Matric Notes Chemistry 10th Chapter 10 Acids, Bases and Salts Exercise Short Questions

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Exercise Short Questions

Q1. Name three common household substances having:

a) pH values greater than 7

1. Soap
2. Detergent
3. Shampoo

b) pH values less than 7

1. Vinegar
2. Citrus fruits
3. Butter

c) pH values equal to 7

1. Water
2. NaCl
3. Sugar

Q2. Define a base and explain all alkalies are bases, but all bases are not alkalies.

Ans. A base is a substance which turns red litmus to blue and have 'pH' value greater than 7. Water soluble base is called alkali but some bases are not soluble is water, so all alkalies are bases but all bases are not alkalies.

Q3. Define Bronsted-Lowry base and explain with an example that water is a Bronsted-Lowry base.

Ans. Bronsted-Lowry base is a substance (molecule or ion) which can accept a proton (H⁺) from another substance. For example, when HCl dissolves in water, HCl acts as an acid and H₂O acts as a base because it accepts a proton.

HCl + H₂O == H₃O⁺ + Cl^-

Q4. How can you justify that Bronste-Lowry concept of acid and base is applicable to non-aqueous solutions?

Ans. According to Bronsted-Lowry concept:

An acid is a compound which donates a proton (H⁺).

A base is a compound which accepts a proton (H⁺).

So, the compounds which have H⁺ ions also act as acids on addition of water e.g., CH₃COOH while the compounds which do not have OH^- ions also act as base e.g., NH₃.

Q5. Which kind of bond forms between Lewis acid and base?

Ans. Coordinate covalent bond is formed between Lewis acid and base.

Q6. Why does H ion acts as Lewis acid?

Ans. Because it has an empty orbital that can accommodate a pair of electrons.

Q7. Name two acids used in manufacture of fertilizers.

Ans. Sulphuric acid and nitric acid both are used in manufacture of fertilizers.

Q8. Define pH. What is the pH of pure water.

Ans. 'pH' is the negative logarithm of molar concentration of the hydrogen ions.

pH = -log[H⁺]

The 'pH' value of pure water is 7.

Q9. How many times a solution of pH 1 will be stronger than that of a solution having pH 2?

Ans. The 'pH' scale is logarithmic, so a solution of 'pH' 1 is 10 times higher concentration of [H] than that of a solution of pH 2.

Q10. Define the following:

Ans. i. Normal Salt:

A normal formed by the total replacement of ionizable H ions of an acid by a positive metal ion or NH₄ ions is called normal salt or neutral salt. These salts are neutral to litmus.

HCl + KOH ----> KCl + H₂O

ii. Basic Salt:

Basic salts are formed by the incomplete neutralization of a polyhydroxy base by an acid.

Al(OH)₃ +HCl -----> Al(OH)₂Cl + H₂O

Q11. Na₂SO₄ is a neutral salt while NaHSO₄ is an acidic salt. Justify.

Ans. In Na₂SO₄, there is total replacement of ionizable H ions and it cannot further react with acid or base. While in NaHSO₄ one replaceable H ions is present which can be replaced by a positively charged (metal) ion.

Q12. Give a few characteristic properties of salts.

Ans. There are following characteristics of salts.

1. Salts are ionic compounds found in crystalline form.
2. They have high melting and boiling points.
3. They are usually neutral.
4. They have water of crystallization which is responsible for shapes of crystals e.g., (CuSO₄.5H₂O)

Q13. How are the soluble salts recovered from water?

Ans. Soluble salts are recovered from water by evaporation and crystallization.

Q14. How are insoluble salts prepared?

Ans. For the preparation of insoluble salts usually solutions of soluble salts are mixed. During the reaction exchange of ionic radical takes place to produce two new salts. One of the salt is insoluble and other is soluble. The insoluble salt precipitates (solidify in solution) e.g.,

AgNO₃ + NaCl ----> AgCl + NaNO₃

Na₂CO₃ + CuSO₄ -----> CuCO₃ + Na₂SO₄

Q15. Why is a salt neutral? Explain with an example.

Ans. Salts are neutral compounds although, they do not have equal number of positive and negative ions but they have equal number of positive and negative charges. e.g.

NaCl ----> Na⁺ + Cl^-

Q16. Name an acid used in the preservation of food.

Ans. i. Benzoic acid is used for food preservation.

ii. Acetic acid is also used for food preservation i.e. in pickles.

Q17. Name the acids present in:

i. Vinegar    ii. Ant sting    iii. Citrus fruit    iv. Sour milk

Ans. 

• Source        Acid

1. Vinegar        Acetic acid
2. Ant sting        Formic acid
3. Citrus Fruit    Citric acid
4. Sour milk        Lactic acid

Q18. How can you justify that Pb(OH)NO₃ is a basic salt?

Ans. Pb(OH)NO₃ is a basic salt because it is formed by the incomplete neutralization of a polyhydroxy base by an acid and it contains replaceable OH^- ion.

Pb(OH)₂ + HNO₃ -----> Pb(OH)NO₃ + H₂O

It can react with acids to form normal salts.

Pb(OH)NO₃ + HNO₃ ------> Pb(NO₃)₂ +  H₂O

Q19. You are in need of an acidic salt. How can you prepare it?

Ans. An acidic salt is formed by the partial replacement of replaceable H ions of and acid by positive metal ions or NH₄ ions.

H₂SO₄ + KOH -----> KHSO₄ + H₂O

H₃PO₄ + NaOH -------> NaH₂PO₄ + H₂O

Q20. Which salt is used to prepare plaster of Paris?

Ans. Calcium sulphate (CaSO₄.2H₂O) is used to prepare plaster of Paris.