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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 ca... 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 fermentation process is optimized at lower temperatures, specifically around 30°C, because at this temperature yeast is most active and efficient in converting sugars into ethanol. At higher temperatures, such as 80°C, the yeast cells can become denatured, leading to a decrease in their enzyme activity. This denaturation reduces the effectiveness of the fermentation process and can halt the production of ethanol entirely.
Step 3
Draw the structure of a molecule of ethanoic acid, CH₃COOH, showing all covalent bonds
Answer
The structure of ethanoic acid (acetic acid) can be represented as:
O
||
H - C - C - OH
|
H
This diagram includes all covalent bonds; with the carbon atom central to the structure, bonded to a hydroxyl group (OH) and a carbonyl group (C=O).
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
To determine the mass of ethanol required to raise the temperature of the water by 30°C, follow these additional steps:
- Allow the water temperature to stabilize before starting.
- After lighting the wick, burn the ethanol until the water temperature rises to the desired level (30°C).
- Once achieved, extinguish the flame and record the highest temperature reached.
- Measure the final mass of the burner containing the ethanol.
- Calculate the mass of ethanol burned by subtracting the final mass of the burner from the initial mass recorded. The resulting mass will indicate how much ethanol was required to achieve the temperature rise.
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 (1-5).
- The y-axis will represent the mass of alcohol burned (in grams).
- Plot points for each alcohol as follows:
- Methanol (1 carbon): 0.37 g
- Ethanol (2 carbons): 0.28 g
- Propanol (3 carbons): 0.25 g
- Butanol (4 carbons): 0.23 g
- Pentanol (5 carbons): 0.22 g
- Connect the points to visualize the trend.