WEBVTT

1
00:00:00.000 --> 00:00:08.498
Here is the problem: 10 g of NaOH is dissolved in water to make 250 mL of solution. What is the molarity?

2
00:00:08.948 --> 00:00:12.663
Molarity is moles of solute per litre of solution.

3
00:00:13.463 --> 00:00:15.181
Molar mass of NaOH.

4
00:00:15.631 --> 00:00:17.280
Convert grams to moles.

5
00:00:17.730 --> 00:00:19.541
Convert the volume to litres.

6
00:00:19.991 --> 00:00:21.953
Molarity is moles per litre.

7
00:00:22.753 --> 00:00:28.511
So the answer is M equals 1.00008 mol/L.

8
00:00:28.961 --> 00:00:41.929
Molarity (mol/L, written M) uses the volume of the whole solution, not of the solvent alone. To make a solution, weigh the solute, dissolve it in less solvent, then top up to the final volume.

9
00:00:42.729 --> 00:00:54.037
n equals MV: 1.00008 times 0.25 equals 0.250019 mol, which checks out.