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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: khood on March 01, 2009, 03:57:10 PM

Title: equilibrium question
Post by: khood on March 01, 2009, 03:57:10 PM

How many mL of a 10.4% solution by mass of KOH would you need to dilute to a final volume of 15 L to achieve a pH equal to 11.15?  The molecular weight of KOH is 56.1 g/mol...

attempt at a solution: 
(15L)(10^(-2.85)mol/L OH-)(1:1 mol ratio) = 0.02119 mol of KOH

0.02119 mol KOH (56.1 g/mol)(100 g solution/10.4 g KOH).

but I don't know the density of the solution so I don't know how to complete the last step.. I could be completely wrong in my methods but this is what makes sense to me..

any help on how to solve the problem would be appreciated!!!

Title: Re: equilibrium question
Post by: Borek on March 01, 2009, 05:50:44 PM

Quote from: khood on March 01, 2009, 03:57:10 PM

but I don't know the density of the solution so I don't know how to complete the last step.

You are right, you can't solve without density. What you wrote seems OK to me, although I must admit I am usually doing it using other methods, so I can be wrong.

Perhaps you are expected to consult density tables?