Determination of the Solubility of Calcium Hydroxide
250 cm3 volumetric flask
250cm3 conical flask
White ceramic tile
Quantities to be used
25cm3 Hydrochloric acid solution @ 0.3moldm-3
225cm3 Distilled Water
Excess Methyl Orange indicator
Excess Calcium Hydroxide solution @ 0.015moldm-3
Excess distilled water (for washing glassware)
Making the Hydrochloric acid solution
The hydrochloric solution provided is of a very high concentration compared to the concentration of the calcium hydroxide. Because the ratio of moles of hydrochloric acid to calcium hydroxide is 2:1, the concentration of the hydrochloric acid must be about twice as much as the calcium hydroxide:
Ca(OH)2(aq) + 2HCl(aq) → CaCl2 + 2H2O
No. of Moles 1 2
The hydrochloric acid provided is of very high concentration compared to the calcium hydroxide, and so this will cause a very high error. Diluting the hydrochloric acid will reduce the error, because more calcium hydroxide will be needed to be added to complete the titration, and so a lot of drops of lower concentration hydrochloric acid would yield a smaller error than a few drops of higher concentration hydrochloric acid.
The hydrochloric solution will be diluted 10 times to reduce the concentration from 0.3moldm-3 to 0.03moldm-3. This new concentration will therefore be twice the concentration of the calcium hydroxide.
Ensure the pipette has been washed with distilled water and then washed with hydrochloric acid. Is this has not been done, first completely wash the pipette with distilled water. This will ensure that all traces of previous solutions have been removed. Then fill the pipette with hydrochloric acid using the pipette pump. When the pipette has been filled pass the 25cm3 line, allow the pipette to empty. You have now primed the pipette. This will reduce the chance of further dilution or contamination when the pipette is used to measure 25cm3.
Use the pipette pump to fill the clean pipette with hydrochloric acid. The bottom of the meniscus of the hydrochloric acid must be on the 25cm3 line. This ensures that there is exactly 25cm3 of the hydrochloric acid in the pipette, and that an accurate concentration of 0.03moldm-3 will be produced. Add this into a clean and dry volumetric flask. Wash with distilled water and allow to dry if it is not clean. Empty the pipette into the volumetric flask, and touch the end of the pipette onto the side of the volumetric flask, to empty that final trace of the acid. Fill up the volumetric flask with distilled water up to the 250cm3 mark. Ensure the bottom of the meniscus is on the 250cm3 line. Add a rubber bung into the end of the volumetric flask, and shake to mix the hydrochloric acid with the water. Turn the volumetric flask upside down and allow the air bubble to mix the solution. Turn it upside down several times to fully dilute the solution.