chemistry paper 2 knowledge

fluorine

fluorine

F₂

pale yellow

gas

chlorine

Cl₂

pale green

gas

bromine

Br₂

orange-brown

liquid

iodine

I₂

grey (can form poisonous purple vapours)

solid

halogen displacement reactions

	Cl-	Br-	I-
Cl2		yellow/orange solution	brown solution n black ppt
Br2	no change		brown solution n black ppt
I2	no change	no change

cation flame test

red Li⁺

yellow Na⁺

lilac K⁺

orange / red Ca²⁺

green / blue Cu²⁺

cation hydroxide precipitate test

ion	colour of hyd.ppt	dissolves w excess NaOH?
Fe 2+	green
Fe 3+	orange/brown
Cu 2+	blue
Ca 2+	white	no
Mg 2+	white	no
Zn 2+	white	yes
Al 3+	white	yes

testing for sulfate ions (SO₄^2-)

few drops of HCl

few drops of BaCl₂

if present → white preciptate of BaSO₄ (insoluble in HCl)

testing for carbinate ions (CO₃^2-)

few drops of HCl

if present → effervescence as CO₂ produced

can be confirmed by limewater

testing 4 Halide ions (Cl^-, Br^-, I^-)

few drops of HNO₃

then few drops of AgNO₃

if present → precipitate

ion	colour
Cl -	white ppt
Br -	cream ppt
I -	yellow ppt

choosing reaction pathway

% yield

atom economy

can by-products be used, or toxic?

rate of reaction

possibly equilibrium condition

continuous vs batch process

factor	continuous	batch
cost of factory equiptment	high	low
rate of production	high	low
shut-down times	rare	often
workforce	few ppl needed	many ppl needed
ease of automation	relatively easily	relatively difficult

making ethanol - fermentation of renewable raw materials (glucose)

advantages	disadvantages
cost of raw materials low	rate of reaction low
conditions (temp n pressure) r moderate	% yield is low - around 15%
energy requirement is low	product has low purity n needs filtering/fractional distillation

making ethanol - hydration of non renewable raw material (ethene)

temp 300^oC, pressure 60 atmospheres, phosphoric acid catalyst

C₂H_4(g) + H₂O_(g) = C₂H₅OH_(g)

advantages	disadvantages
rate of reaction high	cost of raw materials high
% yield high - around 95%	conditions (temp n pressure) r high which is £££ to maintain
product has high purity n no by-products	energy requirement high

haber process

N_2(g) + 3H_2(g) = 2NH_3(g)

H = -93kJmol

pressure 200 atm (compromise, higher pressure would be better as fewer mol of gas on right, but expensive n hazardous)

temp 450^oC (compromise, lower would be better as forward direction exothermic but then rate too slow)

iron catalyst (doesn’t change equilibrium position. makes reaction faster)

unreacted gases recycled

contact process

pressure 2 atm (equilibrium position already lies quite far to right, so only small increase is needed to push gases through converter)

temp 450^oC (forward reaction is exothermic so low temp will increase yield but compromise made to achieve reasonable rate and catalyst only works at temps above 380^oC)

vanadium (V) oxide catalyst - V₂O₅

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stage 3 v exothermic - would produce hazardous acidic mist

so carried out in 2 stages where SO₃ passed through some previously produced H₂SO₄ to make H₂S₂O₇ (oleum)

this then added to water to make larger vol of H₂SO₄

steel

Fe

strong

buildings, bridges, cars

duralium

Al, Cu

lightweight

aircraft parts

solder

Sn, Cu

low mp

joining electrical parts

brass

Cu, Zn

strong, resists corrosion

bells, propellers on ships

ceramics

hard non-metallic materials (brick, china porcelain, glass) formed of metals n non-metals in giant lattice

high mp, hard stuff but brittle n poor conductors of heat n elec

glass

made by melting sand then cooling to solidify

Most of the glass we use is soda-lime glass. This is made by melting a mixture of sand (silicon oxide), sodium carbonate, and limestone, then allowing the molten liquid to cool and solidify.

Borosilicate glass is made by heating sand with boron trioxide. Borosilicate glass has a much higher melting point than soda-lime glass.

Glass is transparent, strong and a good thermal insulator, which makes it useful for windows.

clay ceramic

made from heating clay. can be glazed to be waterproof

metals

conduct elec well n r strong

Cu conducts elec well but Al used in overhead cables as its stronger n more lightweight

polymers

tough, flexible insulators, low compressive strength, squash easily

composites

made from 2 or more materials w diff properties, eg fibres embedded in polymer resin. eg. fibreglass or carbon fibre

made from the reinforcement and the matrix (binds the reinforcement together)

concrete

composites of small stones, sand n cement

but low tensile strength (fancy word basically j tension) so reinforced w steel

plywood

layers of wood set at right angles w glue n layer inbetween, so resists bending n strengthens it

extracting aluminium

aluminium ore (bauxite) contains Al₂O₃

more reactive than carbon so cannot be extracted in same way as iron or copper

if Al₂O₃ dissolved in molten cryolite, mp reduced from over 2000^oC to 950^oC

Al₂O₃ dissociates from its ions n electrolysis used to extract

carbon monoxide CO

produced from incomplete combustion of fuels containing carbon

toxic, colourless, odourless gas

attaches to haemoglobin - reduces amount of O₂ blood can carry - increase chance of heart disease

symptoms - breathing difficulties, drowsiness, even death

particulates

small particles that can settle deep in lungs - breathing problems, bronchitis, increasing chance of heart disease

produced during incomplete combustion n in industrial processes

PM10 r only 10micrometre in diamter (x10^-6)

acid rain

formed from NO_x produced in high temp of car engines which dissolves in moisture in air, from SO₂ produced when ff (which contain sulfur impurities) burned

alternative bio fuels

ethanol from fermentation of plants:	pros	cons
	carbon neutral	engines need to be converted
	only other product is water	not widely available

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biodiesel from veg oil:	pros	cons
	carbon neutral	£££ to make
	engines don’t need to be converted	could increase food prices if farmers grow crops for biodiesel instead of food

other key terms

lithium oxide Li₂O

sodium oxide Na₂O

sodium peroxide Na₂O₂

potassium peroxide K₂O₂

potassium superoxide KO₂

formulas

acid + alk → salt + water

acid + metal oxide → salt + water

acid + carbonate → salt + water + carbon dioxide

acid + metal → salt + hydrogen

alkali metal + water → metal hydroxide + hydrogen gas

metal + oxgen → metal oxide

metal oxide = alk

non metal oxide = acid

alkanes from crude oil

metal properties

1. Melting point - the temperature at which a solid melts into a liquid.

2. Conductivity - how well a material conducts electricity.

3. Strength - the ability of a material to resist an applied force (it is hard to change the shape of a strong material).

4. Hardness - how well a material can resist being scratched or indented (hard materials don't scratch).

5. Brittleness - how easily a material breaks when a force it applied (brittle materials snap easily).

6. Stiffness - how well a material can resist bending (a stiff material won't bend very much).