WEBVTT

1
00:00:00.000 --> 00:00:04.214
Here is the problem: What is the molar mass of Na2CO3?

2
00:00:04.664 --> 00:00:10.690
Add the atomic weights of all 6 atoms in one formula unit of Na2CO3.

3
00:00:11.490 --> 00:00:21.951
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
00:00:22.401 --> 00:00:29.332
Look up each atomic weight (g/mol). IUPAC standard atomic weights (abridged, conventional values).

5
00:00:29.782 --> 00:00:32.615
Multiply each count by its atomic weight.

6
00:00:33.065 --> 00:00:34.539
Add the contributions.

7
00:00:35.339 --> 00:00:37.220
Mass percent of each element.

8
00:00:38.020 --> 00:00:45.764
So the answer is M(Na2CO3) equals 105.988 g/mol.

9
00:00:46.214 --> 00:00:57.360
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
00:00:58.160 --> 00:01:02.200
Percent composition adds to 100.00 percent.

11
00:01:02.650 --> 00:01:07.433
Elements: sodium times 2, carbon times 1, oxygen times 3.