SOLUTION: I was wondering if anyone could help me with a mixture A chemist needs to prepare 12oz of a 9% hydrochloric acid solution. Find the amount of a 4% solution and the amount of a 1

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The total amount of solution has to be 12 ounces, so let the amount of 4% solution be x ounces and the amount of 12% solution be 12 - x ounces.

4% of the x ounces of 4% solution is pure acid. 12% of the 12 - x ounces of 12% solution is pure acid. When you add these two together, you get something that is 9% times 12 ounces pure acid. Symbolically,



Solve for x to get the amount of 4% solution. Subtract this result from 12 to get the amount of 12% solution. Hint: This will be much easier to avoid errors if you first multiply both sides of the equation by 100 to get rid of the decimal fractions.

John

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The total amount of acid is 12*0.09 = 1.08
Now you need to decide how much 4% needs to be mixed with 12% to yield that same amount of acid.
Let x be the amount of 4%. Let y be the amount of 12%.
You know that x + y = 12
So y = 12-x
TotalAcid = 0.04x + 0.12y
1.08 = 0.04x + 0.12(12-x)
1.08 = 0.04x + 1.44 - 0.12x
-0.36 = - 0.08x
4.5 = x
That means y = 12-4.5 = 7.5
So we need 7.5oz og 12% and 4.5oz of 4%
Make sure to check your answer
Does 4.5*0.04 + 7.5*0.12 = 12*0.09???