MATERIALS REQUIRED Chemicals solid calcium hydroxide- Ca(OH) bromothymol blue in

Question

MATERIALS REQUIRED Chemicals solid calcium hydroxide- Ca(OH) bromothymol blue indicator hydrochloric acid (0.07 M) saturated Ca(OH)2 solution Equipment 250-ml Erlenmeyer flasks 250-mL beaker 100-mL graduated oylinder 10.00-mL pipet, bulb hot plate thermometer glass stirring rod funnel filter papers Common Equipment balance PROCEDURE CAUTION: GOGGLES must be worn at all times while in the lab. Part I- Solubility of calcium hydroxide at room tempe rature 1. Pipet 10.00 ml of the saturated solution provided into a clean 250-mL. Erlenmeyer flask (you may want to filter the sample using a funnel and filter paper to ensure that no solid is present), Add about 25 ml water to this flask and a few drops ( 3 drops) of bromothymol blue indicator Record the exact concentration of the standardized HCl and titrate until its color changes to yellow at the end point 2. 3. Perform two more titrations and record data on Data Sheet. 4. Discard the reaction mixtures into the waste container. Part II-Solubility of calcium hydroxide at high temperature Add 100 mL of distilled water into a 250-mL beaker and bring it to a boil on a hot plate. 5 minutes with occasional stirring and then turn off the hot plate. a filter paper Mlask. Add about 25 mL water to this flask and a few drops 3 drops) of bromothymol blue 1. 2. Add about 2 grams of Ca(OH): to the water while stirring. Continue boiling gently for about 3. Record the temperature of the solution and quickly filter the hot solution using a funnel and 4. Let the filtrate cool. Pipet 10.00 mL of this solution into a clean, dry 250-mL. Erlenmeyer 8- water to this flask and a few drops (-3 drops) of bromothymol blue indicator. tns Blu

Explanation / Answer

I'll do it with the first determination at 25 °C.

At the equivalence point you have the following reaction:
2HCl + Ca(OH)2 <-------> CaCl2 + 2H2O

moles HCl/moles Ca(OH)2 = 2/1
moles HCl = 2 moles Ca(OH)2

This means that when we get the moles of HCl we can determine the moles of the base used so:
moles HCl = 0.07 *0.0035 = 0.000245 moles
moles OH- = 0.000245 / 2 = 0.0001225 moles

To get the concentration, we need the volume in which was dissolved:
[OH] = 0.0001225 / 0.035 = 0.0035 M

We also know that Ca(OH)2 ------> Ca2+ + 2OH-

So, with this the concentration of Ca:
[Ca] = 0.0035 / 2 = 0.00175 M

finally the Ksp = [Ca][OH]2
Ksp = 0.00175 * (0.0035)2 = 2.14x10-8

Finally the dG:
dG = -RTlnKsp

Use this expression when you calculated the other Ksp values and took an average of those values.

Hope this helps

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