Investigating the Concentration of Citric Acid

Investigating the Concentration of Citric Acid

Problem

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I have been set the task of determining the concentration of a sample

of citric acid, using only a 1.0 M solution of sodium hydroxide and

any laboratory glassware that is required. I have also been given the

RMM of citric acid as 210g and I have been told that one mole of

citric acid will react with 3 moles of sodium hydroxide.

My Experiment

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Using this information I have determined that the best way to conduct

this experiment is to do a titration. This will allow me to determine

the amount of impure citric acid required to neutralise a known volume

of 1.0 M sodium hydroxide. Consequently, by calculating the correct

volume of pure citric acid that would be required to neutralise this

volume of sodium hydroxide, I can calculate the percentage purity of

the citric acid.

Calculating the Amount of Citric Acid

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In order to make this experiment a good titration, I must use a

reasonable amount of citric acid. This is so that the amount of citric

acid needed to neutralise the sodium hydroxide is not so small that it

is difficult to read off the burette, and so that it is not so large

that it takes more than 50cm3, and so 2 burettes must be used. I think

that I can safely assume that in this experiment the percentage purity

will be greater than 50%. Therefore, if I calculate the amount of pure

citric acid required to neutralise 25cm3 of sodium hydroxide when the

citric acid is 100% pure, I should easily be within the confines of my

50 cm3 burette. I will therefore now calculate the required mass of

sodium hydroxide:

Ratio citric acid : sodium hydroxide

1 : 3

Concentration of sodium hydroxide = 1.0 M

Therefore, require concentration of citric acid = 1.0 M /3 = 0.33 M

I will be using a volumetric flask which can hold 250cm3 of liquid.