Formula Unit Mass


 
 
Concept Explanation
 

Formula Unit Mass

Formula Unit Mass: The simplest combination of ions that produces an electrically neutral unit is called a formula unit of the ionic compound e.g. formula unit for sodium chloride is NaCl. Formula unit for ammonium sulphate is(NH_4)_2SO_4. The formula unit mass of a substance is the sum of the atomic masses of all atoms in a formula unit of a compound. We use the term ‘formula unit’ for those substances, which have their constituent particles as ions. Similarly, we use ‘molecular mass’ for atoms.

For example :

The molecular formula for ammonium sulphate is (NH_4)_2SO_4 

Empirical formula of ammonium sulphate is   (NH_4)_2SO_4

Therefore, the formula unit mass of (NH_4)_2SO_4 can be calculated as: 

 

Types of atoms

Number of atoms

(step 1)

Atomic mass

(step 2)

Mass of each type of         atom

(step 3)

        N           214.007amu28.014 amu
        H          81.008 amu8.064 amu
       S          132.06 amu32.06 amu 
                 415.99 amu63.996 amu

Formual mass of (NH_4)_2SO_4

  132.134 amu
Sample Questions
(More Questions for each concept available in Login)
Question : 1

What is the mass of glucose ?

Right Option : B
View Explanation
Explanation
Question : 2

Which of the following statement / statements are correct :

(a) The molecular formula for ammonium sulphate is (NH_4)_2SO_4 

(b) Empirical formula of ammonium sulphate is   (NH_4)_2SO_4

 

Right Option : C
View Explanation
Explanation
Question : 3

The molecular formula for __________________ is (NH_4)_2SO_4 .

Right Option : A
View Explanation
Explanation
 
 


Students / Parents Reviews [20]