How many grams of NaCl are needed for 250 mL of a 0.5 M solution?

Answer

You need 7.3 g of NaCl.

Explanation

Step 1 — Convert the volume to litres

Molarity is moles per litre, so the millilitres have to go first:

250 mL ÷ 1000 = 0.250 L

Step 2 — Find the moles of solute

n = c × V = 0.5 mol/L × 0.250 L = 0.125 mol

Step 3 — Work out the molar mass of NaCl

element	mass
Na	22.99 g/mol
Cl	35.45 g/mol
NaCl	58.44 g/mol

Step 4 — Convert moles to grams

m = n × M = 0.125 mol × 58.44 g/mol = 7.31 g

Check

Half a mole per litre in a quarter of a litre is one eighth of a mole. One eighth of 58.44 g is a little over 7 g, which is the answer — so the volume conversion was done in the right direction.