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SS1: Chemistry 2nd Term Theory Questions – Acid, Bases and Salts I

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SS1: Chemistry 2nd Term Theory Questions – Acid, Bases and Salts I

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Question 1

(a) Define acid in terms of the following (i) Arrhenius (ii) Bronsted-Lowry (iii) Lewis

Answer – 

i. Arrhenius defined an acid as a substance that dissociates in water to produce hydrogen ion (H+) or proton.

ii. Bronsted-Lowry defined an acid as a proton donor.

iii. Lewis defined an acid as an electron-pair acceptor

 

(b) Give five examples of Organic acid and its sources

Answer – 

 

Organic Acid

Source

1.

Ethanoic acid

Vinegar

2.

Citric acid

Lime, Lemon

3.

Fatty acid

Fats and oils

4.

Amino acid

Protein

5.

Lactic acid

Milk

Question 2

a (i) What is the basicity of an Acid (ii) Give the basicity of the following acids 

(I) HCOOH  (II) H3PO4  (III) HNO3 

Answer – 

HCOOH – 1

H3PO4 – 3

HNO3 – 1

 

b. Write an equation to show the dissociation of each of the following 

(i) CH3COOH  (ii) H2CO3  (iii) HCOOH

Answer – 

i. CH3COOH ⇌ H+ + CH3COO–

ii. H2CO3 ⇌ 2H+(aq) + CO2-(aq)

iii. HCOOH ⇌ H+(aq)+ HCOO–(aq)

Question 3

a. State one difference between

i. A Strong acid and a Concentrated acid

Answer – 

Concentrated acid is an acid solution having a high amount of acid molecules per unit volume of the solution.

While

A strong acid is an acid that is completely dissociated or ionized in an aqueous solution.

 

ii. Give one reason why tetraoxosulphate (VI)acid is regarded as a dibasic acid

Answer – 

H2SO4 is considered dibasic because it has 2 replaceable hydrogen ions (H+).

 

b. Mention three general uses of acid

Answer – 

i. Hydrochloric acid is used by industries to make chemicals.

ii. Citric acid is used in making a fruit juice.

iii. Boric acid is used as a mild antiseptic or germicide.

Question 4

(a) How would you prove that a given colourless liquid is an acid

Answer – 

Litmus test

Acids turn blue litmus red. If the colourless liquid is an acid, it would turn blue litmus red. If this does not happen, then it is not referred to as a mixed anhydride because, when dissolved in water, it forms two acids; HNO3 and HNO2. The equation for the reaction goes thus:

(b) Nitrogen(IV)Oxide is described as a mixed acid anhydride. Explain using appropriate equations

Answer – 

NO2(g) + H2O(l) → HNO3(aq) + HNO2(aq)

(c) Give three physical properties of acid

Answer – 

(i) Acids are electrolytes

(ii) They have sour taste

(iii) Concentrated forms of acid are corrosive e.g. HCl, H2SO4 … etc.

Question 5

a. Using a well-balanced equations state how HCl reacts with the following compounds  

Answer –

(i) Mg   (ii) NaOH   (iii) CaCO3

i. Mg(s) + 2HCl  →  MgCl2(s) + H2(g)

ii. HCl(aq) + NaOH(aq) →   NaCl + H2O(l)

iii. CaCO3(s) + 2HCl(aq) →  CaCl2(s) + CO2(g) + H2O(l)

 

b. Acids are prepared using various methods  

Give four methods of preparing acid

Answer –

(i) Combination of constituent elements

This method is suitable for the preparation of hydrochloric acid and other hydrogen halides.

E.g. By bubbling hydrogen gas and bromine vapour in the presence of platinum catalyst; hydrogen bromide is produced.

:- \( \scriptsize H_{2(g)} + Br_{2(g)} \; \overset{Platinum}{\rightarrow} \; HBr_{(g)} \)

 

(ii) Action of acid anhydride in water

E.g.

(a) SO2(g) + H2O(l)   → H2SO3(aq)

(b) NO2(g) + H2O(l)  →  HNO3(aq) + HNO2

 

(iii) Displacement Reaction

E.g. Dilute hydrochloric acid, which is a strong acid, displaces weak trioxocarbonate (IV) acid from trioxocarbonate (IV).

2HCl(aq) + CaCO3(s)   →  CaCl2 + H2O + CO2.

A solution of carbon (IV) oxide in water gives a weak acid trioxocarbonate (IV) acid.

H2O(l) + CO2(g)  → H2CO3(aq).

 

(iv) Precipitation Reaction

This method is used when preparing ethanoic acid from its salt. If hydrogen sulphide gas for example is bubbled into a solution of lead (II) oxide ethanoate, black lead (II) sulphate will be precipitated while ethanoic acid solution is formed.

(CH3COO)2F(aq) + H2S(g)  → PbS(s) + CH3COOH(aq)

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