NON-MEATALS, D. Acid, Base and Salt

Total Questions: 56

1. Antacids are - [Chhattisgarh P.C.S (Pre) 2016]

(a) Base
(b) Acid
(c) Salt
(d) Buffer
(e) None of these

Correct Answer: (a) Base

Solution:Antacids are substances that neutralize stomach acid (hydrochloric acid, HCl) to relieve heartburn, indigestion, and upset stomach. To neutralize an acid, they must be basic (alkaline) in nature. Antacids are bases. They are formed by aluminium hydroxide, magnesium hydroxide, magnesium carbonate, magnesium trislicate, calcium carbonate etc. It is used as a medicine to reduce excessive acid formed in stomach or prevent it from forming.

2. Goldsmiths uses aqua regia, which is prepared by mixing – [U.P.P.C.S. (Mains) 2014]

(a) Nitric acid and Sulphuric acid
(b) Nitric acid and Hydrochloric acid
(c) Sulphuric acid and Hydrochloric acid
(d) Citric acid and Benzoic acid

Correct Answer: (b) Nitric acid and Hydrochloric acid

Solution:Aqua regia (Latin for "royal water") is a fuming yellow or red liquid, an acidic, corrosive and oxidative mixture of three parts concentrated hydrochloric acid (HCl) and one part concentrated nitric acid (HNO₃). It is called aqua regia because it is one of the few acid mixtures that can dissolve the 'noble' metals – Gold (Au), Platinum (Pt) and Palladium (Pd).

3. pH value shows the Numeric value of – [M.P.P.C.S. (Pre) 1996]

(a) Quality of chemical used for developing photographic negatives
(b) Analysing the acidic or basic nature of a solution
(c) Analysing the intensity of an earthquake
(d) Analysing for checking purity of milk

Correct Answer: (b) Analysing the acidic or basic nature of a solution

Solution:The pH scale measures the acidity or basicity of a solution. The solution with a pH less than 7 is said to be acidic while the solution with the pH greater than 7 is basic or alkaline. The pure water has a pH value 7.

The logarithm of the reciprocal of hydrogen ion concentration in moles per litre is measured by pH scale from 0 to 14.

4. The pH of a solution changes from 3 to 6. The H⁺ ion concentration will : [66th B.P.S.C. (Pre) 2020]

(a) increase 3 times
(b) decrease 3 times
(c) decrease 10 times
(d) decrease 1000 times
(e) None of the above/More than one of the above

Correct Answer: (d) decrease 1000 times

Solution:pH is a logarithmic scale used to specify the acidity or basicity (alkalinity) of an aqueous solution. It inversely indicates the concentration of hydrogen ions (H⁺) in the solution as it approximates the negative of the base 10 logarithm of the molar concentration of hydrogen ions (H⁺) in a solution. Each number represents a 10-fold change in the acidity/basicity of the solution. If the pH number is increased by 1, it means H⁺ ion concentration is decreased by 10 times. Hence, if the pH of a solution changes from 3 to 6, the H⁺ ion concentration will decrease 1000 times, and it will become less acidic.

The pH scale is logarithmic, meaning a change of one pH unit represents a tenfold change in H⁺ ion concentration.

pH = - $l o g₁₀ [H⁺]$
If pH changes from 3 to 6, the change is 6 - 3 = 3 units.
A decrease in pH by 1 unit means a 10 times increase in H⁺ concentration.
An increase in pH by 1 unit means a 10 times decrease in H⁺ concentration.
So, an increase in pH by 3 units (from 3 to 6) means the H⁺ ion concentration will decrease by $1 0³$ , which is 1000 times.

5. Which of the following has pH value 7? [64th B.P.S.C (Pre) 2018]

(a) Pure Water
(b) Neutral solution
(c) Basic solution
(d) Acidic solution
(e) None of the above/More than one of the above

Correct Answer: (e) None of the above/More than one of the above

Solution:

Pure water at 25°C has a pH of 7 because the concentrations of H⁺ and OH⁻ ions are equal.

A neutral solution is defined as one that has a pH of 7.

Basic solutions have pH > 7.

Acidic solutions have pH < 7.

Since both pure water and a neutral solution have a pH of 7, option (e) "More than one of the above" is the correct choice.

6. Which among the following solutions has pH value more than 7? [67th B.P.S.C. (Pre) 2022]

(a) Buffer solution
(b) Basic solution
(c) Acidic solution
(d) Neutral solution
(e) None of the above/More than one of the above

Correct Answer: (b) Basic solution

Solution:The pH value of pure water and neutral solution is 7. In general, water with pH lower than 7 is considered acidic and greater than 7 is considered basic.

7. A solution turns red litmus blue. The pH of solution is : [Chhattisgarh P.C.S. (Pre) 2014]

(a) 7
(b) 6
(c) 5
(d) 6.5
(e) None of the above

Correct Answer: (e) None of the above

Solution:When a red litmus paper is immersed in a base or alkaline, the red litmus paper turns blue indicating the given solution as alkaline/base. When a blue litmus paper is immersed in an acid, the litmus paper turns red from blue indicating acid. The solution having pH value less than 7 is acidic and the solution having pH value more than 7 would be basic. According to the question, the red litmus paper turns blue which shows alkaline/basic nature of the solution. Thus, it has the pH value more than 7. Therefore, none of the above are correct.

8. You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. Which of them will turn red litmus to blue? [68th B.P.S.C. (Pre) 2022]

(a) Distilled water
(b) Acid
(c) Base
(d) More than one of the above
(e) None of the above

Correct Answer: (c) Base

Solution:As established, basic solutions are characterized by their ability to turn red litmus paper blue. Distilled water is neutral and will not change the color of red litmus. An acidic solution will turn blue litmus red (or leave red litmus unchanged).

9. Why does dry HCl gas not change the colour of dry litmus paper? [68th B.P.S.C. (Pre) 2022]

(a) HCl gas acts as a dehydrating agent.
(b) Blue litmus becomes dry in the presence of dry HCl gas.
(c) No H₃O⁺ ions are present. Litmus changes colour only in the presence of H₃O⁺ ions.
(d) More than one of the above
(e) None of the above

Correct Answer: (c) No H₃O⁺ ions are present. Litmus changes colour only in the presence of H₃O⁺ ions.

Solution:All acidic aqueous solutions contain protonated water, known commonly as the hydronium ion (H₃O⁺). Dry HCl gas does not change the colour of dry litmus paper, because in the absence of water no hydronium (H₃O⁺) ions are formed. As HCl is not in aqueous form nor is the litmus paper wet and thus the lack of presence of hydrogen (H⁺) or hydronium (H₃O⁺) ions leads to the litmus paper not changing its colour. However, it is to be noted that blue litmus paper becomes red due to a higher concentration of H⁺/H₃O⁺ ions (i.e. in the case of acids), while red litmus paper becomes blue due to higher concentration of OH⁻ ions (i.e. in the case of bases).

10. Which of the following may be a possible pH value of an acidic solution? [Chhattisgarh P.C.S. (Pre) 2018]

(a) 6
(b) 7
(c) 8
(d) 9

Correct Answer: (a) 6

Solution:If the pH of a solution is less than 7, the solution is called acidic; if the pH is about 7, the solution is neutral, and if the pH is greater than 7, the solution is called basic. Out of the given options, only 6 is less than 7, making it a possible pH value for an acidic solution.

In an acidic solution, the concentration of hydrogen ions (H⁺) is greater than the concentration of hydroxide ions (OH⁻).

12 3 4 5 6 Next »