[hester4]

Calcium hydroxide Ca(OH)2, is the cheapest strong base available. It is generally used for industrial operations in which a high concentration of OH-is not required. Ca(OH)2(s) is soluble in water only to the extent of 0.16 g Ca(OH)2/100.0 mL at 25 0C. What is the pH of saturated Ca(OH)2(aq) at 250C?

OK, here is what I did:

40.08 + (16.00 x 2) + (1.008 x 2)=74.096

1mol Ca(OH)2 / 74.096g Ca(OH)2 x 0.16g Ca(OH)2 / 100mL x 1000mL / 1L

After you do the math for that equation, you come up with: 0.02159, this is the OH- concentration.

pOH = -log(OH) pOH = -log(0.02159) = 1.666

pH + pOH = 14.00

We have the OH, so pH = 14.00 - pOH pH = 14.00 - 1.666

pH = 12.334 = 12.3

Here is my question, (it's probably a stupid one), when I am finding the OH- concentration, do I multiply 0.02159 by 2?

Isn't the balanced equation: Ca(OH)2 <> Ca(2+) + 2OH-?

If I did that, the answer would come out to be 12.6.  Both of these answers are choices on my homework (multiple choice).  Any help is appreciated and if I am doing anything else wrong please let me know.

[Borek]

Here is my question, (it's probably a stupid one), when I am finding the OH- concentration, do I multiply 0.02159 by 2?

Isn't the balanced equation: Ca(OH)2 <> Ca(2+) + 2OH-?

Yes, yes.

[Albert]

when I am finding the OH- concentration, do I multiply 0.02159 by 2?

Isn't the balanced equation: Ca(OH)2 <> Ca(2+) + 2OH-?

If I did that, the answer would come out to be 12.6.  Both of these answers are choices on my homework (multiple choice).  Any help is appreciated and if I am doing anything else wrong please let me know.

Yes, indeed. The right answer is 12.64.

[hester4]

Thank you guys very much.