Question

An organic compound has an empirical formula of CH2O and had an approximate molecular weight of 117. What is its molecular formula?

Answer 1

Given :

▪ Empirical formula = CH_2O

▪ Molecular weight = 117

To Find :

▪ Molecular formula of this organic compound.

Concept :

↗ Empirical Formula (EF) :

Formula depicting constituent atom in their simple ratio.

↗ Molecular Formula (MF) :

Formula depicting actual number of atoms in one molecule of the compound.

↗ Relation b/w MF and EF :

$\bigstar\:\underline{\boxed{\bf{\red{n=\dfrac{Molecular\:mass}{Empirical\:Formula\:mass}}}}}$

Calculation :

☢ Empitical formula mass :

$\implies\sf\:EFM = 1(C)+2(H)+1(O)\\ \\ \implies\sf\:EFM=1(12)+2(1)+1(16)\\ \\ \implies\sf\:EFM=12+2+16\\ \\ \implies\:\underline{\underline{\bf{EFM=30\:unit}}}$

☢ Molecular formula :

$\dashrightarrow\sf\:n=\dfrac{MM}{EFM}\\ \\ \dashrightarrow\sf\:n=\dfrac{117}{30}\\ \\ \dashrightarrow\bf\:n=3.9\approx 4\\ \\ \dashrightarrow\sf\:MF=(EF)_n\\ \\ \dashrightarrow\sf\:MF=(CH_2O)_4\\ \\ \dashrightarrow\underline{\boxed{\bf{\purple{MF=C_4H_8O_4}}}}\:\gray{\bigstar}$

Answer 2

GIVEN:

• Emipirical formula of required compound : CH₂O
• Molecular weight : 117

TO FIND:

• Molecular formula

SOLUTION:

Concepts:

1. Molecular formula (MF) : Chemical formula which indicates exact number of atoms and molecules
2. Empirical formula (EF) : The ratio or proportion of atoms or molecules in a compound or moelcular formula
3. Relation between MF & EF : Molecular formula = (Empirical formula)ₙ , where n = Mass of MF/Mass of EF

______________________________________

Now , finding the value of n & mass of EF

EFM : Mass of CH₂O

Where

• Molecular mass of C = 12
• Molecular mass of H₂ = 1(2) = 2
• Molecular mass of O = 16

Substituting we have

→ 12 + 2 + 16

→ Mass of CH₂O = 30g

__________________________

→ n = MFM/EFM

→ n = 117/30

→ n = 3.9 ≈ 4

Finding molecular formula

MF = (EF)ₙ

→ MF = (CH₂O)₄

→ Molecular formula ( MF ) = C₄H₈O₄

.°. Molecular formula = C₄H₈O₄