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Description
Solutions of a soluble calcium salt are mixed with solutions of other soluble salts (sodium oxalate, sodium phosphate, and sodium oleate) that form insoluble calcium salts. By varying the relative amounts mixed so that one or the other chemical becomes limiting, the volume ratio for the maximum formation of precipitate is determined.
Safety
Oxalates are toxic. Sodium phosphate is corrosive. Wear goggles and apron. Do not ingest the chemicals. Wash spills with water. Wash hands after the experiment.
Procedure
Calcium Oxalate
1. Select a 12-well strip. Place 4 drops of distilled water into each of the first 9 wells of the strip. Add 1 drop of 0.1 M calcium chloride to well-1, 2 drops to well-2, etc., and finally add 9 drops to well-9.
2. Add 9 drops of 0.1 M sodium oxalate to well-1, 8 drops to well-2, etc., and finally add 1 drop to well-9.
3. Mix each of the wells with a toothpick. Sorry, your browser does not support mp4 format video. Try a different browser.
4. Allow to settle for 5 minutes. Hold the strip up to eye level to facilitate observations. Note the level of the precipitate in each of the wells by looking through the side of the wells. Identify the well with the largest amount (volume) of precipitate. Determine the drop ratio for this well.
5. On the basis of the ratio of drops, write a balanced equation for the formation of calcium oxalate.
6. Wash the 12-well strip at the sink. Use a cotton swab to scrub each well. Wash hands.
Calcium Phosphate
1. Select a 12-well strip. Place 4 drops of distilled water into each of the first 9 wells of the strip. Add 1 drop of 0.1 M calcium chloride to well 1, 2 drops to well 2, etc., and finally add 9 drops to well 9.
2. Add 9 drops of 0.1 M sodium phosphate to well 1, 8 drops to well 2, etc., and finally add 1 drop to well 9. Mix each of the wells with a toothpick.
3. Allow to settle for 20 minutes. (Heating the strip in the steam from a hot water bath (Use a 250 mL beaker.) sometimes speeds the settling process.)
4. Hold the strip up and observe the level of the precipitate in each of the wells by looking through the side of the wells. Identify the well with the largest amount (volume) of precipitate. Determine the ratio of drops for this well.
5. On the basis of the ratio of drops, write a balanced equation for the formation of calcium phosphate.
6. Wash the 12-well strip at the sink. Use a cotton swab to scrub each well. Wash hands.
Calcium Oleate
1. Oleates are one of the compounds found in soaps. The precipitate studied here is commonly called soap scum.
2. Select a 12-well strip. Place 4 drops of distilled water into each of the first 8 wells of the strip. Add 1 drop of 0.1 M calcium chloride to well 1, 2 drops to well 2, etc., and finally add 8 drops to well 8.
3. Add 8 drops of 0.1 M sodium oleate to well 1, 7 drops to well 2, etc., and finally add 1 drop to well 8. Mix each of the wells with a toothpick.
4. Allow to settle for 20 minutes. (Heating the strip in the steam from a hot water bath sometimes speeds the settling process.)
5. Hold the strip up and observe the level of the precipitate in each of the wells by looking through the side of the wells. Identify the well with the largest amount (volume) of precipitate. Determine the ratio of drops for this well.
6. On the basis of the ratio of drops, write a balanced equation for the formation of calcium oleate.
7. Wash the 12-well strip at the sink. Use a cotton swab to scrub each well. Wash hands.
Questions
1. Write the reactions with coefficients that match the wells with the most precipitate. See table on the protocol in the lab to determine cation to anion ration.
2.Write the correct balanced equations for the formation of the three precipitates studied.
3. How do the experimental ratios compare to the actual ratios for each reaction?
Final conclusion: