Organic Chemistry and IUPAC NamingIB MYP Chemistry: Topic test

1. 1
   A restaurant kitchen in Dubai cooks on gas burners fuelled by propane, C₃H₈. The propane is stored as a liquid in steel cylinders and burns in plenty of air. Propane is one of the alkanes found in crude oil.

   (a)

   Propane is an alkane. Which molecular formula is that of hexane, the alkane with six carbon atoms?

   [1 mark]

   • AC₆H₁₀
   • BC₆H₁₂
   • CC₆H₁₄
   • DC₆H₁₆

   (b)

   Which pair of products forms when propane burns completely in plenty of air?

   [1 mark]

   • ACarbon monoxide and hydrogen
   • BCarbon dioxide and water
   • CCarbon and water
   • DCarbon dioxide and hydrogen

   (c)

   Write the balanced symbol equation for the complete combustion of propane.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Ripening bananas give off ethene gas, C₂H₄. A research team in Ecuador wants to detect ethene in a shipping container full of bananas. They bubble a sample of gas from the container through bromine water, which is orange-brown.

   (a)

   Which molecular formula is that of an alkene?

   [1 mark]

   • AC₄H₈
   • BC₄H₁₀
   • CC₃H₈
   • DC₅H₁₂

   (b)

   Which feature of an ethene molecule makes it react with bromine?

   [1 mark]

   • AA –COOH group
   • BFour hydrogen atoms
   • CA carbon–carbon single bond
   • DA carbon–carbon double bond

   (c)

   Describe what the team sees if the gas contains ethene, and explain why this happens.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Fermentation of sugar by yeast makes ethanol and carbon dioxide, so the volume of gas collected shows how fast fermentation is happening. A school in Accra investigates the best temperature for fermentation. The students dissolve 20 g of sugar in 200 cm³ of water, add 5 g of yeast and keep the mixture in a water bath. They measure the volume of carbon dioxide collected in 10 minutes.

   (a)

   Write a hypothesis for how temperature will affect the rate of fermentation, giving a scientific reason, and name one variable the students must keep the same.

   [3 marks]

   (b)

   The students repeat the test at four temperatures. They collect 6 cm³ of gas at 15 °C, 19 cm³ at 25 °C, 44 cm³ at 35 °C and 9 cm³ at 45 °C. Describe the trend, explain the results and suggest one improvement to the investigation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In Accra, Ghana, drinking water is sold in small sealed sachets made from poly(ethene). The sachets are cheap, light and safe, and millions are bought every day. Used sachets are often dropped in the street, where they block drains and cause flooding. Poly(ethene) is made from ethene, which comes from crude oil. The government is considering a ban on the sachets.

   (a)

   Explain how ethene is obtained from crude oil and how poly(ethene) is then made from it.

   [6 marks]

   (b)

   Discuss the advantages and disadvantages of poly(ethene) sachets and decide whether the government should ban them.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A chemist in Pune is given the molecular formula C₅H₁₂ and is asked to draw and name every possible alkane with this formula. She starts with the unbranched chain, pentane, and then rearranges the carbon atoms into branched chains.

   (a)

   How many different structural isomers have the molecular formula C₅H₁₂?

   [1 mark]

   • A2
   • B5
   • C3
   • D4

   (b)

   One of the branched isomers has the condensed structural formula CH₃CH(CH₃)CH₂CH₃. What is its IUPAC name?

   [1 mark]

   • A2-methylbutane
   • B1-methylbutane
   • C3-methylbutane
   • D2-methylpropane

   (c)

   Explain what is meant by the term structural isomers, using the isomers of C₅H₁₂ as an example.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A homeowner in Istanbul removes limescale from a kettle by leaving vinegar in it overnight. Limescale is mainly calcium carbonate. Vinegar is a dilute solution of ethanoic acid, CH₃COOH. When the vinegar is added, the limescale fizzes slowly and gradually dissolves.

   (a)

   Which gas causes the fizzing?

   [1 mark]

   • AHydrogen
   • BCarbon dioxide
   • COxygen
   • DCarbon monoxide

   (b)

   What is the name of the salt formed in the reaction?

   [1 mark]

   • ACalcium methanoate
   • BCalcium carbonate
   • CEthyl ethanoate
   • DCalcium ethanoate

   (c)

   Hydrochloric acid of the same concentration would make the limescale fizz much faster. Explain why ethanoic acid is called a weak acid and why it reacts more slowly.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A student in Mumbai wants to make the ester ethyl methanoate, which has a fruity smell, by heating methanoic acid with ethanol and a few drops of a catalyst in a boiling tube. She plans to hold the tube directly in a Bunsen burner flame and then sniff the tube to check the smell.

   (a)

   Write the word equation for the reaction and name a suitable catalyst.

   [3 marks]

   (b)

   Evaluate her plan: explain why heating the tube directly in the flame is unsafe, suggest a safer way to heat it, describe how she should safely check the smell, and state one other safety precaution.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A refinery in Ruwais, in the United Arab Emirates, separates crude oil into fractions by fractional distillation. The boiling points of the first six unbranched alkanes are: methane −162 °C, ethane −89 °C, propane −42 °C, butane 0 °C, pentane 36 °C and hexane 69 °C. The government is also considering fermenting waste dates, which are rich in sugar, to make ethanol to blend with petrol so that less crude oil is burned.

   (a)

   Describe the trend in the boiling points, predict with a reason whether heptane boils above or below 69 °C, and explain how this trend allows crude oil to be separated by fractional distillation.

   [6 marks]

   (b)

   Discuss the advantages and disadvantages of making ethanol from waste dates to blend with petrol, and reach a justified conclusion.

   [6 marks]

   Total for question 8: 12 marks

End of questions