Dillutions?

Question

You need 100 ml of a .1 M solution.
You have 100 ml of a 10 M solution.

how would you make up the .1 M solution.

Answer 1

First, make the 0.1M solution. What you do is add solvent (ex. water to an aqueous solution) to the 10M solution. M is a unit meaning moles of solute (stuff that gets dissolved) per liter of solvent (stuff that does the dissolving). So 10M means:

10mol/1L
So 100mL of this stuff means:

10mol/L * 0.100L = 1mol
This means you have 1 mol of solute in your 100 mL.

To have 0.1M you need 0.1mol/L, or since you need 100mL:

0.1mol/1L = x mol/0.1 L
Solving for x gives 0.01 mol.

To get 0.01 mol from the solution you already have (the 10M):
0.01mol= (10mol/L) * y L
Solving for y gives 10mL (0.01L)

So take 10mL of your 10M solution. Now you need another 90mL of solvent to make the 0.01mol/0.1L solution. Just add 90mL of pure solvent, and you'll have 100 mL of 0.1M solution