Empirical & molecular formula

2011-09-25 2:49 am

An organic compound ,Y, which contains only carbon, hydrogen and oxygen, has a relative molecular mass of about 173. When 0.430g of Y is burnt in excess oxygen, 1.100g of carbon dioxide and 0.450g of water are formed.
a) What is the empirical formula of Y?
b) What is the molecular formula of Y?

回答 (1)

老爺子

2011-09-25 5:01 am

✔ 最佳答案

a)
Mass of C in Y = Mass of C in CO2
Mass of H in Y = Mass of H in H2O

In 0.430 g of Y :
Mass of C = 1.100 ´ [12/(12 + 16´2)] = 0.300 g
Mass of H = 0.450 ´ [1´2/(1´2 + 16)] = 0.050 g
Mass of O = 0.430 - (0.300 + 0.050) = 0.080 g

Mole ratio C : H : O
= 0.300/12 : 0.050/1 : 0.080/16
= 0.025 : 0.050 : 0.005
= 5 : 10 : 1

Hence, empirical formula of Y = C5H10O

b)
Let (C5H10O)n be the molecular formula of Y.

Molar mass of Y :
(12´5 + 1´10 + 16)n ≈173
86n ≈ 173
n = 2

Hence, the molecular formula of Y = C10H20O2

參考: 老爺子

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