Separate Chemistry 2

What can we use to identify some metal ions?

Flame tests

Flame test results for metal ions: lithium, sodium, potassium, calcium and copper

• Lithium- Red

• Sodium- Yellow

• Potassium- lilac

• Calcium- orange-red

• Copper blue-green

How do we test for metal ions with hydroxide precipitates?

• Some metal ions form metal hydroxide precipitates

• The sample solution is placed in a test tube and a few drops of dilute sodium hydroxide are added

What colour precipitate will copper, iron (+2) and iron (+3) form when dilute sodium hydroxide was added?

• Copper- blue

• Iron (+2)- green

• Iron (+3) brown

What kind of compounds do transition metals form?

Coloured compounds

What kind of compounds do non-transition metals form?

White or colourless compounds

What is the test for sulfate ions?

• Add dilute hydrochloric acid and then barium chloride solution

• Sulfate ions form a white precipitate of barium sulfate

What is the test for carbonate ions?

• Add acid

• Carbonate ions form bubbles of carbon dioxide

What is the test for halide ions?

• Add dilute nitric acid then silver nitrate solution

• Chloride ions form white precipitate

• Bromine ions form a cream precipitate

• Iodine ions form a yellow precipitate

What are the halides?

Chlorine, bromine, iodine

What is the test for ammonium ions?

• Add sodium hydroxide solution

• When adding heat to the substance in the test tube ammonia gas is produced

• You can test for the ammonia with damp red litmus paper that will turn blue if ammonia is present

What is the test for ammonia?

• Damp red litmus paper turns blue (This one is more important)

• Hydrogen chloride gas reacts with ammonia to form a white smoke of ammonium chloride

What are instrumental methods of analysis?

Analysis using machines to detect and analyse substances

What are the improvements of instrumental methods of analysis compared to chemical tests and analysis?

• Sensitivity- they can detect very small amounts of different substances

• Accuracy- They measure amounts of different substances very accurately

• Speed of tests- they carry out each analysis quickly and the machines can run all the time

What is a flame photometer?

An instrumental method of analysis based on flame tests which can measure the brightness of a spectrum of light emitted by the metal ions (You do not need to recall how a flame photometer works)

What can the data from a flame photometer be used for?

• Identifying the metal ions present in a sample by comparing the spectrum of light they produce with a different spectrum from a known substance

• Determining the concentration of ions in a solution using a calibration curve

What are the names of the first 4 alkanes?

Methane, ethane, propane, butane

What are alkenes?

A homologous series of unsaturated hydrocarbons

What does a hydrocarbon being saturated mean?

It only contains single bonds

What does a hydrocarbon being unsaturated mean?

It has double bonds

What is the molecular formula for alkenes?

C_nH_2n

How should you draw hydrocarbons?

• Hydrogen can only make 1 bond so you only draw one line

• Carbon can make 4 bonds so you have to draw 4 lines

• If there is a double bond for a carbon, the 2 lines count as 2 bonds

What is a functional group?

A characteristic of a molecule that tells you what homologous series it belongs to

What happens in the complete combustion of alkenes?

• Carbon is oxidised to make carbon dioxide

• Hydrogen is oxidised to make water vapour

What colour compounds do alkenes form when added to bromine water?

They produce colourless compounds

Why can bromine react with alkenes?

• Because they are unsaturated (Have double carbon bonds)

• Double bonds can open up to the bromine and become single bonds (Remember bromine goes around in pairs)

What is the test to tell the difference between alkanes and alkenes?

• Add a few drops of bromine water

• The solution stays orange in an alkane

• The solution is decolourised in an alkene

What is an addition reaction?

When two reactants join together so make a single, large product

What are addition polymers?

Relatively large molecules made by combining smaller molecules

What is a polymer?

• A substance of high average molecular mass

• Made up of repeating units

• Contains many monomers

What is a monomer?

A molecule that can bind to identical molecules to form a polymer

Equation model for polymerisation

• The two lines sticking out are the new bonds formed when the double bond is broken

• n is the number of units linked together

What are the properties and uses of these different polymers?

See image

Polymer	Properties	Uses
Poly(ethene)	Flexible, cheap, good electrical insulator	Plastic bags, bottles, clingfilm
Poly(propene)	Flexible, shatterproof, has a high softening point	Buckets and bowls
Poly (chloroethene) (PVC)	Tough, cheap, long-lasting, good electrical insulator	Window frames, gutters, pipes, insulation for electrical wires
PTFE Poly(tetrafluoroethene)	Tough, slippery, resistant to corrosion, good electrical insulator	Non-stick coating for frying pans, containers for corrosive substances, insulation for electrical wires

What is a condensation reaction?

This reaction is when two small molecules (monomers) react with each other and release a small molecule like water or alcohol

What kind of polymer is polyester?

A condensation polymer

What monomers does polyester have to have?

• A molecule containing two carboxylic acid groups (a dicarboxylic acid group)

• A molecule containing two alcohol groups (a diol group)

What does a carboxylic acid group look like?

See image

What does an alcohol functional group look like?

See image

What kind of link is formed when a molecule containing two carboxylic acid groups and a molecule containing two alcohol groups react?

• They form and ester link each time they react with each other

• One molecule of water forms each time an ester link forms

How are long polyester molecules made from carboxylic acid groups and alcohol groups?

• Polymers need two different monomers- a molecules containing two carboxylic acid groups and another molecule containing two alcohol groups

• When these two molecules react, the carboxylic acid group gives up an OH molecule and the alcohol gives up a H atom- this produces a water molecule

• The two molecules have a free bond at the end and can then join together by forming an ester link

• Another molecule with the similar groups to this one can react with it

• This process continues producing a very long polyester molecule

What are biological polymers?

Naturally occurring polymers

Examples of naturally occurring polymers?

• DNA- Found in the nucleus of cells, has a double helix structure

  • Made of monomers called nucleotide which contain a base (which can differ), a sugar and a phosphate

• Proteins- polymers made from monomers called amino acids

  • Each amino acid has two reactive functional groups which allow many amino acids to bond together to form a protein

What is is the polymer starch, made of?

Many sugar monomers joined together

What is the main raw material needed to make addition polymers and condensation polymers?

Crude oil

What does biodegradable mean?

• Materials that will eventually rot away:

  • Microbes feed on them

  • This breaks them down

What are the advantages and disadvantages of most artificial polymers not being biodegradeable?

• Advantage- objects made from polymers last a long time

• Disadvantage- It will not break down easily when disposed of

How effective are landfill sites at disposing of polymers?

• Polymers are not biodegradable so they last for many years

• We are running out of landfill sites to contain them

How effective is burning polymers at disposing of them?

Many polymers release toxic gasses when they are burnt

How effective is recycling polymers?

• Polymers can be melted and formed into new objects

• We can break them down into new raw materials

How effective are biodegradable polymers at solving polymer problems of disposal?

These are being developed and they will rot away in landfill sites which solves the problems of polymers not being disposed of effectively

Advantages of landfill sites?

• Waste is disposed of quickly

• Waste is out of sight once covered over

Disadvantages of landfill sites?

• Space for landfill sites is running out

• Most polymers are not biodegradable and will last for many years

• Landfill sites are unsightly and attract pests

What is the functional group of alcohols?

-OH

What is the homologous series of alcohols like?

• They have the functional group -OH

• Have similar chemical properties

• Has the general formula C_nH_2n+1OH

• Show a gradual variation in physical properties, such as boiling point

What do all alcohols end with in their name?

-ol

What is the functional group -OH of alcohols called?

A hydroxyl group

What are the reactions of alcohols with water and sodium and what do they do when ignited?

Methanol, ethanol and propanol all:

• Dissolve in water to form a neutral solution

• React in sodium to produce hydrogen

• Burn in air

How can ethanol be oxidised into ethanoic acid?

• Combustion

• Can be oxidised by chemicals called oxidising agents

• The action of microbes

How is ethanol produced?

• Produced from carbohydrates in an aqueous solution by a process called fermentation

• Carbon dioxide is also produced from this reaction

• The carbohydrates can be sugars from fruit like grapes or the breakdown of starch from wheat or barley

• Yeast is a single-celled fungus that provides enzymes for the fermentation to happen

Why is fractional distillation used to obtain a concentrated solution of ethanol?

Ethanol has a lower boiling point than water

Note that it is not possible to obtain pure ethanol by this method alone, The rest of the water must be absorbed chemically.

How is fractional distillation used to obtain a concentrated solution of ethanol?

• A filtered mixture from fermentation is heated up in a flask

• Pure ethanol boils at 78^oC and when boiled, a vapour with a high proportion of ethanol in it will rise up the fractionating column

• The column has a heat gradient so it is coolest at the top- this causes any water that may have evaporated to condense because of the difference in temperature

• The ethanol vapour is condensed in the condenser and then is collected in a beaker

• This gives us our concentrated ethanol solution

What are the characteristics of carboxylic acids?

• Have the same functional group -COOH

• Have similar chemical properties

• Has the general formula C_nH_2n+1COOH

• Shows a gradual variation in physical properties such as boiling points

What is the naming convention of carboxylic acids?

Names end in -anoic acid

What is the name of the functional group of carboxylic acids, -COOH?

A carboxyl group

How does carboxylic acid react with carbonates, reactive metals and water?

• Reacts with carbonates to produce a salt, water and carbon dioxide

• Reacts with magnesium and other reactive metals to produce a salt and hydrogen

• Dissolves in water to produce acidic solutions

Why are carboxylic acids weak acids?

They can only partially dissociate into ions when they are dissolved in water

What are nanoparticles?

Structures consisting of only a few hundred atoms

Why are nanoparticulate materials useful compared to bulk materials?

They are materials that have different properties from the same substance as a bulk material. This makes them useful for:

• Sunscreens- they still absorb harmful UV light but cannot be seen

• Lightweight strong materials such as carbon nanotubes in tennis rackets

• Future drug delivery systems- buckyballs consist of hollow balls of carbon atoms

• Catalysts- because they are made up of small particles unlike bulk materials, they have a larger surface area, increasing the rate of reaction

What is the surface area to volume ratio like for nanoparticles and how is this useful?

Nanoparticles have a very small size meaning they have a very large volume to surface area ratio. This makes them useful as catalysts because they will have a larger surface area, for example coatings for self-cleaning surfaces and clothes

What are the hazards and risks of nanoparticles?

• They can be inhaled, absorbed through the skin or transported into cells

• Take a long time to break down

• Attract toxic substances to their surfaces

General properties and examples of glass ceramics?

• Transparent

• Hard but brittle

• Poor conductors of heat and electricity

• Examples: Window glass, bottles

General properties and examples of clay ceramics?

• Opaque

• Hard but brittle

• Poor conductors of heat and electricity

• Examples: bricks, china, porcelain

General properties and examples of polymers?

• Vary from transparent, translucent and opaque

• Poor conductors of heat and electricity

• Often tough and ductile

• Example: Bottle, crates, carrier bags

General properties and examples of objects made of metals?

• Can be polished to a shine

• Good conductors of heat and electricity

• Hard, tough and ductile

• Example: Cars, bridges, electrical cables

What is the general formula of a carboxylic acid group?

C_nH_2n+1COOH

What is the nature of the product in addition polymerisation?

• Only a single product- the polymer

• Non biodegradable

• Resistant to acids

What is the nature of the product in condensation polymerisation?

• Two products- the polymer and water (or another small molecule)

• Biodegradable

• Hydrolyzed by acid (broken down by acids)

What are the melting and boiling points of polymers and why are they solid at room temperature

• They have relatively high boiling points

• There are weak intermolecular forces holding a polymer together, but there are so many that to break all of these would require quite a lot of energy

• This means that there would be enough intermolecular forces holding the structure of a polymer together to be solid at room temperature

What is the test for aluminium and calcium ions?

• Add sodium hydroxide

• They both turn white

How can we distinguish between aluminium and calcium ions?

• Add excess sodium hydroxide

• Calcium stays white

• Aluminium turns colourless