WEBVTT

1
00:00:00.000 --> 00:00:03.413
Here is the problem: What is the molar mass of Li2O?

2
00:00:03.863 --> 00:00:08.879
Add the atomic weights of all 3 atoms in one formula unit of Li2O.

3
00:00:09.679 --> 00:00:19.977
Count the atoms of each element. Subscripts multiply everything inside the brackets before them, and a hydrate coefficient multiplies the whole water (or other) unit.

4
00:00:20.427 --> 00:00:27.474
Look up each atomic weight (g/mol). IUPAC standard atomic weights (abridged, conventional values).

5
00:00:27.924 --> 00:00:30.780
Multiply each count by its atomic weight.

6
00:00:31.230 --> 00:00:32.705
Add the contributions.

7
00:00:33.504 --> 00:00:35.373
Mass percent of each element.

8
00:00:36.173 --> 00:00:42.315
So the answer is M(Li2O) equals 29.879 g/mol.

9
00:00:42.765 --> 00:00:54.456
The molar mass is the mass of one mole of formula units. It equals the sum of the atomic weights of every atom in the formula, and numerically matches the formula mass in daltons (u).

10
00:00:55.256 --> 00:00:59.238
Percent composition adds to 100.00 percent.

11
00:00:59.688 --> 00:01:03.194
Elements: lithium times 2, oxygen times 1.