Question

i have a 5 M stock solution of kcl and i need a 400mM working concentration (1x). if i want to make a 10 ml of a 2x concentration, how much 5 M stock and how much water do i need to add together

Answer 1

Answer:

8.4 ml of water is needed to make a 10 ml of a 2x concentration.

Explanation:

From question,

$M1= 5M,$

$M2= 400mM \times 2 (2 \times solution) =0.8M,$

$V2= 10ml$

$V1=  \frac{(M2 \times V2)}{M1}$

This gives $V1 = 1.6 ml$

V1 is the available volume of water in the stock solution.

To obtain 10ml of 2x concentration, the volume of water required is: $10-1.6 =8.4ml$of water.

Hence 8.4 ml of water is needed to make a 10 ml of a 2x concentration.