Plan
The aim of this experiment is to find the concentration of a sample of limewater solution in g dm3. I am required to design my own experiment and choose a range of appropriate equipment and apparatus. The indicator will be supplied to me. I am provided with 250 cm3 of limewater, which has been made such that it contains approximately 1g dm3 of calcium hydroxide. Also available is hydrochloric acid which has a concentration of 2.00 mol dm3, this concentration is too much though so it is necessary to dilute it.
Apparatus and chemicals-
Pipette 25cm3, Volumetric flask 500cm3, Conical flask 250cm3, Burette, White tile, Clamp and stand, Indicator (methyl orange), Limewater (250cm3 with 1g dm3 of calcium hydroxide), Hydrochloric acid- standard solution (conc. 2.00 mol dm3),Distilled water.
Acid + Metal Hydroxide => Salt + Water
Limewater + Hydrochloric acid => Calcium chloride + Water + Hydrogen
Ca(OH)2(aq) + 2HCl(aq) => CaCl2 + 2H2O(aq)
In order for the experiment to be accurate and reliable it will be necessary to dilute the Hydrochloric acid significantly. It is in my belief that a concentration of 0.1mol dm3 would enable me to achieve reliable results. This would require a dilution factor of twenty. I will be making 500 cm3 of dilute hydrochloric acid. I will also be using 25cm3 of Limewater.
In order to reduce errors it is necessary to choose accurate and reliable equipment. That is why I have chosen the pipette, volumetric flask and burette. All of these instruments have an accuracy of ±0.05cm3, which is suitable for my experiment and should produce accurate and reliable results. In making my choice of indicator I also had to be very careful. The Limewater used will be a relatively weak base so it will be appropriate to use methyl orange as it has an end point on the ph scale between 8-5. Whereas phenolphthalein indicator has an end point much higher up in the ph scale. So if I were to use the phenolphthalein indicator then the end point (colour change) would be reached before the equivalence point (when the chemicals, acid-base break up).