CBSE Class 10 Chemistry Acids Base and Salts Worksheet Set C

Acids Base and Salts Notes Class 10 Science

Ionisable and non-ionisable compounds
An ionisable compound when dissolved in water or in its molten state, dissociates into ions almost entirely.
Example: NaCl, HCl, KOH, etc.
A non-ionisable compound does not dissociate into ions when dissolved in water or in its molten
state. Example: glucose, acetone, etc

Acids and Bases
An acid is any hydrogen-containing substance that is capable of donating a proton (hydrogen ion) to another substance. A base is a molecule or ion able to accept a hydrogen ion from an acid. Acidic substances are usually identified by their sour taste.

Arrhenius theory of acids and bases
Arrhenius acid – when dissolved in water, dissociates to give H+ (aq) or H₃O+ ion.
Arrhenius base – when dissolved in water, dissociates to give OH− ion.
Examples
Acids: Hydrochloric acid (HCl), Sulphuric acid (H2SO4), Nitric acid (HNO₃)
Bases: Sodium hydroxide (NaOH), Potassium hydroxide (KOH), Calcium hydroxide (Ca(OH)₂

Physical test

a. Taste
An acid tastes sour whereas a base tastes bitter.
The method of taste is not advised as an acid or a base could be contaminated or corrosive.
Example: The taste of curd, lemon juice, orange juice, and vinegar are all sour. Because they contain acids, Baking soda has a bitter taste.

b. Effect on indicators by acids and bases
An indicator is a chemical substance which shows a change in its physical properties, mainly colour or odour when brought in contact with an acid or a base.

Below mentioned are commonly used indicators and the different colours they exhibit:

Acid-Base Reactions
A neutralisation reaction occurs when an acid reacts with a base. A salt and water are the end products of
this reaction. An acid–base neutralisation reaction is formulated as a double-replacement reaction in this standard approach.

Reactions of acids and bases

a) Reaction of acids and bases with metals
Acids, in general, react with metals to produce salt and hydrogen gas. Bases, in general, do not react with metals and do not produce hydrogen gas.
Acid + active metal → salt + hydrogen + heat
2HCl + Mg → MgCl₂ + H₂ (↑)
Hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen
Base + metal → salt + hydrogen + heat
2NaOH + Zn → Na₂ZnO₂ + H₂ (↑)
Sodium hydroxide + Zinc → Sodium zincate + Hydrogen
A more reactive metal displaces the less reactive metal from its base.
2Na + Mg (OH)₂ → 2NaOH + Mg
Sodium + Magnesium hydroxide → Sodium hydroxide + Magnesium

b) Reaction of acids with metal carbonates and bicarbonates
Acids produce carbon dioxide, as well as metal salts and water, when they react with metal carbonates or metal bicarbonates. Sodium chloride, carbon dioxide, and water are formed when sodium carbonate interacts with hydrochloric acid. Allowing carbon dioxide gas to travel through lime water turns it milky.
Acid + metal carbonate or bicarbonate → salt + water + carbon dioxide.
2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂
H₂SO₄ + Mg (HCO₃)₂ → MgSO₄ + 2H2O + 2CO₂
Effervescence indicates liberation of CO₂ gas.

c) Reaction of Acid with Base

1. Reaction of metal oxides and hydroxides with acids
Metal oxides or metal hydroxides are basic in nature.
Acid + base → salt + water + heat
H₂SO₄ + MgO → MgSO₄ + H₂O
2HCl + Mg (OH)₂ → MgCl₂ + 2H₂O

2. Reaction of non-metal oxides with bases
Non-metal oxides are acidic in nature
Base + Nonmetal oxide → salt + water + heat
2NaOH + CO₂→ Na₂CO₃ + H₂O

3. Reaction of acids and base
A very common acid is hydrochloric acid. The reaction between strong acid says hydrochloric acid and strong base say sodium hydroxide forms salt and water. The complete chemical equation is shown below. HCl (strong acid) + NaOH (strong base) → NaCl (salt) + H2O (water)

Acids and bases in water
When added to water, acids and bases dissociate into their respective ions and help in conducting electricity.

Difference between a base and an alkali
Base: Bases undergo neutralisation reaction with acids. They are comprised of metal oxides, metal hydroxides, metal carbonates and metal bicarbonates. Most of them are insoluble in water. Alkali: An alkali is an aqueous solution of a base, (mainly metallic hydroxides). It dissolves in water and dissociates to give OH− ion. All alkalis are bases, but not all bases are alkalis.

Hydronium ion
Hydronium ion is formed when a hydrogen ion accepts a lone pair of electrons from the oxygen atom of a water molecule, forming a coordinate covalent bond.

Dilution
Dilution is the process of reducing the concentration of a solution by adding more solvent (usually water) to it.
It is a highly exothermic process.
To dilute acid, the acid must be added to water and not the other way round.

Strength of acids and bases
Strong acid or base: When all molecules of a given amount of an acid or a base dissociate completely in
water to furnish their respective ions, H+(aq) for acid and OH−(aq) for base).
Weak acid or base: When only a few of the molecules of a given amount of an acid or a base dissociate in water to furnish their respective ions, H+(aq) for acid and OH−(aq) for base).

Universal indicator
A universal indicator has a pH range from 0 to 14 that indicates the acidity or alkalinity of a solution.
A neutral solution has pH=7

pH :
The pH of pure water is 7.
The pH scale ranges from 0 to 14.
If pH < 7 → acidic solution
If pH > 7→ basic solution

Salts
A salt is a combination of an anion of an acid and a cation of a base.
Examples – KCl, NaNO₃ ,CaSO₄, etc.
Salts are usually prepared by the neutralisation reaction of an acid and a base.

Common salt
Sodium Chloride (NaCl) is referred to as common salt because it’s used all over the world for cooking.

Family of salts
Salts having the same cation or anion belong to the same family. For example, NaCl, KCl, LiCl. pH of salts
A salt of a strong acid and a strong base will be neutral in nature. pH = 7 (approx.).
A salt of a weak acid and a strong base will be basic in nature. pH > 7.
A salt of a strong acid and a weak base will be acidic in nature. pH < 7.
The pH of a salt of a weak acid and a weak base is determined by conducting a pH test.

Chemicals from common salt
Sodium chloride is a common salt. NaCl is its molecular formula. The fundamental element in our meals i sodium chloride. It is used in our food as a flavour enhancer as well as a preservative From common salt, we may make the following four compounds
1. Sodium hydroxide or lye or caustic soda.
2. Baking soda or sodium hydrogen carbonate or sodium bicarbonate
3. Washing soda or sodium carbonate decahydrate
4. Bleaching powder or calcium hypochlorite

Preparation of Sodium hydroxide
The strong base sodium hydroxide is a common and useful one. Preparing a solution of sodium hydroxide (NaOH) in water requires extra caution because the exothermic reaction releases a lot of heat. It’s possible that the solution will spatter or boil. Here’s how to manufacture a sodium hydroxide solution safely, as well as recipes for a variety of NaOH strengths.

Chemical formula – NaOH (Also known as – caustic soda)
Preparation (Chlor-alkali process):
Electrolysis of brine (solution of common salt, NaCl) is carried out.
At anode: Cl₂ is released At cathode: H₂ is released
Sodium hydroxide remains in the solution.

Bleaching powder

Bleaching powder is soluble in water and is used as a bleaching agent in textile industries. It is also used as an oxidizing agent and a disinfectant in many industries. It should also be noted that bleaching powder is synthesized by the reacting chlorine gas on dry slaked lime i.e. Ca(OH)₂.
Chemical formula – Ca(OCl)Cl or CaOCl₂
Preparation – Ca(OH)₂(aq)+Cl₂(g)→CaOCl₂(aq)+H₂O(l)
On interaction with water – bleaching powder releases chlorine which is responsible for bleaching action.

Uses of Bleaching Powder
It is used for bleaching dirty clothes in the laundry, as a bleaching agent for cotton and linen in the textile industry.

It is a strong oxidizing agent, hence used as an oxidizer in many industries.
It is used as a disinfectant which is used for disinfecting water to make potable water.

   

Question : A metal carbonate X on reacting with an acid gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, a gas G that is obtained at anode during electrolysis of brine is passed on dry Y, it gives a compound Z, used for disinfecting drinking water. Identify X, Y, G, and Z. 

Answer : The gas that is evolved at anode during the electrolysis of brine is chlorine. Hence, G is chlorine.

When chlorine gas is passed over dry slaked lime - Ca(OH)₂, it produces bleaching powder which is used for disinfecting drinking water. Hence, Y is slaked lime (calcium hydroxide) and Z is calcium oxy-chloride (bleaching powder).

Since Y and Z are calcium salts, therefore X is also a calcium salt. Since, X is a metal carbonate, it is calcium carbonate. Carbonates react with acids to produce carbon dioxide gas which when through a solution of slaked lime (Y) forms insoluble calcium carbonate.