NIOS Class 10 Acids, Bases and Salts Worksheet 8 Answers

This chapter explains acids, bases and salts used in daily life and their properties.

This post explains the answers of questions of worksheet 8 including explanation, diagrams. These solutions will help you complete your assignments and TMA also.

NIOS Class 10 Science (212) Worksheet 8 Solutions

Q1. Name the scientist who first classified acid and bases on their physical structure and how did they again get classified on the basis of their chemical structure? Give reason in support of your answer.

Answer

Robert Boyle was the first to classify acids and bases on the basis of their physical properties. According to him :

Acids: The substance sour in taste and turns blue litmus into red are called acids.

Bases: The substance bitter in taste and turns red litmus into blue are called bases.

Later. Svante Arrhenius classified acids and bases on the basis of their chemical structure. According to him

Acids: The substances which contain hydrogen  and release H⁺ ions in aqueous solution.

Bases :The substances which contain hydroxyl group and release OH^- ions in aqueous solution.

Reason

 The classification done by Arrhenius is more scientific and reliable because it depends on chemical composition and ionisation behaviour of the substances.

 

Q2. What changes would you observe by testing soap with litmus paper?

Answer

Soap is a basic or alkaline substance so when we taste it with litmus paper it shows following changes –

(i)    It turns red litmus to blue.

(ii)   It does not show changes with blue litmus.

Reason

Soap solution contains alkaline salts like sodium or potassium salts of fatty acids and these salts hydrolyse in water to produce OH^- ion that make the solution basic.

 

Q3. Name the acid which is present in the following items: gastric juice, soft drink, tea, vinegar, lemon juice, sour milk, milk of magnesia.

Answer

Substance	Acid
Gastric juice	Hydrochloric acid
Soft drink	Carbonic acid
Tea	Tannic acid
Vinegar	Acetic acid
Lemon juice	Citric acid
Sour milk (curd)	Lactic acid
Milk of magnesia	Magnesium hydroxide(basic)

Note : Milk of magnesium is a mild base which contains magnesium hydroxide.

 

Q4. What happen when sulphuric acid is dissolved in water?

Answer

When sulphuric acid is dissolved in water, it ionises to produce hydrogen ions and bisulphate ions and further ionises to give sulphate ions.

H₂SO₄ + H₂O → H⁺ + HSO₄^-

HSO₄^- → H⁺ + SO₄^2-

This process is highly exothermic so heat is released. Therefore, acids are added slowly to water and never add water to acids.

 

Q5. Explain the process of self-dissociation of water.

Answer

Water plays an important role in acid-base chemistry. It helps in the dissociation of acid and base and produce H⁺_(aq) and OH^-_(aq) ions. But water itself undergoes dissociation, the process is called self-dissociation of water.

Self-Dissociation of Water

`H_2 O ⇌ H_((aq))^+    + OH_((aq))^-`

The dissociation of water is very small, only about 3 molecules of a billion (10⁹) dissociate at 25ºC.

At 25ºC(298K)

 [H⁺] =[OH^-]= 1.0 ×10^-7mol/lit

In pure water and in all neutral aqueous solutions, the concentration of H⁺ and OH^- ions is equal.

H⁺] =[OH^-]

The product of the concentrations of H and OH ions is a constant at given temperature. This is called the ionic product of water (K_w).

K_w = H⁺] =[OH^-]

So, K_w = (1.0 ×10^-) (1.0 ×10^-7) =1.0 ×10^-14

So, the self- dissociation of water is the basis of neutrality, acidity and alkalinity of solutions.

 

Q6. Calculate the p^H of 1.0 × 10^-5 molar solution of HNO₃.

Answer

HNO₃ is a strong acid and is completely dissociates into ions in its solution.

HNO₃ →H⁺_(aq) + NO^-_3(aq)

This is clear that one mole of HNO₃ give one mole of H ions, therefore, the concentration of H ions would be equal to that HNO₃

[H⁺] = 1.0 ×10^-5 mol/L

Now

P^H = -log[H⁺]

P^H = -log (1.0 ×10^-5)

P^H = -(log ×10^-5)

= -(-5 ×log10)   [log10= 1]

= - (-5 ×1) = 5

Thus, the p^H of 1.0 × 10^-5 molar solution of HNO₃ is 5.

 

Q7. The chemical formula of a substance is 2CaSO₄.4H₂O. what is the commercial and common nae of this substance? Mention its uses.

Answer

Common name: Plaster of Paris.

Commercial name: Calcium sulphate hemihydrate

Use of Plaster of Paris

   1. Used in making toys, idols, showpieces.

   2. Used for making casts for fractured bones.

   3. Used in coating walls and ceilings.

   4. Used for making fire proof material.

   5. Used for making ‘chalk’ for blackboard.

 

Q8. Baking soda is manufactured by Solvey’s process. Explain the process and its uses.

Answer

Solvey’s Process

This process is mainly used in  making Washing soda but Baking soda (Sodium hydrogen carbonate) is an intermediate product.

Raw materials

   1. Lime stone (CaCO₃)

   2. Sodium chloride (Brine solution)

   3. Ammonia (NH₃)

Process

    1.  Cabon dioxide gas is obtained by heating limestone.

CaCO₃ → CaO +CO₂

    2.  CO₂ is passed in Brine solution (Concentrated solution of NaCl in water) which is saturated with ammonia.

    NaCl + NH₃ + CO₂ +H₂O →NaHCO₃ + NH₄Cl

    3. Baking soda (NaHCO₃) is soluble in water and crystallises out as white crystals. Its solution in water is basic and mild and non-corrosive base.

    4. On heating sodium hydrogen carbonate  decomposes into sodium carbonate , CO₂ and water.

      2NaHCO₃  →Na₂CO₃ + H₂O + CO₂

    

   Uses of Baking Soda (Sodium hydrogen carbonate)

    1. In cooking

    2. Making baking powder (a mixture of sodium hydrogen carbonate and tartaric acid)

    3.  In antacid

    4. In soda acid fire extinguishers

 

Q9. Are you suffering from tooth decaying problem? If yes, give reasons in support of your answer.

Answer

 

Yes, tooth decay is a common problem.

Reason

We have some bacteria in our mouth. We eat food which contains sugar or starch. The bacteria in our mouth act on food particles left in the mouth and produce acids. These acids react with the calcium phosphate (enamel) of the teeth, when the p^H in the mouth falls below 5.5, the enamel gets corroded and tooth starts decaying slowly.

Q10. How does bleaching powder sterilize water?

Answer

 Chemical formula of bleaching powder is CaOCl₂. When it is added water,it release chlorine.

CaOCl₂ + H₂O → Ca (OH)₂ +Cl₂

The chlorine dissolves in water and forms hypochlorous acid which is a strong oxidising agent and kills bacteria, germs present in water.

Cl₂ + H₂O → HOCl +HCl

So, bleaching powder sterilizes water by releasing chlorine.