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hester4

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Finding the pH of saturated Ca(OH)2

« on: March 19, 2006, 03:09:08 pm » 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)=74.0961mol Ca(OH)2 / 74.096g Ca(OH)2 x 0.16g Ca(OH)2 / 100mL x 1000mL / 1LAfter 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) = 1.666pH + pOH = 14.00We have the OH, so pH = 14.00 - pOH pH = 14.00 - 1.666pH = 12.334 = 12.3Here 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. Logged

Borek

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Re:Finding the pH of saturated Ca(OH)2

« Reply #1 on: March 19, 2006, 03:36:40 pm » Quote from: hester4 on March 19, 2006, 03:09:08 pm

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. Logged Chembuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Albert

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Re:Finding the pH of saturated Ca(OH)2

« Reply #2 on: March 19, 2006, 03:37:33 pm » Quote from: hester4 on March 19, 2006, 03:09:08 pm

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. Logged

hester4

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Re:Finding the pH of saturated Ca(OH)2

« Reply #3 on: March 19, 2006, 03:43:32 pm » Thank you guys very much. Logged

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