Question

Five solutions A, B, C, D, and E when tested with universal indicator showed pH as 4, 1, 11, 7, and 9, respectively.
1. Arrange the pH in increasing order of hydrogen-ion concentration.
2. Which solution is
(a) neutral?
(b) strongly alkaline?
(c) strongly acidic?
(d) weakly acidic?
(e) weakly alkaline? [3 marks]

Answer 1

1. pH is the measure of acidity or basicity of a solution and mathematically it is expressed as a negative logarithm of hydronium ion concentration.
$pH=-log\left[H^{+}\right]$

So pH is inversely proportional to the hydronium ion concentration.

The pH can be arranged in the increasing order of the concentration of hydrogen ions as: 11 < 9 < 7 < 4 < 1.
[0.5 Marks]

2.
(a) Solution D has pH = 7, hence its neutral
[0.5 Marks]

(b) Higher the pH, more alkaline is the solution.
Solution C with pH 11 is strongly alkaline.
[0.5 Marks]

(c) Lower the pH, more acidic is the solution.
Hence, solution B with pH 1 is strongly acidic.
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(d)Lower the pH, more acidic is the solution.
Therefore, solution A with pH 4 is weakly acidic.
​​​​​​​ [0.5 Marks]

(e) Higher the pH, more alkaline is the solution.
Solution E with pH 9 is weakly alkaline.
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