C3.4.4 Titration calculations

Titrations are used to find the volumes of solutions that react exactly

The concentrations are calculated using balanced symbol equations and moles

Worked example

A student found that 25.0cm3 of sodium hydroxide solution with an unknown concentration reacted with

exactly 20.0cm3 of 0.50mol/dm3 hydrochloric acid. What was the concentration of the sodium hydroxide

solution?

The equation for this reaction is: NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)

The concentration of the HCl is 0.50mol/dm3, so 0.50mol of HCl are dissolved in 1000cm3 of acid.

Therefore 20.0cm3 of acid contains 20 x 0.50/1000mol = 0.010mol HCl

The equation for the reaction tells us that 0.010mol of HCl will react exactly with 0.010mol of NaOH.

This means that there must be 0.010 moles of NaOH in the 25.0cm3 of solution in the conical flask.

So, the concentration of NaOH solution = (0.010/25) x 1000 = 0.40mol/dm3…read more

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