Quick answer: Crude oil is a mixture of hydrocarbons separated by fractional distillation into fractions with different chain lengths and boiling points. This Chemistry 9-10 worksheet on crude oil and hydrocarbons gives 20 problems from easy to hard: hydrocarbon vocabulary, alkane formulae and spot the alkenes. The worked answers are on a separate page, and the worksheet is a free printable PDF.
These 20 problems train you to use the general formulae of alkanes and alkenes, read fractionating column and boiling point diagrams, balance combustion and cracking equations and carry out mole and mass calculations. They are written for GCSE, IGCSE, O Level, CBSE Class 9-10 and NGSS high school chemistry.
Work through them in order: the first five check the basic ideas, the middle ten need calculations or explanations, and the last five are longer questions that combine several steps. Use the Ar values given in each problem.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: GCSE C7
Problem 1 Hydrocarbon vocabulary ★★★
Kamau in Nairobi is revising. Complete each sentence.1. A hydrocarbon contains only ______ and ______ atoms.
2. Alkanes are called ______ hydrocarbons because they have only ______ bonds.
3. The general formula of the alkanes is ______.
4. Crude oil is separated by ______ distillation.
Problem 2 Alkane formulae ★★★
Chiamaka in Lagos writes alkane formulae from their carbon numbers.1. Write the molecular formula of the alkane with 6 carbon atoms.
2. Then write the formula of the alkane with 11 carbon atoms.
3. An alkane has 42 hydrogen atoms. How many carbon atoms does it have?
Problem 3 Spot the alkenes ★★★
Aarav in Pune has a list of hydrocarbons: C₄H₁₀, C₄H₈, C₅H₁₂, C₃H₆, C₆H₁₂, C₂H₆.1. Which of them are alkenes?
2. Then state the rule you used.
3. Finally, give the formula of the alkene with 8 carbon atoms.
Problem 4 Test for unsaturation ★★★
Emma in Leeds has two colourless liquids, hexane and hex-1-ene, in unlabelled bottles. She adds a few drops of orange bromine water to a sample from each bottle and shakes.1. Predict what she sees with hexane.
2. Then predict what she sees with hex-1-ene.
3. Which bottle contains the alkene?
Problem 5 Reading the column ★★★
The diagram shows a fractionating column with exits A to F (top to bottom). Bilal in Lahore knows the fractions leave in this order: refinery gases, petrol, kerosene, diesel, fuel oil, bitumen.2. Which exit gives bitumen?
3. Which exit gives the most viscous liquid other than bitumen?
4. Exit B is petrol. Is petrol more or less flammable than diesel (exit D)?
Problem 6 Complete combustion equations ★★★
Mei in Singapore studies fuel gases. Balance each complete combustion equation.1. C₄H₁₀ + O₂ → CO₂ + H₂O
2. C₅H₁₂ + O₂ → CO₂ + H₂O
3. Finally, explain why the balanced equation for butane has 13O₂ and not 6.5O₂.
Problem 7 Trends along the series ★★★
Diego in Texas compares two fractions. Petrol has shorter chains than diesel.1. Complete the sentence: diesel has a ______ boiling point, a ______ viscosity and is ______ to ignite than petrol. (Use higher or lower, harder or easier.)
2. Then explain the trend in boiling point using the size of the molecules.
Problem 8 Balance the cracking ★★★
Wanjiru in Nairobi studies cracking.1. Complete: C₁₄H₃₀ → C₁₀H₂₂ + ______.
2. Then name the type of hydrocarbon of the second product.
3. Finally, write the equation for cracking C₁₆H₃₄ into C₈H₁₈ and one other product only.
Problem 9 Mass of carbon dioxide ★★★
A camping stove in Leeds burns propane, C₃H₈. A canister releases 44 g of propane. (Ar: C = 12, H = 1, O = 16.)1. Write the balanced equation for complete combustion.
2. Then calculate the moles of propane burnt.
3. Finally, calculate the mass of carbon dioxide produced.
Problem 10 Reading a molecule ★★★
Priya in Chennai draws a compound Z.2. Then state whether Z is saturated or unsaturated and give the reason.
3. Finally, predict its result with bromine water.
Problem 11 Carbon percentage and soot ★★★
Fatima in Kano compares three fuels. (Ar: C = 12, H = 1.)1. Calculate the percentage by mass of carbon in methane CH₄.
2. Then calculate the same for ethane C₂H₆ and ethene C₂H₄.
3. Which of the three would be expected to burn with the sootiest flame? Explain.
Problem 12 Boiling points of alkanes ★★★
Kofi in Accra plots boiling points of the first five alkanes.2. Then state whether pentane is a gas or a liquid at 25 °C and give the reason.
3. Finally, describe the trend. The rises between points were 73, 47, 41 and 37 °C. Estimate the boiling point of hexane if the next rise is about 33 °C.
Problem 13 Fuel tank conversion ★★★
A motorbike tank in Pune holds 45 dm³ of petrol. The density of petrol is 0.74 g/cm³.1. Convert 45 dm³ to cm³.
2. Then calculate the mass of petrol in grams.
3. Finally, convert the mass to kilograms.
Problem 14 Why fractions separate ★★★
Nia in Cardiff asks why hot vapour that enters the bottom of the column leaves at different heights.1. Explain what happens to a petrol vapour molecule as it rises.
2. Then explain why a bitumen molecule does not rise far.
3. Finally, suggest why the top of the column is kept cooler than the bottom.
Problem 15 Supply and demand ★★★
A refinery in Houston processes 5000 tonnes of crude oil. It yields 18 % petrol and 24 % fuel oil. Half of the fuel oil is cracked, and 40 % by mass of the cracked fuel oil becomes petrol-range hydrocarbons.1. Calculate the mass of petrol obtained by distillation.
2. Then calculate the mass of fuel oil cracked and the extra petrol made.
3. Finally, calculate the percentage increase in petrol.
Problem 16 Ethene from a big alkane ★★★
Cracking can be written C₁₆H₃₄ → C₈H₁₈ + 4C₂H₄. (Ar: C = 12, H = 1.)1. Show that the equation is balanced.
2. Then calculate the relative formula mass of C₁₆H₃₄.
3. Finally, calculate the mass of ethene formed from 1.0 kg of C₁₆H₃₄ if the reaction goes to completion.
Problem 17 Bromine addition by mass ★★★
Ethene reacts with bromine: C₂H₄ + Br₂ → C₂H₄Br₂. A sample of 2.8 g of ethene is passed into excess bromine. (Ar: C = 12, H = 1, Br = 80.)1. Calculate the moles of ethene.
2. Then calculate the mass of bromine that reacts.
3. Finally, calculate the mass of C₂H₄Br₂ formed and show that mass is conserved.
Problem 18 Design an identification test ★★★
Three colourless liquids are known to be hexane, hex-1-ene and water, but the labels were lost. Hexane and hex-1-ene do not mix with water.1. Describe a simple test, using only bromine water, that can identify the alkene.
2. Then explain how you can tell hexane from water by looking at the mixture with bromine water.
3. Finally, explain why hex-1-ene reacts but hexane does not.
Problem 19 Air needed for burning ★★★
In a workshop in Lahore 2.0 dm³ of propane gas burns completely. All gas volumes are measured at the same temperature and pressure. Air is 21 % oxygen by volume.1. Write the balanced equation.
2. Then calculate the volume of oxygen needed.
3. Finally, calculate the volume of air needed and the volume of carbon dioxide produced.
Problem 20 Find the faulty statements ★★★
Student notes: (a) “Alkenes are saturated because they contain many hydrogen atoms.” (b) “Cracking is a chemical change that needs a high temperature.” (c) “Fractional distillation breaks C–C bonds.” (d) “The fraction at the top of the column has the highest viscosity.”1. Decide which statements are wrong.
2. Then rewrite each wrong statement correctly.
