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A strong acid H-X dissociates in aqueous solution - AQA - A-Level Chemistry - Question 14 - 2022 - Paper 3

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A strong acid H-X dissociates in aqueous solution. H₂X(aq) ↔ 2H⁺(aq) + X⁻(aq) What is the pH of a 0.020 mol dm⁻³ solution of this acid?

Worked Solution & Example Answer:A strong acid H-X dissociates in aqueous solution - AQA - A-Level Chemistry - Question 14 - 2022 - Paper 3

Step 1

Calculate the concentration of H⁺ ions in the solution

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Answer

Since H-X is a strong acid, it dissociates completely in water. Thus, the concentration of hydrogen ions, [H⁺], is equal to the concentration of the acid. Therefore, for a 0.020 mol dm⁻³ solution of H-X, we have:

[H+]=0.020 mol dm−3[H^+] = 0.020 \, mol \, dm^{-3}

Step 2

Calculate the pH using the formula

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Answer

The pH can be calculated using the formula:

pH=−log⁡10[H+]\text{pH} = -\log_{10}[H^+]

Substituting the value of [H⁺]:

pH=−log⁡10(0.020)\text{pH} = -\log_{10}(0.020)

Calculating this gives:

pH=1.70\text{pH} = 1.70

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