A pH 3.0 solution of HCl(aq) is diluted by adding water to produce a pH 5.0 solution - HSC - SSCE Chemistry - Question 15 - 2013 - Paper 1
Question 15
A pH 3.0 solution of HCl(aq) is diluted by adding water to produce a pH 5.0 solution.
Which row in the following table correctly identifies an appropriate volume of... show full transcript
Worked Solution & Example Answer:A pH 3.0 solution of HCl(aq) is diluted by adding water to produce a pH 5.0 solution - HSC - SSCE Chemistry - Question 15 - 2013 - Paper 1
Step 1
Identify the pH values of the solutions
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Answer
The initial solution has a pH of 3.0, meaning it has a high concentration of H<sub>3</sub>O<sup>+</sup> ions. The target solution has a pH of 5.0, which indicates a much lower concentration of H<sub>3</sub>O<sup>+</sup> ions.
Step 2
Calculate the concentration change
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Answer
The pH scale is logarithmic. The difference between pH 3.0 and pH 5.0 is 2 units. Since each unit change in pH represents a tenfold difference in concentration, we can express the change as:
[H3O+]final=10−5M.
[H3O+]initial=10−3M.
This means for every mole of H<sub>3</sub>O<sup>+</sup>, we need to dilute it to achieve the reduction in concentration.
Step 3
Determine the dilution factor
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Answer
The dilution factor can be calculated as:
D=[H3O+]final[H3O+]initial=10−510−3=100.
This indicates that we need to dilute the initial solution by a factor of 100.
Step 4
Identify the appropriate volumes from the table
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Answer
Using the dilution factor of 100, if we take 1 mL of the original solution, we would need to add 99 mL of water to achieve a total volume of 100 mL. However, among the choices given:
Choice (C) with 10 mL of original solution and 990 mL of water is appropriate. When combined, it gives a total of 1000 mL, which follows the dilution factor correctly.
Therefore, the correct answer is (C).
