1. Comment on the effect a variation from these assumptions will have on the sol
ID: 783932 • Letter: 1
Question
1. Comment on the effect a variation from these assumptions will have on the solubility of calcium carbonate
a. the pH of the buffer does not remain at its set point but drifts lower upon dissolution of calcium carbonate.
b. The temperature in the lab is either higher or lower than 25degrees celcius as assumed in our constants in our data table.
c. The CO2 level in the lab is higher or lower than that assumed in our constants in our data table.
2. Why do you think we need to convert the calcium carbonate to calcium chloride befoe we do our EDTA titrations? What specific condition in our titrations require this?
Explanation / Answer
a) Calcium Carbonate is a base, so it is neutralized by the acid in the buffer. If the pH lowers, that means there is more acid in the buffer, so more calcium carbonate will be able to dissolve and be neutralized. Solubility will increase.
b) Generally, as temperature rises, the rate of reactions increase, and solubility increases. (Think of trying to dissolve sugar in hot tea or cold tea) So, at a higher temperature, more calcium carbonate will dissolve, at a lower temperature less will dissolve.
c) When calcium carbonate is converted to Calcium Chloride, CO2 is released, so if more is in the atmosphere, less will dissolve to keep equilibrium. So solubility will decrease.
2) When you convert the Calcium Carbonate to Calcium Chloride, you do it by adding HCl. You do this to dissolve the solid Calcium Carbonate and make it a liquid that will mix readily with the ETDA and allow you to ascertain the calcium content in the titration.
Read this link, it explains things well. I think this may even be the same experiment you are working on: http://faculty.ccri.edu/aahughes/GenChemII/Lab%20Experiments/Calcium_Analysis_EDTA_Titration.pdf
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