Determination of the Solubility of Calcium Hydroxide.

GCSE Science

Sanjay Devalia

Determination of the Solubility of Calcium Hydroxide

Apparatus

250 cm3 volumetric flask

25cm3 pipette

Pipette pump

Burette

250cm3 conical flask

Small funnel

Rubber bung

White ceramic tile

Burette clamp

G clamp

Lab stand

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.

Method

Wash the burette with distilled water by filling, and then emptying the burette with distilled water. Then fill with, and allow the calcium hydroxide solution to empty through the burette. The burette has now been primed, and is free from any contaminants, or any risk of further dilution into water.
Fill the burette with the calcium hydroxide solution, by passing it through filter paper, until the bottom of the meniscus has reached the 0cm3 mark. When filling the burette, place a funnel onto the top of the burette and fill. Fill the burette so ...

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Method

Wash the burette with distilled water by filling, and then emptying the burette with distilled water. Then fill with, and allow the calcium hydroxide solution to empty through the burette. The burette has now been primed, and is free from any contaminants, or any risk of further dilution into water.
Fill the burette with the calcium hydroxide solution, by passing it through filter paper, until the bottom of the meniscus has reached the 0cm3 mark. When filling the burette, place a funnel onto the top of the burette and fill. Fill the burette so that the funnel is at eye level, and there is no risk of the calcium hydroxide solution spilling into the eyes.
Clamp the burette to the lab stand, and clamp the lab stand to the table using the g clamp.
If the pipette has not been washed and primed, wash it out with distilled water. Then fill with the hydrochloric acid solution and empty. The pipette has now been primed. Pipette 25cm3 of the hydrochloric acid solution, made earlier, into a clean and dry conical flask. If the conical flask is not clean, wash it out with distilled water and allow to dry.
Add 3 drops of methyl orange indicator into the conical flask containing calcium hydroxide. Methyl orange indicator is to be used, because it is the suitable indicator when reacting a strong acid and a strong alkali. Hydrochloric acid is the strong acid in this case, and calcium hydroxide is the strong alkali in this experiment. Swirl the conical flask thoroughly to ensure the methyl orange indicator is completely mixed with the calcium hydroxide solution. Place this conical flask onto a white ceramic tile.
Place the burette over the conical flask so that the calcium hydroxide solution can be transferred into the conical flask. Record the volume of calcium hydroxide solution in the burette.
Open the burette and allow the calcium hydroxide solution to slowly drip into the hydrochloric acid solution. Whilst the calcium hydroxide is dripping into the sodium carbonate, constantly mix the hydrochloric acid so that the calcium hydroxide solution is completely mixing with the hydrochloric acid solution. Allow the calcium hydroxide solution to drip into the hydrochloric acid solution, until the hydrochloric acid solution changes colour from yellow to pink. When the colour changes, close the burette so that no more calcium hydroxide solution is dripping into the hydrochloric acid solution.
Calculate the quantity of sulphuric acid solution which has been used by reading the burette. Record this reading.
repeat steps 4-8 until there 3 results with a concurrent difference of 0.1cm3 of calcium hydroxide solution used

Risk Assessment

Calcium hydroxide is caustic and can cause blindness. Therefore, it must not be allowed to make contact with skin, as it can cause serious hazards to health. Therefore, goggles must be worn at all times within the laboratory to reduce the risk of blindness. A lab coat and gloves must also be worn in order to reduce contact with skin. To ensure the calcium hydroxide cannot make contact with skin, the solution must always be kept in closed glassware, and must always be kept as far from the edge of the table as possible to reduce the chance of it falling over and any accidents occurring. Hydrochloric acid is corrosive, and can also cause blindness. To reduce risks of any health hazards, goggles must be worn to reduce risk of blindness; a lab coat must be worn to reduce risk of corrosion on clothes and skin; and gloves must be worn to reduce the risk of corrosion to the skin when handling the equipment and containers of the hydrochloric acid. The hydrochloric must also be kept in glassware at all times and must be kept as far from the edge of the table as possible to reduce chance of spillage.

The burette containing the calcium hydroxide must be secured to the lab stand and the stand must be secured to the table, to ensure the burette cannot fall and release the caustic calcium hydroxide. Therefore, a burette clamp will be used to secure the burette to the lab stand, and a G clamp will be used to secure the lab stand to the table. When filling the burette with the calcium hydroxide, the burette must be taken off the clamp and must be filled when the funnel is at eye level. This will ensure that if the calcium hydroxide spills, it will not spill into the eyes. This will reduce the risk of blindness

Food and drink must not be eaten in the room, since a trace of either solution may be indirectly ingested, and could cause serious health hazards.

You must also know the location of the eye wash and know how to use the eye wash in an emergency. This will reduce the chance of s serious injury in the case of an emergency.

Explanation

The plan will provide precise and reliable results if followed correctly. There is minimum risk of contamination, because all the glassware will be washed using distilled water. This will reduce risk of contamination because if the glassware has been used in previous experiments with different chemicals, they will be washed out. The burette and conical flask will also be primed to reduce contamination from other chemicals.

Drops will be used to add the Calcium Hydroxide solution into the Hydrochloric acid solution. This will ensure accurate results because a drop is about 1cm3 and so when the colour if the indicator changes, there will be a maximum concurrent difference of 1cm3 and so accurate results will be achieved.

When carbon dioxide is passed through calcium hydroxide, a fine precipitate is formed. This precipitate is calcium carbonate. Passing the calcium hydroxide through filter paper ensures that no precipitate is allowed into the burette, and so the titration can be carried out as accurately as possible.

Bibliography

Salters Advanced Chemistry: Chemical Ideas