CDS Chemistry · Chemistry in Everyday Life
Elements and Compounds in Everyday Use
What magnesium, calcium, strontium, barium and the noble gases do in life and industry, and the everyday uses of carbon dioxide, nitrogen and potassium nitrate.
Why this matters
Six CDS questions, each a use matched to a substance. Two of them pack several facts into one item (a four-element match-the-list and a three-statement check), so a single table of uses covers most of the page.
Concept 1 of 2: Uses of group 2 metals and noble gases
A handful of elements have one famous job each. Magnesium sits at the heart of chlorophyll, calcium makes muscles contract, strontium colours fireworks red, and barium sulphate shows the gut on an X-ray. Among the noble gases, xenon gives the bright flash in a camera.
Definition
The uses:
- Magnesium: the central atom of chlorophyll, so it traps sunlight in photosynthesis.
- Calcium: controls muscle contraction; also builds bones and teeth.
- Strontium: gives a crimson-red flame (fireworks, flares).
- Barium: barium sulphate is the X-ray contrast meal for the alimentary canal; barium salts give a green flame.
- Xenon: fills photographic flash tubes. Neon: red advertising signs. Argon: electric bulbs.
| Element | Use or property |
|---|---|
| Magnesium | Traps sunlight in chlorophyll |
| Calcium | Controls muscle contraction |
| Strontium | Red colour in flames |
| Barium | Sulphate used to X-ray the alimentary canal |
| Xenon | Bright flash in a photographer's flashgunQ |
| Neon | Red glow in advertising signs |
CDS 2016 (II) matched Mg, Ca, Sr and Ba to these four uses in one item.
Practice this concept4 quick reps
The same idea in a real exam question:
CDS · 2016 · CDS (II) 2016 — General Knowledge · Q26Moderate
Example 1 · Chemistry in Everyday Life · Common Chemicals and Their Uses
Match List-I with List-II and select the correct answer using the code given below the Lists :
Code :
| List-I (Element) | List-II (Property/Use) |
|---|---|
| A. Mg | 1. Gives red colour to flame |
| B. Ca | 2. Sulphate compound used in medicine to examine the alimentary canal of a patient |
| C. Sr | 3. Traps the energy of sunlight in photosynthesis |
| D. Ba | 4. Control of muscle contraction |
Strontium is red, barium is green
In flame colours and fireworks, strontium gives crimson red and barium gives green. CDS swaps the pair in match-the-list options.
Flash tubes use xenon, not neon
A photographic flash is xenon, which gives a near-white burst. Neon glows red and is used in signs; argon fills bulbs.
Magnesium, not iron, is in chlorophyll
Chlorophyll has magnesium at its centre. Iron is the central atom of haemoglobin in blood.
Concept 2 of 2: Everyday uses of carbon dioxide, nitrogen and potassium nitrate
These are the household-and-shop uses CDS asks about: the gas that makes drinks fizz, the gas in a crisp packet, the chemical in a fire extinguisher, and the salt that is a fertilizer, a gunpowder ingredient and a meat preservative all at once.
Definition
The uses:
- Carbon dioxide is dissolved under pressure to make soft drinks fizzy; it also forms a little carbonic acid.
- A soda-acid fire extinguisher holds sodium hydrogen carbonate solution and sulphuric acid; mixing them gives CO₂.
- Nitrogen is flushed into food packets to stop the food oxidising.
- Potassium nitrate is a fertilizer, the oxidiser in gunpowder, and a meat preservative (E252).
- Tooth decay starts when the mouth's pH falls below 5.5.
| Substance | Everyday use |
|---|---|
| Carbon dioxide | Makes soft drinks fizzyQ |
| Sodium hydrogen carbonate + sulphuric acid | Soda-acid fire extinguisher |
| Nitrogen | Flushed into food packets against oxidationQ CDS 2026 (I): this statement and 'tooth decay below pH 5.5' were correct; 'Mg > Fe > Zn' was the wrong one (zinc is above iron). |
| Potassium nitrate | Fertilizer, gunpowder, meat preservativeQ |
Practice this concept4 quick reps
The same idea in a real exam question:
CDS · 2023 · CDS (I) 2023 — General Knowledge · Q49Moderate
Example 2 · Chemistry in Everyday Life · Common Chemicals and Their Uses
What is the chemical composition of a soda-acid type fire extinguisher?
The extinguisher uses the hydrogen carbonate
Soda-acid extinguishers use sodium hydrogen carbonate with sulphuric acid. Sodium carbonate or sodium chloride in the options is wrong.
Zinc is above iron
The reactivity order is Mg > Zn > Fe. A statement with 'Mg > Fe > Zn' is the incorrect one.
Soft drinks hold carbon dioxide, not ammonia or phosgene
Fizz comes from CO₂ dissolved under pressure. NH₃, PH₃ and COCl₂ (phosgene) are toxic gases offered as distractors.
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (2)
Uses of group 2 metals and noble gases6 rows
| Element | Use or property |
|---|---|
| Magnesium | Traps sunlight in chlorophyll |
| Calcium | Controls muscle contraction |
| Strontium | Red colour in flames |
| Barium | Sulphate used to X-ray the alimentary canal |
| Xenon | Bright flash in a photographer's flashgunQ |
| Neon | Red glow in advertising signs |
CDS 2016 (II) matched Mg, Ca, Sr and Ba to these four uses in one item.
Everyday uses of carbon dioxide, nitrogen and potassium nitrate4 rows
| Substance | Everyday use |
|---|---|
| Carbon dioxide | Makes soft drinks fizzyQ |
| Sodium hydrogen carbonate + sulphuric acid | Soda-acid fire extinguisher |
| Nitrogen | Flushed into food packets against oxidationQ CDS 2026 (I): this statement and 'tooth decay below pH 5.5' were correct; 'Mg > Fe > Zn' was the wrong one (zinc is above iron). |
| Potassium nitrate | Fertilizer, gunpowder, meat preservativeQ |
Watch out for (6)
- Strontium is red, barium is green→ Uses of group 2 metals and noble gases
- Flash tubes use xenon, not neon→ Uses of group 2 metals and noble gases
- Magnesium, not iron, is in chlorophyll→ Uses of group 2 metals and noble gases
- The extinguisher uses the hydrogen carbonate→ Everyday uses of carbon dioxide, nitrogen and potassium nitrate
- Zinc is above iron→ Everyday uses of carbon dioxide, nitrogen and potassium nitrate
- Soft drinks hold carbon dioxide, not ammonia or phosgene→ Everyday uses of carbon dioxide, nitrogen and potassium nitrate
Test yourself on a real paper
Sit a past CDS paper, timed and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.