Question

What is the molar mass of product hydrocarbon when 2 moles of methyl bromide reacts with large excess of sodium in dry ether?

• A. 15.0 g mol$^{-1}$
• B. 30.0 g mol$^{-1}$
• C. 7.5 g mol$^{-1}$
• D. 40.0 g mol$^{-1}$

Answer 1

Answer: (B)

30.0 g/mol

Answer 2

In the Wurtz reaction, two moles of methyl bromide react with sodium to form 1 mole of ethane:

$$2\, \text{CH}_3\text{Br} + 2\, \text{Na} \rightarrow \text{CH}_3\text{CH}_3 + 2\, \text{NaBr}$$

Ethane (CH$_3$CH$_3$) has a molar mass of:

$$2 \times 12\, \text{g/mol} + 6 \times 1\, \text{g/mol} = 24 + 6 = 30\, \text{g/mol}$$

Thus, the molar mass of the product hydrocarbon is 30.0 g/mol.