Titration - apparatus, technique, calculation

Label the apparatus by dragging and dropping the labels on the right...
Burette Conical flask Graduated Pipette Volumetric Flask
Conical
flask
Volumetric
flask
Pipette
Burette
Wash with distilled water only
Wash with distilled water only
Wash with distilled water only
Wash with distilled water only
Wash with distilled water and then with the solution going into it
Wash with distilled water and then with the solution going into it
Wash with distilled water and then with the solution going into it
Wash with distilled water and then with the solution going into it

The Technique of Titration

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:

Buretteto 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.
A standard solution is one of exactly known concentration and of a known solute.
Titration Apparatus

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.

Often a titration is repeated until successive titres are within 0.1 cm3.

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.

Try out the titration below:

Find the concentration of a solution of barium hydroxide...
The accurate concentration of the barium hydroxide solution is unknown, but it is approximately 0.03 mol dm-3. You are also provided with a 0.600 mol dm-3 solution of hydrochloric acid and some methyl orange indicator.

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.

Dilution should be done using a graduated pipette and volumetric flask. The apparatus should be washed appropriately and used with complete regard for accuracy.
Acid-Base Titration
The acid-base indicator used is methyl orange. This is yellow in alkaline solution, red in acidic solution, and orange at the end-point of the titration.
A Strong Acid - Strong Base Titration

Volume of Ba(OH)2(aq) = 25.0 cm3
Concentration of Ba(OH)2(aq) = approx. 0.03 mol dm-3
Concentration of HCl(aq) = 0.060 mol dm-3

Volume of HCl added from burette = cm3

Calculating the concentration of the barium hydroxide solution...

Use the following steps in your calculation:

  1. Work out the amount in moles of the substance for which both the concentration and volume are known. In this case it is the hydrochloric acid (concentration 0.060 mol dm-3, volume 23.75 cm3). Give your answer to 3 significant figures.

Moles of HCl = mol      

  1. Now decide on the amount in moles of barium hydroxide that has reacted.

Moles of Ba(OH)2 = mol      

  1. Now work out the concentration of the barium hydroxide solution given that the amount in moles calculated above is dissolved in 25.0 cm3 of solution.

Concentration of Ba(OH)2(aq) = mol dm-3      

  1. Calculate the concentration of the barium hydroxide solution in g dm-3 (Ar: Ba 137.5; O 16; H 1;).

Concentration of Ba(OH)2(aq) = g dm-3