The technique of titration is used to find out accurately how much of a chemical substance is dissolved in a given volume of a solution, that is, the concentration of the solution.
The technique uses a particular set of apparatus with which volumes of solutions can be measured to an accuracy of greater than 0.1 cm3. Three important pieces of apparatus are:
|Burette||to measure accurately the volume of a solution added. The scale can be read to an accuracy of half a division, that is to 0.05 cm3.|
|Pipette||to deliver an accurate volume of a solution. Often this is 25 cm3.|
|Volumetric flask||to make up an accurate volume of a solution, for example, 250 cm3. This could be a standard solution.|
|For each piece of apparatus volume readings are taken at the bottom of the meniscus.|
In a titration the pipette is used to transfer 25 cm3 (usually to ±0.05 cm3) of a solution into a conical flask. Another solution that reacts with the pipetted solution in the conical flask is carefully added from a burette until it has all exactly reacted. This is called the end point of the titration (or equivalence point of the reaction). There needs to be a way of knowing when the end point is reached. An indicator of some kind may be needed. For example, in the titration of a strong acid and a strong base a few drops of methyl orange or phenolphthalein could be used.
Numerous variables can be calculated from the data obtained from a titration, such as the unknown concentration of a solution if the balanced equation for the chemical reaction is known.
Ba(OH)2(aq) + 2HCl(aq) ® BaCl2(aq) + 2H2O(l)
This balanced chemical equation shows that:
1 mol Ba(OH)2 º 2 mol HCl
For an accurate titration, the volume of solution delivered from the burette at the end-point should be in the region of 25 cm3. Because the concentration of the barium hydroxide solution is approximately 0.03 mol dm-3:
25 cm3 0.03 mol dm-3 Ba(OH)2(aq) º 25 cm3 0.06 mol dm-3 HCl(aq).
Since the concentration of the hydrochloric acid is 0.600 mol dm-3, there is a need to dilute this solution to one-tenth of its original concentration.
Use the following steps in your calculation:
Moles of HCl = mol
Moles of Ba(OH)2 = mol
Concentration of Ba(OH)2(aq) = mol dm-3
Concentration of Ba(OH)2(aq) = g dm-3