Question

The number of grams of bromine that will completely react with 5 g of pentene is: (Atomic mass of Br = 80 u)

• A. \( 22.4 \, \text{g} \)
• B. \( 8.4 \, \text{g} \)
• C. \( 11.4 \, \text{g} \)
• D. \( 54.2 \, \text{g} \)

Hint:

Alkenes undergo addition reactions with halogens in 1:1 mole ratioAlways calculate moles first before converting to mass.

Answer 1

The Correct Option is C

Step 1: Write the reaction.
Pentene reacts with bromine by addition reaction:
\[ C_5H_{10} + Br_2 \rightarrow C_5H_{10}Br_2 \]

Step 2: Determine mole ratio.
From the equation:
\[ 1 \text{ mole of pentene reacts with } 1 \text{ mole of } Br_2 \]

Step 3: Calculate molar mass of pentene.
\[ M(C_5H_{10}) = 5 \times 12 + 10 \times 1 = 60 + 10 = 70 \, \text{g/mol} \]

Step 4: Calculate moles of pentene.
\[ \text{Moles} = \frac{5}{70} = \frac{1}{14} \]

Step 5: Use mole ratio.
Moles of \( Br_2 \) required = \( \frac{1}{14} \)

Step 6: Calculate molar mass of bromine.
\[ M(Br_2) = 2 \times 80 = 160 \, \text{g/mol} \]

Step 7: Find mass of bromine.
\[ \text{Mass} = \frac{1}{14} \times 160 = 11.43 \, \text{g} \]
\[ \boxed{11.4 \, \text{g}} \]