To determine the concentration of a limewater solution Essay Example

for the Titration Experiment:Fig.1.

Diluting the acid:The reason for diluting this acid is because it will produce more accurate results as it will be easier to see the endpoint colour change during titration. If it was left with its same concentration, the indicator would change colour too rapidly to control or see.1gmol-3 can be converted into moles using the equation:Amount (moles) = Mass (g) = 1 _ = approximately 1_ = 0.01 mol dm-3Molar Mass 74.1 100The molar ratio of the equation is a 1:2 ratio between calcium hydroxide and hydrochloric acid, therefore two moles of acid react with the limewater.

This means that the molar value for the calcium carbonate must be doubled to fit the molar ratio for the molar value of the hydrochloric acid:Amount (moles) = Mass (g) = 2 _ = approximately 2_ = 0.02 mol dm-3Molar Mass 74.1 100The acid should be diluted to the same amount to increase accuracy of results; therefore I plan to dilute the hydrochloric acid with concentration of 2.00 mol dm-3 by a dilution factor of 100 to 0.02 mol dm-3The equipment I plan to use to dilute the acid is a 250ml volumetric flask and a 25ml pipette, both of which are very high in accuracy which will benefit my results in finding the exact concentration of the limewater solution.

To dilute the acid I plan to first measure out 25ml of the 2.00 mol dm-3 hydrochloric acid using a 25ml pipette, making sure that the bottom of the meniscus is on the line (see fig.2.). Then place this measured amount into the 250ml volumetric flask and add distilled water up until the 250ml line.

This

process will dilute the acid to 0.2 mol dm-3 therefore by repeating the process again the molar will be diluted a further 10% and will be 0.02 mol dm-3 which is a sensible concentration to use for titration. Read about 6 Strong AcidsMethod:The experiments should be performed at room temperature and pressure as this will increase accuracy in the results produced.

Once the acid has been fully diluted to 0.02 mol dm-3 the calcium chloride can be titrated.Measure out 25ml of calcium hydroxide into a conical flask using a 25ml pipette by squeezing the pipette pump until the solution is past the 25ml line and then removing the pump to lower the meniscus exactly onto the line, (see Fig.2.).

Add a few drops of phenolphthalein; the colour of the solution should turn pink or fuchsia coloured which will indicate a solution of high pH value. The indicator will turn colourless below pH 8 when the limewater has become fully neutralised by the hydrochloric acid.To begin the titration, set up the equipment as shown in fig.1. Fill the burette with the diluted hydrochloric acid using a funnel which must be removed at the start of the titration as it will decrease accuracy of results by increasing the volume of the acid in the burette.

Place the conical flask of calcium hydroxide under the burette and on top of the white tile so that the colour change of the phenolphthalein is more evident to see.