Question

if you're given a 40% solution of KCl, how do you dilute to make 500 mL of a 10%solution of KCL?

Answer 1

We need to apply dilution law, which is based on the mass conservation principle

initial mass = final mass

this apply for moles as weel ( if there is no reaction, which is the case )

mol of A initially = mol of A finally

or, for this case

moles of A in stock = moles of A in diluted solution

Recall that

mol of A = Molarity of A * Volume of A

then

moles of A in stock = moles of A in diluted solution

Molarity of A in stock * Volume of A in stock = Molarity of A in diluted solution* Volume of A in diluted solution

Now, substitute known data

C1V1 = C2V2

40% * V1 = 10% 500

V1 = 10/40 * 500 = 125 mL

then,

use 125 mL of the 40% solution, add water up to v = 500 mL to get the 10% solution