Organic Chemistry Exam Style Qs

What is meant by the term catalyst? (2)

m1: a substance which increases the rate of reaction m2: and is chemically unchanged at the end of the reaction

Explain how a catalyst works (2)

m1: provides an alternative pathway m2: alternative path has a lower activation energy

Give three reasons why cracking is carried out (3)

m1: over/greater supply of long-chain hydrocarbons m2: high demand for short-chain hydrocarbons m3: alkenes used to make polymers

One of the compounds sometimes present in crude oil has the formula

C₆H₁₂S

Explain why it is important to remove this compound from a fuel (2)

m1: forms sulfur dioxide when burned m2: which causes specified problem for the environment

Two reactions that can occur when hydrocarbon A is burned in air are represented by these equations.

Equation for reaction 1 CH₄ + 2O₄ → CO₂ + 2H₂O

Equation for reaction 2 CH₂ + 1½O₂ → CO + 2H₂O

Explain why a different product is formed in reaction 2 and why this product is dangerous.

m1: incomplete combustion m2: carbon monoxide is a toxic/poisonous gas m3: reduces capacity in the blood to carry oxygen

Explain what is meant by the term isomerism (2)

m1: compounds with the same molecular formula but a m2: different displayed formula

When heptene is added to bromine water, and the mixture is shaken, a reaction occurs.

State the type of reaction and give the colour of the bromine water before and after the reaction with hepten (3)

m1: type of reaction → addition m2: colour before → orange m3: colour after → colourless

Compare the hydrocarbons in fractions D and F in terms of

• boiling point

• size of molecules

• viscosity

(3)

m1: D have a higher boiling point m2: larger molecules m3: more viscious

The alkanes are a homologous series of hydrocarbons obtained from the fractions in crude oil.

Describe how crude oil is separated into fractions in industry. (4)

m1: fractional distillation m2: crude oil vaporised m3: fractions condense m4: fractions have different boiling points

Explain why some compounds are described as hydrocarbons. (2)

m1: they all contain hydrogen and carbon m2: only

All alkanes in a homologous series have the same general formula

State two other features of a homologous series (2)

m1: similar chemical properties m2: gradual change m3: same functional group

Describe how the boiling point, colour and viscosity of the fuel oil fraction differ from those of the gasoline fraction. (3)

m1: have higher boiling points m2: have higher viscosities m3: darker in colour

Compare the hydrocarbons in fractions D and F in terms of

• boiling point

• size of molecules

• viscosity

(3)

m1: higher boiling point m2: larger molecules m3: more viscious

Explain why cracking is an important process in the oil industry. (4)

m1: produces smaller, shorter chain molecules m2: which have greater demand m3: smaller chain molecules burn more cleanly m4: crude oil has a surplus of long-chain molecules m5: alkenes used to make alcohols/polymers/etc

The alkanes are a homologous series of hydrocarbons obtained from the fractions in crude oil.

Describe how crude oil is separated into fractions in industry. (4)

m1: fractional distillation m2: crude oil vaporised m3: fractions condense m4: fractions have different boiling points

State the meaning of the term biodegrade (2)

m1: polymer breaks down m2: by bacteria

What is the meaning of the term polymer? (2)

m1: long chain molecule m2: formed when many small molecules join together

Explain why addition polymers that are buried in landfill sites remain chemically unchanged for many years (2)

m1: they do not biodegrade m2: because they are inert/unreactive

Use the diagram to state two changes that occur during the formation of poly(ethene). (2)

m1: one of the bonds in the double bonds break m2: many molecules join together

These are two methods used to dispose of the polymer

• burying in landfill sites

• burning

Discuss the environmental problems caused by these two methods of disposal.

m1: polymers will remain in landfill indefinitely m2: as they are inert and do not biodegrade m3: burning produces greenhouse gases m4: and causes global warming as greenhouses gases trap warm air in the atmosphere m5: combustion produces toxic gases