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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

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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:

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Answer

The fermentation process is optimized at 30°C because at this temperature, yeast remains active and efficient in converting carbohydrates into ethanol. Higher temperatures can lead to the denaturation of enzymes in the yeast, causing a loss of activity, which would impede the fermentation process.

Step 2

In this reaction ethanol is:

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Answer

In this reaction, ethanol is B: oxidised. The process involves the loss of electrons, indicating that ethanol is being converted to ethanoic acid.

Step 3

Draw the structure of a molecule of ethanoic acid, CH₃COOH, showing all covalent bonds.

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The structure of a molecule of ethanoic acid (CH₃COOH) is:

    H   O
     \  ||
      C--C
     /   \  
    H    O
     
    H

Here, the covalent bonds are represented between carbon (C), oxygen (O), and hydrogen (H) atoms.

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.

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Answer

After lighting the wick, allow the ethanol to burn until the temperature of the water rises by 30°C. Then, carefully record the maximum temperature achieved. Finally, extinguish the flame and measure the final mass of the burner. The mass of ethanol burned can be calculated by subtracting the final mass from the initial mass of the burner.

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.

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Answer

A graph should be created with the x-axis representing the number of carbon atoms in each alcohol, and the y-axis indicating the mass of alcohol burned in grams. According to the given data:

  • Methanol (1 C): 0.37 g
  • Ethanol (2 C): 0.28 g
  • Propanol (3 C): 0.25 g
  • Butanol (4 C): 0.23 g
  • Pentanol (5 C): 0.22 g

Each point on the graph should reflect these mass values corresponding to the respective number of carbon atoms.

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