Part C Titration of Saturated Ca(OH)2 Solution 1. The saturated Ca(OH)2 solution

Question

Part C Titration of Saturated Ca(OH)2 Solution

1. The saturated Ca(OH)2 solution should have settled by now. (1 g calcium hydroxide disolved in water.) Take care not to stir up any of the solid from the bottom.  Set up a funnel with a clean piece of filter paper and a flask to catch the filtrate.

2. Using a plastic disposable pipet, draw the solution off the top of the saturated Ca(OH)2 solution and transfer to the funnel for filtration.  Collect 3540 mL of the filtrate and cover it.  If the filtrate is still cloudy, repeat the filtration.

3. Using a volumetric pipet, place 10.00 mL of the filtrate into a clean 50 mL Erlenmeyer flask.  Add 3 drops of bromothymol blue indicator and titrate with the HCl. Record the initial and final buret volume readings to the nearest 0.01 mL.  Repeat the titration twice for a total of three trials.

Our values were 7.85 mL, 7.73 mL, and 7.74 mL

Question:

Determine the concentration of [Ca2+] in Part C.

HCl concentration 0.67 M

Explanation / Answer

The volume of HCl required is 7.735 mL. (V1) [ Among the three readings two vaues 7.73 and 7.74 mL are differ in second decimal; so the required volume is 7.735 mL ; mean of the two readings]

Molarity of HCl, M1 = 0.67 M

1 equiv of HCl will react with 1 equiv of OH- ion.

volume of OH- ion(V2) = 10 mL

Molarity of HCl = M2

V1M1 = V2M2

M2 = V1M1/V2 = (7.735 x 0.67)/10 = 0.52 M

The conncentration of OH- ion = 0.52 M

Ca(OH)2 <---------> Ca2+ + 2 OH-

1 equivalent Ca(OH)2 will produce 1 equiv of Ca2+ ion and 2 equiv of OH- ion

So [Ca2+] =[OH-]/2 = 0.52 / 2 = 0.26 M

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