A student must make 500 mL of a 1.5 M HCl solution. The student has plenty of water and a stock solution of 6.0 M HCl to use. What volume of the 6.0 M HCl solution must be added to what volume of water to make the desired 500 mL of 1.5 M solution?

Question

I don't really know how to start this. I've tried a couple of ways. I got that you need .75 moles of HCl and therefore you need .125 L of the 6.0 M solution, but I don't really think that that's correct and if it is I don't know what to do to find what volume of water you would need.

Answer 1

Here is another way: You want to dilute it 4 times, so use one part 6M acid, three parts water.

dividing 500mL by four parts is indeed one part 125mL of the acid, and then three parts water.

Answer 2

Thanks! That makes a lot more sense.

Answer 3

Molarity of the first and volume of the first = molarity of the 2nd