Monday, 1 October 2018

How to Calculate the percentage mass of an element in a compound



In this article, we are going to take some examples on how to calculate the percentage mass of an element in a compound.




Percentage mass of an element = (molar mass of element) / (molar mass of Compound) * 100%

Related:



Example 1
Calculate the percentage by mass of Sodium(Na)  in Sodium trioxocarbonate (iv). [Na= 23, O=16, C=12] .

Solution
Compound = Na2CO3

Read all about molar mass

Molar mass= [2(23) + 12 + 3(16)]
Molar mass= 106

Percentage mass of Na = 23/106 * 100
Percentage mass of Na = 43.4%


Example 2
Calculate the percentage by mass of Water of crystallization in Magnesium tetraoxosulphate (vi) heptahydrate. [Mg =24, S=32, O=16]

Solution
Compound = MgSO4 . 7H2O

Molar mass of Compound = 246 [How I got the Molar mass]

Molar mass of Water of crystallization  = 7[2(1) + 16] = 126


Percentage mass of water of crystallization = 126/246 * 100
Percentage mass of Na = 51.2%




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