Sec 4 Combined Science (Chemistry) Organic Chemistry topical questions

Define the term hydrocarbon and name the homologous series with general formula CₙH₂ₙ₊₂.

Name two fractions from crude oil and one use of each.

Aqueous bromine is added to separate samples of propane and propene. State the observation for each.

Fermentation is carried out at about 35 °C. State why a temperature of 65 °C would give a poor yield of ethanol.

State the general formulae of the alkanes and of the alkenes, and name the series whose members decolourise aqueous bromine at room temperature.

Name the two products of the complete combustion of any hydrocarbon, and write the balanced equation for the complete combustion of methane.

Explain how fractional distillation separates crude oil into fractions, and state why it is a physical separation.

(a) Write the balanced equation for the complete combustion of propane. (b) Write the equation for the reaction of methane with chlorine, and state the condition needed.

A refinery produces far more heavy fuel oil than customers want. (a) Name the process that converts heavy fractions into more useful small molecules and state what is fed in and what comes out. (b) Write an equation for decane, C₁₀H₂₂, cracking to octane, C₈H₁₈, and one other product. Identify the other product's homologous series. (c) State why cracking helps match supply to demand.

Dodecane, C₁₂H₂₆, cracks to give ethene and one other hydrocarbon. (a) Deduce the formula and name of the other product. (b) State the homologous series of each product. (c) Explain why every cracking reaction produces at least one alkene.

Three fractions leave a distillation column: A — boils below 40 °C, 1–4 carbon atoms per molecule; B — boils between 40 °C and 205 °C, 4–12 carbons; C — boils above 350 °C, more than 20 carbons. (a) Match each fraction to a use: bottled cooking gas, petrol, road surfacing. (b) State how viscosity and ease of ignition change from A to C. (c) Explain the boiling-point trend in terms of the molecules.

Gas jars of aqueous bromine are prepared. Propane is bubbled through jar 1 and propene through jar 2; jar 2 is then repeated with the gas first passed through a UV lamp's beam. (a) State and explain the observation in jar 1. (b) State and explain the observation in jar 2. (c) Explain, using bonds, why the two hydrocarbons behave differently.

A student prepares ethanol from glucose and then converts part of it to ethanoic acid. (a) Name the process, the organism and two conditions for step 1, and write the equation. (b) Name the type of reaction for step 2 and give the two reagents/conditions that achieve it in the laboratory. (c) Write an equation for step 2 and name the homologous series of the product.

Margarine is made from sunflower oil by passing hydrogen through the warm oil over a nickel catalyst. (a) Name the type of reaction and describe what happens at the molecular level. (b) Explain why the product is more solid than the original oil. (c) Sunflower oil is described as polyunsaturated. State what this means and why partly hardened margarine may still decolourise bromine water.

(a) Ethene polymerises to poly(ethene). Write the equation in words or symbols, showing the repeat unit. (b) Explain why poly(ethene) is non-biodegradable, and state two environmental problems this causes. (c) Compare physical and chemical recycling of poly(ethene), giving one advantage of each.

A country considers blending bioethanol, made by fermenting sugar-cane juice, into its petrol. Evaluate this plan. In your answer, use chemistry from this chapter (fermentation, combustion, the carbon balance) and weigh at least one advantage and one disadvantage before reaching a conclusion.

A winemaker ferments glucose solution to make ethanol. (a) State the organism and two conditions, and write the equation. (b) The vessel is sealed but fitted with a one-way valve. Explain why both features are needed. (c) Explain why fermentation eventually stops, naming the limiting reactant. (d) Explain how distillation afterwards produces a stronger drink.

A town sorts its plastic waste. About 40% is clean poly(ethene) packaging film, 25% is poly(propene) bottles, and the rest is mixed, dirty plastic. The council must choose between landfill, burning for energy, physical recycling and chemical recycling. (a) State why landfill is the least sustainable option. (b) Give one advantage and one disadvantage of burning the mixed plastic for energy. (c) Which route best suits the clean poly(ethene) film? Justify your choice. (d) State two social or economic issues any recycling scheme must overcome.