Chemistry Paper 2 Mistakes

Can alcohols be used as fuels?

Explain your answer.

Yes — burning alcohols is a v/ exothermic reaction

During cracking, hydrocarbons are often passed over a substance so that they break apart.

What is the general name for this type of substance?

Hot catalyst

Describe the types of cracking.

• Catalytic cracking — passing hydrocarbons over a hot catalyst

• Steam cracking — mixing hydrocarbons w/ steam + heating to v/ high temp → thermal decomposition occurs

Name the gas produced when ethanol reacts with sodium.

Hydrogen

Describe all the reactions of alcohols.

• air — alcohol + oxygen → carbon dioxide + water

• water — dissolves to form neutral solution

• sodium — alcohol + sodium → hydrogen + salt

• oxidising agents — produces carboxylic acids

True or false? Ethene can be manufactured by the dehydration of ethanol.

True

Describe the reaction of fermentation.

• glucose → ethanol + carbon dioxide

  • aqueous solution of ethanol produced

• conditions:

  • 35°C

  • yeast enzyme catalyst

  • anaerobic conditions

Describe the combustion of hydrocarbons.

• hydrocarbons + oxygen → carbon dioxide + water

  • hydrogen + oxygen → water

  • carbon + oxygen → carbon dioxide

• Hydrogen and oxygen are oxidised

• Releases energy

What is the name of this amino acid? H₂NCH₂COOH

Glycine

What do amino acids have?

Two functional groups in same molecule

Describe how amino acids react.

• Condensation polymerisation — produces polypeptides

• Diff. amino acids can be combined in same chain — produces proteins

Ethanol reacts with oxygen to give ethanoic acid.

Give the name of the other product that is formed.

Water

Look at the diagram.

Identify the monomer.

Dialcohol

Describe condensation polymerisation.

• Two diff. monomers w/ same functional groups on each monomer

• Small molecules (e.g. water) often lost (condensation reactions)

______________ + ____________ ______ → polyester + _________

• ethanediol

• hexaneoic acid

• water

How many types of monomers are there in addition polymerisation?

1

What can alkenes be used to do in addition polymerisation?

Form polymers — e.g. poly(ethene) and poly(propene)

Describe what happens in addition polymerisation reactions.

Many small molecules (monomers) join together to form v/ large molecules (polymers)

In addition polymers, why does the repeating unit have the same atoms as the monomer?

No other molecule is formed in the reaction.

What happens during thermal decomposition? [2 marks]

Large molecules are broken down into smaller molecules by heat.

The diagram shows a reaction which takes place in an oil refinery.

Compounds Y and Z are both useful substances.

Compound Y is unsaturated. Compound Z is saturated.

a) Suggest one use for compound Y. [1 mark]

b) Suggest one use for compound Z. [1 mark]

a) Making polymers

b) Fuel

The hydrocarbon C₁₆H₃₄ was heated strongly in the absence of air.

This is one of the reactions which took place:

C₁₆H₃₄ C₆H₁₄ + C₆H₁₂ + 2C₂H₄

This type of reaction is carried out because there is a greater demand for the products than for the original hydrocarbon.

Suggest two reasons for this. [2 marks]

• Smaller molecules are more reactive (flammable) — useful as fuels

• Produces unsaturated compounds (alkenes)

Small molecules of substances called monomers can be joined together in polymerisation — ethene → poly(ethene).

Complete the equation to show the formation of the polymer from the monomer propene. [1 mark]

• bonds beyond rounded brackets

• no double bond

• ‘n’ on outside

The equation shows the cracking of a hydrocarbon compound into two different compounds, A and B.

Why is compound A useful in industry? [1 mark]

Compound A is reactive.

Fibreglass is a composite material consisting of glass fibres and what other material?

Plastic

Describe how different types of glass are made.

• Soda lime glass — heating mixture of sand, sodium carbonate + limestone

• Borosilicate glass — heating mixture of sand and boron trioxide

  • melts at higher temps than soda lime

Describe how clay ceramics like pottery and bricks are made.

• Shaping wet clay

• Heating in furnace

• The properties of polymers depend on what ______________ they are made from and the ______________ under which they are made.

• For example, ______ __________ (LD) and _______ __________ (HD) ______________ are produced from __________.

• monomers

• conditions

• low density

• high density

• poly(ethene)

• ethene

Describe the differences between low density and high density poly(ethene).

• LD — weaker forces of attraction (chains further apart) → low melting point + soft

• low density — less particles per unit volume

• HD — higher forces of attraction (chains closer) → higher melting point

• high density — more particles per unit volume

Describe the properties of thermosoftening polymers.

• Individual, tangled polymer chains

  • easily separated + melted by heat

    • weak intermolecular forces b/ chains

    • chains easy to separate at lower temps

    • less energy needed to break chains

Describe the properties of thermosetting polymers.

• Polymer chains w/ crosslinks

• Don’t melt when heated

Describe what composites are.

Matrix/binder surrounding + binding fibres of fragments of other material (reinforcement)

Give and describe the properties of four types of composites.

• Carbon fibre reinforced polymer — carbon fibres + polymer resin

  • hard + v/ brittle

  • strong, stiff + lightweight

• Fibreglass — glass fibres + polymer resin

  • hard + v/ brittle

  • strong, stiff + lightweight

• Reinforced concrete — steel + concrete

  • can be broken using machinery

• Chipboard — wood chips + resin glue

  • strong in all directions

When hydrogen peroxide is added to manganese dioxide, the hydrogen peroxide decomposes into water and oxygen. The chemical equation for this reaction is shown below.

What is the catalyst in this reaction?

Manganese dioxide

Describe how to do a flame test.

• Pass nicrome wire through flame to sterilise it

• Dip it into metal ion solution + run through flame again

  • produces coloured flame

List all the positive metal ions used in the flame tests and their positive results.

• Lithium (Li⁺) - crimson

• Sodium (Na⁺) - yellow

• Potassium (K⁺) - lilac

• Calcium (Ca²⁺) - orange-red

• Copper (Cu²⁺) - green

If a sample contains a mixture of metal ions, a flame test may be inconclusive. Why?

Metal ion that is in highest conc. may mask others

How do you perform the positive metal hydroxides tests?

• Add sodium hydroxide to metal ion solution

• Precipitate produced

List all of the positive metal ions used in the sodium hydroxides tests and the coloured precipitate they produce.

• Aluminum (Al³⁺) - white (dissolves in excess NaOH)

• Magnesium (Mg²⁺) - white

• Calcium (Ca²⁺) - white

• Copper (Cu²⁺) - blue

• Iron (Fe²⁺) - green

• Iron (Fe³⁺) - brown

What is the half equation for the production of copper hydroxide?

Cu²⁺ + 2OH^- → Cu(OH)₂

What is the half equation for the production of aluminium hydroxide?

Al³⁺ + 3OH^- → Al(OH)₃

What is the half equation for the production of magnesium hydroxide?

Mg²⁺ + 2OH^- → Mg(OH)₂

What is the half equation for the production of calcium hydroxide?

Ca²⁺ + 2OH^- → Ca(OH)₂

What is the half equation for the production of iron (II) hydroxide?

Fe²⁺ + 2OH^- → Fe(OH)₂

What is the half equation for the production of iron (III) hydroxide?

Fe³⁺ + 3OH^- → Fe(OH)₃

When you add excess NaOH to an ____________ ion solution, the precipitate formed ___________.

• aluminium

• dissolves

How do you perform the halides tests for negative metal ions?

• Add dilute nitric acid + silver nitrate

  • precipitate produced

Why can’t hydrochloric acid be used for the halide ion tests?

• Contains chlorine

• Would react + produce precipitate

List the negative halide ions and the colour of the precipitate produced for the halide ion tests.

• Bromine (Br^-) - cream

• Chlorine (Cl^-) - white

• Iodine (I^-) - yellow

How do you perform the test for sulfate ions?

• Add hydrochloric acid + barium chloride

• White precipitate

Carbonates react with ________ _____ to form _______ _______ gas.

• dilute acids

• carbon dioxide

What are 2 examples of instrumental methods?

• Gas chromatography

• Flame emission spectroscopy

Why are instrumental methods better than chemical tests? (4)

They are:

• sensitive

• quantitative

• accurate

• rapid

How do you perform flame emission spectroscopy?

• Sample put into flame and light given out passed through spectroscope

• Output is line spectrum — can be analysed to identify metal ions in solution + measure their concentrations

Concrete is a composite material made from gravel and what other material?

Cement

Algae first produced gas X about 2.7 billion years ago. Soon after that, gas X started appearing in the atmosphere. What is gas X and explain why?

• Oxygen

• Algae performs photosynthesis → releases oxygen gas

What is meant by the term precipitation reaction?

Solid product formed during reaction b/ solutions

During waste water treatment, sedimentation produces effluent and... what?

Sewage sludge

Describe what needs to be removed from different types of waste water.

• Sewage + agricultural waste water — organic matter + harmful microbes

• Industrial waste water — organic matter + harmful chemicals

What does sewage treatment include?

• Screening + grit removal

• Sedimentation → produces sewage sludge + effluent

• Anaerobic digestion of sewage sludge

• Aerobic biological treatment of effluent

Describe how quality water is produced.

• Water passed through mesh screen → removes larger bits

• Chemicals added (makes solids + microbes clump → forms sediment + sink)

• Anaerobic digestion of sewage sludge

• Water sterilised w/ chlorine (kills microbes)

Explain the differences in relative ease when obtaining potable water from different sources.

• Cheaper + easier to get potable water f/ groundwater + wastewater than saltwater

  • saltwater is plentiful → good for countries w/ little fresh water

The line between the C and H represents a _______ bond.

covalent

Potable water can be produced through various processes.

For example, water can be passed through ______ beds to remove any solids.

mesh

Figure 1 shows the percentage of electricity generated in the UK between 2007 and 2017 using:

• oil

• solar energy

Describe the changes in the percentage of electricity generated in the UK between 2007 and 2017 using:

• oil

• solar energy

Use data from Figure 1 in your answer. [3 marks]

• Use of oil decreased by 0.8%

• Use of solar energy increased by 3.4%

• Use of oil increased f/ 2007 → 2009

Oil contains carbon and some sulfur.

When oil is burned, the products of combustion may be released into the atmosphere.

Explain the environmental effects of releasing these products of combustion into the atmosphere. [6 marks]

• Combustion of carbon dioxide:

  • carbon dioxide

    • greenhouse gas → increase in surface temps → global warming

    • climate change

  • carbon particulates

    • global dimming + respiratory issues in humans

  • carbon monoxide (incomplete combustion)

    • almost undetectable + toxic

• combustion of sulfur:

  • sulfur dioxide

    • acid rain → damages buildings + statues

    • damages trees + aquatic life

    • respiratory problems in humans

Suggest one reason why using solar energy is a more sustainable way of generating electricity than burning oil. [1 mark]

Solar is renewable

The alkane with nine carbon atoms in a molecule is called nonane.

Nonane will condense lower in a fractionating column during fractional distillation than the other alkanes in Table 1.

Explain why. [2 marks]

You should refer to the temperature gradient in the fractionating column.

• Nonane has higher boiling point

  • condensed where column has higher temp

A food colouring contains a dye.

Plan an investigation to determine the Rf value for the dye in this food colouring. [6 marks]

$R_f$= distance moved by substance / distance moved by solvent

Your plan should include the use of:

• a beaker

• a solvent

• chromatography paper

• Set up apparatus

• Wait for solvent to travel up paper until it is near top

• Mark solvent front

• Dry paper

• Measure distance b/ start line + centre of spot using ruler

• Measure distance b/ start line + solvent front using ruler

• Use measurements to calculate Rf value

Two students investigated a dye in a food colouring using paper chromatography.

Each student did the investigation differently.

The Rf values they determined for the same dye were different.

How did the students’ investigations differ? [1 mark]

• Different length of paper used

• Different period of time used

• Different size of beaker used

• Different solvent used

Different solvent used

Poly(ethene) is a thermosoftening polymer.

Suggest why poly(ethene) is easier to recycle than thermosetting polymers. [2 marks]

• Poly(ethene) melts

  • can be reshaped into new products

Ethene produces different forms of poly(ethene).

How can different forms of poly(ethene) be produced from ethene? [1 mark]

Diff reaction conditions

Two different forms of poly(ethene) are:

• high density poly(ethene) (HDPE)

• low density poly(ethene) (LDPE)

Figure 4 represents part of the structures of HDPE and LDPE.

Explain why HDPE has a higher density than LDPE. [2 marks]

• Polymer chains closer together

  • more atoms per unit volume

Figure 5 shows three monomers, A, B and C.

Monomer A can react with monomer B and with monomer C to produce polyesters.

Complete Table 2 to show the formula of the small molecule produced when:

• monomer A reacts with monomer B

• monomer A reacts with monomer C

[1 mark]

Reacting monomers	Formula of small molecule produced
A and B	1
A and C	2

1. H₂O

2. HCl

Some fertilisers are described as NPK fertilisers because they contain three elements needed for healthy plant growth.

Which two compounds each contain two of these elements? [2 marks]

• Ammonium nitrate

• Ammonium phosphate

• Calcium chloride

• Calcium phosphate

• Potassium chloride

• Potassium nitrate

• Ammonium phosphate

• Potassium nitrate

Rocks containing calcium phosphate are treated with acid to produce soluble salts that can be used as fertilisers.

Name the soluble salts produced when calcium phosphate reacts with:

• nitric acid

• phosphoric acid

[2 marks]

• Calcium nitrate

• Triple superphosphate

Ammonium sulfate is a compound in fertilisers.

Ammonium sulfate can be made using an industrial process or in the laboratory.

In the industrial process, the following steps are used:

• React streams of ammonia solution and sulfuric acid together.

• Evaporate the water by passing the solution down a warm column.

• Collect dry crystals continuously at the bottom of the column.

In the laboratory, the following steps are used:

• React ammonia solution and sulfuric acid in a conical flask.

• Evaporate water from the solution until crystals start to form.

• Leave to cool and crystallise further.

• Separate the crystals using filtration.

• Dry the crystals between pieces of filter paper.

Evaluate the two methods for producing a large mass of ammonium sulfate. [4 marks]

• Industrial process is:

  • quicker

  • larger scale – uses more ammonia solution + sulfuric acid

  • a continuous process – dry crystals collected continuously

• I think that industrial process is faster + better for producing large mass of ammonium sulfate

Potash alum is a chemical compound.

The formula of potash alum is KAl(SO₄)₂

Give a test to identify the Group 1 metal ion in potash alum. [2 marks]

You should include the result of the test.

• Flame test

• Lilac flame

Copper can be obtained by:

• processing copper ores

• recycling scrap copper

Suggest three reasons why recycling scrap copper is a more sustainable way of obtaining copper than processing copper ores. [3 marks]

Recycling:

• conserves copper ores

• uses less energy

• reduces waste

Copper is extracted from low-grade ores by phytomining.

Describe how copper is extracted from low-grade ores by phytomining. [4 marks]

• Grow plants

• Burn plants → produces ash

• Ash dissolved in acid → produces solution of copper compound

• Electrolysis of solution

Copper is extracted from low-grade ores by phytomining.

Phytomining has not been widely used to extract copper.

Suggest two reasons why. [2 marks]

• Land not available

• Phytomining takes a long time

A student investigated how a change in concentration affects the rate of the reaction between zinc powder and sulfuric acid.

The equation for the reaction is: Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)

This is the method used:

• Pour 50 cm3 of sulfuric acid of concentration 0.05 mol/dm3 into a conical flask.

• Add 0.2 g of zinc powder to the conical flask.

• Put the stopper in the conical flask.

• Measure the volume of gas collected every 30 seconds for 5 minutes.

• Repeat steps 1 to 4 with sulfuric acid of concentration 0.10 mol/dm³

Figure 8 shows the apparatus used.

The student made an error in setting up the apparatus in Figure 8.

What error did the student make? [1 mark]

Delivery tube in sulfuric acid

Ethanol can be produced from ethene and steam.

The equation for the reaction is: C₂H₄(g) + H₂O(g) ⇌ C₂H₅OH(g)

The forward reaction is exothermic.

Explain how the conditions for this reaction should be chosen to produce ethanol as economically as possible. [6 marks]

• Higher temp = higher rate

  • more frequent collisions

• Higher pressure = higher rate

  • more frequent collisions

• Catalyst used for higher rate

  • reduced activation energy

• Higher temp = lower yield

  • exothermic reaction

• Higher pressure = higher yield

  • more molecules on left

• Higher temps + pressure use more energy → increased costs

• Chosen temp is compromise b/ rate and yield

Describe what humans use the Earth’s resources to do.

• Provide:

  • warmth

  • shelter

  • food

  • transport

• Natural resources (supplemented by agriculture) provide:

  • food

  • timber

  • clothing

  • fuels

• Finite resources (from Earth, oceans + atmosphere) processed → provides energy + materials

Describe what is meant by sustainable development.

Development that meets needs of current generations without compromising ability of future generations to meet their own needs

State some examples of natural products that are supplemented or replaced by agricultural and synthetic products.

• Fertilisers – natural manure → synthetic fertilisers (e.g. ammonium nitrate – produced using ammonia f/ Haber process)

• Rubber – natural rubber (f/ tree sap) → synthetic polymers (e.g. poly(butadiene) for tyres + washers)

• Textiles:

  • wool → synthetic fibres – acrylic or poly(propene)

  • cotton → polyester

  • silk → nylon

• Wood – used in construction → PVC or composites (e.g. MDF)

• Linseed oil – used in paints → acrylic resin

Describe what potable water is.

• Safe to drink

  • low levels of dissolved salts + microbes

• NOT pure water — contains dissolved substances

Describe how most potable water is produced.

• Rain → water w/ low levels of dissolved substances (fresh water)

  • collects in ground, lakes + rivers

• Pass water through filter beds → remove diff sizes of insoluble solids

• Sterilise — kills microbes

  • w/ chlorine, ozone, or UV light

Describe how and why desalination is done.

• Limited supplies of fresh water → desalination of salty water/sea water

  • done by distillation or reverse osmosis → require large amounts of energy

What is bioleaching?

Using bacteria to produce leachate solutions (contain metal compounds)

How can copper be obtained from solutions of copper compounds?

• Displacement using scrap iron

• Electrolysis