Learning Objectives:• To be able to read titration questions and understand the information that they contain

Calculating Mr Values from Ar Values

Reading the Questions

Many people have difficulties in getting the important information out of the questions. You have to know HOW to read these questions.

The first thing to do is to identify the acid and the alkali used. The names will be in the question and the formulae will be in the equation.

Possible Acids Possible Alkalis

Hydrochloric Acid, HCl Sodium Hydroxide, NaOH

Sulphuric Acid, H2SO4 Sodium Carbonate, Na2CO3

Step 1

Find the numbers that fit with the acid and the alkali. What you want to know will always be the same. There is a table that you can fill in. The table always looks the same. Try to fill in as much as possible.

Acid Alkali

Concentration(mol.dm-3)

Volume (dm3)

Number of moles

Calculate the volume of 0.2 mol.dm-3 sodium hydroxide, NaOH, that will neutralize 20 cm3 of 0.25 mol.dm-3 hydrochloric acid, HCl, according to the equation:

NaOH + HCl NaCl + H2O

Acid Alkali

Concentration(mol.dm-3)

Volume (dm3)

Number of moles Hint

Write the information from the question in the table. Show also the variables you don’t have in the question

0.2 mol.dm-3Calculate the volume of sodium hydroxide, NaOH, that will neutralize of hydrochloric acid, HCl, according to the equation:

NaOH + HCl NaCl + H2O

Acid (HCl)

Alkali (NaOH)

Concentration(mol.dm-3)

Volume (dm3)

Number of moles

0.2 mol.dm-3

0.25 mol.dm-30.25 mol.dm-30.20 cm30.020 dm-3

Click on the cells in the table to see if you can get that piece of information from the question.