process with chemical equation. Name the products formed at anode and cathode.$
Common Salt and Chemicals from It
27 (A) $(a) Give the chemical name and formula of Plaster of Paris. (b) Write the chemical equation of its preparation. (c) Give any two uses of it.$
Water of Crystallisation
27 (B) $(a) Name the acid present in ant’s sting. (b) Give reason : (i) While diluting an acid, it is recommended that the acid should be added to water. (ii) Baking soda is used as an antacid.$
Chemical Properties of Acids and Bases
27 (b) $Write the preparation of following compounds with balanced chemical equation : (i) Baking soda (ii) Bleaching powder (iii) Plaster of Paris$
Common Salt and Chemicals from It
The pH plays an important role in our daily life. Strength of acids and bases depends on the number of $\mathrm{H^+}$ ions and $\mathrm{OH^-}$ ions produced by these respectively. pH scale helps in predicting the strength of acids and bases by measuring hydrogen ion concentration in a solution.
28 (a) $What type of indicator is used to predict how strong an acid or base is ?$
pH Scale and its Importance
In the given diagram, when electricity is passed through an aqueous solution of a common salt, a substance ‘Z’ is produced, along with the evolution of gases ‘X’ and ‘Y’. When a burning matchstick is brought near the gas ‘Y’, it burns with a pop sound, whereas ‘X’ is used for disinfecting drinking water. When ‘X’ is passed through slaked lime, an insoluble substance ‘A’ is produced.
28 (a) $Write the names of the gases ‘X’ and ‘Y’.$
Common Salt and Chemicals from It
The pH plays an important role in our daily life. Strength of acids and bases depends on the number of $\mathrm{H^+}$ ions and $\mathrm{OH^-}$ ions produced by these respectively. pH scale helps in predicting the strength of acids and bases by measuring hydrogen ion concentration in a solution.
28 (b) $\mathrm{H^+}$
pH Scale and its Importance
In the given diagram, when electricity is passed through an aqueous solution of a common salt, a substance ‘Z’ is produced, along with the evolution of gases ‘X’ and ‘Y’. When a burning matchstick is brought near the gas ‘Y’, it burns with a pop sound, whereas ‘X’ is used for disinfecting drinking water. When ‘X’ is passed through slaked lime, an insoluble substance ‘A’ is produced.
28 (b) $Write the balanced chemical equation for the formation of substance ‘Z’.$
Common Salt and Chemicals from It
The pH plays an important role in our daily life. Strength of acids and bases depends on the number of $\mathrm{H^+}$ ions and $\mathrm{OH^-}$ ions produced by these respectively. pH scale helps in predicting the strength of acids and bases by measuring hydrogen ion concentration in a solution.
28 (c) $What are strong acids and weak acids ?$
pH Scale and its Importance
In the given diagram, when electricity is passed through an aqueous solution of a common salt, a substance ‘Z’ is produced, along with the evolution of gases ‘X’ and ‘Y’. When a burning matchstick is brought near the gas ‘Y’, it burns with a pop sound, whereas ‘X’ is used for disinfecting drinking water. When ‘X’ is passed through slaked lime, an insoluble substance ‘A’ is produced.
28 (c) (i) $\mathrm{CO_2}$
Common Salt and Chemicals from It
In the given diagram, when electricity is passed through an aqueous solution of a common salt, a substance ‘Z’ is produced, along with the evolution of gases ‘X’ and ‘Y’. When a burning matchstick is brought near the gas ‘Y’, it burns with a pop sound, whereas ‘X’ is used for disinfecting drinking water. When ‘X’ is passed through slaked lime, an insoluble substance ‘A’ is produced.
28 (c) (ii) $Identify the substance ‘A’ and write the balanced chemical equation of the reaction which takes place in its preparation.$
Common Salt and Chemicals from It
The pH plays an important role in our daily life. Strength of acids and bases depends on the number of $\mathrm{H^+}$ ions and $\mathrm{OH^-}$ ions produced by these respectively. pH scale helps in predicting the strength of acids and bases by measuring hydrogen ion concentration in a solution.
28 (c) OR $(i) Under what condition is rainwater called acid rain ? (ii) In the following acids, identify weak acids : Nitric acid, hydrochloric acid, acetic acid, sulphuric acid, formic acid.$
pH Scale and its Importance

2025

42 q

2 $The formula of washing soda is$
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Common Salt and Chemicals from It
2 $You have three aqueous solutions A, B and C as given below : A - Potassium nitrate B - Ammonium chloride C - Sodium carbonate The ascending order of the pH of these solutions is :$
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pH Scale and its Importance
2 $The warning sign shown in the given figure must invariably be displayed/pasted on the containers which contain hydroxide of :$
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Chemical Properties of Acids and Bases
2 $Which of the given option represents a family of salts ?$
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Neutralisation and Salt Formation
2 $In order to prepare dry hydrogen chloride gas in humid atmosphere the gas produced is passed through a guard tube (drying tube) which contains :$
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Chemical Properties of Acids and Bases
3 $A few pieces of granulated zinc are taken in a test tube and 2 mL of sodium hydroxide solution is added to it. When the contents are warmed, the product formed is :$
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Reactions with Metals and Carbonates
3 $The following table shows the pH values of four solutions A, B, C and D on a pH scale : The solutions A, B, C and D respectively are of a$
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pH Scale and its Importance
3 $The body of human beings works within the pH range of :$
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pH Scale and its Importance
3 $A common feature observed in the crystals of washing soda, copper sulphate, gypsum and ferrous sulphate is that all$
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Water of Crystallisation
3 $In one formula unit of salt ‘X’, seven molecules of water of crystallisation are present. The salt ‘X’ is :$
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Water of Crystallisation
3 $The chlorine produced during the electrolysis of brine solution is used in the manufacture of :$
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Common Salt and Chemicals from It
4 $Consider the following reactions : (i) Dilute hydrochloric acid reacts with sodium hydroxide. (ii) Magnesium oxide reacts with dilute hydrochloric acid. (iii) Carbon dioxide reacts with sodium hydroxide. It is found that in each case :$
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Neutralisation and Salt Formation
4 $A metal, ‘X’, on treatment with sodium hydroxide liberates a gas ‘G’. It also liberates the same gas, ‘G’ on treatment with dilute sulphuric acid. Based on above information, ‘X’ and ‘G’ respectively are$
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Reactions with Metals and Carbonates
5 $Tooth enamel is made up of calcium hydroxyapatite (a crystalline form of calcium phosphate). This chemical starts corroding in the mouth when the pH is :$
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pH Scale and its Importance
5 $When a mixture of baking soda and tartaric acid is heated (or mixed in water) a product ‘X’ is formed, which is responsible for making breads and cakes soft and spongy. The product ‘X’ is$
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Common Salt and Chemicals from It
6 $The nature of aqueous solution of potassium nitrate is :$
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pH Scale and its Importance
6 $Juice of tamarind turns blue litmus to red. It is because of the presence of a chemical compound called$
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Chemical Properties of Acids and Bases
7 $The water of crystallization is present in (i) Bleaching Powder (ii) Plaster of Paris (iii) Washing Soda (iv) Baking Soda$
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Water of Crystallisation
Question Nos. 17 to 20 consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option (a), (b), (c) and (d) as given below :
18 $Assertion (A) : Concentrated nitric acid is diluted by adding water slowly to acid with constant stirring. Reason (R) : Concentrated nitric acid is easily soluble in water.$
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Chemical Properties of Acids and Bases
22 $Giving reason, state the advantage of using baking powder over baking soda for the preparation of bread or cakes.$
Common Salt and Chemicals from It
22 $A chemical compound ‘X’ is used to bleach washed clothes in laundry as well as to make drinking water free from germs. Identify ‘X’. How is this compound represented ? Write the method of its preparation along with the chemical equation for the reaction that occurs.$
Common Salt and Chemicals from It
22 $\mathrm{HCl}$
Chemical Properties of Acids and Bases
27 $Write chemical formula of washing soda. How is it obtained from baking soda ? List two uses of washing soda.$
Common Salt and Chemicals from It
28 (a) $State the chemical property in each case on which the following uses of baking soda are based upon : (i) as an anti-acids (ii) as a constituent in making baking powder (iii) in soda-acid fire-extinguishers$
Common Salt and Chemicals from It
28 (a) $Common salt is an important raw material for various chemicals of daily use. State in brief the method of preparation of (i) Sodium hydroxide, and (ii) Sodium hydrogen carbonate from common salt. Write balanced chemical equations of the reactions that occur.$
Common Salt and Chemicals from It
28 (a) $In an experiment a student dipped pH papers in four different solutions A, B, C and D and reported his observation as given below : Solution A B C D Colour of pH paper Light green Blue Green Red (i) In which one of these solutions is the concentration of (1) hydrogen / hydronium ions; (2) hydroxyl ions maximum ? (ii) Give one example each of the two solutions identified in (i) above. (iii) What would be the pH of the resultant mixture obtained when these two solutions are mixed together in equal proportions ? Justify your answer.$
pH Scale and its Importance
28 (b) $(i) Name the gas liberated when an acid reacts with a metal. How is this gas tested ? (ii) Write the chemical equation for the reaction of zinc metal with (1) hydrochloric acid, and (2) sodium hydroxide Name the compound of zinc obtained in each case.$
Reactions with Metals and Carbonates
28 $Two substances ‘A’ and ‘B’ are burnt in air separately. For ‘A’, ashes are collected and dissolved in water to get solution ‘X’, while for ‘B’, fumes produced are passed through water to get solution ‘Y’. Both the solutions ‘X’ and ‘Y’ are then tested with pH paper. (a) If ‘X’ gives light blue colour and ‘Y’ gives orange colour to the pH paper, then write the nature and range of pH of ‘X’ and ‘Y’. (b) Which one of the two - A and B, is a metal ? Justify your answer.$
pH Scale and its Importance
28 (b) $Design an experimental set-up to demonstrate that “Alcohol and glucose contain hydrogen but are not categorised as acids”. Also give the reason to justify this fact.$
Chemical Properties of Acids and Bases
28 (b) $Write chemical equations to show what happens when an acid reacts with a (i) metal (ii) base and (iii) carbonate Write the name of the main product formed in each case.$
Chemical Properties of Acids and Bases
Acid-base indicators can be used to distinguish between an acid and a base. Universal indicator, a mixture of several indicators, shows different colours at different concentrations of acids and bases, thereby indicating their pH on the pH scale of 0 – 14. The pH of a solution is measured by pH paper, which is a paper impregnated with a universal indicator.
37 (a) $Solution P is a strong acid while solution Q is a strong base. On the pH scale, where would you place the solutions P and Q ?$
pH Scale and its Importance
Seawater contains many salts dissolved in it. Common salt is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt and is mined like coal. The common salt is an important raw material for chemicals of daily use.
37 (a) $Write balanced chemical equations to show the products formed during electrolysis of brine.$
Common Salt and Chemicals from It
Common salt is a very important chemical compound for our daily life. It’s chemical name is sodium chloride and it is used as a raw material in the manufacture of caustic soda, washing soda, baking soda etc. It is also used in the preservation of pickles, butter, meat etc.
37 (i) $Name the acid and the base from which common salt can be obtained.$
Neutralisation and Salt Formation
Common salt is a very important chemical compound for our daily life. It’s chemical name is sodium chloride and it is used as a raw material in the manufacture of caustic soda, washing soda, baking soda etc. It is also used in the preservation of pickles, butter, meat etc.
37 (ii) $State the nature (acidic/basic/neutral) of sodium chloride. Give reason for the justification for your answer.$
Neutralisation and Salt Formation
Seawater contains many salts dissolved in it. Common salt is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt and is mined like coal. The common salt is an important raw material for chemicals of daily use.
37 (b) $List two uses of any one product obtained during electrolysis of brine.$
Common Salt and Chemicals from It
Acid-base indicators can be used to distinguish between an acid and a base. Universal indicator, a mixture of several indicators, shows different colours at different concentrations of acids and bases, thereby indicating their pH on the pH scale of 0 – 14. The pH of a solution is measured by pH paper, which is a paper impregnated with a universal indicator.
37 (b) $A solution has a pH of 7. Name a compound you would use to (i) increase its pH, and (ii) decrease its pH.$
pH Scale and its Importance
Common salt is a very important chemical compound for our daily life. It’s chemical name is sodium chloride and it is used as a raw material in the manufacture of caustic soda, washing soda, baking soda etc. It is also used in the preservation of pickles, butter, meat etc.
37 (iii) (A) $What happens when electric current is passed through an aqueous solution of sodium chloride (called brine)? Name the products obtained along with the corresponding places in the electrolytic cell where each of these products is obtained.$
Common Salt and Chemicals from It
Seawater contains many salts dissolved in it. Common salt is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt and is mined like coal. The common salt is an important raw material for chemicals of daily use.
37 (c) (i) $A mild non-corrosive basic salt ‘A’, used for faster cooking, is strongly heated to produce a compound ‘B’, that is used for removing permanent hardness of water. Identify A and B and also write the equation for the reaction that occurs when A is heated.$
Common Salt and Chemicals from It
Acid-base indicators can be used to distinguish between an acid and a base. Universal indicator, a mixture of several indicators, shows different colours at different concentrations of acids and bases, thereby indicating their pH on the pH scale of 0 – 14. The pH of a solution is measured by pH paper, which is a paper impregnated with a universal indicator.
37 (c) (i) $When the pH of a solution is decreased from 4 to 2, what effect does it produce on its hydronium ion concentration ? State the colour change shown by the pH paper.$
pH Scale and its Importance
Acid-base indicators can be used to distinguish between an acid and a base. Universal indicator, a mixture of several indicators, shows different colours at different concentrations of acids and bases, thereby indicating their pH on the pH scale of 0 – 14. The pH of a solution is measured by pH paper, which is a paper impregnated with a universal indicator.
37 (c) (ii) $A person is feeling pain and irritation in the stomach due to indigestion. What could be the pH of the fluid in the stomach ? Write the common name of the medicines people use for remedy. Give the chemical name of “milk of magnesia” often used for this purpose.$
pH Scale and its Importance
Common salt is a very important chemical compound for our daily life. It’s chemical name is sodium chloride and it is used as a raw material in the manufacture of caustic soda, washing soda, baking soda etc. It is also used in the preservation of pickles, butter, meat etc.
37 (iii) (B) $How is washing soda obtained from sodium chloride? Give chemical equation of the reactions involved in the process.$
Common Salt and Chemicals from It
Seawater contains many salts dissolved in it. Common salt is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt and is mined like coal. The common salt is an important raw material for chemicals of daily use.
37 (c) (ii) $Define water of crystallisation. Give two examples of salts that have water of crystallisation.$
Water of Crystallisation

Solution	A	B	C	D
Colour of pH paper	Light green	Blue	Green	Red

2024

29 q

1 $When 2 mL of sodium hydroxide solution is added to few pieces of granulated zinc in a test tube and then warmed, the reaction that occurs can be written in the form of a balanced chemical equation as :$
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Reactions with Metals and Carbonates
2 $An aqueous solution of a salt turns blue litmus to red. The salt could be the one obtained by the reaction of :$
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Neutralisation and Salt Formation
2 $Select a pair of natural indicator from the following :$
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Chemical Properties of Acids and Bases
2 $Juice of tamarind turns blue litmus to red. It is because of the presence of an acid called :$
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Chemical Properties of Acids and Bases
2 $The acid produced in our stomach during digestion and the base used to neutralise the excess acid during indigestion respectively are :$
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pH Scale and its Importance
3 $An aqueous solution ‘A’ turns phenolphthalein solution pink. When another aqueous solution ‘B’ is added to the pink solution, the pink colour disappears. Now when a few drops of solution ‘A’ are added to this reaction, the mixture appears pink again. The respective changes in the nature of the solution are from :$
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Chemical Properties of Acids and Bases
3 $A chemical compound used in glass, soap and paper industries is$
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Common Salt and Chemicals from It
3 $Four solutions, namely glucose, alcohol, hydrochloric acid and sulphuric acid filled in four separate beakers are connected one by one in an electric circuit with a bulb. The solutions in which the bulb will glow when current is passed are :$
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Chemical Properties of Acids and Bases
3 $The salt present in tooth enamel is :$
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pH Scale and its Importance
4 $An aqueous solution of sodium chloride is prepared in distilled water. The pH of this solution is :$
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pH Scale and its Importance
5 $\mathrm{FeSO_4}$
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Water of Crystallisation
6 $Tooth decay begins at the pH of :$
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pH Scale and its Importance
Q. 17 to 20 consists of two statements – Assertion (A) and Reason (R), answer these questions selecting the appropriate option given below :
17 $Assertion (A) : Oxides of metals show basic characters. Reason (R) : Oxides of metals react with acid to form salt and water.$
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Chemical Properties of Acids and Bases
21 (a) $1 gram of solid sodium chloride was taken in a clean and dry test tube and concentrated sulphuric acid was added to it. (i) Name the gas evolved in the reaction. (ii) What will be observed when this gas is tested with (I) dry, and (II) wet blue litmus paper ? Write your conclusion about the nature (acidic/basic) of this gas.$
Chemical Properties of Acids and Bases
21 (b) $Some metals react with acids to produce salt and hydrogen gas. Illustrate it with an example. How will you test the presence of this gas ?$
Reactions with Metals and Carbonates
27 $A small amount of copper oxide was taken in a beaker and dilute hydrochloric acid was added with continuous stirring of the solution. Name the compound formed and state the colour of its solution. Write balanced chemical equation for the reaction that occurs. Based on the reaction, state the nature (acidic/basic) of copper oxide.$
Chemical Properties of Acids and Bases
27 $\mathrm{CaSO_4 \cdot \frac{1}{2}\,H_2O}$
Water of Crystallisation
28 $(i) The pH of a sample of tomato juice is 4.6. How is this juice likely to be in taste ? Give reason to justify your answer. (ii) How do we differentiate between a strong acid and a weak base in terms of ion-formation in aqueous solutions ? (iii) The acid rain can make the survival of aquatic animals difficult. How ?$
pH Scale and its Importance
32 $A compound which is prepared from gypsum has the property of hardening when water is mixed in right quantity with it : (i) Write common name and the chemical name of this compound. (ii) Give chemical equation for its preparation. (iii) List its two uses.$
Common Salt and Chemicals from It
34 (a) $\mathrm{FeSO_4}$
Water of Crystallisation
34 (a) $\mathrm{H^+}$
pH Scale and its Importance
34 (a) $Explain chlor-alkali process and write balanced chemical equations for the reactions that occur. Name the gases obtained at the anode and cathode respectively. Mention two uses each of the two gases obtained in the above process.$
Common Salt and Chemicals from It
34 (b) $An acid ‘X’ present in tamarind when mixed with ‘Y’, produces a mixture ‘Z’. ‘Z’ on addition to a dough when heated makes cakes soft and spongy. ‘Y’ is prepared from common salt and helps in faster cooking. (i) Write the common names of ‘X’, ‘Y’ and ‘Z’, and the chemical formula of ‘Y’. (ii) How is ‘Y’ prepared and how does it help in making cakes soft and spongy ? Illustrate the reaction with suitable chemical equation. (iii) Write the name and chemical formula of a mild base other than ‘Y’ used as an antacid.$
Common Salt and Chemicals from It
34 (b) $Name and state in brief the process which is used to prepare sodium hydroxide from sodium chloride. In this process along with the main product two gases ‘X’ and ‘Y’ are also given off at the two electrodes. Name ‘X’ and ‘Y’ specifying the name of their respective electrode at which each gas is obtained. One of these gases when reacts with dry calcium hydroxide produces a compound ‘Z’ which is widely used in water treatment plants and textile industries. Name Z and write chemical equation for the reaction involved in its formation.$
Common Salt and Chemicals from It
34 (b) $Common salt is a very important raw material as many compounds of industrial use can be prepared from it. Explain, giving chemical equations, the method of preparation of washing soda from sodium chloride. List four industrial/domestic uses of washing soda.$
Common Salt and Chemicals from It
Salts play a very important role in our daily life. Sodium chloride which is known as common salt is used almost in every kitchen. Baking soda is also a salt used in faster cooking as well as in baking industry. The family of salts is classified on the basis of cations and anions present in them.
37 (a) $Identify the acid and base from which Sodium chloride is formed.$
Neutralisation and Salt Formation
Salts play a very important role in our daily life. Sodium chloride which is known as common salt is used almost in every kitchen. Baking soda is also a salt used in faster cooking as well as in baking industry. The family of salts is classified on the basis of cations and anions present in them.
37 (b) $Find the cation and the anion present in Calcium sulphate.$
Neutralisation and Salt Formation
Salts play a very important role in our daily life. Sodium chloride which is known as common salt is used almost in every kitchen. Baking soda is also a salt used in faster cooking as well as in baking industry. The family of salts is classified on the basis of cations and anions present in them.
37 (c) $“Sodium chloride and washing soda both belong to the same family of salts.” Justify this statement.$
Neutralisation and Salt Formation
Salts play a very important role in our daily life. Sodium chloride which is known as common salt is used almost in every kitchen. Baking soda is also a salt used in faster cooking as well as in baking industry. The family of salts is classified on the basis of cations and anions present in them.
37 (c) OR $Define the term pH scale. Name the salt obtained by the reaction of Potassium hydroxide and Sulphuric acid and give the pH value of its aqueous solution.$
pH Scale and its Importance

2023

44 q

1 $When Sodium bicarbonate reacts with dilute hydrochloric acid, the gas evolved is :$
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Reactions with Metals and Carbonates
1 $In the experimental setup given below, it is observed that on passing the gas produced in the reaction in the solution ‘X’ the solution ‘X’ first turns milky and then colourless. The option that justifies the above stated observation is that ‘X’ is aqueous calcium hydroxide and$
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Reactions with Metals and Carbonates
1 $Select a pair of olfactory indicators from the following :$
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Chemical Properties of Acids and Bases
2 $In the given experimental set-up, if the experiment is carried out separately with each of the following solutions the cases in which the bulb will glow is/are : (i) Dilute hydrochloric acid (ii) Dilute sulphuric acid (iii) Glucose solution (iv) Alcohol$
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Chemical Properties of Acids and Bases
2 $Select the correct option(s) in the following table : Option Natural Sources Acid present (i) Tamarind Tartaric acid (ii) Tomato Acetic acid (iii) Ant sting Oxalic acid (iv) Nettle sting Methanoic acid$
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Chemical Properties of Acids and Bases
2 $Few drops of aqueous solution of ammonium chloride are put on a universal indicator paper. The paper turns pink. Study the following table and choose the correct option.$
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pH Scale and its Importance
2 $A solution turns the colour of turmeric to reddish brown. If the same solution is poured on universal indictor, its colour would change to -$
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pH Scale and its Importance
4 $The table below has information regarding pH and the nature (acidic/basic) of four different solutions. Which one of the options in the table is correct ? Option Solution Colour of pH paper Approximate pH value Nature of solution (a) Lemon juice Orange 3 Basic (b) Milk of magnesia Blue 10 Basic (c) Gastric juice Red 6 Acidic (d) Pure water Yellow 7 Neutral$
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pH Scale and its Importance
4 $When zinc reacts with sodium hydroxide, the product formed is :$
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Reactions with Metals and Carbonates
4 $Fresh milk has a pH of 6. To delay its curdling, a chemical substance is added to it, which is :$
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Common Salt and Chemicals from It
4 $Acid present in tomato is :$
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pH Scale and its Importance
4 $There are four solutions A, B, C, and D with pH values as follows : Solution A B C D pH 2.0 7.0 8.0 12.0 Which solution(s) would liberate hydrogen gas with zinc ?$
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Reactions with Metals and Carbonates
4 $Two salts ‘X’ and ‘Y’ are dissolved in water separately. When phenolphthalein is added to these two solutions, the solution ‘X’ turns pink and the solution ‘Y’ does not show any change in colour, therefore ‘X’ and ‘Y’ are$
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Chemical Properties of Acids and Bases
4 $Which of the following gives the correct increasing order of acidic strength ?$
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pH Scale and its Importance
5 $Sodium hydroxide is termed an alkali while Ferric hydroxide is not because :$
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Chemical Properties of Acids and Bases
6 $Hydronium ions are formed by the reaction between :$
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Chemical Properties of Acids and Bases
6 $The name of the salt used to remove permanent hardness of water is :$
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Common Salt and Chemicals from It
6 $Select washing soda from the following :$
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Common Salt and Chemicals from It

Option	Natural Sources	Acid present
(i)	Tamarind	Tartaric acid
(ii)	Tomato	Acetic acid
(iii)	Ant sting	Oxalic acid
(iv)	Nettle sting	Methanoic acid

Option	Solution	Colour of pH paper	Approximate pH value	Nature of solution
(a)	Lemon juice	Orange	3	Basic
(b)	Milk of magnesia	Blue	10	Basic
(c)	Gastric juice	Red	6	Acidic
(d)	Pure water	Yellow	7	Neutral

Solution	A	B	C	D
pH	2.0	7.0	8.0	12.0

\mathrm{CH_3COOH}

	Salt	Parent acid	Parent base	Nature of salt
(a)	Sodium acetate	$\mathrm{CH_3COOH}$	NaOH	Neutral
(b)	Sodium carbonate	$\mathrm{H_2CO_3}$	NaOH	Basic
(c)	Sodium chloride	HCl	NaOH	Acidic
(d)	Sodium nitrate	$\mathrm{HNO_3}$	NaOH	Acidic

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Neutralisation and Salt Formation

Q. No. 17 to 20 are Assertion – Reasoning based questions. These consists of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below :
17 $Assertion (A) : It is advised that while diluting an acid one should add water to acid and not acid to water keeping the solution continuously stirred. Reason (R) : The process of dissolving an acid into water is highly exothermic.$
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Chemical Properties of Acids and Bases
21 (a) $On heating ‘X’ at 373 K, it loses water molecules and becomes ‘Y’. ‘Y’ is a substance which doctors use for supporting fractured bones in the right position. (i) Identify ‘X’ and ‘Y’. (ii) How can ‘X’ be reobtained from ‘Y’ ?$
Common Salt and Chemicals from It
21 (a) $(i) A compound ‘X’ which is prepared from gypsum has the property of hardening when mixed with proper quantity of water. Identify ‘X’ and write its chemical formula. (ii) State the difference in chemical composition between baking soda and baking powder.$
Common Salt and Chemicals from It
21 (A) $A student took a small amount of copper oxide in a conical flask and added dilute hydrochloric acid to it with constant stirring. He observed a change in colour of the solution. (i) Write the name of the compound formed and its colour. (ii) Write a balanced chemical equation for the reaction involved.$
Chemical Properties of Acids and Bases
21 (B) $The industrial process used for the manufacture of caustic soda involves electrolysis of an aqueous solution of compound ‘X’. In this process, two gases ‘Y’ and ‘Z’ are liberated. ‘Y’ is liberated at cathode and ‘Z’, which is liberated at anode, on treatment with dry slaked lime forms a compound ‘B’. Name X, Y, Z and B.$
Common Salt and Chemicals from It
21 (b) $Write balanced chemical equation for the reaction that occurs when : (i) blue coloured copper sulphate crystals are heated and (ii) Sodium hydrogen carbonate is heated during cooking.$
Water of Crystallisation
21 (b) $Two solutions M and N give Red and Blue colour respectively with a universal indicator. (i) In which solution will the hydrogen ion concentration be more ? Justify your answer. (ii) If both M and N solutions are mixed and the resultant mixture is tested with a universal indicator, it turns green. What is the nature of the salt formed ? Justify your answer.$
pH Scale and its Importance
24 $A knife which is used to cut a fruit was immediately dipped into water containing drops of blue litmus solution. If the colour of the solution is changed to red, what inference can be drawn about the nature of the fruit and why ?$
Chemical Properties of Acids and Bases
27 $A chemical compound X is used in glass, soap and paper industries. On treatment with ethanoic acid, it forms salt, water and carbon dioxide. (a) Identify X. (b) How is this compound obtained from brine ? Write the equations involved. (c) State the number of molecules of water of crystallization present in compound X.$
Common Salt and Chemicals from It
27 $(a) Write a balanced equation to show the reaction that occurs when a piece of aluminium is dipped in a dilute solution of (i) sulphuric acid and (ii) sodium hydroxide. (b) Write the colour of the solution formed when copper oxide is treated with hydrochloric acid. Give reason for this observation.$
Reactions with Metals and Carbonates
27 $\mathrm{YCl}$
pH Scale and its Importance
28 (a) $(i) What property do acids and bases have in common ? Explain it with an example. (ii) A compound which is prepared from gypsum has the property of hardening when mixed with water. Identify the compound and write its formula. How is this compound prepared ? Describe it in the form of a chemical equation only.$
Water of Crystallisation
28 $5{\cdot}5$
Common Salt and Chemicals from It
28 (a) $A substance ‘X’ is used as a building material and is insoluble in water. When it reacts with dil. HCl, it produces a gas which turns lime water milky. (i) Write the chemical name and formula of ‘X’. (ii) Write chemical equations for the chemical reactions involved in the above statements.$
Reactions with Metals and Carbonates
28 $\mathrm{HCl}$
Chemical Properties of Acids and Bases
28 $(a) Suggest one remedial measure each to counteract the change in pH in human beings in following cases : (i) Production of too much acid in stomach during indigestion (ii) Stung by a honey bee / nettle leaves (b) Fresh milk has a pH of 6. When it changes into curd will its pH increase or decrease ? Why ?$
pH Scale and its Importance
28 (b) $(i) Write the chemical name and Molecular formula of tooth enamel. (ii) How does it get corroded ? What is the preventive measure for this ?$
pH Scale and its Importance
28 (b) $A metal ‘M’ on reacting with dilute acid liberates a gas ‘G’. The same metal also liberates gas ‘G’ when reacts with a base. (i) Write the name of gas ‘G’. (ii) How will you test the presence of this gas ? (iii) Write chemical equations for the reactions of the metal with (1) an acid and (2) a base.$
Reactions with Metals and Carbonates
32 $(a) How is a universal indicator better than litmus solution ? (b) State two features of pH scale. (c) Why should we not add water to a concentrated acid ?$
pH Scale and its Importance
32 $(i) Why is acidified water considered to be a good conductor of electricity ? (ii) Write a chemical equation showing the ionic products formed on dissolving potassium hydroxide in water. (iii) Care must be taken while diluting concentrated nitric acid with water. Why ?$
Chemical Properties of Acids and Bases
32 $Write the chemical composition of tooth enamel. Under what conditions of pH it starts corroding ? Explain the reason of tooth decay and suggest one method to prevent it.$
pH Scale and its Importance
The teacher while conducting practicals in the laboratory divided the students into three groups and gave them various solutions to find out their pH and classify them into acidic, basic and neutral solutions. Group A – Lemon juice, vinegar, colourless aerated drink Group B – Tomato juice, coffee, ginger juice Group C – Sodium hydroxide, sodium chloride, lime water
37 (a) $For the solutions provided, which group is/are likely to have pH value (i) less than 7, and (ii) greater than 7 ?$
pH Scale and its Importance
The teacher while conducting practicals in the laboratory divided the students into three groups and gave them various solutions to find out their pH and classify them into acidic, basic and neutral solutions. Group A – Lemon juice, vinegar, colourless aerated drink Group B – Tomato juice, coffee, ginger juice Group C – Sodium hydroxide, sodium chloride, lime water
37 (b) $List two ways of determining pH of a solution$
pH Scale and its Importance
The teacher while conducting practicals in the laboratory divided the students into three groups and gave them various solutions to find out their pH and classify them into acidic, basic and neutral solutions. Group A – Lemon juice, vinegar, colourless aerated drink Group B – Tomato juice, coffee, ginger juice Group C – Sodium hydroxide, sodium chloride, lime water
37 (c) $Explain, why the sour substances such as lemon juice are effective in cleaning the tarnished copper vessels.$
Chemical Properties of Acids and Bases
The teacher while conducting practicals in the laboratory divided the students into three groups and gave them various solutions to find out their pH and classify them into acidic, basic and neutral solutions. Group A – Lemon juice, vinegar, colourless aerated drink Group B – Tomato juice, coffee, ginger juice Group C – Sodium hydroxide, sodium chloride, lime water
37 (c) OR $“pH has great importance in our daily life.” Justify this statement by giving two examples.$
pH Scale and its Importance

The 10 board questions to practise first

The questions and kinds of question the board asked most often come first. Each one says how often and when.

Question 1
Asked 4 times: 2023*, 2024*, 2025*, 2026 (* = numbers or wording changed that year) See all 4 times it was asked
23 $\mathrm{NaOH}$
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Question 2
Asked 3 times: 2023*, 2024*, 2026 (* = numbers or wording changed that year) See all 3 times it was asked
18 $To a small amount of copper oxide in a beaker, when we add dilute hydrochloric acid slowly with stirring, the change in the colour of the solution is due to the formation of :$
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Question 3
Asked 3 times: 2023*, 2024*, 2026 (* = numbers or wording changed that year) See all 3 times it was asked
22 $Four solutions, namely fructose, ethanol, hydrochloric acid and sodium hydroxide filled in four separate beakers are connected one by one in an electric circuit with a bulb. The solutions in which the bulb will glow when current is passed are :$
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Question 4
Asked 3 times: 2024*, 2025*, 2026 (* = numbers or wording changed that year) See all 3 times it was asked
17 $Tamarind is a natural source of which acid ?$
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Question 5
Asked 3 times: 2023*, 2024*, 2026 (* = numbers or wording changed that year) See all 3 times it was asked
27 (A) $(a) Give the chemical name and formula of Plaster of Paris. (b) Write the chemical equation of its preparation. (c) Give any two uses of it.$
Question 6
This type asked 3 times: 2023, 2025, 2026. This one: 2026 See all 3 of this type
27 (a) $\mathrm{HCl}$
Question 7
This type asked 3 times: 2023, 2024, 2026. This one: 2026 See all 3 of this type
25 $(a) A compound ‘A’ is used in soda-lime fire-extinguisher and decomposes on heating to form compound ‘B’. Compound ‘B’ is used for removing permanent hardness of water. Identify ‘A’ and ‘B’. (b) Write chemical formula of Plaster of Paris. At what temperature gypsum is heated to obtain Plaster of Paris ?$
Question 8
This type asked 3 times: 2023, 2025, 2026. This one: 2026 See all 3 of this type
23 $Which one of the following chemicals is used in soda-acid fire-extinguishers ?$
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Question 9
This type asked 3 times: 2024, 2025, 2026. This one: 2026 See all 3 of this type
19 $An aqueous solution turns red litmus blue. Excess addition of which of the following solution would reverse the change ?$
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Question 10
This type asked 3 times: 2023, 2024, 2026. This one: 2026 See all 3 of this type
21 $The pH of the gastric juices released during digestion is :$
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Quick revision

8 most-asked questions · 14 key points · 14 formulas · 5 diagrams

Checked against NCERT Science (CBSE Class 10), Chapter 2.

Most asked in board papers

1
pH in everyday life: tooth decay, antacids, bee and ant stings, acid rain, body pH, and the natural sources of acids
Asked 4 times: 2026, 2025, 2024, 2023 · 1 mark
2
Reactions of acids and bases: with metals (hydrogen, pop test), carbonates ( $\ce{CO2}$ turns lime water milky), metal oxides, neutralisation
Asked 4 times: 2026, 2025, 2024, 2023 · 1 mark
3
Indicators, ions in water and safety: olfactory and natural indicators, why acid solutions conduct, dry HCl, adding acid to water
Asked 4 times: 2026, 2025, 2024, 2023 · 1 mark
4
pH scale and strength: arrange solutions by pH, $\ce{H+}$ concentration, strong and weak acids, universal indicator
Asked 4 times: 2026, 2025, 2024, 2023 · 1 mark
5
Baking soda, baking powder and washing soda: preparation with equation, formula and uses
Asked 4 times: 2026, 2025, 2024, 2023 · 1 mark
6
Chlor-alkali process: products at anode and cathode, equation and uses; bleaching powder from chlorine
Asked 4 times: 2026, 2025, 2024, 2023
7
Salts: family of salts, parent acid and base, and whether a salt solution is acidic, basic or neutral
Asked 4 times: 2026, 2025, 2024, 2023 · 1 mark
8
Water of crystallisation and Plaster of Paris: define, examples, heating copper sulphate or gypsum, uses
Asked 4 times: 2026, 2025, 2024, 2023

Must-know points

Indicators: Acids turn blue litmus red; bases turn red litmus blue. Phenolphthalein turns pink in a base; methyl orange turns red in an acid; turmeric turns reddish brown in a base. Olfactory indicators (onion, vanilla essence, clove oil) change their odour in acidic or basic media: useful for a visually impaired student.
Acids with metals: Acid + metal gives salt + hydrogen gas. Test: bring a burning candle near the gas; it burns with a pop sound. Example: $\ce{Zn + H2SO4 -> ZnSO4 + H2}$ .
Bases with metals: Some metals react with a base too and give hydrogen, with a salt whose negative ion has the metal and oxygen: zinc and sodium hydroxide give sodium zincate, $\ce{Zn + 2NaOH -> Na2ZnO2 + H2}$ . Not every metal does this.
Carbonates and hydrogencarbonates with acids: Metal carbonate or hydrogencarbonate + acid gives salt + water + carbon dioxide. $\ce{CO2}$ turns lime water milky ( $\ce{CaCO3}$ forms); excess $\ce{CO2}$ makes it clear again (soluble $\ce{Ca(HCO3)2}$ ).
Neutralisation and oxides: The reaction between an acid and a base to give a salt and water is a neutralisation reaction. Metallic oxides are basic (CuO with HCl gives a blue-green solution of $\ce{CuCl2}$ ). Non-metallic oxides are acidic ( $\ce{CO2}$ with lime water).
Ions in water: Acids give $\ce{H+}$ ions in water, shown as $\ce{H+(aq)}$ or hydronium $\ce{H3O+}$ ; bases give $\ce{OH-}$ ions. So their solutions conduct electricity. Glucose and alcohol contain hydrogen but give no $\ce{H+}$ , so they are not acids. Dry HCl gas gives no $\ce{H+}$ without water. Bases soluble in water are alkalis.
Diluting an acid: Dissolving an acid or a base in water is highly exothermic. The acid must always be added slowly to water with constant stirring. Adding water to a concentrated acid can make the mixture splash out and the glass break.
pH scale and strength: pH runs from 0 (very acidic) to 14 (very alkaline); 7 is neutral. Higher the hydronium ion concentration, lower the pH. Acids that give more $\ce{H+}$ ions are strong (HCl); those that give fewer are weak (acetic acid). A universal indicator, a mixture of indicators, shows different colours at different pH.
pH in everyday life: Body: 7.0 to 7.8. Acid rain: pH below 5.6. Stomach makes HCl; excess is neutralised by antacids such as milk of magnesia. Tooth decay starts when mouth pH falls below 5.5: enamel (calcium hydroxyapatite) corrodes; basic toothpaste prevents it. Bee sting: rub baking soda. Nettle and ant stings inject methanoic acid.
Family of salts and pH of salts: Salts with the same positive or negative radical belong to a family (NaCl and $\ce{Na2SO4}$ : sodium salts; NaCl and KCl: chloride salts). Strong acid + strong base gives a neutral salt (pH 7, NaCl). Strong acid + weak base: acidic ( $\ce{NH4Cl}$ ). Weak acid + strong base: basic ( $\ce{Na2CO3}$ , $\ce{CH3COONa}$ ).
Chlor-alkali process: Electricity is passed through brine (aqueous NaCl). Chlorine at the anode, hydrogen at the cathode, sodium hydroxide near the cathode. Named for its products: chlor for chlorine, alkali for sodium hydroxide.
Bleaching powder: Made by the action of chlorine on dry slaked lime; written $\ce{CaOCl2}$ . Uses: bleaching cotton and linen, and wood pulp; bleaching washed clothes in laundry; an oxidising agent in industry; disinfecting drinking water.
Baking soda and washing soda: Baking soda $\ce{NaHCO3}$ : mild non-corrosive base; on heating gives $\ce{CO2}$ , which makes cakes soft and spongy. Baking powder = baking soda + tartaric acid. Also used in antacids and soda-acid fire extinguishers. Washing soda $\ce{Na2CO3.10H2O}$ : glass, soap and paper industries, borax, cleaning, removing permanent hardness of water.
Water of crystallisation and Plaster of Paris: The fixed number of water molecules in one formula unit of a salt: $\ce{CuSO4.5H2O}$ (blue, turns white on heating), $\ce{Na2CO3.10H2O}$ , gypsum $\ce{CaSO4.2H2O}$ , $\ce{FeSO4.7H2O}$ . Gypsum heated at 373 K gives Plaster of Paris, $\ce{CaSO4.1/2H2O}$ : used for fractured bones, toys, decoration. With water it sets back to hard gypsum.

Formulas

Acid and metal

\ce{Zn + H2SO4 -> ZnSO4 + H2 ^}

Zinc and sodium hydroxide

\ce{Zn + 2NaOH -> Na2ZnO2 + H2 ^}

Carbonate and hydrogencarbonate with acid

\begin{gathered}\ce{Na2CO3 + 2HCl -> 2NaCl + H2O + CO2} \\ \ce{NaHCO3 + HCl -> NaCl + H2O + CO2}\end{gathered}

Lime water test for CO2

\begin{gathered}\ce{Ca(OH)2 + CO2 -> CaCO3 v + H2O} \\ \ce{CaCO3 + H2O + CO2 -> Ca(HCO3)2}\end{gathered}

Neutralisation

\ce{NaOH + HCl -> NaCl + H2O}

Metal oxide with acid

\ce{CuO + 2HCl -> CuCl2 + H2O}

Chlor-alkali process

\ce{2NaCl(aq) + 2H2O(l) -> 2NaOH(aq) + Cl2(g) + H2(g)}

Bleaching powder

\ce{Ca(OH)2 + Cl2 -> CaOCl2 + H2O}

Baking soda (from brine)

\ce{NaCl + H2O + CO2 + NH3 -> NH4Cl + NaHCO3}

Heating baking soda

\ce{2NaHCO3 ->[heat] Na2CO3 + H2O + CO2}

Washing soda

\ce{Na2CO3 + 10H2O -> Na2CO3.10H2O}

Plaster of Paris from gypsum

\ce{CaSO4.2H2O ->[373 K] CaSO4.1/2H2O + 3/2H2O}

Plaster of Paris sets

\ce{CaSO4.1/2H2O + 3/2H2O -> CaSO4.2H2O}

Heating copper sulphate crystals

\ce{CuSO4.5H2O ->[heat] CuSO4 + 5H2O}

Diagrams to practise

Zinc with dilute sulphuric acid, testing hydrogen (Figure 2.1): label test tube with zinc granules and dilute H₂SO₄ · delivery tube · soap solution with bubbles · burning candle: pop sound
Carbon dioxide through lime water (Figure 2.2): label sodium carbonate with dilute HCl · delivery tube · calcium hydroxide solution · lime water turns milky
Acid solution conducts electricity (Figure 2.3): label beaker with dilute HCl · two nails fixed on a cork · bulb · 6 V battery and switch
Preparation of HCl gas (Figure 2.4): label solid NaCl with conc. H₂SO₄ · guard tube with calcium chloride · dry and moist blue litmus · HCl gas
Products of the chlor-alkali process (Figure 2.8): label brine · Cl₂ at anode, H₂ at cathode · NaOH near cathode · uses: bleaching powder, HCl, soaps, fuels

Mistakes that cost marks

Adding water to acid

Always add the acid to water, slowly, with stirring. The reverse heats the small amount of water so fast that acid splashes out.

Getting the pH order backwards

Lower pH means more

\ce{H+}

ions: pH 1 is more acidic than pH 4. Going from pH 4 to pH 2 makes the

\ce{H+}

concentration 100 times larger.

Mixing up the soda formulas

Baking soda is

\ce{NaHCO3}

(sodium hydrogencarbonate). Washing soda is

\ce{Na2CO3.10H2O}

. Plaster of Paris is

\ce{CaSO4.1/2H2O}

; gypsum is

\ce{CaSO4.2H2O}

. Bleaching powder (

\ce{CaOCl2}

) has no water of crystallisation.

Wrong natural acid

Vinegar: acetic acid. Orange, lemon: citric. Tamarind: tartaric. Tomato: oxalic. Curd (sour milk): lactic. Ant sting and nettle sting: methanoic acid.

Calling every salt neutral

Find the parent acid and base. NaCl and

\ce{KNO3}

are neutral;

\ce{NH4Cl}

is acidic (turns universal indicator pink or blue litmus red);

\ce{Na2CO3}

and

\ce{NaHCO3}

are basic.

Forgetting the anode and cathode in chlor-alkali

Chlorine forms at the anode, hydrogen at the cathode, and sodium hydroxide near the cathode. Balance it with 2NaCl and

\ce{2H2O}

Introduction

Question

2.1 Understanding the Chemical Properties of Acids and Bases

Questions

2.2 What do all Acids and all Bases have in Common?

Questions

2.3 How Strong are Acid or Base Solutions?

Questions

2.4 More about Salts

Questions

Exercises

What the board has asked from this chapter

2026

2025

2024

2023

The 10 board questions to practise first

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Most asked in board papers

Must-know points

Formulas

Diagrams to practise

Mistakes that cost marks