Question

A compound of nitrogen and oxygen is 36.8% nitrogen. A second compound of nitrogen and oxygen is 25.9% nitrogen. What is the ratio of masses of oxygen in the two compounds per gram of nitrogen?

Answer 1

Assume you have one hundred grams of each compound to make dealing with the percentages easier.

Compound 1)

N: 36.8g
O: 100g - 36.8g = 63.2g oxygen/36.8g nitrogen = 1.7g oxygen/1g nitrogen

Essentially, if you round the numbers up, it's a 2:1 ratio of oxygen to nitrogen.

Compound 2)

N: 25.9g
O: 100g - 25.9g = 74.1g oxygen/25.9g nitrogen = 2.86g oxygen/1g nitrogen

Here, if you round up, it would be a 3:1 ratio of oxygen to nitrogen.


Disclaimer: Someone correct me if I'm wrong, as I'm completely out of the loop today.

Answer 2

That was the answer I had, but apparently the correct answer is 5:3??? I have no idea how they're getting that.

Answer 3

Let's go back to the 1.717 for the first one and 2.86 for the second. I think you have interpreted the problem wrong. You have calculated the ratio of N to O in each but I think the problem wants to calculate the ratio of the O in the first one to the O in the second one.We can do that by using the 1.717 for O in the first one per 1g N and 2.86 for O in the second one per 1g N.
Now the ratio of the two is
1.717/1.717 = 1.000
2.86/1.717 = 1.666
To try to find the small whole numbers, the easy way is to multiply by 2 to obtain 2.00 to 3.33 which doesn't work so we try multiplying by 3 and we get
3.00 to 5.00. I think that is the answer you are looking for.

Answer 4

That makes sense!! Thank you!