1. The oxygen-to-carbon ratio in that sample is x over 36.0 HIGHLIGHT
QUESTION:
A 32.0 g sample of a compound contains 16.0 g oxygen, 12.0 g carbon, and 4.0 g hydrogen. How much oxygen is present in a sample of this compound that contains 36.0 g carbon? A g, B g, C g, D g
The Law of Definite Composition says that the percentage of each element in any sample of the compound (as long as it’s pure) is constant.
The ratio of the amounts of any two elements is constant. Let x = amount of oxygen in the sample containing 36.0 g carbon.
SCRIPT:
A 32.0 g sample of a compound contains 16.0 g oxygen, 12.0 g carbon, and 4.0 g hydrogen. How much oxygen is present in a sample of this compound that contains 36.0 g carbon? A g, B g, C g, D g
PAUSE
CLICK.
The Law of Definite Composition says that the percentage of each element in any sample of the compound (as long as it’s pure) is constant.
CLICK
Mathematically, this implies that the ratio of the amounts of any two elements is constant.
If we let x be the amount of oxygen in the sample containing 36.0 grams of carbon…
The oxygen-to-carbon ratio in that sample is x over 36.0
HIGHLIGHT
This oxygen-to-carbon ratio in the 32 gram sample is 16.0 grams oxygen over 12.0 grams of carbon
Since these two ratios are equal, we can solve for x.
By multiplying both sides by 36.0 grams, we get x equals grams
The correct answer is C.
Given the choices, we can actually figure out the answer using common sense.
There’s more oxygen than carbon in the sample. The oxygen-to-carbon ratio is 16-to-12.
Since we’re looking for the amount of oxygen in a sample containing 36 grams of carbon, we’re looking for a number larger than 36 grams.
The only choice that is larger than 36 grams is choice C.
PAUSE END RECORDING.

2. Video ID: © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08