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Ethanol is made by fermentation of a carbohydrate dissolved in water, in the presence of yeast - Edexcel - GCSE Chemistry - Question 10 - 2019 - Paper 1
Question 10
Ethanol is made by fermentation of a carbohydrate dissolved in water, in the presence of yeast. The reaction is carried out at 30°C. Explain why the reaction is car... show full transcript
Worked Solution & Example Answer:Ethanol is made by fermentation of a carbohydrate dissolved in water, in the presence of yeast - Edexcel - GCSE Chemistry - Question 10 - 2019 - Paper 1
Step 1
Explain why the reaction is carried out at a temperature of 30°C rather than at a temperature of 80°C.
Answer
The reaction is carried out at 30°C because yeast, which is a biological catalyst, provides enzymes that are active at this temperature. At 80°C, the high heat can denature these enzymes, leading to a reduced rate of fermentation or stopping the reaction entirely. Furthermore, the optimal temperature for yeast growth is around 30°C, ensuring that yeast cells are active and viable.
Step 3
Draw the structure of a molecule of ethanoic acid, CH3COOH, showing all covalent bonds.
Answer
The structure of ethanoic acid (CH3COOH) includes a carbon atom bonded to three hydrogen atoms (methyl group), another carbon atom double-bonded to an oxygen (carbonyl group), and single bonded to a hydroxyl group (-OH):
O
||
H3C-C-
|
OH
Step 4
Describe the remaining steps of the method that are needed to determine the mass of ethanol required to raise the temperature of the water by 30°C.
Answer
After lighting the wick, allow the ethanol to burn for a fixed period while observing the temperature of the water. Stir the water gently during the heating process to ensure even heat distribution. Once the temperature reaches 30°C above the initial temperature, extinguish the flame and measure the final temperature. Then, weigh the burner again to determine the mass of ethanol consumed by subtracting the final mass from the initial mass recorded before heating.
Step 5
Draw a graph of the mass of each alcohol required to raise the temperature of 100 cm³ of water by 10 °C against the number of carbon atoms in one molecule of that alcohol.
Answer
To plot the graph, the x-axis will represent the number of carbon atoms in each alcohol (methanol = 1, ethanol = 2, propanol = 3, butanol = 4, pentanol = 5) and the y-axis will represent the mass of alcohol burned in grams based on the values provided:
- Methanol: 0.37 g
- Ethanol: 0.28 g
- Propanol: 0.25 g
- Butanol: 0.23 g
- Pentanol: 0.22 g
Using a graphing tool, create a scatter plot with these coordinates and connect the points to show the relationship.