Question

A compound (molecular mass 64.59 u) has the following data :
`{:("Element","Relative No. of atoms","% Composition"),("A",3.10,37.215),("B",7.80,7.8),("C",1.55,54.98):}`
Determine :
(i) Atomic masses of the elements A, B, C
(ii) Simplest atomic ratios of the element
(iii) Molecular formula of the compound.

Answer 1

Step I : Calculation of the atomic masses of the elements
Atomic mass of element `= ("Percentage of element")/("Relative no. of atoms")`
Atomic mass of `A =(37.215)/(3.10)=12 `u
Atomic mass of `B=(7.8)/(7.8)=1.0` u
Atomic mass of `C = (54.98)/(1.55)=35.5` u
Step II. Calculation of simplest atomic ratios of the elements
`{:("Element","Relative no. of atoms","Simplest atomic ratio"),("A",3.10,(3.10)/(1.55)=2),("B",7.8,(7.8)/(1.55)=5),("C",1.55,(1.55)/(1.55)=1):}`
Step III. Calculation of the molecular formula
Empirical formula of compound `= A_(2)B_(5)C`
Empitical formula mass of the compound `= 2 xx 12 + 5 xx 1.0 +35.5 = 64.5` u
`n=("Molecular mass")/("Empirical formula mass")=(64.59)/(64.5)=1`
`:.` Molecular formula `=1 (A_(2)B_(5)C)=A_(2)B_(5)C`.