Question

Determine the molecular formula of a compound that contains 26.7%P, 12.1%N , and 61.2%Cl , and has a molar mass of 464 g/mol.

Answer 1

Ans) In the unknown compound, percentage of P, N and Cl present is:

P = 26.7% , N = 12.1% , Cl = 61.2%

Lets assume we have 100g of the unknown compound. So, according to percentages given, in 100g of the compound P is 26.7g , N is 12.1g and Cl is 61.2g

Now we have to calculate the number of moles of the elements present in the compound.

No. of moles of P = 26.7/30.9 = 0.86 moles

No. of moles of N = 12.1/14 = 0.86 moles

No. of moles of Cl = 61.2/35.5 = 1.72 moles

So, the skeleton chemical equation will be

P_0.86​​​N_0.86​​​Cl_1.72

To write the empirical formula, we will divide number of moles of each component by the smallest number of moles.

P_0.86/0.86​​​N_0.86/0.86Cl_1.72/0.1.72

P₁​​​​​​N₁​​​​​​Cl₂ (empirical formula)

Molar mass of the empirical formula = 30.9 + 14 + (2 × 35.5)

= 115.9 g/mol

Molar mass of the molecular formula = 464 g/mol

To calculate the molecular formula, we will divide molar mass of molecular formula by the molar mass of empirical formula.

464/115.9 = 4

Now we will mutiply this factor by the subscripts of the empirical formula

P₁​​​​​​N₁Cl₂ × 4 = P₄​​​​​​N₄Cl₈

Therefore, the molecular formula is P₄​​​​​​N₄​​​​​​Cl_8.