chemistry
posted by Ciarra on .
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?

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

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. 
That makes sense!! Thank you!