Class 10 Science Notes

Chapter 2: Acid Bases and Salts

CBSE Class 10 Science Notes Chapter 2 Acid Bases and Salts provides a concise summary for quick revision. Key points include characteristics of acidsand Bases, characteristics of chemical reactions of acid and bases , and salts formed and also the importance of pH.

Acid

Taste sour and change blue litmus paper to red.

Highly reactive with metals and release hydrogen gas.

Common acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and acetic acid (CH₃COH)

Definition : Acids are that compounds which releases H⁺ ions on hydrolysis or reaction with water.

Acid solution conducts electricity as they release ions which are essential for conduction of electricity.

Now Acids are of mainly two types -

(i) Natural Acids: Acids which are obtained from natural sources are called Natural Acids or Organic Acids. Examples: Methanoic acid (HCOOH) Acetic acid (CH3COOH) Oxalic acid (C2H2O4) etc.

(ii) Mineral Acids: Acids that are prepared from minerals are known as Mineral Acids Example; Inorganic acids, man-made acids or synthetic acid are also known as Mineral Acids. Example: Hydrochloric acid (HCl) Sulphuric acid (H2SO4) Nitric acid (HNO3) Carbonic acid (H2CO3) Phosphoric acid (H3PO4) etc.

Chemical of reaction of acids

Reaction of acid with metal

Acids give hydrogen gas along with respective salt when they react with a metal.

Metal + Acid → Salt + Hydrogen

Examples:

Hydrogen gas and zinc chloride are formed when hydrochloric acid reacts with zinc metal.

Zn + HCl → ZnCl₂ + H₂

Reaction of acid with metal carbonates

Acids give carbon dioxide gas and respective salts along with water when they react with metal carbonates.

Metal carbonate + Acid → Salt + Carbon dioxide + Water

Examples:

Hydrochloric acid gives carbon dioxide gas, sodium chloride along with water when reacts with sodium carbonate.

Na₂CO₃ → NaCl + CO₂ + H₂O

Reaction of acids with metal hydrogencarbonate

Acids give carbon dioxide gas, respective salt and water when they react with metal hydrogen carbonate.

Acid + Metal hydrogen carbonate → Salt + Carbon dioxide + Water

Example:

Sulphuric acid gives sodium sulphate, Carbon dioxide gas and water when it reacts with sodium bicarbonate.

NaHCO₃ + H₂SO₄ → Na₂S +CO₂ + H₂O

Bases

Tastes bitter and change red litmus paper to blue.
Usually used to form soaps.
Common bases include sodium hydroxide, sodium carbonate, milk of magnesia, potassium hydroxide etc.

Reactions of Bases

Reaction of Bases with metals

Bases also form salt and hydrogen gas when they reacts with metal. But there are some metals which don't react with bases like gold, silver etc.
Base + Metal → Salt + Hydrogen gas
When sodium hydroxide reacts with Zinc it forms Sodium zincate and Hydrogen gas

2NaOH + Zn → Na₂ZnO₂ + H₂

Reaction of Bases with metal carbonates

Generally bases don't react with metal carbonates are also basic.
We have provided the table for the nature of metal or non metal oxide carbonates etc. Go and checkout the table as it will help in the reactions.

Extras

Acids + Metallic Oxide → Salt + Water

Bases + Metallic Oxides → No reaction

Except when bases react with the amphoteric metal oxides as they are both acidic and basic in nature.

Acid + Non Metallic Oxide → No reaction

Bases + Non Metallic Oxide → Salt + Water

How Acids and Bases react with each other

When Acid and Base react with each other.,they Neutralise each others effect and convert the solution to neutral only when where acid and base are equally powerful. This is called neutralisation reaction and it also involves the release of heat.

NaOH + HCl → NaCl+ H₂O

What makes an Acid an Acid and a Base a Base?

Now all the compounds which are acidic, the factor that would be common between them is the release of H⁺ ions when they react with water.
Now the Base have the same thing but the different ion. The bases release OH_- ion in the presence of water.
Due to this properties of Acids and Base, they are able to conduct electricity due to the presence of ions.
Now ethanol also whose chemical formula ends with OH don't conduct electricity because it don't get electrolysed to release any ion.
For example when diluted Sulphuric acid is added to Sodium Chloride HCl gas is produced and when we will test it by a litmus paper there wouldn't be any change but if we add some water to it, it will turn the blue litmus paper to red. So the acid only shows their properties when they are reacted with water.

HCl + H₂O → H₃O⁺ + Cl^-

H⁺ + H₂O → H₃O⁺

Same with NaOH

NaOH + H₂ → Na⁺ + OH^-

Now all Bases do not dissolve in water like Cuo but the soluble ones are called Alkali. Alkali are soapy to touch, bitter in taste and corrosive in nature. Examples are Sodium Hydroxide, Potassium Hydroxide etc. are Alkali.

How to add Acid or Base to water

Now when water is added to acid, and exothermic reaction occurs which releases a good amount of heat. So due to the heat the water evaporates and it splash out and can cause burns if it fall on our body.

So we have to add acid or base to water at slow pace with constant stirring. It will also release heat but the water will absorb the heat and will not cause any accident.
So water to acid ❌❌
But acid to water ✅✅

How to measure the strength of Acid or Base

Now the strength of Acid is determined by the concentration of H⁺ ions
And the strength of base is determined by the concentration of the OH⁺ ions
So to;meaure the concentration of these ions, we use the pH scale(In german p stands for power).
The pH scale ranges from 0 to 14, the low value indicates more concentration of H⁺ ions and vice versa
The paper impregnated with universal indicator is used to measure pH value

Practice Questions

Define a chemical reaction and list its characteristics.
What is a balanced chemical equation? Why should chemical equations be balanced?
Explain oxidation and reduction with examples.

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