What are acids - Chemical properties | science Class 10

Acid and properties - class X notes

What is an Acid ? it is most important topic of NCERT Acid , base and Salt chapter 2 in Class 10th. Questions are frequently asked in the CBSE board and ICSE Board exam from Acid .

“Chemistry – Acid class 10 notes “ will be very beneficial for the students who are engaged in the preparation of upcoming board exam.

In this topic, the following terms will be illustrated.

Contents :

* What is and Acid

* Physical properties of acids

* Types of acid : Organic acid, Inorganic acid, Strong acid, Weak acid, Dilute acid , Concentrated Acid

* Chemical Properties of Acids : Chemical Reactions

* Preparation of acids

* Uses of acids

* Fire extinguisher , Acid Rain, Dilution of acid

What is and Acid

According to Arrhenius , Those substances which dissociate into hydrogen ions ( H⁺ ) in aqueous solution are called acids.

Hydrogen ion ( H⁺ ) is too reactive. It react with water molecule to form hydronium ion ( H₃O⁺) .

i.e. acids are the substance which produce hydronium ions ( H₃O⁺) in aqueous solution . e.g. HCl, H₂SO₄ , CH₃COOH, etc

HCl (aq) = H⁺ + Cl^–

H⁺ + H₂O = H₃O⁺

Poperties of Acids:

The term acid has been derived from the latin word ‘acidus’ which means sour. i.e acids are sour in taste.

It turns blue litmus red.

It destroys body tissue.

It corrode metal surface.

It react with metal to produce hydrogen gas.

Types of acids:
1. On the basis of origin:

Organic acid:

It is derived from living organism like plants and animals.

Organic acid	sources
Citric acid	Fruits
Acetic acid	Vinegar
Oxalic acis	Tomato
Tartaric acid	Tarmind
Lactic acid	Milk, Curd
Formic acid	Antsting, Nettle sting
Ascorbic acid	Guava, Amla

Its molecules consists carbon atom along with hydrogen and other atoms

It is a weak acid.

Inorganic acid:

It is derived from minerals, so it is also called mineral acid. e.g HCl, H₂SO₄ etc.

Its molecule does not contain carbon atom except carbonic acid ( H₂CO₃ ).

It is strong acid except carbonic acid ( H₂CO₃ ).

Common Name of Inorganic Acid

* H₂SO₄ - Oil of vitriol

* HCl - Muriatic acid

* HNO₃ - Aqua fortis , spirit of niter

2. On The Basis of Strength:

Strong acid:

An acid which completely dissociates into ions is called strong acid.

Its each molecule dissociates into Hydrogen ions.

Inorganic acids are strong acid except carbonic acid (H₂CO₃) .

Weak Acid:

An acid which does not completely dissociates into ions is called weak acid.

Its few molecule dissociates into ions.

Organic acids are weak acid .

3. On The Basis of Concentration:

Dilute Acid:

If amount of hydrogen ions ( H ⁺ ) are very low in per unit volume of solution, then acid is said to be dilute acid.
i.e in dilute acid , amount of water is very large than amount of acid.

Concentrated Acid:

If amount of hydrogen ions ( H ⁺ ) are large in per unit volume of solution, then acid is said to be concentrated acid.
i.e in concentrated acid , amount of water is less than amount of acid.

Physical Properties of acids:

1. Taste:

Acids are sour in taste.

2. Physical State:

Some acids are solid and some are liquid at room temperature.

Solid Acids	Boric acid ( H₃BO₃ ) Oxalic acid ( COOH )₂ Tartaric acid( C₄H₆O₆) Citric acid ( C₆H₈O₇ ) Phosphoric acid ( H₃PO₄ )
Liquid acid	Acetic acid - ( CH₃COOH ) Formic acid - ( HCOOH ) Carbonic acid- (H₂CO₃) Hydrochloric acid - HCl Sulphuric acid - H₂SO₄ Nitric acid - HNO₃ etc.

3. Effect on Skin:

All minerals acid except carbonic acid are harmful for skin . it destroys body tissue.

Organic acid and carbonic acid do not effect on skin.

4. Corrosive nature:

Inorganic acid corrode metal surface.

Organic acid and carbonic acid are not corrosive.

5. Conductivity of electricity

Aqueous solution of acid are good conductor of electricity due to formation of ions.

6. Change Colour of Indicators:

Acid change color of some indicators.

Indicator	Color changed
Litmus	Blue to red
Methyl orange	Orange to pink

Chemical Reactions:

Acid +	Reactant =	Product
Dilute ( HCl or H₂SO₄ )	Metal	Salt + H₂
	Metal oxide	Salt + H₂O
	Alkali	Salt + H₂O
	Metal carbonate	Salt + CO₂ + H₂O
	Metal bi-carbonate	Salt + CO₂ + H₂O
	Metal sulphite	Salt + SO₂ + H₂O
	Metal bi-sulphite	Salt + SO₂ + H₂O
	Metal sulphide	Salt + H₂S
	Pb(NO₃)₂	Salt + HNO₃
Concentrated (H₂SO₄)	Metal Chloride Metal Nitrate	Salt + HCl Salt + HNO₃

Chemical Reaction of acid ( Dilute HCl or H₂SO₄ )

1. Reaction With Metals:

Acid react with metal to form metal salt and hydrogen gas.

Acid + Metal → salt + H₂

(a) Dilute HCl and H₂SO₄ react explosively with active metal like K, Na, Ca .

2HCl + 2Na → 2NaCl + H₂ + Heat

(b) Dilute HCl and H₂SO₄ react moderately with less active metal like Mg, Zn, Fe.

2HCl + Mg→ MgCl₂ + H₂

2HCl + Zn → ZnCl₂ + H₂

Fe + H₂SO₄ → FeSO₄ + H₂

(c) HNO₃ is not used for this reaction because of it is very strong oxidizing agent which oxidize hydrogen into water.
Only magnesium (Mg) and manganese (Mn) produce hydrogen gas with very dilute nitric acid ( 1%).

Mn + HNO₃ ( 1%) → Mn(NO₃)₂ + H₂

2. Reaction With Metal Oxide:

Metal oxide + Acid → salt + H₂O

e.g : CuO + 2HCl → CuCl₂ + H₂O

ZnO + 2HCl → ZnCl₂ + H₂O

3. Recation with metal carbonate:

Metal carbonate + Acid → salt + H₂O + CO₂

e.g

Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

4. Recation with metal bicarbonate:

Metal bicarbonate + Acid → salt + H₂O + CO₂

e.g

NaHCO₃ + HCl → NaCl + H₂O + CO₂

Ca(HCO₃ )₂ + 2HCl → CaCl₂ + 2H₂O + 2CO₂

5. Recation with metal sulphite or bisulphite :

Metal sulphite + Acid → salt + H₂O + SO₂

Metal bisulphite + Acid → salt + H₂O + SO₂

e.g.

CaSO₃ + 2HCl → CaCl₂ + H₂O + SO₂

Ca(HSO₃) + H₂SO₄ → CaSO₄ + H₂O + SO₂

6. Reaction with Base ( alkalis ) :

Base + Acid → Salt + H₂O

Acid react with base to form salt and water only. This reaction is called neutralization reaction.

HCl + NaOH → NaCl + H₂O

Strong acid + Strong base → Neutral salt + H₂O

Strong acid + Weak base → Acidic salt + H₂O

Weak acid + Strong base → Basic salt + H₂O

Weak acid + Weak base → Neutral salt + H₂O

7. Reaction with nitrate :

Only nitrate of lead metal react with dilute HCl or H₂SO_{4 .}

Pb(NO₃)₂ + 2HCl → PbCl₂ + 2HNO₃

Pb(NO₃)₂ + H₂SO₄ → PbSO₄ + 2HNO₃

Other metal nitrate react with concentrated H₂SO₄ on heating.

Below 200^OC

KNO₃ + H₂SO₄ → KHSO₄ + HNO₃

Above 200^OC

2KNO₃ + H₂SO₄ → K₂SO₄ + 2HNO₃

8. Reaction between conc. H₂SO₄and metal Chloride:

Metal chloride react only with concentrated H₂SO₄ on heating.

Below 200^OC

NaCl + H₂SO₄ → NaHSO₄ + HCl

Above 200^OC

2NaCl + H₂SO₄ → Na₂SO₄ + 2HCl

9. Reaction between conc. HNO₃ and Nonmetal:

S + 6HNO₃ → H₂SO₄ + 6NO₂ + 2H₂O

P + 5HNO₃ → H₃PO₄ + 5NO₂ + H₂O

Preparation of acids:

1. By Synthesis :

Binary acids ( acid containing two atoms ) are prepared by this method.

H₂ + Cl₂→ 2HCl

H₂ + Br₂→ 2HBr

H₂ + S→ H₂S

2.By the action of water on acidic oxide (acid anhydride)

SO₃ + H₂O → H₂SO₄

SO₂ + H₂O → H₂SO₃

CO₂ + H₂O → H₂CO₃

P₂O₅ + H₂O → 2H₃PO₄

N₂O₅ + H₂O → 2HNO₃

2NO₂ + H₂O → HNO₃ + HNO₂

NO₂ gives two acid , so it is called double acid anhydride.

3. Oxidation of Non-metals by Conc. HNO₃ :

S + 6HNO₃ → H₂SO₄ + 6NO₂ + 2H₂O

P + 5HNO₃ → H₃PO₄ + 5NO₂ + H₂O

4. Reaction between conc. H₂SO₄and metal Chloride:

Metal chloride react with concentrated H₂SO₄ on heating to produce hydrochloric acid .

Below 200^OC

NaCl + H₂SO₄ → NaHSO₄ + HCl

Above 200^OC

2NaCl + H₂SO₄ → Na₂SO₄ + 2HCl

5. Reaction between metal nitrate and acid :

Only nitrate of lead metal react with dilute HCl or H₂SO₄ to produce nitric acid _.

Pb(NO₃)₂ + 2HCl → PbCl₂ + 2HNO₃

Pb(NO₃)₂ + H₂SO₄ → PbSO₄ + 2HNO₃

Other metal nitrate react with concentrated H₂SO₄ on heating to produce nitric acid _.

Below 200^OC

KNO₃ + H₂SO₄ → KHSO₄ + HNO₃

Above 200^OC

2KNO₃ + H₂SO₄ → K₂SO₄ + 2HNO₃

General Uses of Acids:

Acid	Uses in
Acetic acid	Vinegar and cooking
Boric acid	Eyewash and antiseptic
Benzoic acid	Preservation of food Making of perfume and medicine
Citric acid	Food preservation Preparation of vitamine C
Carbonic acid	Use in soft drink
Hydrochloric acid	Cleaning of metal item
Nitric acid	Making explosive
Oxalic acid	Ink stain remover
Phosphoric acid	Fertilizers
Tartaric acid	Baking powder

Aqua-regia :

Mixture of 3 part of conc. Hydrochloric acid and 1 part of Conc. Nitric acid is called aqua regia .

It dissolves all metals even nobel metal like platinum and gold etc.

Fire extinguisher:

It is a device used in putting off fire .

Metal carbonate or bicarbonate and acid are used in fire extinguisher to produce CO₂ gas.

Acid and carbonate are kept in separate chamber in fire extinguisher.

On emergency , they are allowed to react with each other to form CO₂ gas.

As carbon dioxide does not support burning, it put off the fire.

Test For Hydrogen Gas:

It is tested by burning a lighted candle near it.

If the gas burns with pop sound , then it confirm that the evolution of hydrogen gas.

Burning with pop sound is the characteristics test for hydrogen gas.

Acid Rain:

Rain containing nitric acid and sulfuric acid is called acid rain.
When pH of rain water is less than 5.6, it is called acid rain.
When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.

Formation of Acid Rain:

Burning of fossil fuels release oxides of sulphur and nitrogen.

NO₂ and SO₂ form nitric acid and sulfuric acid on reaction with water of rain droplets.

Effect of Acid Rain:

Acid rain causes damage to the trees , historical monuments and other building.

Tajmahal which is made of marble is getting damage due to acid rain. Marble is calcium carbonate ( CaCO₃ ) which react with acid and thus get corrode.

Dilution of acid: