Question

How many grams of NaOH (MW = 40.0) are there in 500.0 mL of a 0.225 M NaOH solution?

Answer 1

Given: Molar mass of NaOH=40 g/mol

Volume of NaOH solution=500 mL

Molarity of solution=0.225 M

Molarity of solution is defined as number of moles of solute in 1 L of solution. Thus,

$M=\frac{n}{V}$

Thus, to calculate the mass of NaOH, first calculate its number of moles by rearranging the above equation and putting values of volume and number of moles.

$n=M\times V=0.225 M(\frac{ mol/L}{1 M})\times 500 mL(\frac{10^{-3} L}{1 mL})=0.1125 mol$

Now, number of moles are related to mass as follows:

$n=\frac{m}{M}$

Here, M is molar mass

Rearranging and putting the values of number of moles and molar mass thus,

$m=n\times M=0.1125 mol\times 40 g/mol=4.5 g$

Therefore, mass of NaOH in 500 mL of 0.225 M NaOH solution is 4.5 g.

Answer 2

There are 4.5 grams of NaOH in 500.0 mL of a 0.225 M NaOH solution.

HOW TO CALCULATE MASS:

• The mass of a substance can be calculated by multiplying the number of moles by its molar mass. That is;

• mass (g) = no. of moles (mol) × molar mass (g/mol).

• However, the number of moles can be calculated by multiplying the molarity by the volume (in litres) of NaOH.

• no. of moles = molarity × volume

• no. of moles = 0.225M × 0.500L

• no. of moles = 0.1125mol

• Molar mass of NaOH = 23 + 1 + 16 = 40g/mol

• mass of NaOH = 0.1125 × 40

• mass of NaOH = 4.5grams.

• Therefore, there are 4.5 grams of NaOH in 500.0 mL of a 0.225 M NaOH solution.

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