Acid Bases and Salts MCQ Questions

Food has sour and bitter flavours because of acids and bases in it. Acids have a sour taste and cause blue litmus to turn red, whereas bases have a bitter taste and cause red litmus to turn blue. Turmeric is another natural indicator, similar to litmus. The reaction of an acid with a base produces a salt, which is a neutral chemical.

Acid Bases and Salts MCQ Chemistry Questions with Solutions

Q-1: Which of the following is the correct classification of Dolomite?

1. An acid salt
2. A mixed salt
3. A normal salt
4. A double salt

Answer: d) double salt

Explanation: A double salt is a crystalline salt with the content of a mixture of two simple salts but a distinct crystal structure.

Dolomite is a double salt consisting of calcium carbonate (CaCO₃) and magnesium carbonate (MgCO₃) salts.

Q-2: Acetic acid is weak acid because

1. Its aqueous solution is acidic
2. It is highly ionised
3. It is weakly ionised
4. It contains the COOH group.

Answer: c) It is weakly ionised

Explanation:

In an aqueous solution, a weak acid is one that ionises just minimally. Acetic acid (found in vinegar) is a highly common weak acid because it doesn’t dissociate much in solution, Its ionisation may be seen below.

CH₃COOH(aq)⇄H⁺(aq)+CH₃COO⁻(aq)

As a result, it is less effective at donating protons.

Because acetic acid’s ionisation is incomplete, the equation is shown with a double arrow.

Q-3: What will be the pH of the solution on mixing a 50 mL solution of a strong acid of pH=1 with a 50 mL solution of strong acid of pH =2.

1. 0.74
2. 1.76
3. 1.5
4. 1.26

Answer: d) 1.26

Explanation:

We know that pH= -log[H⁺]

Molarity= number of moles/V(L)

Step-1: Calculate the [H⁺] for a strong acid with pH =1

1=-log [H⁺] [H⁺]= 10^-1M

Step-2: Calculate the [H⁺] for a strong acid with pH= 2

2=-log[H⁺] [H⁺]= 10^-2M

Step-3: Calculate the moles of H⁺ for a strong acid with pH =1

Moles of H⁺= [H⁺] ×V(L)

= 10^-1M × 0.050

= 0.005moles

Step-4: Calculate the moles of H⁺ for a strong acid with pH =2

Moles of H⁺= [H⁺] ×V(L)

= 10^-2M × 0.050

= 0.0005 moles

Step-5 Calculate the total moles of H⁺ in the solution

Total moles of H⁺ = (0.005+ 0.0005) moles

= 0.0055 mol

Total volume of mixture = (0.05 +0.05)L

= 0.1L

Step-6 Calculate the total concentration of H⁺ in the solution.

= 0.0055 mol /0.1L

= 0.055 M

Now, pH of the solution = -log[H⁺]

=-log[0.055]

= 1.26

Q-4: Which of the following is not an amphiprotic species?

1. HCO₃^–
2. HPO₄^2-
3. OH^–
4. H₂PO₄^2-

Answer: c) OH^–

Explanation: Amphiprotic ions are those ions which can gain or lose hydrogen ions.

Except OH^–, all other species are amphiprotic in nature. OH^– can gain a proton to form H₂O but it cannot lose. Hence it is not amphiprotic.

Q-5: Three reactions involving H₂PO₄^– are given below :

i) H₃PO₄ + H₂O → H₃O⁺ + H₂PO₄^–

ii) H₂PO₄^–+ H₂O → HPO₄^2- + H₃O⁺

iii) H₂PO₄^– + OH^–→ H₃PO₄ + O^2-

In which of the following above H₂PO₄^– act as an acid?

1. ii only
2. i) and ii)
3. iii) only
4. i) only

Answer: a) ii only

Explanation: An acid is a material that loses protons and we can clearly see that, only in ii) H₂PO₄^– is donating a proton to water . Thus it acts as an acid.

Q-6: Which of the following compound is most acidic?

1. Cl₂O₇
2. P₄O₁₀
3. SO₃
4. B₂O₃

Answer: a) Cl₂O₇

Explanation: Acidic strength is the tendency of a molecule/compound to liberate protons. In case of proton deficient compounds, acidic strength is governed by the positive oxidation state of the central atom. More is the value of positive oxidation state, more is the acidic strength.

The oxidation states of Cl,P,S and B are +7,+5,+6 and +3 respectively.

This shows that Cl₂O₇ is the most acidic.

Q-7: Identify the basic salt from the following.

1. Na₂CO₃
2. NaNO₃
3. KCl
4. NH₄Cl

Answer: a) Na₂CO₃

Explanation: There are three main classification of salts:

Acidic Salt: A salt that is formed by the neutralisation of strong acid and weak base.

Basic Salt: A salt that is formed by the neutralisation of strong base and weak acid.

Neutral Salt: A salt that is formed by the neutralisation of strong acid and strong base.

The hydrolysis of salt can let us know the acid and base from which it is made up.

On hydrolysis of Na₂CO₃ , we will get NaOH(strong base) and H₂CO₃ (weak acid). Since the effect of strong things is always taken into account, hence it is a basic salt.

Q-8: Which of the following can be considered as an example of olfactory indicators?

1. Onion
2. Methyl orange
3. Turmeric
4. China rose

Answer: a) Onion

Explanation: A substance whose smell varies when it is mixed with an acidic or basic solution is said to be an olfactory indicator. In the laboratory, olfactory indicators can be used to determine whether a solution is a basic or an acid, a procedure known as olfactory titration.

Some common examples are Onion, vanilla, clove oil etc.

Q-9: The pH of a solution obtained by mixing 50.00 mL of 0.20 M weak acid HA (K_a = 10^-5) and 50.00 mL of 0.20M NaOH at room temperature is

1. 2
2. 3
3. 5
4. 9

Answer: d) 9

Explanation: Salt is formed when equal amounts of acids and bases react neutralising the effect of each other.

Here, weak acid(HA) reacts with strong base(NaOH) in the same proportion, thus a basic salt is formed.

Step-1- Calculate the moles of acid

Moles of acid = Molarity × V(L)

= (0.20 mol/L)×(0.05L)

= 0.01 mol

Step-2- Calculate the moles of base

Moles of acid = Molarity × V(L)

= (0.20 mol/L)×(0.05L)

= 0.01 mol

The formula used for calculating pH of a basic salt is:

pH= ½( pK_a + pK_w + log c)

As pK_a = -logK_a

= -log(10^-5)

= 5

At room temperature, pK_w = 14

‘C’ is the concentration of the salt (NaA)

Let us consider a reaction,

Total volume(L)= (0.05+0.05)L= 0.1L

C= Moles of NaA/Total volume

= 0.01/0.1

= 0.1M

Substituting the values in the formula,

pH= ½(5+14+log(0.1)

= 9

Hence, the pH of the solution is 9.

Q-10: The pH of a solution prepared from 0.005 mole of Ca(OH)₂ in 100cc water is

a)10

b) 12

c) 11

d) 13

Answer: d) 13

Explanation:

Step-1-Calculate the [OH^–] in the solution

We know that,

Molarity = Number of moles/Volume(in L)

= 0.05 M

Since there are two OH^– ions, therefore [OH^–] = 2× 0.05

= 0.1 M

Note: 100cc =100mL = 0.1L

Step-2– Calculate pOH

pOH = -log[OH^–]

= -log(0.1)

= 1

As, pK_w = pH +pOH

Also, at room temperature, pK_w = 14

Substituting the values,

14= pH+1

pH= 13

Hence, the pH of the solution is 13.

Q-11: The pH of 0.1 M solution of the following salts increases in the order

1. NaCl<NH₄Cl<NaCN<HCl
2. HCl< NH₄Cl<NaCl<NaCN
3. NaCN<NH₄Cl<NaCl<HCl
4. HCl<NaCl<NaCN<NH₄Cl

Answer: HCl< NH₄Cl<NaCl<NaCN

Explanation: pH is the measure of whether the solution is acidic, basic or neutral on the basis of its value.

With a pH of 7, salts of a strong acid and a strong base are neutral. Salts of a strong acid and weak base, on the other hand, are acidic with a pH less than 7, and salts of a strong base and weak acid are basic with a pH greater than 7.

NaCl is the salt of strong acid( HCl) and strong base (NaOH) which makes it overall neutral

NH₄Cl is the salt of strong acid (HCl) and weak base(NH₄OH ) which makes it acidic but not more than HCl.

NaCN is the salt of weak acid (HCN) and strong base (NaOH) which makes it basic.

HCl is a strong acid.

Thus, the correct order of pH is

HCl< NH₄Cl<NaCl<NaCN

Q-12: Which of the following is not a use of Bleaching powder?

1. Bleaching agent
2. Oxidising agent
3. Used in soda-acid fire extinguishers.
4. Disinfectant

Answer: c) Used in soda-acid fire extinguishers

Explanation: Bleaching powder is represented as CaOCl₂.

There are many applications of Bleaching powder:

(i) It is used for bleaching cotton and linen in the textile industry.

(ii) bleaching wood pulp in paper factories and for bleaching washed clothes in laundry.

(iii) as an oxidising agent in many chemical industries.

(iv) to make drinking water free from germs.

Q-13: What is the correct formula of Plaster of Paris?

1. CaSO₄
2. CaSO₄.1/2H₂O
3. CaSO₄.2H₂O
4. Ca(OH)₂

Answer: b) CaSO₄.1/2H₂O

Explanation:

Plaster of Paris is a material used by doctors to maintain shattered bones in the proper position. Plaster of Paris is a white powder that transforms into gypsum when mixed with water, resulting in a hard solid mass.

Its chemical name is calcium sulphate hemihydrate with the chemical formula of CaSO₄.1/2H₂O.

Q-14: If a solution of sodium hydrocarbonate is heated, the product formed is

1. NH₄Cl
2. NaNO₃
3. Na₂CO₃
4. Na₂CO₃.10H₂O

Answer: c) Na₂CO₃

Explanation: The following reaction takes place:

Q-15: Which of the following salts do not contain water of crystallisation?

a) Baking Soda

b) Gypsum

c) Red vitriol

d) Copper sulphate

Answer: a) Baking soda

Explanation: Water molecules found inside crystals are known as water of crystallisation or water of hydration in chemistry.

Gypsum has a chemical formula of CaSO₄.2H₂O

Baking soda has a chemical formula of Na₂CO₃

Red vitriol has a chemical formula of CoSO₄.7H₂O

Copper sulphate has a chemical formula of CuSO₄.5H₂O

Practise Questions on Acid Bases and Salts

Q-1: What happens when an acid solution is combined with a base solution in a test tube?

1. the solution’s temperature rises.
2. The temperature of the solution drops.
3. The solution’s temperature remains constant.
4. The production of salt occurs

Select the correct option from below:

(A) (a) only

(B) (a) and (c)

(C) (b) and (d)

(D) (a) and (d)

Q-2: To make Plaster of Paris, what temperature is gypsum heated to?

1. 25^oC
2. 75^oC
3. 80^oC
4. 100^oC

Q-3: The pH of a 2.0 M solution of NH₄Cl is

(K_b(NH₃) = 1.8× 10^-5)

1. 4.48
2. 6
3. 8
4. 3

Q-4: The salt having pH dependent of its concentration is

a)(CH₃COO)C₅H₅NH

b) NH₄CN

c) NaCl

d) K₂CO₃

Q-5: In a dilute aqueous solution of ammonia, which of the following is present?

1. OH^– + NH₃
2. OH^– + NH₄⁺
3. H₃O⁺ + NH₂^–
4. None of these

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