Question

A student needed to make 100.0 mL of 0.20M NaOH solution. How many grams of sodium hydroxide does the student need to weigh out

Answer 1

0.8 g

Step-by-step explanation:

The molarity of a solution is calculated with the following formula:

`M=(n)/(V)`

where:

n is the number of moles of the solute

V is the volume of the solution

In this problem we have:

V = 100.0 mL = 0.1 L is the volume of the solution

M = 0.20 is the molarity

So the number of moles of NaOH in the solution must be

`n=MV=(0.20)(0.1)=0.02 mol`

The molar mass of NaOH is

`M_m = 40 g/mol`

Therefore, the mass of NaOH needed in the solution is:

`m=nM_m = (0.02)(40)=0.8 g`