NDA Chemistry · Acids, Bases and Salts

Common Acids — Names, Formulas, Sources and Uses

The everyday acids the NDA tests by source (the acid in a bee sting, in tomatoes, in vinegar), by use (etching glass, cleaning gold), and by formula (naming the oxy-acids of a halogen).

All Acids, Bases and Salts notes NDA Chemistry strategy

Why this matters

The largest subtopic — eight PYQs, almost all single-fact recall. The bank repeats a tight set: natural acids and their sources, mineral acids and their industrial uses, the oxy-acid naming pattern, and two acid-reaction facts (which reaction gives NO gas, and which carbonate does NOT give CO2). Learn the source table and the two reaction traps and this subtopic is free marks.

Concept 1 of 4: Natural acids and their sources

Many foods and stings owe their sour taste or sting to a specific acid. The bank pairs each source to its acid — bee sting to formic acid, vinegar to acetic acid, curd to lactic acid. Learn the pairs both ways.

Definition

The source↔acid pairs the bank tests (these follow the NCERT natural-acid table):

Bee sting / Nettle sting / Ant sting → methanoic acid (formic acid, HCOOH).
Vinegar → ethanoic acid (acetic acid, CH3COOH).
Curd → lactic acid.
Lemon / Orange (citrus) → citric acid.
Tamarind / Grapes → tartaric acid.
Tomato / Spinach → oxalic acid (the NCERT-listed answer for tomato).

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).

Practice this conceptself-check · 5 quick reps

The same idea in a real exam question:

NDA · Sep 2022 · Q105Moderate

Example 1 · Acids, Bases and Salts · Common Acids: Names, Formulas and Uses

Bee sting leaves an acid which causes pain and irritation. The acid released is

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.

Drill 2 more on natural acids and their sources

Concept 2 of 4: Mineral acids and their uses

Each common mineral acid has a signature industrial job. Hydrofluoric acid etches glass; dilute nitric acid cleans gold and silver; sulphuric acid is the workhorse 'king of chemicals'. The bank asks 'principal use of X' or 'which acid does job Y'.

Definition

The use↔acid facts the bank tests:

Hydrofluoric acid (HF) — used to etch glass (it attacks silica, SiO2).
Dilute nitric acid (HNO3) — used by goldsmiths to clean gold and silver (it dissolves base-metal impurities without attacking the noble metal).
Sulphuric acid (H2SO4) — the 'king of chemicals'; used in fertilisers, car batteries and many industrial processes.

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

Practice this concept4 quick reps

The same idea in a real exam question:

NDA · Sep 2017 · Q82Easy

Example 2 · Acids, Bases and Salts · Common Acids: Names, Formulas and Uses

The principal use of hydrofluoric acid is

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.

Drill 1 more on mineral acids and their uses

Concept 3 of 4: Naming oxy-acids: hypo-, -ous, -ic, per-

The oxy-acids of a halogen (or sulphur, etc.) differ only in how many oxygen atoms they carry. The prefix/suffix encodes the count: 'hypo...ous' is the fewest oxygens, '...ic' is more, 'per...ic' is the most. Bromine's series runs HOBr, HBrO2, HBrO3, HBrO4.

Definition

The bromine oxy-acid series (lowest to highest oxidation state of Br):

Hypobromous acid = HOBr (also written HBrO) — the 'hypo...ous' name marks the lowest oxygen count.
Bromous acid = HBrO2.
Bromic acid = HBrO3.
Perbromic acid = HBrO4 — 'per...ic' marks the highest oxygen count.

The same naming pattern applies to chlorine: hypochlorous (HOCl), chlorous (HClO2), chloric (HClO3), perchloric (HClO4).

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)

Practice this concept4 quick reps

The same idea in a real exam question:

NDA · Apr 2021 · Q56Moderate

Example 3 · Acids, Bases and Salts · Common Acids: Names, Formulas and Uses

Which one of the following is the chemical formula of Hypobromous acid ?

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.

Concept 4 of 4: Acid reactions: nitric acid with metals, and carbonates with HCl

Two reaction facts recur. First: dilute nitric acid with copper gives NO gas, but concentrated nitric acid gives NO2 instead. Second: every carbonate (limestone, chalk, marble — all CaCO3) fizzes CO2 with HCl, but quicklime (CaO) gives no CO2 because it has no carbonate.

Definition

The two reaction facts:

Dilute HNO3 + Cu → NO gas (nitric oxide); concentrated HNO3 + Cu → NO2 (nitrogen dioxide). The concentration decides the gas.
Carbonates + HCl → CO2 — limestone, chalk and marble are all CaCO3 and all fizz CO2.
Quick lime (CaO) + HCl → CaCl2 + H2O only, with no CO2, because CaO is an oxide, not a carbonate.

Dilute nitric acid with copper

3\,\text{Cu} + 8\,\text{HNO}_3(\text{dil.}) \rightarrow 3\,\text{Cu(NO}_3)_2 + 2\,\text{NO}\uparrow + 4\,\text{H}_2\text{O}

Worked example

Limestone, chalk, marble and quick lime are each treated with dilute HCl. Which one does NOT release carbon dioxide, and why?

Practice this concept4 quick reps

The same idea in a real exam question:

NDA · Apr 2019 · Q102Moderate

Example 4 · Acids, Bases and Salts · Common Acids: Names, Formulas and Uses

Which one of the following will NOT produce carbon dioxide on reacting with an aqueous solution of hydrochloric acid?

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.

Drill 1 more on acid reactions: nitric acid with metals, and carbonates with hcl

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.

Formulas (1)

Acid reactions: nitric acid with metals, and carbonates with HCl
Dilute nitric acid with copper
$3\,\text{Cu} + 8\,\text{HNO}_3(\text{dil.}) \rightarrow 3\,\text{Cu(NO}_3)_2 + 2\,\text{NO}\uparrow + 4\,\text{H}_2\text{O}$

Reference tables (3)

Natural acids and their sources6 rows

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 uses4 rows

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-4 rows

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)

Watch out for (6)

Bee and nettle stings = methanoic acid, not acetic
→ Natural acids and their sources
Tomato = oxalic acid (in the bank)
→ Natural acids and their sources
Glass etching = hydrofluoric acid only
→ Mineral acids and their uses
Hypobromous acid is HOBr, not HBr
→ Naming oxy-acids: hypo-, -ous, -ic, per-
Quick lime has no carbonate, so no CO2
→ Acid reactions: nitric acid with metals, and carbonates with HCl
Dilute HNO3 gives NO, concentrated gives NO2
→ Acid reactions: nitric acid with metals, and carbonates with HCl

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