Separate Chemistry 2

Why must the test for an ion be unique?

Each ion must produce a distinct result so it can be reliably identified and distinguished from other ions.

What are the flame-test colours for common metal ions?

Li⁺ = red; Na⁺ = yellow; K⁺ = lilac; Ca²⁺ = orange-red; Cu²⁺ = blue-green.

What is the flame test for lithium ions?

Lithium ions produce a red flame.

What is the flame test for sodium ions?

Sodium ions produce a yellow flame.

What is the flame test for potassium ions?

Potassium ions produce a lilac flame.

What is the flame test for calcium ions?

Calcium ions produce an orange-red flame.

What is the flame test for copper(II) ions?

Copper(II) ions produce a blue-green flame.

How can aluminium ions be tested using sodium hydroxide solution?

Add sodium hydroxide solution; a white precipitate forms.

How can calcium ions be tested using sodium hydroxide solution?

Add sodium hydroxide solution; a white precipitate forms.

How can copper(II) ions be tested using sodium hydroxide solution?

Add sodium hydroxide solution; a blue precipitate forms.

How can iron(II) ions be tested using sodium hydroxide solution?

Add sodium hydroxide solution; a green precipitate forms.

How can iron(III) ions be tested using sodium hydroxide solution?

Add sodium hydroxide solution; a brown precipitate forms.

How can ammonium ions be tested?

Add sodium hydroxide solution and warm; ammonia gas is released.

How can ammonia gas be identified?

Ammonia turns damp red litmus paper blue.

How can carbonate ions be tested?

Add dilute acid; carbon dioxide is produced, which turns limewater cloudy.

How can sulfate ions be tested?

Add dilute hydrochloric acid followed by barium chloride solution; a white precipitate forms.

How can chloride ions be tested?

Add dilute nitric acid followed by silver nitrate solution; a white precipitate forms.

How can bromide ions be tested?

Add dilute nitric acid followed by silver nitrate solution; a cream precipitate forms.

How can iodide ions be tested?

Add dilute nitric acid followed by silver nitrate solution; a yellow precipitate forms.

What is the core practical for qualitative analysis?

Identify ions in unknown salts using the specified tests for cations and anions.

How can ions in an unknown salt be identified?

Perform the appropriate cation and anion tests and compare the observations with known results.

What are instrumental methods of analysis?

Methods using scientific instruments to identify or measure substances.

What are advantages of instrumental methods of analysis?

They can improve sensitivity, accuracy and speed compared with some traditional chemical tests.

What can a flame photometer be used for?

Determining the concentration of metal ions in dilute solutions and identifying metal ions.

How can a flame photometer determine ion concentration?

Compare the sample's result with a calibration curve.

How can a flame photometer identify metal ions?

Compare the measured data with reference data for known ions.

What is an alkane?

A saturated hydrocarbon containing only carbon-carbon single bonds.

What are the molecular formulae of methane, ethane, propane and butane?

Methane = CH₄; ethane = C₂H₆; propane = C₃H₈; butane = C₄H₁₀.

Why are alkanes saturated hydrocarbons?

They contain only carbon-carbon single bonds and therefore have the maximum possible number of hydrogen atoms.

What is an alkene?

An unsaturated hydrocarbon containing a carbon-carbon double bond.

What are the molecular formulae of ethene, propene and butene?

Ethene = C₂H₄; propene = C₃H₆; butene = C₄H₈.

What is the functional group in alkenes?

The carbon-carbon double bond, C=C.

Why are alkenes unsaturated?

They contain a C=C double bond, so they do not contain the maximum possible number of hydrogen atoms.

What happens when ethene reacts with bromine?

Ethene undergoes an addition reaction with bromine, breaking the C=C double bond and forming 1,2-dibromoethane.

How can bromine water distinguish between alkanes and alkenes?

An alkene decolourises orange bromine water, whereas an alkane does not react under these conditions.

What are the products of complete combustion of alkanes and alkenes?

Carbon dioxide and water.

What is a polymer?

A substance with a high average relative molecular mass made from small repeating units.

What is a monomer?

A small molecule that joins with other molecules to form a polymer.

How is poly(ethene) formed?

Ethene molecules undergo addition polymerisation to form poly(ethene).

What is an addition polymer?

A polymer formed when monomers containing C=C double bonds join together without producing another small molecule.

How is poly(propene) formed?

Propene molecules undergo addition polymerisation.

How is poly(chloroethene) (PVC) formed?

Chloroethene molecules undergo addition polymerisation.

How is poly(tetrafluoroethene) (PTFE) formed?

Tetrafluoroethene molecules undergo addition polymerisation.

How can you deduce a monomer from an addition polymer?

Identify the repeating unit, replace the single bonds between repeating units with a C=C double bond and complete the monomer structure.

How can you deduce an addition polymer from its monomer?

Open the C=C double bond and join the monomers into a repeating chain.

How are the uses of polymers related to their properties?

Polymers are selected for uses based on properties such as strength, flexibility, durability, chemical resistance and electrical insulation.

Why is poly(ethene) useful?

It is lightweight, durable and chemically resistant, making it useful for products such as packaging and containers.

Why is poly(propene) useful?

It is strong, lightweight and resistant to chemicals, making it useful for products such as packaging and containers.

Why is PVC useful?

It is durable, chemically resistant and can be made rigid or flexible, making it useful for pipes, cables and other products.

Why is PTFE useful?

It is very chemically resistant and has a low-friction surface, making it useful for non-stick coatings and other applications.

Why are polyesters condensation polymers?

They form when monomers join and a small molecule, water, is eliminated.

How is a polyester formed?

A monomer containing two carboxylic acid groups reacts with a monomer containing two alcohol groups.

What is produced each time an ester link forms in a polyester?

One molecule of water is formed.

What problems are associated with polymers?

Starting materials may be limited, polymers can persist in landfill because they are non-biodegradable, combustion can produce gases, and polymers must be sorted for recycling.

Why can polymers persist in landfill sites?

Many synthetic polymers are non-biodegradable, so microorganisms cannot readily break them down.

Why can disposal of polymers by combustion be problematic?

Combustion can produce potentially harmful gases and contributes to pollution.

Why must polymers be sorted before recycling?

Different polymers have different properties and melting points, so they need to be separated before being melted and reformed.

What are advantages of recycling polymers?

It reduces waste sent to landfill, conserves raw materials and can reduce environmental impacts.

What are disadvantages of recycling polymers?

Sorting and processing can be expensive and energy-intensive, and not all polymers are easily recyclable.

What is DNA made from?

DNA is a polymer made from four different types of monomer called nucleotides.

What is starch?

A polymer based on sugar molecules.

What are proteins?

Polymers based on amino acids.

What are the molecular formulae of methanol, ethanol, propanol and butanol?

Methanol = CH₃OH; ethanol = C₂H₅OH; propanol = C₃H₇OH; butanol = C₄H₉OH.

What is the functional group in alcohols?

The hydroxyl group, –OH.

What happens when alcohols are dehydrated?

They lose water and form alkenes.

What is the alcohol combustion core practical?

Investigate the temperature rise produced in a known mass of water by burning ethanol, propanol, butanol and pentanol.

What are the molecular formulae of methanoic, ethanoic, propanoic and butanoic acids?

Methanoic acid = HCOOH; ethanoic acid = CH₃COOH; propanoic acid = C₂H₅COOH; butanoic acid = C₃H₇COOH.

What is the functional group in carboxylic acids?

The carboxyl group, –COOH.

What properties do solutions of carboxylic acids have?

They have typical acidic properties because they release hydrogen ions in solution.

What happens when ethanol is oxidised?

Ethanol is oxidised to ethanoic acid.

How can the oxidation of other alcohols be predicted?

Alcohols in the same homologous series undergo similar reactions because they contain the same functional group.

Why do members of a homologous series have similar reactions?

They contain the same functional group.

How is ethanol produced by fermentation?

Yeast enzymes convert carbohydrates in an aqueous solution into ethanol and carbon dioxide.

What conditions are required for fermentation?

Yeast, an aqueous carbohydrate solution and suitable warm conditions; oxygen is limited.

How is a concentrated solution of ethanol obtained from fermentation?

By fractional distillation of the fermentation mixture.

What is the core practical involving alcohols?

Investigate the temperature rise produced in a known mass of water by burning ethanol, propanol, butanol and pentanol.

How does the size of a nanoparticle compare with an atom or molecule?

Nanoparticles are much larger than individual atoms and molecules but are still extremely small.

How are nanoparticle properties related to their uses?

Their very high surface area to volume ratio gives them useful properties that can differ from larger particles.

Why are nanoparticles useful in sunscreens?

Nanoparticles can provide UV protection while being small enough to reduce the visible whitening associated with larger particles.

What is a possible risk of some nanoparticulate materials?

Their small size means they may enter cells or biological systems, so some nanoparticles could have harmful effects.

Why must the risks of nanoparticles be considered?

Their effects on health and the environment may differ from larger particles because of their small size and high surface area to volume ratio.

What are glass and clay ceramics generally like?

They are hard and resistant to high temperatures but can be brittle.

What are polymers generally like?

They are lightweight and can be flexible, durable and resistant to chemicals.

What are composites?

Materials made by combining two or more different materials to produce improved or specific properties.

What are metals generally like?

They are strong, malleable and good conductors of heat and electricity.

How should a material be selected for a particular use?

Choose a material whose physical and chemical properties meet the requirements of the intended use.

Why is data useful when selecting materials?

Data allows the properties of different materials to be compared objectively and the most suitable material to be selected.