Chemical mixture problem

I'm getting ready for my next exam Thursday and I've got a hold of the regular solution problems but I can't figure this one out.

A tank contains 600 gallons of a 15% HCL solution. How many gallons must be drained and then replaced with pure HCL in order to obtain a solution that is 27% HCL.

I've tried this several different ways but I can't come up with 84.7059 drained and replaced with pure HCL as an answer.

Quote:

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Originally Posted by Turtle13

I'm getting ready for my next exam Thursday and I've got a hold of the regular solution problems but I can't figure this one out.

A tank contains 600 gallons of a 15% HCL solution. How many gallons must be drained and then replaced with pure HCL in order to obtain a solution that is 27% HCL.

I've tried this several different ways but I can't come up with 84.7059 drained and replaced with pure HCL as an answer.

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oops editing.

As this is an exam question I do not feel comfortable working out the answer for you without some working. My answer is 72 gallons for reference


Consider the 600 gallons as pure HCl and impure solvent. You can consider the percentage concentration as vol/vol meaning that x% means x gallons HCl per gallon solvent.

If you get the amount of HCl in there as though it were pure HCl, you'll get a value in L.

Do the same for the 27% and the difference should be how much you need to put in

No, this is a from a review sheet. I'd give you some of the work, but I've been setting them up as a table then formulating the equation. I've literally erased the work 3 times already.

"Getting ready" for an exam does not = exam question.

For instance, here is the previous problem.
http://i7.photobucket.com/albums/y30...t/IMG_5385.jpg

Quote:

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Originally Posted by Turtle13

I'm getting ready for my next exam Thursday and I've got a hold of the regular solution problems but I can't figure this one out.

A tank contains 600 gallons of a 15% HCL solution. How many gallons must be drained and then replaced with pure HCL in order to obtain a solution that is 27% HCL.

I've tried this several different ways but I can't come up with 84.7059 drained and replaced with pure HCL as an answer.

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An unusual problem.HCL is agas.Water solutions of 32 % by weight are sold as muriatic acid.If it were a pure liquid why does the question ask you to drain some of thr 15% solution?

bjh

Quote:

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Originally Posted by bjhopper

An unusual problem.HCL is agas.Water solutions of 32 % by weight are sold as muriatic acid.If it were a pure liquid why does the question ask you to drain some of thr 15% solution?

bjh

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I'm assuming that 600 gallons is the maximum that the container holds although the problem doesn't say that. It's a college algebra class not chemistry so I had no clue what an HCL solution is.

I'm moving on for now and going to hope that he doesn't put a mixture problem like that on the exam.

Quote:

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Originally Posted by bjhopper

An unusual problem.HCL is agas.Water solutions of 32 % by weight are sold as muriatic acid.If it were a pure liquid why does the question ask you to drain some of thr 15% solution?

bjh

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Now that you clarify this problem it is not hard. Use vol/vol basis
tank contains 510 gals of water 600x.85
final tank contains 438 gals water 600x .73
gals water to remove 72
72 /.85 = total gals to remove 84.7


bjh