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Determination of the solubility of calcium hydroxide

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Introduction

Determination of the solubility of calcium hydroxide Objective I have to plan an experiment to find the solubility of calcium hydroxide (Ca (OH) 2) by titrating the saturated solution (limewater) against a solution of an acid whose concentration I know. I have been given a sample of limewater that contains approximately 0.015 mol/dm-3 of calcium hydroxide and a solution of hydrochloric acid whose concentration is 0.300 mol/dm-3. I will have to dilute one of these solutions. Planning 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: Making the Hydrochloric acid solution Ca (OH)2(aq) + 2HCl(aq) � CaCl2 + 2H2O No. of Moles 1 2 Because the hydrochloric acid provided is of very high concentration it will cause a very high error whilst titrating. Diluting the hydrochloric acid will reduce the error, because more calcium hydroxide will need 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. ...read more.

Middle

I will fill the burette again this time allowing the liquid to fill the tubing below the tap before use. 3. I then mount the burette vertically on a clamp stand, being careful that the clamp is not over tightened. I will record the volume in the burette reading the burette at eye level, taking the meniscus reading, and noting down the value. 4. Depending on whether the top of the burette is broken off (as it commonly is) or still intact I will fill it with the solution to the nearest 10 cm3. This is so I am able to clearly read the following results without having to use a calculator. If there is time I will keep a small volume of the end point solution to compare with the others. 5. Then I will put 25cm� of limewater into a conical flask using a 25cm� bulb pipette. At first, 25cm� of limewater will be measured using a measuring cylinder and then poured it into a beaker. 6. I use a 25cm� bulb pipette to draw up the limewater. The pump will be placed on the tip of the bulb pipette, which is in the solution; drawing up slowly the limewater to the graduation mark on the scale. ...read more.

Conclusion

The volumetric flask of 250cm3 is used to make standard solution of a particular volume. If it is filled correctly i.e. the bottom of the meniscus rests on the calibration line, the error is +0.2cm3. The percentage error = error x 100 = 0.2 x 100/250 = 0.08% The percentage error is low and therefore the flask measures the volume to a high degree of accuracy. One drop from a burette has a volume of approximately +0.05cm3. All the burette readings should include 2 decimal places in which the second figure is either 0 or 5. An error of one drop in a volume of 25.00cm3 gives a percentage error: The percentage error = error x 100 = 0.05 x 100/25 = 0.2% This is also low, meaning that the equipment has high accuracy. The beakers are useful for measuring broad volumes of a solution. This is not very accurate but can give an approximate volume. I used it to measure the volume of water because the volume of water needed was approximate. Conical flasks are good for titrations as they have a narrow neck (enough to fit in the burette tip, without breaking it when swirling), but broad base. This is particularly useful as the narrow neck prevents spillage when swirling and the broad base makes the solution and end-point easy to see. ...read more.

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