Use the law of constant composition to complete the table summarizing the amounts of nitrogen and oxygen produced upon the decomposition of several samples of dinitrogen monoxide.

Mass N2O 
Mass N 
Mass O 
Sample A 
2.85 g 
1.82 g 
1.03 g 
Sample B 
4.55 g 
_____ 
_____ 
Sample C 
_____ 
_____ 
1.35 g 
Sample D 
_____ 
1.11 g 
_____ 
Solution 29P
Step 1:
First, let’s see what is the law of constant composition :
Law of constant composition states that ‘samples of a pure compound always contain the same elements in the same mass proportion.’
Now, let’s solve the blanks using the given data .
Step 2:
Let’s consider, sample B :
Given : Mass of N2O : 4.55 g
First, let’s calculate the molar mass of N2O :
Molar mass of Nitrogen (N) = 14.0067
Molar mass of Oxygen (O) = 15.9994
Hence molar mass of N2O = 2(14.0067) + 15.9994
= 28.0134 + 15.9994
= 44.0128 g
If 44.0128g of N2O contains 28.0134g of N, then mass of N in 4.55g of N2O will be :
= 4.55
= 0.6364 4.55
= 2.89 g 2.9 g
Hence, mass of N in sample B is 2.9 g
Now we have the mass of N and N2O, let’s calculate mass of O :
Using law of constant composition, we can calculate as :
Mass of O = Mass of N2O Mass ratio of O
If 44.0128g of N2O contains 15.9994g of O, then mass ratio of O in any sample will be :
= 0.3635
Therefore , Mass of O = 4.55 g 0.3635
= 1.65 g
Hence, mass of O in sample B is 1.65 g
Step 3:
Let’s consider, sample C :
Given : Mass of O = 1.35 g
We know the molar mass of N2O from the above calculation = 44.0128 g
Now, let’s calculate mass of N2O in the sample :
If 44.0128g of N2O contains 15.9994g of O, then mass ratio of O in any sample will be :
= 0.3635
Let’s consider mass of N2O as ‘x’
unknown mass of N2O in sample C(x) mass ratio of O = mass of O
x 0.3635 = 1.35 g
x =
x = 3.71 g
Hence, mass of N2O in sample C is 3.71 g
Now, let’s calculate mass of N in the sample :
If 44.0128g of N2O contains 14.0067g of N, then mass ratio of N in any sample will be :
= 0.6364
Therefore mass of N will be :
Mass of N2O mass ratio of N = mass of N
3.71g 0.6364 = mass of N
2.36 g
Hence, mass of N in sample C is 2.36 g