Question

An unknown substance is obtained by police. The forensics laboratory has

determined it is made of nitrogen and oxygen. If 74.66 grams are nitrogen
and the police obtained a 250 gram sample, what is the percent
composition of oxygen in the sample?

Answer 1

70.0 %

Step-by-step explanation:

Step 1: Given data

• Mass of nitrogen (mN): 74.66 g

• Mass of the compound (mNxOy): 250 g

Step 2: Calculate the mass of oxygen (mO) in the compound

The mass of the compound is equal to the sum of the masses of the elements that form it.

mNxOy = mN + mO

mO = mNxOy - mN

mO = 250 g - 74.66 g = 175 g

Step 3: Determine the percent composition of oxygen in the sample

We will use the following expression.

%O = mO / mNxOy × 100%

%O = 175 g / 250 g × 100% = 70.0 %