Which of the following solutions has the highest pH?
(A) 1.0 mol L⁻¹ acetic acid
(B) 0.10 mol L⁻¹ acetic acid
(C) 1.0 mol L⁻¹ hydrochloric acid
(D) 0.10 mol L⁻¹ hydrochloric acid - HSC - SSCE Chemistry - Question 13 - 2015 - Paper 1
Question 13
Which of the following solutions has the highest pH?
(A) 1.0 mol L⁻¹ acetic acid
(B) 0.10 mol L⁻¹ acetic acid
(C) 1.0 mol L⁻¹ hydrochloric acid
(D) 0.10 mol L⁻¹ hyd... show full transcript
Worked Solution & Example Answer:Which of the following solutions has the highest pH?
(A) 1.0 mol L⁻¹ acetic acid
(B) 0.10 mol L⁻¹ acetic acid
(C) 1.0 mol L⁻¹ hydrochloric acid
(D) 0.10 mol L⁻¹ hydrochloric acid - HSC - SSCE Chemistry - Question 13 - 2015 - Paper 1
Step 1
Determine the pH of 1.0 mol L⁻¹ acetic acid
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Answer
Acetic acid is a weak acid, and its dissociation can be represented as:
CH3COOH↔H++CH3COO−
Using the acid dissociation constant (pKₐ ≈ 4.76), we can calculate the concentration of hydrogen ions at 1.0 mol L⁻¹.
Step 2
Determine the pH of 0.10 mol L⁻¹ acetic acid
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Answer
For 0.10 mol L⁻¹ acetic acid, a similar calculation can be performed. The equilibrium will favor the undissociated acetic acid more due to the lower concentration, thus resulting in a higher pH compared to the 1.0 mol L⁻¹ solution.
Step 3
Determine the pH of 1.0 mol L⁻¹ hydrochloric acid
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Answer
Hydrochloric acid (HCl) is a strong acid and dissociates completely:
HCl→H++Cl−
Thus, the pH can be calculated as:
pH=−log[1.0]=0
Step 4
Determine the pH of 0.10 mol L⁻¹ hydrochloric acid
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Answer
For 0.10 mol L⁻¹ hydrochloric acid, since it is a strong acid, the pH can be directly calculated as:
pH=−log[0.10]=1
Step 5
Comparison of pH values
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Answer
By comparing the calculated pH values:
1.0 mol L⁻¹ acetic acid (pH lower than 2)
0.10 mol L⁻¹ acetic acid (pH around 3)
1.0 mol L⁻¹ hydrochloric acid (pH = 0)
0.10 mol L⁻¹ hydrochloric acid (pH = 1)
The solution with the highest pH is 0.10 mol L⁻¹ acetic acid, which is option (B).
