Question

Environment friendly refrigerant R 134a is used in the new generation domestic refrigerators. Its chemical formula is

1. CHCIF₂
2. C₂CI₃F₃
3. C₂CL₂F₄
4. C₂H₂F₄

Answer 1

Correct Answer - Option 4 : C₂H₂F₄

Concept:

Nomenclature of refrigerants:

Saturated hydrocarbon refrigerant is given as C_mH_nF_pCl_q where 2m + 2 = n + p + q must be satisfied. Nomenclature is then written as R - (m - 1)(n + 1)p.

Unsaturated hydrocarbon refrigerant must satisfy 2m = n + p + q and nomenclature is then written as R - 1(m - 1)(n + 1)p.

Inorganic refrigerant uses nomenclature R - (700 + Molecular mass).

Calculation:

Given:

For R-134a, we have

m – 1 = 1 i.e. m = 2.

n + 1 = 3 i.e. n = 2 and p = 4.

It must satisfy this 2m + 2 = n + p + q therefore, we get q = 0.

∴ we get, C₂H₂F₄

C₂H₂F₄ has two structures out of which one is symmetrical and one is asymmetrical the 'a' in 134a stands for asymmetrical structure.