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# OCR A-level Chemistry pH calculations

1. Determination of pH
2. The ionic product of water
3. The dissociation constant
4. Buffer calculations

pH and the hydrogen ion concentration are related by the equation pH = -log₁₀[H⁺].

Water molecules dissociate into hydrogen and hydroxide ions in solution. The ionic product of water describes the relationship between the two at equilibirum.

In solution, strong acids/bases completely dissociate into ions, but weak acids/bases only partially dissociate. The acid dissociation constant is Ka and is related to pKa by the expression pKa = -log₁₀Ka. The pH of a weak acid can be calculated by pH = 1/2 pKa - 1/2 log₁₀c.

A buffer solution maintains a constant pH when small volumes of acid or base are added. The pH of a buffer solution can be calculated by the equation pH = pKa - log₁₀[acid]/[salt].

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If the concentration of hydrogen ions of a solution is 1 x 10⁻⁸ mol l⁻¹, what is the hydroxide concentration?

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# ✅

If a solution has hydroxide ion concentration 1.2 x 10⁻⁵ mol l⁻¹, what will the pH of the solution be?

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# ✅

What does the term amphoteric describe?

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# ✅

What is the pH when Kw is 5.5 x 10⁻¹⁶?

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# ✅

At 303 K, Kw has a value of 1.471 x 10⁻¹⁴. What is the pH of water?

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# ✅

If an acid has a high pKa value, is there a high or low degree of dissociation?

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# ✅

Glycolic acid has Ka 1.3 x 10⁻⁴. Calculate it's pKa.

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# ✅

What is the pH of a 1.2 x 10⁻⁴ mol l⁻¹ solution with Ka 2.3 x 10⁻³?

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# ✅

If the concentration of acid and base in a buffer solution is the same, what will the pH be?

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# ✅

A pH 4.7 buffer solution is composed of 2.3 x 10⁻⁴ mol l⁻¹ acid and 2.8 x 10⁻⁴ mol l⁻¹ acid. Calculate pKa.

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