Hydrochloric acid - Very corrosive, irritant.
Limewater (alkali) - Irritant.
Phenolphthalein Indicator - May cause irritation of the respiratory and
digestive tract if ingested. Can also cause CANCER.
Now, to perform the titration the first thing that needs to be done is to dilute the HCL to a suitable concentration. To do this you will need the pipette and the pipette filler to collect exactly 25ml of HCL (making sure that the level of the 25ml line is at the bottom of the meniscus). Then to place this into a volumetric flask and topping it up to 250ml with distilled water and then to turn the volumetric flask up & down rather than shaking. This is now ready for titration.
(By doing this we will create a 0.20 mol dm-3 solution as we were provided with 2 mol dm-3 at the start).
(To maintain this accuracy ALL apparatus must be washed with distilled water before and after use as some will be used more then once and any remaining chemicals will affect the outcome.)
By using the pipette again collect exactly 25ml of Calcium hydroxide in a conical flask with some phenolphthalein placed in it (5 drops should be enough).
(The need for the phenolphthalein indicator is to show the user when a neutralization reaction has occurred as that is the moment when the solution is no longer alkaline and it below PH 8.4)
Next, set up the washed & clean burette on the clamp stand and add the dilute HCL into the top of the burette with a funnel, making sure the tap is closed. Fill up to the 0.00ml mark (making sure that the level of the 0.00ml line is at the bottom of the meniscus).
Then place the conical flask of calcium hydroxide under the burette and the white tile under the flask.
Begin to let the acid pour slowly into the calcium hydroxide and stir the conical flask slowly. When the solution starts to loose its colour slow the rate of the acid more and the moment the solution looses all colour stop, this is the end point. The solution should turn from pink to colourless.
By reading off the side of the burette what volume is left and taking this away from the starting volume (which should be 0.00ml) you will calculate the volume of acid used to neutralise the alkali.
The test must be performed a further three times for any accurate results to become
apparent.
Sources: Chemistry 1 book, Endorsed by OCR, Authors: Brian Ratcliff, Helen Eccles, David Johnson, John Nicholson and John Raffan. Part 1 Chapter 2 (Atoms, molecules and stoichiometry) page 24 was used to help me balance my chemical equation.
This website was used to help me gain information on the hazards of Phenolphthalein Indicator.
Results:
Average = 3.70 cm3 + 3.50 cm3 + 3.60 cm3
3
Average = 3.60 cm3
Number of mol. of acid used in titration:
Concentration (C) = Numb of Mol (N)
Volume (V)
N = C x V
N = 0.20 mol dm-3 x 3.60 cm3
N = 0.20 mol dm-3 x 3.6x10-3
N = 7.20 x 10 – 4 moles
Equation: 2HCl (aq) + Ca(OH)2 (aq) → 2H20(l) + CaCl2(aq)
The number of mol. of Ca(OH)2:
HCL : Ca(OH)2
2 : 1
7.2 x 10 – 4 moles : 3.60 x 10 – 4 moles
Concentration of the limewater in mol dm-3:
Concentration (C) = Numb of Mol (N)
Volume (V)
N = 3.60 x 10 – 4 moles
V = 25 cm3 = 0.025 dm–3
C = 3.60 x 10 – 4 moles
0.025 dm–3
C = 0.0144 mol dm–3 = 0.01 mol dm–3
Average:
Average = 3.70 cm3 + 3.50 cm3 + 3.60 cm3
3
Average = 3.60 cm3
Concentration of the limewater in g dm-3:
To calculate the concentration of the limewater in g dm-3 we multiply the concentration of the limewater in mol dm-3 by the relative molecular mass of limewater.
C = 0.0144 mol dm–3 x 74.1 = 1.06704 g dm-3 = 1.07 g dm-3
