Question

Deduce the molecular formulae of the compound obtained from the following pairs of element 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

1)CCl4
2)NH3
3)CO2
4)CaO

Answer 2

Answer:

• (a) The molecular formula of the compound is $CCl_{4}$.
• (b) The molecular formula of the compound is $NH_{3}$ .
• (c) The molecular formula of the compound is $CO_{2}$ .
• (d) The molecular formula of the compound is $CaO$ .

Explanation:

The basic steps involved in deduction of the molecular formulae of the compound which is obtained from the following pairs of element by the cross multiplication method is:

Step 1: The symbols are written.

Step 2: The valency of the respective radical is written below the symbols.

Step 3: With the respective valency, the symbols of the radicals are cross multiplied.

Step 4: The Chemical formula of the compound was written.

(a) C (Valency 4)& Cl (Valency 1) :

• The symbols are C and Cl .
• The valency are  4  and  1 .
• The valency is cross multiplied  
• C → 1        Cl → 4
• The molecular formula of the compound is $CCl_{4}$

(b) N(Valency 3)& H(Valency 1) :

• The symbols are N and H .
• The valency are  3  and  1 .
• The valency is cross multiplied .  
• N → 1        H → 3
• The molecular formula of the compound is $NH_{3}$

(c) C(Valency 4)& O(Valency 2) :

• The symbols are C and O .
• The valency are  4  and  2 .
• The valency is cross multiplied  
• C → 2        O → 4
• The molecular formula of the compound is $CO_{2}$

(d)  Ca(Valency 2)& O(Valency 2) :

• The symbols are C and O .
• The valency are 2 and  2 .
• The valency is cross multiplied  
• C → 2        O → 2
• The molecular formula of the compound is $CaO$

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