Acids, Bases and Salts · Class 10 Science: quick revision, 60 bites

Acids and Bases at a Glance

Sour vs soapy

Takeaway. Sour-red-acid; soapy-blue-base.

Indicators

The colour detectives

Takeaway. Four indicators, four colour pairs — memorise the table.

Olfactory Indicators

Detecting with your nose

Onion, vanilla and clove are **smell indicators**: their odour fades or changes in a **base** (and stays in acid). They let visually-impaired students identify acids and bases — and examiners love asking about them.

Takeaway. Onion and vanilla lose their smell in bases.

Acid + Metal → Salt + H₂

Reaction family #1

Takeaway. Metal + acid fizzes hydrogen — confirmed by the pop.

Acid + Carbonate → Salt + Water + CO₂

Reaction family #2

Takeaway. Carbonate + acid gives CO₂ — milky limewater, clearing in excess.

Acid + Metal Oxide → Salt + Water

Reaction family #3 — with a colour change

Metal oxides neutralise acids just as bases do — so **metal oxides are BASIC oxides**.

Takeaway. Black CuO + acid → blue-green solution; metal oxides act basic.

Base + Non-metal Oxide → Salt + Water

The mirror reaction

CO₂ and SO₂ neutralise bases the way acids do — **non-metal oxides are ACIDIC oxides**.

Takeaway. Non-metal oxides act acidic — the mirror of family #3.

Neutralisation

Reaction family #5 — the peace treaty

Takeaway. Acid + base cancel into salt + water.

Antacids, Soil and Bee Stings

Neutralisation in your medicine box

Takeaway. Medicine, farming and first aid all run on neutralisation.

Zinc + Base — Yes, Really

Some metals fight both sides

Takeaway. Zn and Al give hydrogen with bases too — most metals don't.

Pop vs Milky

Two gases, two tests — never swap

Takeaway. Pop = H₂; milky = CO₂. Lock it in.

Turmeric Tells on Soap

The kitchen indicator

Takeaway. Turmeric: yellow in acid/neutral, red-brown in base.

Board Favourites

How the board asks this

Takeaway. Gas tests + indicator colours = most of this topic's marks.

Never Taste, Never Touch

Lab safety, one line

Takeaway. Indicators exist so your tongue never has to.

Memory Pack

Whole topic in three lines

Takeaway. Three lines carry the indicators-and-reactions topic.

All Acids Release H⁺

One particle explains everything

Different acids, same behaviour — because in water they all release the **hydrogen ion (H⁺)**. Sourness, litmus-reddening, metal-fizzing: all of it is H⁺ chemistry.

Takeaway. Acidity = H⁺ ions in water.

The Hydronium Ion

The proton's taxi

Takeaway. In water, H⁺ always travels as H₃O⁺.

All Bases Release OH⁻

The bases' common particle

And neutralisation, at its core, is just the two signatures meeting: **H⁺ + OH⁻ → H₂O**.

Takeaway. Basicity = OH⁻ ions; neutralisation = H⁺ meeting OH⁻.

The Conductivity Experiment

The glowing-bulb verdict

Takeaway. Glow = ions = acid; no glow = no ions = not an acid.

Dry HCl vs Moist Litmus

The chapter's most famous experiment

Takeaway. No water → no H⁺ → no acidity. Water switches acids on.

Acid Into Water — Never the Reverse

The rule that prevents burns

Takeaway. Acid to water, slowly, stirring — always.

Dilution = Fewer Ions Per Drop

What watering-down really does

Adding water to an acid or base doesn't destroy ions — it spreads the same ions through more liquid. The **concentration of H₃O⁺ (or OH⁻) per unit volume falls**, so the solution becomes LESS acidic (or basic).

Takeaway. Dilution lowers ion concentration, not ion count.

Alkali vs Base

A base you can dissolve

Takeaway. Alkali = the water-soluble subset of bases.

Strong vs Weak Acids and Bases

Fully split vs barely split

Takeaway. Strong = complete ionisation; weak = partial.

Strong ≠ Concentrated

Two words people mix up

Takeaway. Strength is chemistry; concentration is quantity.

Battery Acid Conducts

Ions at work in your inverter

Car and inverter batteries use dilute sulphuric acid precisely because its ions conduct — the H₃O⁺ and SO₄²⁻ ions shuttle charge between the plates. No ions, no battery.

Takeaway. Every battery's electrolyte is applied ionisation.

Dissolving Is Exothermic

Heat you can feel

Both acids in water AND bases in water release heat. Dropping NaOH pellets into water warms the beaker noticeably; concentrated H₂SO₄ into water can approach boiling. This heat is exactly why the dilution safety rule exists.

Takeaway. Acid/base + water = heat — respect it.

Board Favourites

The four bankers

Takeaway. These four 'why's rotate through every board paper.

Water Ionises Itself (a Little)

Even pure water has ions

A tiny fraction of water molecules split into H₃O⁺ and OH⁻ — equal amounts, which is why pure water is neutral. Acids tip the balance toward H₃O⁺; bases toward OH⁻. The pH scale (next topic) measures exactly this balance.

Takeaway. Neutral = equal H₃O⁺ and OH⁻ — water's own equilibrium.

Memory Pack

Whole topic in three lines

Takeaway. Three lines, the whole ion story.

The pH Scale

Acidity gets a number

Takeaway. 0-6 acid, 7 neutral, 8-14 base.

pH Is Logarithmic

Every step is a 10× jump

Each unit of pH = a **ten-fold** change in H⁺ concentration. pH 2 is 10× more acidic than pH 3, and 100× more than pH 4. Small pH differences hide big chemistry.

Takeaway. One pH step = 10 times the hydrogen ions.

Universal Indicator

One strip, whole scale

A mixture of indicators that shows a **different colour at each pH** — red/orange/yellow through the acids, **green at neutral**, blue to violet through the bases. Dip a pH paper strip, match the colour chart, read the pH.

Takeaway. Colour → pH: red acid, green neutral, violet base.

pH Values to Memorise

The table exams pull numbers from

Takeaway. Stomach 1.2 → water 7 → blood 7.4 → magnesia 10.

The Body's pH Window

Life lives in a narrow band

Living cells work only around **pH 7.0–7.8**. Blood is buffered at ~7.4; a shift of half a unit is a medical emergency. The same narrowness is why acid rain devastates rivers — aquatic life cannot survive when the water leaves the window.

Takeaway. 7.0–7.8 is the survival band for living processes.

Acid Rain

When the sky turns sour

Takeaway. Below 5.6 = acid rain — pollution turned to falling acid.

Digestion, Acidity and Antacids

The fire in your stomach

Takeaway. Antacid = mild base = portable neutralisation.

Tooth Decay Below pH 5.5

The number your dentist lives by

Mouth bacteria turn leftover **sugar into acids**. When mouth pH drops **below 5.5**, tooth enamel — **calcium phosphate**, your body's hardest material — starts dissolving. Bases never harm enamel; acid does.

Takeaway. Sugar → bacterial acid → pH < 5.5 → enamel dissolves.

Soil pH and Crops

The farmer's pH report

Takeaway. Lime lifts soil pH; compost lowers it — chemistry farming.

Why a Sting Hurts, and What Stops It

First aid by neutralisation

Takeaway. A sting is an acid injection, so the cure is always a mild base.

Where pH Came From

A brewery gave us pH

Søren Sørensen invented the pH scale in 1909 at the Carlsberg brewery lab, to control beer fermentation. The 'p' stands for *potenz* — power — so pH literally reads 'the power of hydrogen'.

Takeaway. pH = the power of hydrogen, born in a brewery.

Lower pH = MORE Acid

The direction slip

Takeaway. Down the scale = up the acidity.

Worked: Ranking by pH

Compare like an examiner

Takeaway. Sort pH high→low to rank acidity low→high.

Board Favourites

The five staples

Takeaway. Five questions cover nearly every pH mark.

Memory Pack

Whole topic in three lines

Takeaway. Three lines, the whole pH topic.

pH of Salts

A salt remembers its parents

Takeaway. Judge a salt's pH by its parent acid and base.

The Chlor-Alkali Process

Brine's big break

Named for its products: **chlor**(ine) + **alkali** (NaOH). One salt solution feeds three industries.

Takeaway. Electrolysed brine = NaOH + Cl₂ + H₂.

Uses of NaOH, Cl₂ and H₂

Where the Big 3 go

Takeaway. Alkali cleans, chlorine disinfects, hydrogen fuels.

Bleaching Powder (CaOCl₂)

Chlorine meets lime

Takeaway. Dry slaked lime + Cl₂ = the bleach that also cleans water.

Baking Soda (NaHCO₃)

The kitchen's mild base

Takeaway. Sodium hydrogencarbonate — mild enough to eat, useful enough to put out fires.

Baking Powder = Soda + Tartaric Acid

Why cakes rise

In the oven, baking soda decomposes — **2NaHCO₃ → Na₂CO₃ + H₂O + CO₂** — and the CO₂ bubbles puff the cake. The **tartaric acid** in baking powder then neutralises the bitter Na₂CO₃, keeping the taste clean.

Takeaway. CO₂ raises the cake; tartaric acid erases the bitterness.

Washing Soda (Na₂CO₃·10H₂O)

Ten waters strong

Heat baking soda to get sodium carbonate, then **recrystallise** with water: Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O.

Takeaway. The carbonate with ten waters — industry's basic salt.

Water of Crystallisation

Dry crystals hiding water

The crystals feel perfectly dry — the water is chemically locked inside the structure.

Takeaway. Crystals can carry water without being wet.

The Copper Sulphate Demo

Blue, white, blue again

Takeaway. Blue↔white with water leaving and returning — crystallisation water made visible.

Plaster of Paris (CaSO₄·½H₂O)

The doctor's white powder

Takeaway. Gypsum − 1½ waters at 373 K = plaster of Paris.

How PoP Sets

Why the cast hardens

Takeaway. Setting = PoP taking its water back to become gypsum.

Baking Soda vs Washing Soda

The sodas, side by side

Takeaway. Bicarb bakes; the ten-water carbonate cleans.

One Family, Everywhere

Chapter chemicals in your day

Takeaway. NaCl's children run your kitchen, bathroom and hospital.

Board Favourites

The formulas the board demands

Takeaway. Five formulas + three whys = the marks of this topic.

Memory Pack

Whole topic in three lines

Takeaway. Three lines, the whole salt family.