Use the law of constant composition to complete the table summarizing the amounts of iron and chlorine produced upon the decomposition of several samples of iron(III) chloride.

Mass FeCI3 
Mass Fe 
Mass Cl 
Sample A 
3.785 g 
1.302 g 
2.483 g 
Sample B 
2.175 g 
________ 
________ 
Sample C 
_________ 
2.012 g 
________ 
Sample D 
_________ 
________ 
2.329 g 
Solution 30P
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:
Use the law of constant composition to complete the table summarizing the amounts of iron and chlorine produced upon the decomposition of several samples of iron(III) chloride.
Let’s consider, sample B :
Given : Mass of FeCl3 : 2.175 g
First, let’s calculate the molar mass of FeCl3 :
Molar mass of Iron (Fe) = 55.845
Molar mass of Chloride (Cl) = 35.453
Hence molar mass of FeCl3 = 55.845 + 3(35.453)
= 55.845 + 106.359
= 162.204 g/mol.
If 162.204 g of FeCl3 contains 55.845 g of Fe, then mass of Fe in 2.175g of FeCl3 will be :
= 2.175
= 0.3442 2.175
= 0.748 g
Hence, mass of Fe in sample B is 0.748 g
Now we have the mass of Fe and FeCl3, let’s calculate mass of Cl :
Using law of constant composition, we can calculate as :
Mass of Cl = Mass of FeCl3 Mass ratio of Cl
If 162.204 g of FeCl3 contains 106.359 g of Cl, then mass of Cl in any sample will be :
= 0.6557
Therefore , Mass of Cl = 2.175 g 0.6557
= 1.426 g
Hence, mass of Cl in sample B is 1.426 g
Step 3:
Let’s consider, sample C :
Given : Mass of Fe = 2.012 g
We know the molar mass of FeCl3 from the above calculation = 162.204 g/mol
Now, let’s calculate mass of FeCl3 in the sample :
If 162.204 g of FeCl3 contains 55.845 g of Fe, then mass of Fe in sample will be :
= = 0.3442
Let’s consider mass of FeCl3 as ‘x’
unknown mass of FeCl3 in sample C(x) mass ratio of Fe = mass of Fe
x 0.3442 = 2.012 g
x =
x = 5.845 g
Hence, mass of FeCl3 in sample C is 5.845 g
Now, let’s calculate mass of Cl in the sample :
If 162.204 g of FeCl3 contains 106.359 g of Cl, then mass of Cl in any sample will be :
= 0.6557
Therefore mass of Cl will be :
Mass of FeCl3 mass ratio of Cl = mass of Cl
5.845g 0.6557 = mass of O
3.832 g
Hence, mass of Cl in sample C is 3.832 g