WEBVTT

1
00:00:00.000 --> 00:00:03.471
Here is the problem: What is the molar mass of KCl?

2
00:00:03.921 --> 00:00:08.878
Add the atomic weights of all 2 atoms in one formula unit of KCl.

3
00:00:09.678 --> 00:00:19.709
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
00:00:20.159 --> 00:00:27.078
Look up each atomic weight (g/mol). IUPAC standard atomic weights (abridged, conventional values).

5
00:00:27.529 --> 00:00:30.431
Multiply each count by its atomic weight.

6
00:00:30.882 --> 00:00:32.345
Add the contributions.

7
00:00:33.145 --> 00:00:35.061
Mass percent of each element.

8
00:00:35.861 --> 00:00:41.910
So the answer is M(KCl) equals 74.548 g/mol.

9
00:00:42.360 --> 00:00:53.622
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
00:00:54.422 --> 00:00:58.462
Percent composition adds to 100.00 percent.

11
00:00:58.912 --> 00:01:02.209
Elements: potassium times 1, chlorine times 1.