Water consists of hydrogen and oxygen, and the approximate ratio, by mass, of hydrogen to oxygen is 2:16. Approximately

BTGmoderatorDC wrote: ↑

Wed Feb 03, 2021 5:45 pm

Water consists of hydrogen and oxygen, and the approximate ratio, by mass, of hydrogen to oxygen is 2:16. Approximately how many grams of oxygen are there in 144 grams of water?

(A) 16
(B) 72
(C) 112
(D) 128
(E) 142


OA D

Source: Official Guide

The ratio, by mass, of hydrogen to oxygen is 2:16
This means that, for every 2 grams of hydrogen, there are 16 grams of oxygen.
2 + 16 = 18
So, for every 18 grams of water 2 grams are hydrogen, and 16 grams are oxygen.
In other words, 16/18 of water is oxygen.
Simplify fraction to say: 8/9 of water is oxygen.

Approximately how many grams of oxygen are there in 144 grams of water?
Since we know that 8/9 of water is oxygen, we can write:
Weight of oxygen = (8/9)(144) = 128

So, there are 128 grams of oxygen in 144 grams of water.

Answer: D

Cheers,
Brent

BTGmoderatorDC wrote: ↑

Wed Feb 03, 2021 5:45 pm

Water consists of hydrogen and oxygen, and the approximate ratio, by mass, of hydrogen to oxygen is 2:16. Approximately how many grams of oxygen are there in 144 grams of water?

(A) 16
(B) 72
(C) 112
(D) 128
(E) 142


OA D

Source: Official Guide

Solution:

We are given that the ratio of hydrogen to oxygen in water, by mass, is 2 : 16. Using our ratio multiplier, we can rewrite this as 2x : 16x. We can now use these expressions to determine how much oxygen is in 144 grams of water.

2x + 16x = 144
18x = 144
x = 8

Since x is 8, we know that there are 16 x 8 = 128 grams of oxygen in 144 grams of water.

Answer D