Question

Which of the following statements is correct about an aqueous solution of an acid and of a base?
(i) Higher the pH, stronger the acid
(ii) Higher the pH, weaker the acid
(iii) Lower the pH, stronger the base
(iv) Lower the pH, weaker the base
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)

Answer 1

A substance will be known as an acid if it gives out positive hydrogen ions that is ${H^ + }$ ions when dissolved in water. A substance will be known as a base if it gives out hydroxide ions that is $O{H^ - }$ ions when dissolved in water. We can check the strength of an acid or a base by calculating the concentration of hydrogen ions in the solution and with the help of the pH scale. Acids have pH below 7 while bases have pH above 7.

Complete step by step solution:
An acidic substance is a substance which includes acid within itself. A basic substance is a substance which includes base within itself. Aqueous solutions are solutions dissolved in water. An acid is known as a strong or a weak acid depending on the number of positive hydrogen ions it releases in the water when dissolved. A base is known as a strong or a weak base depending on the number of negative hydroxide ions it releases in the water when dissolved.
The pH scale starts from 0 and ends at 14, 0 indicating most acidic and 14 indicating most basic. The pH value of 7 indicates neutrality.
Hence lower the pH, weaker the base and higher the pH, weaker the acid.
Therefore, the correct statements are (ii) and (iv).

Note:
The universal indicator can be used as universal indicator paper or solution. So, when the universal indicator comes in contact with a solution, it changes its colour according to the pH value of the solution. There is a particular colour for each pH value in the pH chart. We can tell whether the solution is a strong or weak acid or whether the solution is a strong or weak base by checking the pH value of the appeared colour in the pH chart.