ACIDS, Bases and SaltsBy: Sukhvinder

Acids, Bases and Salts

117 different chemical elements are known to us. These elements combine to form a large number of compounds.

On the basis of their properties all the compounds can be classified into- Acids, bases and Salts.

Indicators for testing Acids and Base

An indicator is a dye that changes color when it is put into an acid or a base.

Common indicators- Litmus, Methyl orange and Phenolphthalein.

Changes in indicators.

An acid turns blue litmus to red. A base turns red litmus to blue. Methyl orange indicator gives red color in

acid solution. Methyl orange indicator gives yellow color

in basic solution. Phenolphthalein is colorless in acid

solution. Phenolphthalein gives pink color in basic

solution.

Natural indicator Litmus

Litmus is a natural indicator. It is a purple dye extracted from a type of plant called Lichen.

It is neither acidic nor basic.

Some more natural indicators

Turmeric- contains a yellow dye which turns red in basic solution.

The red cabbage extract which is neutral in nature remains red in acidic solution but turns green on adding to basic solution.

Olfactory indicators.

Onion has a characteristic smell . When basic solution is added to a strip treated with onions then the smell can’t be detected. Acids don’t have any effect.

Vanilla extract has a characteristic pleasant smell. In basic solution the smell can’t be detected whereas acids do not destroy the smell.

Acids.

Acids are sour in taste and turn blue litmus red.

The acids present in plant materials and animals are called organic acids.

Citric acid. Tartaric acid. Oxalic acid. Methanoic acid. Organic acids are weak acids

Mineral acids

The acids prepared from the minerals of the earth are called mineral acids.

Hydrochloric acid Sulphuric acid Nitric acid The mineral acids are strong acids.

Properties of Acids.

Acids have a sour taste. Acids turn blue litmus red. Acid solutions conduct electricity.

Properties of acids

Acids react with metals to form hydrogen gas.

Metal + Acid → Salt + Hydrogen gas Eg. Zn(s) +H SO (aq)₂ ₄ → ZnSO +H (g)₄ ₂

Properties of acids.

Acids react with metal carbonates to from carbon dioxide gas.

Metal carbonate +Acid → Salt + carbon dioxide +Water.

Na CO (s) + 2HCl(aq) ₂ ₃ → 2NaCl (aq) +CO (g) +H O(l)₂ ₂

Properties of acids

Acids react with bases to form salt and water. This is called neutralization reaction.

Acid + Base → Salt + Water NaOH (aq) + HCl (aq) → NaCl (aq) + H O (l)₂

Properties of acids

Acids react with metal oxides to form salt and water.

Metal oxide + Acid → Salt + Water CuO (s) + 2HCl (aq) → CuCl₂ (aq) + H O (l)₂

Properties of acids

Acids have corrosive nature. The mineral acids cause severe burns

on the skin and attack and eat up meterials like cloth, wood, metal and stone work.

What do acids have in common?

An acid is a substance that releases H+ ions in an aqueous solution › Aqueous means water

Example: when hydrochloric acid is dissolved in water, the compound separates into chlorine ions (Cl-) and hydrogen ions (H+)

Strong acids

A strong acid breaks down completely in water and gives off many H+ ions

HCl H SO₂ ₄ HNO₃

Weak Acids

A weak acid only partially breaks down. It gives off much less H+ than a strong acid

CH COOH₃ H CO₂ ₃ H SO₂ ₃

Uses of Mineral Acids in Industries

Sulphuric acid is used in manufacture of fertilizers (like ammonium sulphate ), paints ,dyes ,chemicals, plastics, synthetic fibres, detergents, explosives and car batteries.

Nitric acid is used for making fertilizers , explosives, dyes and plastics.

Hydrochloric acid is used for removing oxide film before galvanizing.

Bases A base is a substance that releases

hydroxide (OH-) ions in an aqueous solution

Example: When sodium hydroxide (NaOH) is dissolved in water, the compound separates into sodium ions (Na+) and hydroxide ions (OH-)

Bases

The solution of substances like caustic soda, lime(chuna) and washing soda are bitter in taste and soapy to touch.

Bases are those chemical substances which have a bitter taste

Most of the bases do not dissolve in water those bases which dissolve in water without any chemical reaction have a special name .They are called alkali.

Example- NaOH, KOH, Ca(OH) , NH OH.₂ ₂

Characteristics of Bases

Bases usually taste bitter Bases feel slippery Bases contain hydroxide ions (OH-) Bases are the chemicals opposites of acids. A base is a chemical substance which can

neutralize an acid. All the metal oxides and metal hydroxides are

base. For example- Sodium oxide(Na O₂ ) is a metal

oxide so it is a base and Sodium hydroxide(NaOH) is a metal hydroxide , so it is a base.

What do all the bases have in common. A base is a substance which dissolves

in water to produce Hydroxide ions(OH ions⁻ )

NaOH(s) → Na ⁺ (aq) + OH ⁻ (aq)

KOH(s) → K ⁺ (aq) + OH ⁻ (aq)

A common property of all the bases is that they produce hydroxide ion when dissolved in water.

Water

Base/Alkali Sodium ions Hydroxide ions

Base/Alkali Pottasium ions Hydroxide ions

Water