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Methyl benzoate is commonly added to perfumes as it has a pleasant smell - Scottish Highers Chemistry - Question 3 - 2018
Question 3
Methyl benzoate is commonly added to perfumes as it has a pleasant smell. A student carries out a reaction to produce methyl benzoate using the following apparatus. ... show full transcript
Worked Solution & Example Answer:Methyl benzoate is commonly added to perfumes as it has a pleasant smell - Scottish Highers Chemistry - Question 3 - 2018
Step 1
Step 2
Suggest a reason why there is a small test tube filled with cold water in the neck of the tube containing the reaction mixture.
Answer
The small test tube filled with cold water acts as a condenser to prevent the escape of volatile or gaseous reactants or products during the reaction. This helps maintain the reaction mixture and improves yield.
Step 4
Explain why benzoic acid is the limiting reactant.
Answer
To determine the limiting reactant, we first calculate the number of moles:
For benzoic acid: Moles = mass (g) / molar mass (g/mol) = 5.0 g / 122 g/mol = 0.041 moles
For methanol: Moles = mass (g) / molar mass (g/mol) = 2.5 g / 32 g/mol = 0.078 moles
The balanced equation shows that 1 mole of benzoic acid reacts with 1 mole of methanol. Therefore, to fully react with 5 g of benzoic acid, it would require 5 g of benzoic acid to react with 0.041 moles of methanol. Since we have more than enough methanol (0.078 moles available), benzoic acid is the limiting reactant.
Step 5
Calculate the cost, in £, of the benzoic acid needed to make 100 g of methyl benzoate using the student's method.
Answer
First, calculate how much benzoic acid is needed to produce 100 g of methyl benzoate:
From the reaction, the molar ratio of benzoic acid to methyl benzoate is 1:1. Therefore, producing 100 g of methyl benzoate requires 5 g of benzoic acid:
Cost for 500g of benzoic acid = £39.80 Cost for 1g = £39.80 / 500 = £0.0796 Cost for 5g = 5 * £0.0796 = £0.398
Thus, the total cost for the benzoic acid needed to make 100 g of methyl benzoate is approximately £0.398.