chemistry question (simple) or math. Please explain it. Please I really do not get it?

Question

have 5M NAOH
10% Sds
Want to make .2M NaOH
1%SDS
And 5ml of it.
How to do this?

Answer 1

OK, since you're only given the end volume, you start there.

You want to make 5 ml of .2M NaOH with 1%SDS (by volume, we'll assume).

Step 1: Find out how many moles of NaOH you need:
.2 M * 5 ml = .2 moles / liter * .005 L = .001 moles of NaOH in your final solution.

Step 2: Figure out what volume of your 5 M NaOH solution contains .001 moles:
.001 moles / 5 moles/L = 0.0002 L = .2 mL of 5M NaOH solution.

Thus, you start with .2 mL of your initial solution.

Step 3: Determine the volume of SDS in your initial solution, and the volume of SDS you need in the final solution:
10% SDS in .2mL = .02 mL SDS
1% SDS in 5mL = .05 mL SDS

Thus, you need to add .03 mL SDS.

Step 4: Add the volume of the initial solution, the volume of SDS you need to add, then add water to 5 mL.
Initial solution: .2 mL
SDS: .03 mL
Total: .23 mL
Water = 5 mL - .23 mL = 4.77 mL

So, your steps are:
take .2 mL of 5M NaOH w/10% SDS, add .03 mL SDS, then add 4.77 mL H2O.