Concentration of a limewater solution by titration against a standard solution of hydrochloric acid. - page 2
Keywords: Chemistry practical concentration limewater hydrochloric acid titration
By Jenny on 02/07/2009
Level: A Level (Year 13)
Page Number: 2 of 3 pages: 1 2 3
best to use approximately the same amount of hydrochloric acid and limewater, so I will be using about 25cm³ of hydrochloric acid.
Therefore, it needs to have molarity of approximately 0.27 mol dmˉ³ - between 0.02 and 0.03.
To dilute the hydrochloric acid I will put 25 cm³ of the 2.00 mol dmˉ³ hydrochloric acid in a 250 cm³ container and make it up to the mark with distilled water. This means that the 2.00 mol dmˉ³ hydrochloric acid will make up 10% of the solution. I will then shake the flask to mix the acid with the water. The entire solution will now have a concentration of 0.20 mol dmˉ³ (2.00 / 10). This is still too concentrated so I will repeat the procedure, this time putting 25cm³ of the 0.20 mol dmˉ³ hydrochloric acid in another 250 cm³ flask, and again making it up to the mark with distilled water and shaking the mixture. This will give 0.02 mol dmˉ³ hydrochloric acid (0.20 / 10), which is within my limits.
Apparatus
• Ca(OH)² dissolved in water (approximately 0.0135 mol dmˉ³)
• Hydrochloric Acid (2.00 mol dmˉ³ diluted to 0.02 mol dmˉ³)
• 25 cm³ pipette
• 250 cm³ beaker
• 25 cm³ beaker
• Burette
• Clamps
• Stand
• Funnel
• White tile
• Indicator (phenolphthalein)
Method
I will use the pipette to measure out 25.0 cm³ of limewater into a beaker, then having set up the clamp and stand fill up the burette to the mark with the hydrochloric acid using the funnel. I will place the beaker containing the limewater on a white tile under the burette and add 2-3 drops of phenolphthalein as an indicator. Then I will titrate the hydrochloric acid against the limewater until the solution in the beaker becomes clear, measuring the amount of hydrochloric acid in the burette at the start and end to an accuracy of 0.05 cm³.
I will repeat the experiment until I have two results within 0.1 of each other, recording the results in a suitable table.
Results
Burette readings in cm³.
Rough 1 2 3
2nd reading
1st reading
Vol. of HCl added
To make sure my results are as accurate as possible I will rinse through the beakers with the solution they are measuring before use so that there is no film of other liquid on the inside which could affect my results.
I will also ensure each burette reading is accurate by making a simple burette card out of paper to put behind the burette as I make my readings as they are easier to make against a white background.
Also
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