Titrations

L.O: To understand how to set up a titration to find the concentration of

an unknown acid / alkali.

• The concentration of solutions is measured as the number of moles dissolved in one dm3 of water (1dm3 = 1000cm3 = 1 litre).

• This concentration is given in mol dm3 or is sometimes written M .e.g. if 2 moles of a substance are dissolved in 1 dm3 of water, the solution is said to have a concentration of 2 mol/dm3

Concentrations in solution

Number of moles

concentration volume

Moles in a solution.• You are often given different concentrations of

solutions in chemistry e.g. 0.5M HCl

• That means there are 0.5M in 1 litre (1000cm3)So to work out the number of moles of a chemical in

given volume of the solutionNo of moles = volume (l) X Moles per 1000cm3 or

mol/dm3

Try this: how many moles are there in 100cm3 (0.1L) of 2M HCl? 0.1 X 2 = 0.2 Moles

Copy and complete the table

Moles Concentration (mol dm3)

Volume

0.1 3dm3

0.5 200cm3

0.15 1dm3

0.8 600cm3

0.01 2

0.2 0.5

Titrations

http://www.youtube.com/watch?v=b8SOr-ABE8w&feature=related

A solution becomes neutral with the right amount of acids and alkalis (end point)

Indicators

• Weak acid and strong alkali – phenolphthalein• Strong acid and weak alkali – methyl orange

• FIND OUT WHAT COLOUR THE INDICATORS ARE IN ACIDS AND ALKALIS

In your titration measure the volume of acid needed to neutralise the alkali. Work out the number of moles in the acid and alkali you used.

No of moles = volume (l) X Moles per 1000cm3 or mol/dm3

Are they the same?