Question

Suppose you wanted to dissolve 40.0 g NaOH in enough H2O to make 6.00 dm3 of solution

Answer 1

Molarity of solution = 1.6 M

Further explanation

Given

40 g NaOH

6 L solution

Required

Steps to solve the problem of molarity

Solution

No additional information about the question.

If you want to make the solution above, then we just need to put the existing NaOH (40 g) into 6 L of water, then do the stirring (in a warm temperature above the hot plate will speed up the NaOH dissolving process)

But if you want to know the molarity of a solution, then

• 1. we calculate the moles of NaOH

$\tt mol=\dfrac{mass}{MW}$

MW(molecular weight) of NaOH=

Ar Na+ Ar O + Ar H

23 + 16 + 1 = 40 g/mol

so mol NaOH :

$\tt mol=\dfrac{40~g}{40~g/mol}=1~mol$

• 2. Molarity(M)

$\tt M=\dfrac{n}{V}\\\\M=\dfrac{1}{6}\\\\M=0.16$