Photo AI
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, ensuring that they remain in the reaction mixture.
Step 4
Explain why benzoic acid is the limiting reactant. You must include calculations in your answer.
Answer
To determine the limiting reactant, we first calculate the number of moles of each reactant:
-
For benzoic acid:
5.0 ext{ g} imes rac{1 ext{ mole}}{122 ext{ g}} = 0.041 ext{ moles}
-
For methanol:
2.5 ext{ g} imes rac{1 ext{ mole}}{32 ext{ g}} = 0.078 ext{ moles}
From the balanced equation, 1 mole of benzoic acid reacts with 1 mole of methanol. Thus: 1 mole of benzoic acid requires 1 mole of methanol, so: 0.041 moles of benzoic acid would require 0.041 moles of methanol. Since we have 0.078 moles of methanol 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, we need to determine how much benzoic acid is required to produce 100 g of methyl benzoate.
From the reaction, the molar mass of methyl benzoate (C₈H₈O₂) is 136 g, and the molar mass of benzoic acid (C₇H₆O₂) is 122 g.
Using the ratio:
-
5 g of benzoic acid produces 3.1 g of methyl benzoate.
-
Thus, to produce 100 g of methyl benzoate:
ext{Required benzoic acid} = rac{100 ext{ g methyl benzoate} imes 5 ext{ g benzoic acid}}{3.1 ext{ g methyl benzoate}} = 161.3 ext{ g (rounded to 3 significant figures)}.
Next, calculate the cost of 161.3 g of benzoic acid:
- Cost per gram: rac{39.80 ext{ pounds}}{500 ext{ g}} = 0.0796 ext{ pounds/g}
Total cost: ext{Cost} = 161.3 ext{ g} imes 0.0796 ext{ pounds/g} = 12.81 ext{ pounds}.
Rounding to the nearest penny gives £12.81.