Question

You have a 5 M NaCl stock solution. (NaCl F.W. is 58.4) a) How much NaCl (in g) do you need to make 1 liter of the 5 M stock solution? b) How much stock solution will you need if you want to make 100 ml of 50 mM NaCl? c) What is the % concentration of a 50 mM solution of NaCl?

Answer 1

Answer:

a) 292.0 g

b) 1 ml

c) 0.29 %

Explanation:

a) The amount of NaCl can be calculated as follows:

$m = C*V*M$                                      

Where:

m: is the mass of NaCl =?

C: is the concentration of NaCl = 5M

V: is the volume = 1 L

M: is the molar mass of NaCl = 58.4 g/mol

$m = C*V*M = 5 mol/L*1 L*58.4 g/mol = 292.0 g$  

Hence, you need to take 292.0 g of NaCl to make 1 L of 5 M stock solution.

b) We need to use the following equation to find the quantity of stock solution that is needed to make 100 ml of 50 mM of NaCl:

$C_{1}V_{1} = C_{2}V_{2}$

Where:

C₁: is the initial concentration = 5 M

V₁: is the volume of the initial concentration =?          

C₂: is the concentration of the solution to prepare = 50 mM

V₂: is the volume of the solution to prepare = 100 ml

$V_{1} = \frac{C_{2}V_{2}}{C_{1}} = \frac{50 \cdot 10^{-3} M*100 ml}{5 M} = 1 ml$

Therefore, you need 1 ml of the stock solution to make 100 ml of 50 mM NaCl.

c) The % concentration of a 50 mM solution of NaCl is:

$50 \cdot 10^{-3} \frac{mol}{1 L}*\frac{58.4 g}{1 mol}*0.1 L = 0.29 \%$

Hence, the % concentration is 0.29 % (w/v).

I hope it helps you!