A solution of 20.2 g of 1,2-dibromopropane in MeOH upon heating with excess Zn produces 3.58 g of an unsaturated X. The yield (%) is closest to
[Atomic weight of Br is 80]

Options

A. 18
B. 85
C. 89
D. 30

Explanation

To solve the problem, we need to find the yield of the unsaturated compound (X) produced from the reaction of 1,2-dibromopropane with zinc. Here’s a step-by-step breakdown of the solution:

### Step 1: Determine the Molecular Weight of 1,2-Dibromopropane
1,2-Dibromopropane (C3H6Br2) has the following molecular weight:
- Carbon (C): 12 g/mol × 3 = 36 g/mol
- Hydrogen (H): 1 g/mol × 6 = 6 g/mol
- Bromine (Br): 80 g/mol × 2 = 160 g/mol

Total molecular weight = 36 + 6 + 160 = 202 g/mol

### Step 2: Calculate the Moles of 1,2-Dibromopropane
Using the mass of 1,2-dibromopropane:
\[ \text{Moles of 1,2-dibromopropane} = \frac{\text{mass}}{\text{molecular weight}} = \frac{20.2 \text{ g}}{202 \text{ g/mol}} \approx 0.1 \text{ moles} \]

### Step 3: Determine the Moles of Unsaturated Compound (X)
The problem states that 3.58 g of the unsaturated compound (X) is produced. We need to find its molecular weight. Assuming X is propene (C3H6), the molecular weight of propene is:
- Carbon (C): 12 g/mol × 3 = 36 g/mol
- Hydrogen (H): 1 g/mol × 6 = 6 g/mol

Total molecular weight of propene = 36 + 6 = 42 g/mol.

Now, we can calculate the moles of X:
\[ \text{Moles of X} = \frac{3.58 \text{ g}}{42 \text{ g/mol}} \approx 0.085 \text{ moles} \]

### Step 4: Calculate the Theoretical Yield of X
From the reaction, we know that 1 mole of 1,2-dibromopropane produces 1 mole of X. Therefore, the theoretical yield of X from 0.1 moles of 1,2-dibromopropane is:
\[ \text{Theoretical moles of X} = 0.1 \text{ moles} \]

### Step 5: Calculate the Percentage Yield
Now, we can calculate the percentage yield using the actual yield (moles of X produced) and the theoretical yield:
\[ \text{Percentage Yield} = \left( \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \right) \times 100 = \left( \frac{0.085 \text{ moles}}{0.1 \text{ moles}} \right) \times 100 \approx 85\% \]

### Final Answer
The percentage yield of the unsaturated compound (X) is approximately **85%**.

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