Making and investigating buffer solutions

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Making and investigating buffer solutions

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Aim

I will attempt to prepare two buffer solutions. The first buffer solution will have a pH value of 5.2 and will be made from a mixture of 1.0M ethanoic acid and 1.0M sodium ethanoate solution. The second buffer solution will have a pH value of 8.8 and will be made from a mixture of 1.0M ammonia and 1.0M ammonium chloride solution.

Plan

In order to make these buffers, I will need to calculate the exact proportions of salt solution and acid/alkali to add in order to obtain the necessary pH value:

pH = pKa - log [HA]

[A-]

Given that:

The pKa value for 1.0M ammonia and 1.0M ammonium chloride solution is 9.3.

The pKa value for 1.0M ethanoic acid and 1.0M sodium ethanoate solution is 4.8.

For the making of the buffer pH 5.2:

Equations for the dissociation of ethanoic acid and sodium ethanoate respectively:

CH3COOH + H2O - CH3COO- + H3+O

CH3COONa CH3COO- + Na+

Using the equation previously stated:

5.2 = 4.8 - log [HA]

[A-]

5.2 - 4.8 = -