Question

Deduce the molecular formulae of the compound obtained from the following pairs of elements by the cross multiplication method.
A. C (Valency 4) & Cl (Valency 1)
B. N (Valency 3) & H (Valency 1)
C. C (Valency 4) & O (Valency 2)
D. Ca (Valency 2) & O (Valency 2)

Answer 1

a. C (Valency 4) & Cl (Valency 1) :
Step 1 : Write the symbols of the radicals.
C Cl
Step 2 : Write the valency below the respective radical.
C Cl
4 1
Step 3 : Cross-multiply symbols of radicals with their respective valency.

Step 4 : Write down the chemical formula of the compound.
CCl₄


b. N (Valency 3) & H (Valency 1)
Step 1 : Write the symbols of the radicals.
N H
Step 2 : Write the valency below the respective radical.
N H
3 1
Step 3 : Cross-multiply symbols of radicals with their respective valency.

Step 4 : Write down the chemical formula of the compound.
NH₃


C. C (Valency 4) & O (Valency 2)
Step 1 : Write the symbols of the radicals.
C O
Step 2 : Write the valency below the respective radical.
C O
4 2
Step 3 : Cross-multiply symbols of radicals with their respective valency.

Step 4 : Write down the chemical formula of the compound.
CO₂


D. Ca (Valency 2) & O (Valency 2)
Step 1 : Write the symbols of the radicals.
Ca O
Step 2 : Write the valency below the respective radical.
Ca O
2 2
Step 3 : Cross-multiply symbols of radicals with their respective valency.

Step 4 : Write down the chemical formula of the compound.
CaO