AlcoholsIB MYP Chemistry: Subtopic test

1. 1
   A teacher writes the formulae CH₃OH, C₂H₅OH, C₃H₇OH and C₄H₉OH on the board and tells her class that they are the first four members of a family of compounds called alcohols.

   (a)

   What is the functional group of the alcohols?

   [1 mark]

   • AC=C
   • B–COOH
   • C–CH₃
   • D–OH

   (b)

   What is the name of the alcohol with the formula C₃H₇OH?

   [1 mark]

   • APropanol
   • BMethanol
   • CEthanol
   • DButanol

   (c)

   Explain why methanol and ethanol have similar chemical properties.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A bioethanol plant in Thailand makes ethanol from the sugar in sugar cane. The sugar solution is fermented in large tanks that are kept at about 30 °C.

   (a)

   Which equation represents the fermentation of glucose?

   [1 mark]

   • AC₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
   • BC₆H₁₂O₆ → C₂H₅OH + CO₂
   • CC₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
   • DC₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

   (b)

   Why are the tanks kept at about 30 °C?

   [1 mark]

   • AYeast must be killed at this temperature to release the ethanol
   • BThe enzymes in yeast work well at this temperature; much lower is too slow and much higher destroys them
   • CSugar will only dissolve in water at 30 °C
   • DEthanol boils at 30 °C, so it must not be allowed to get hotter

   (c)

   State two other conditions, apart from temperature, that are needed for fermentation to produce ethanol.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student in Cape Town compares the energy released when four alcohols burn. For each alcohol she burns 0.0050 mol in a spirit burner under a metal can containing 100 cm³ of water, and she measures the temperature rise of the water. The temperature rises were: methanol 6 °C, ethanol 11 °C, propanol 17 °C and butanol 22 °C.

   (a)

   To make the comparison fair, the student kept some variables the same. Describe two variables that she should control and one safety precaution she should take.

   [3 marks]

   (b)

   Describe the trend in the results and calculate how much higher the temperature rise was for butanol than for methanol. Give one weakness of her method and suggest one improvement.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Brazil grows large areas of sugar cane. Mills ferment the sugar to make ethanol, which is mixed with petrol or burned on its own as a fuel in cars. The same ethanol is also sold to companies that make perfumes, hand sanitisers and cleaning products.

   (a)

   Discuss the benefits and drawbacks of using ethanol made by fermentation as a fuel instead of petrol.

   [6 marks]

   (b)

   Evaluate the use of ethanol as a solvent in perfumes and hand sanitisers.

   [6 marks]

   Total for question 4: 12 marks

End of questions