NDA Chemistry · Formula sheet
Acids, Bases and Salts formulas
2 formulas, 13 reference tables and 21 common traps for NDA Chemistry Acids, Bases and Salts, grouped by subtopic.
Acid-Base Theory, Oxides and Electrolytes
Learn this subtopic in the notesClassification of oxides: acidic, basic, neutral and amphoteric
| Type | Reacts with | Examples |
|---|---|---|
| Acidic oxide | Bases (forms a salt) | CO2, SO2, NO2 |
| Basic oxide | Acids (forms a salt) | Na2O, MgO, CaO |
| Neutral oxide | Neither acids nor bases | CO, N2O, NO, H2O CO (carbon monoxide) is the neutral oxide the bank loves — CO2 in contrast is acidic. |
| Amphoteric oxide | Both acids and bases | Al2O3, ZnO |
Non-metal oxides tend to be acidic; metal oxides tend to be basic; CO/N2O/NO are neutral; Al2O3/ZnO are amphoteric.
Electrolytes and electrical conductivity of solutions
| Substance in water | Conducts? | Reason |
|---|---|---|
| NaOH (sodium hydroxide) | Yes (basic solution) | Strong electrolyte — gives Na+ and OH- |
| NaCl, CuSO4 (salts) | Yes | Ionise fully into free ions |
| HCl (strong acid) | Yes | Ionises fully into H+ and Cl- |
| CH3COOH (acetic acid) | Weakly | Weak electrolyte — partial ionisation |
| Sugar | No | Non-electrolyte — dissolves as whole molecules, no ions Sugar is the classic non-conducting solution — it is covalent and produces no ions. |
| CH3OH (methanol) | No | Non-electrolyte — covalent, no ions |
The first mineral acid discovered
| Mineral acid | Formula | Note |
|---|---|---|
| Nitric acid | HNO3 | The first mineral acid discovered Nitric acid is the bank's answer for 'first mineral acid discovered'. |
| Hydrochloric acid | HCl | Mineral acid — discovered later |
| Sulphuric acid | H2SO4 | 'King of chemicals', dibasic |
| Phosphoric acid | H3PO4 | Tribasic mineral acid |
Common traps
Match the definition to the right concept
'Acids give H+ and bases give OH- in water' is the Arrhenius concept, not Bronsted-Lowry. Bronsted-Lowry is the proton-transfer (donor/acceptor) one; Lewis is the electron-pair one.
NH3 is a base, not an acid
In a 'how many are Lewis acids?' list, NH3 is the base — its nitrogen lone pair is donated. AlCl3, BF3 and FeCl3 are the Lewis acids (all electron-pair acceptors).
Tribasic = phosphoric acid
Among HCl, HNO3, H2SO4 and H3PO4, the tribasic one is phosphoric acid (H3PO4) — three replaceable H+. HCl and HNO3 are monobasic; H2SO4 is dibasic.
CO is neutral, CO2 is acidic
Carbon monoxide (CO) is a neutral oxide — it forms no salt with acids or bases. Do not confuse it with CO2, which is acidic (it forms carbonic acid / carbonates).
Sugar dissolves but does not ionise
Sugar dissolves freely in water, but it dissolves as neutral molecules, not ions — so its solution does not conduct electricity. Salts, strong acids and strong bases all produce ions and DO conduct.
Common Acids — Names, Formulas, Sources and Uses
Learn this subtopic in the notesAcid reactions: nitric acid with metals, and carbonates with HCl
Dilute nitric acid with copper
Natural acids and their sources
| Source | Acid present |
|---|---|
| Bee sting / Nettle sting / Ant | Methanoic acid (formic acid) Bee, nettle and ant stings all inject methanoic (formic) acid — the cause of the burning pain. |
| Vinegar | Ethanoic acid (acetic acid) |
| Curd / Sour milk | Lactic acid |
| Lemon, orange (citrus) | Citric acid |
| Tamarind, grapes | Tartaric acid |
| Tomato, spinach | Oxalic acid For 'acid in tomatoes', the NCERT-listed answer is oxalic acid (not citric, which is not offered in the bank's options). |
Mineral acids and their uses
| Acid | Principal use |
|---|---|
| Hydrofluoric acid (HF) | Etching glass (attacks SiO2) HF is stored in plastic, not glass, because it dissolves glass — hence its use in etching. |
| Dilute nitric acid (HNO3) | Cleaning gold and silver articles (goldsmith) Goldsmiths use dilute HNO3 — it removes base-metal impurities but leaves the noble metal. |
| Sulphuric acid (H2SO4) | Fertilisers, batteries, industry ('king of chemicals') |
| Hydrochloric acid (HCl) | Cleaning metal surfaces (pickling), lab reagent |
Naming oxy-acids: hypo-, -ous, -ic, per-
| Name | Formula | Oxygen count |
|---|---|---|
| Hypobromous acid | HOBr (HBrO) | Lowest (hypo...ous) The 'hypo-' prefix marks the lowest oxidation state — hypobromous acid is HOBr, not HBr. |
| Bromous acid | HBrO2 | Low (...ous) |
| Bromic acid | HBrO3 | High (...ic) |
| Perbromic acid | HBrO4 | Highest (per...ic) |
Common traps
Bee and nettle stings = methanoic acid, not acetic
The acid in a bee or nettle sting is methanoic acid (formic acid, HCOOH), NOT ethanoic (acetic) acid. Ethanoic acid is the one in vinegar.
Tomato = oxalic acid (in the bank)
Biochemically tomatoes are richest in citric acid, but when citric acid is not an option the NCERT-expected answer for tomato is oxalic acid. Tamarind is the tartaric-acid one — do not swap them.
Glass etching = hydrofluoric acid only
Only hydrofluoric acid (HF) etches glass, because it reacts with the silica (SiO2) in glass. The other mineral acids do not attack glass — that is why they can be stored in glass bottles.
Hypobromous acid is HOBr, not HBr
HBr is hydrobromic acid (no oxygen). Hypobromous acid is the oxy-acid HOBr — the 'hypo...ous' name always means an oxy-acid with the fewest oxygens, never the binary hydracid.
Quick lime has no carbonate, so no CO2
Limestone, chalk and marble are all CaCO3 and fizz CO2 with HCl. Quick lime is CaO — an oxide with no carbonate group — so it gives no CO2 (only CaCl2 and water).
Dilute HNO3 gives NO, concentrated gives NO2
With copper, dilute nitric acid produces NO, while concentrated nitric acid produces NO2. The concentration, not the metal, decides which oxide of nitrogen forms.
The pH Scale and Common Substances
Learn this subtopic in the notesWhat the pH scale measures
Definition of pH
- hydrogen-ion concentration (mol/L)
pH values of common substances
| Substance | Approx. pH | Nature |
|---|---|---|
| Gastric juice | 1.5–2 | Strongly acidic — highest H+ Gastric juice has the lowest pH and therefore the highest H+ concentration of the common options. |
| Lemon juice | 2–3 | Acidic |
| Pure water | 7 | Neutral |
| Human body / blood | 7.0–7.8 | Slightly basic (narrow range) The human body operates in the pH range 7.0–7.8 — the bank's answer. |
| Milk of magnesia | 10 | Basic (antacid) Milk of magnesia (magnesium hydroxide) has pH about 10. |
| Sodium hydroxide solution | 13–14 | Strongly basic |
| Acid rain | below 5.6 | Acidic — rain turns acidic below pH 5.6 For rain to be called 'acid rain', its pH must fall below 5.6. |
Indicators and the acid-base nature of household items
| Item / indicator | Behaviour |
|---|---|
| Turmeric stain + soap then water | Yellow → reddish-brown → yellow Turmeric goes reddish-brown in alkaline soap and back to yellow when the soap is washed away. |
| Toothpaste | Basic (neutralises mouth acid) |
| FeCl3 solution | pH < 7 (acidic, by hydrolysis) FeCl3 = strong-acid + weak-base salt, so it hydrolyses to an acidic solution (pH < 7). |
| NaCl, KCl solution | pH ≈ 7 (neutral) |
| NaOH solution | Basic (pH > 7) |
Common traps
Higher H+ means LOWER pH
The statement 'the higher the hydrogen-ion concentration, the higher its pH' is NOT correct — it is the inverse. More H+ means a lower pH and a more acidic solution.
Acid rain threshold is pH 5.6, not 7
Normal rain is already slightly acidic (about pH 5.6) from dissolved CO2. Rain is only called acid rain when its pH falls BELOW 5.6 — not below 7.
FeCl3 is acidic, not neutral
FeCl3 looks like a simple chloride salt but its solution is acidic (pH < 7) — it is the salt of strong acid HCl and weak base Fe(OH)3, so it hydrolyses. NaCl and KCl, in contrast, are neutral.
Salts and Common Compounds
Learn this subtopic in the notesCommon names and formulas of salts
| Common name | Chemical name / formula |
|---|---|
| Washing soda | Sodium carbonate, Na2CO3·10H2OQ |
| Baking soda | Sodium bicarbonate, NaHCO3 |
| Bleaching powder | Calcium oxychloride, CaOCl2 |
| Gypsum | Calcium sulphate dihydrate, CaSO4·2H2O |
| Brine | Aqueous solution of NaCl (common salt) Brine is NaCl in water — not NaOH, NaHCO3 or Na2CO3. |
| Milk of magnesia | Magnesium hydroxide, Mg(OH)2 |
| Lime water | Calcium hydroxide solution, Ca(OH)2 Lime water is Ca(OH)2 — it does NOT represent calcium carbonate. Limestone, chalk and marble are the CaCO3 ones. |
Compounds manufactured from common salt
| Compound | Made from common salt? | Actual source |
|---|---|---|
| Washing soda (Na2CO3) | Yes | NaCl, via Solvay process |
| Baking soda (NaHCO3) | Yes | NaCl, via Solvay process |
| Bleaching powder | Yes | Chlorine (from NaCl) + slaked lime |
| Plaster of Paris | No | Gypsum (CaSO4·2H2O) Plaster of Paris is the trap — it is made from gypsum, NOT from common salt. |
Bleaching powder: formula, uses and properties
| Property / use | Detail |
|---|---|
| Chemical nature | Oxidising agent (NOT reducing) The bank's wrong statement is 'bleaching powder is a reducing agent' — it is an oxidising agent. |
| Use 1 | Bleaching wood pulp in paper factories |
| Use 2 | Bleaching linen and cotton in textiles |
| Use 3 | Disinfecting drinking water |
| Shared with DDT | Both contain chlorine Bleaching powder and DDT both contain chlorine — bleaching powder is inorganic, DDT is organic. |
Common traps
Lime water is Ca(OH)2, not CaCO3
Limestone, chalk and marble are all calcium carbonate (CaCO3). Lime water is the odd one out — it is a solution of calcium hydroxide, Ca(OH)2, and does NOT represent calcium carbonate.
Milk of magnesia = Mg(OH)2, not a carbonate
Milk of magnesia is magnesium hydroxide, Mg(OH)2 — an antacid base. It is not magnesium carbonate, bicarbonate or sulphate.
Plaster of Paris comes from gypsum, not salt
Washing soda, baking soda and bleaching powder all start from NaCl. Plaster of Paris is the exception — it is made by heating gypsum (CaSO4·2H2O), a calcium mineral, so it is NOT a product of common salt.
Bleaching powder oxidises, it does not reduce
The statement 'bleaching powder is used as a reducing agent' is NOT true — bleaching powder is an oxidising agent (it releases chlorine). Its bleaching and disinfecting actions are oxidation.
Bleaching powder and DDT share chlorine, not calcium
The correct shared fact is that both contain chlorine. They do NOT both contain calcium (DDT has none), and they are not both organic (bleaching powder is inorganic) or both inorganic (DDT is organic).
Water of Crystallization
Learn this subtopic in the notesWater of crystallization of common salts
| Salt | Formula | Water molecules |
|---|---|---|
| Blue vitriol (copper sulphate) | CuSO4·5H2O | 5 |
| Green vitriol (ferrous sulphate) | FeSO4·7H2O | 7 Ferrous sulphate crystal carries 7 water molecules. |
| Washing soda | Na2CO3·10H2O | 10 |
| Gypsum | CaSO4·2H2O | 2 |
| Mohr's salt | FeSO4·(NH4)2SO4·6H2O | 6 |
| Potassium permanganate | KMnO4 | 0 (none) KMnO4 has NO water of crystallization — the bank's answer for 'which salt has none'. |
Water of crystallization and colour
| Form | Colour | Cause |
|---|---|---|
| CuSO4·5H2O (hydrated) | Blue | Water of crystallization The blue colour of copper sulphate crystals is due to water — heat it out and it turns white. |
| CuSO4 (anhydrous, after heating) | White | Water removed |
Common traps
KMnO4 has no water of crystallization
Blue vitriol (5), washing soda (10) and Mohr's salt (6) are all hydrates. Potassium permanganate (KMnO4) is the one with no water of crystallization — there is no dot-water term in its formula.
Blue copper sulphate owes its colour to water
The blue of copper sulphate crystals is caused by the water of crystallization, not by oxygen, nitrogen or hydrogen. Heating drives the water off and the solid turns white.