Methyl benzoate is commonly added to perfumes as it has a pleasant smell - Scottish Highers Chemistry - Question 3 - 2018

The small test tube filled with cold water serves as a condenser to prevent the escape of volatile reactants or products. It helps to condense any vapors back into liquid form, ensuring that the reaction mixture remains contained within the apparatus.

Product X is water (H₂O).

To determine the limiting reactant, we first calculate the number of moles of benzoic acid and methanol used:

For benzoic acid (C₇H₆O₂), the molar mass is 122 g/mol:

Number of moles of benzoic acid = [ \frac{5.0 \text{ g}}{122 \text{ g/mol}} = 0.041 \text{ moles} ]

For methanol (CH₃OH), the molar mass is 32 g/mol:

Number of moles of methanol = [ \frac{2.5 \text{ g}}{32 \text{ g/mol}} = 0.078 \text{ moles} ]

The balanced equation shows that 1 mole of benzoic acid reacts with 1 mole of methanol. Since there are 0.041 moles of benzoic acid available, it limits the reaction because there are less moles of benzoic acid compared to methanol.

To produce 3.1 g of methyl benzoate, 5.0 g of benzoic acid were used. Therefore, to calculate how much benzoic acid is needed for 100 g of methyl benzoate, we can set up a proportion:

[ \text{If } 3.1 \text{ g requires } 5.0 \text{ g of benzoic acid, then } 100 \text{ g requires } X \text{ g of benzoic acid} ]

[ X = \frac{5.0 \text{ g} \times 100 \text{ g}}{3.1 \text{ g}} \approx 161.29 \text{ g} ]

Now, we can compute the cost:

Benzoic acid costs £39.80 for 500 g. Thus, the cost for 161.29 g is:

[ \text{Cost} = 39.80 \times \frac{161.29}{500} \approx £12.84 ]

Rounding to the nearest penny, the cost of the benzoic acid needed is approximately £12.84.