Titration Calculations

Before you go any further, check that you can do the following…

* Calculate: Relative molecular masses from a given chemical formula

* Calculate: Number of Moles  from the mass/RMM equation

* Manipulate: The number of moles equation to get the form you require.

 When you are confronted by a Titration calculation the first rule is:

 

DON’T PANIC!

 

The Second rule is read through the question very carefully.

The Third rule is read through the question carefully again!

 

We are now going to look at a question and hopefully guide the unbelievers (henceforth known as infidels) through a titration calculation. If you know how to do these, go straight to the questions at the end.

The question:

10.0 cm3 of a solution of potassium hydroxide was titrated with a 0.10 M[1] solution of hydrochloric acid. 13.5 cm3 of the acid was required for neutralization. Calculate the concentration of the potassium hydroxide solution.

Step 1

Write down everything you know. Placing the one you know most about on the left (you don’t have to do this, but its just a good idea).

 

Hydrochloric Acid                                                      Potassium hydroxide

Volume used = 13.5 cm3                                          Volume used = 10.0 cm3

Concentration = 0.10 M                                            Concentration = TBD[2]

Step 2

Write the equation or as much as you know about it.

 HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

 This is necessary to check out the ratios of reactants – in this case 1:1 so we don’t have to worry about any ratios.

Step 3

Calculate the Number of Moles used of the reactant you know most about. In this case the HCl(aq)

 

The rule here is Number of Moles = volume × concentration

Step 3

Work out how many moles of the unknown you have used, this is where you may need to multiply up or down the number of moles, so if 1 mole of HCl needed 2 mol of potassium hydroxide, then at this point you would multiply the number of moles of HCl by 2. In this case this is unnecessary.

 

Number of moles of HCl = 0.0014 mol

 

Number of moles KOH = 0.0014 mol – they react in a one to one ratio

Step 4

 

Work out the concentration of the potassium hydroxide.

 

 

Concentration = 0.14 M

Questions

 

1.                  Sodium ethanedioate, Na2C2O4, can be made into a solution of an exact and reliable concentration and so can be used as a standard solution for checking the concentration of a solution containing sulphuric acid. The reaction is summarized by the equation:

 

Na2C2O4 + H2SO4 Na2SO4 + (CO2H)2

 

In a particular experiment 10.0 cm3 of a 0.50 M solution of sodium ethanedioate was found to react with 8.7 cm3 of sulphuric acid. Find the concentration of the concentration of the sulphuric acid.

 

2.                  The equation for the reaction of sodium hydroxide solution with sulphuric acid is:

 

2NaOH(aq) + H2SO4(aq) Na2SO4(aq) + 2H2O(l)

 

 

 

 

[1] M = mol dm-3

[2] To be determined