To Determine the Concentration of a Limewater Solution

(Limewater + Hydrochloric Acid                Calcium Chloride + Water)

From here we would uses a series of mole calculations once we had established the amount of titrate it would require to neutralize an unknown solution on limewater to determine the concentration.

Initially, we will be supplied with 250cm3 of Limewater and HCl 2 mol dm-3. I will need to dilute the HCL down. Originally I had planned to dilute it down to 0.5 mol dm-3, but after testing this initially, I quickly realized that this was far to strong: in fact, it was at least 25 times too strong! Therefore, I realised that I would have to dilute my acid down to at least 0.02mol dm-3. In order to do this I would have to work on a ratio of 1:99 and end up with 250cm3. It is known that in order to dilute this solution down to the appropriate concentration, I will have to be very accurate. I will take 2.5cm3 of 2 mol dm-3 HCL and put this into a measuring cylinder. I will the  fill the cylinder up to 250cm3. This will mean that I will end up with an acid of concentration 0.02 mol dm-3. By using an acid of this lower concentration, it will make it easier to determine the end point of the titration, therefore making it more accurate.

Variable Control

In this experiment I will be keeping all the factors that are not being tested exactly the same. The concentrations of the solutions will be the same throughout, therefore enabling a fair test. The same quantities of Limewater will be used every time a fresh titration is undertaken. I will use a clean conical flask each time to ensure there is no residue acid affecting my results. Temperature and pressure are not an issue, as they do not feature in this experiment. I will keep all these variables the same because otherwise, I could obtain incorrect and inaccurate results, therefore nullifying the point of this experiment.

Apparatus

• Burette

• White Tile
• Conical Flask
• Distilled Water
• Limewater
• Hydrochloric Acid
• Waste beaker
• Measuring Cylinder
• Pipette
• Funnel
• Phenolpthalein

Diagram

Organisation of Work

• I will first make up my diluted acid, using the method before. The apparatus needed for this part of the experiment are simply, a 10ml pipette and a measuring cylinder.
• After making my new acid, the burette will be flushed out using distilled water, and then diluted hydrochloric acid to remove any impurities they my be residual from any previous experiments.
• The burette will then be filled to a suitable level with our acid and the start point will be read off at eye level and recorded.
• 25ml of Limewater will be added to a clean conical flask along with five drops of phenolpthalein.
• The Conical flask will then be placed under the burette and the tap turned on. A rough titration will take place. The limewater solution will be swirled gently to ensure all the acid is evenly distributed throughout.
• As the solution turns from pink to clear, the tap will be turned off and the level of the acid will be read off and recorded.
• A new, clean conical flask will then be taken and filled with 25ml of Limewater and another five drops of phenolpthalein. The burette will be refilled and the new start point recorded.
• This time, the tap will be allowed to run freely until 3cm3 above the amount of titrate used in the first titration. At this point the tap will be slowed to about 4 drops per second.
• Once a larger patch of pink begins to appear in the solution the tap will be stopped, and the tip touched on the edge of the conical flask. We will then use distilled water to flush the sides of the flask to remove and acid from the sides into the solution.
• The tap will then be turned on to about ½ a drop per second. As soon as the drop begins to form on the tip or the burette, it will be touched onto the edge of the flask and flushed with distilled water. This will continue until the solution turns a pale pink / almost clear for 10 seconds. At this point we will know the titration has reached the end point and the level on the burette will be recorded and read off.
• We will take 5 readings in all to insure that we have an accurate range, and the average will be taken from that and used in the calculation to determine the concentration of the Limewater. The final 5 readings must be within 0.1 of each other to ensure accuracy of the average, and these can only be obtained with repeats.

Risk Assessment

• Goggles and lab coats will be warn at all times
• Hydrochloric Acid: HCl (aq) is highly corrosive in strong concentrations. Because of this, extreme caution will be taken whilst handling the solution and making a more dilute concentration.
• Limewater or Calcium Hydroxide: Ca(OH)2 is also corrosive and once again, due to this, caution is essential.
• Because of the corrosive nature of the chemicals that we are using, any spillages will be reported and cleared up immediately and inappropriate behavior in the lab will not be used.
• If the chemicals come into contact with skin or eyes, the skin / eyes will be flushed vigorously with clean, fresh water and if necessary, medical assistance will be sought.

 

Bibliography

• The Physical and Theoretical Chemistry Laboratory Oxford University Chemical and Other Safety Information  - 

•  - Titrations

• Advanced Chemistry for You – by Lawie Ryan, 2000; Stanley Thornes Publishers Ltd.

• Foundation Chemistry – by Cambridge Modular Sciences, 1995; Cambridge University Press

• Chemistry 1 – by Various, 2000; OCR and Cambridge University Press

• Haz-cards