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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: hersheybar22 on October 04, 2010, 06:38:08 PM

Title: hardest question in the world(percent composition)!
Post by: hersheybar22 on October 04, 2010, 06:38:08 PM

The answer to this question is 40%, but i dont know how my teacher got this!
Question: A mixture of KCl and KNO3 is 44.20% potassium by mass. The percent of KCl in the mixture is closest to what percentage?
Thank you!

Title: Re: hardest question in the world(percent composition)!
Post by: Jorriss on October 04, 2010, 10:58:28 PM

Yup, definitely hard question ever posed. Do you have any ideas on how to start cause I dont :(?

Title: Re: hardest question in the world(percent composition)!
Post by: ooosh on October 04, 2010, 11:13:14 PM

It will be easy,if you know how to calculate the "respective" percentage of potassium by mass in KCl and KNO3. I won't calculate for you .Well,if we assume the percentage of potassium by mass in KCl is X%，and Y% in KNO3,the mass of KCl and KNO3 is m and n,respectively.
So,44.2%=(X%*m+Y%*n)/(m+n),you can change it to this:m(X%-44.2%)=n(44.2-Y%).
you get the relation between m and n.

Then you can get the percent of KCl in the mixture =m/(m+n)  *100%.