187 terms

AQA GCSE Combined Science Chemistry - Paper 2

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rate of a chemical reaction
how fast the reactants are changed into products
slow reactions
rusting of iron
chemical weathering
fast reactions
burning
explosions
rate of reaction graphs
steeper line = faster rate
flat = reaction finished
higher line = more reactants and products
collision theory in rate of reaction
1. collision frequency of reacting particles
more collisions = faster rate

2. energy transferred during a collision
particles need to collide with enough energy to be successful
factors affecting rate of reaction
1. temperature
particles have more energy, collide more frequently

2. concentration or pressure
more particles in an area = more frequent collisions

3. surface area
smaller pieces = more area for collisions to happen on
catalyst
a substance that speeds up the rate of reaction without being used up itself
catalyst's affect on rate of reaction
speed it up by decreasing activation energy

do this by creating an alternative reaction pathway with lower activation energy

e.g. enzyme
rate of reaction equation
amount of reactant used up or amount of product formed / time
precipitate
a solid formed in a reaction
precipitate and colour change showing rate of reaction
can observe how long it takes for a solution to lose or gain colour
can observe how long it takes a solution to become cloudy
change in mass showing rate of reaction
1. put reaction on scale
2. is a gas is produced, the mass will decrease
3. the quicker it decreases, the faster the reaction
volume of gas showing rate of reaction
gas syringe to measure vol of gas being produced
more gas given off in one time interval = faster rate
finding reaction rates from graphs
1. calculating mean rate
overall change in y axis / total time taken

2. calculating rate at a point
draw a tangent at the point and find the gradient
reversible reaction
a + b ↔ c + d
rate of reversible reactions
as reactants react, their concentration falls. (forward reaction slows)
as products are made, their concentration rises
(backward reaction speeds up)

eventually forward reaction is at same rate as backward reaction (equilibrium)
equilibrium
both reactions are happening but there is no overall effect
unchanging balance of products and reactants
only occurs in a closed system
position of equilibrium
equilibrium doesn't mean amounts of reactants are equal
lies to left = higher conc. of reactants
lies to right = higher conc. of products
conditions affecting position of equilibrium
temperature
pressure (only in gases)
concentration of reactants and products
exothermic and endothermic reversible reactions
if endothermic in one direction, exothermic in other
energy transferred from surroundings = energy transferred to surroundings
Le Chatelier's Principle
if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change
changes to temperature
decrease temp = equilibrium will more to exothermic direction to create more heat
vice versa for increase temp
changes to pressure
only for gases
increase pressure = equilibrium moves to side with lower molecules of gas
vice versa for decrease pressure
changes to concentration
change concentration = no more equilibrium
increase conc. of reactants = makes more products
decrease conc. of products = less reactants
etc
hydrocarbon
any compound formed from carbon and hydrogen only
alkane formula
Cn H2n+2
alkanes are saturated
each carbon bonds to four other atoms
homologous series
a series of compounds that have similar properties and the same general formula
saturated
bonded with the maximum amount of atoms
first alkane
methane CH4
second alkane
ethane C2H6
third alkane
propane C3H8
fourth alkane
butane C4H10
the shorter the hydrocarbon chain...
the less viscous
the more volatile
the more flammable
lower boiling points
complete combustion
happens in excess of oxygen
releases lots of energy
C and H from the hydrocarbon are oxidised
complete combustion equation
hydrocarbon + oxygen = carbon dioxide + water
crude oil
fossil fuel
formed from remains of plats and animals
remains turn to oil with time, temp, and pressure
non-renewable
finite
mixture of lots of different hydrocarbons
fractional distillation
used to separate hydrocarbon fractions
uses of crude oil
fuel - kerosene, diesel etc
makes new compounds like polymers and solvents
cracking
splitting up hydrocarbons
turns long chain hydrocarbons into shorter chains
catalytic cracking
1. vaporise hydrocarbon
2. pass over hot powered aluminium oxide catalyst
steam cracking
1. vaporise hydrocarbon
2. mix with steam
3. heat to a very high temperature
thermal decomposition
breaking down molecules by heating them
cracking products
shorter chain hydrocarbon + alkene
alkene
hydrocarbons with a double bond between two carbons in their chain
two fewer hydrogens than alkanes
properties of alkenes
unsaturated
c=c bond can open to bond to other atoms
much more reactive than alkanes
alkene formula
Cn H2n
first alkene
ethene C2H4
second alkene
propene C3H6
third alkene
butene C4H8
fourth alkene
pentene C5H10
incomplete combustion
combustion when there isn't enough oxygen in the air
smoky yellow flame
less energy released
happens in alkenes
incomplete combustion equation
alkene + oxygen = carbon + carbon monoxide + water
functional group
group of atoms in a molecule that determine how that molecule typically reacts
alkane functional group
c-c
alkene functional group
c=c
alcohol functional group
-OH
carboxylic acid functional group
-COOH
ester functional group
-COO-
alkene addition reaction
the c=c double bond opens up, allowing a new atom to be added to each carbon
alkene + hydrogen
hydrogenation
hydrogen reacts with c=c to form equivalent alkene
needs a catalyst
e.g. ethene + H2 = ethane
alkene + steam
alcohol is formed
water added across double bond
needs a catalyst
e.g. ethene + steam = ethanol
halogens + alkenes
addition reaction with halogen
each c=c atom bonds with a halogen atom
e.g. bromine + ethene = dibromethane
polymers
long chains of monomers (plastics)
normally carbon based
monomers normally alkenes
polymerisation
monomers becoming polymers
needs high pressure and a catalyst
addition polymers
made from unsaturated monomers
c=c bond opens up to join to another opened up carbon atom
makes polymer chains
poly(name of monomer)
addition polymer diagram
alcohol general formula
Cn H2n+1 OH
first alcohol
methanol CH3OH
second alcohol
ethanol C2H5OH
third alcohol
propanol C3H7OH
fourth alcohol
butanol C4H9OH
alcohol properties
flammable
undergo complete combustion in air
first 4 alcohols soluble in water to make pH 7
react with sodium. 1 product is hydrogen
oxidised to produce carboxylic acids
alcohol uses
solvents because they dissolve things water can't
fuels e.g. spirit burners because they burn cleanly
fermentation
using an enzyme in yeast to convert sugars into ethanol
fermentation equation
fermentation conditions
fastest at 37ºc and in slightly acidic conditions
no oxygen
first carboxylic acid
methanoic acid HCOOH
second carboxylic acid
ethanoic acid CH3COOH
third carboxylic acid
propanoic acid C2H5COOH
fourth carboxylic acid
butanoic acid C3H7COOH
carboxylic acids + carbonates
= salt + water + carbon dioxide
carboxylic acids properties
dissolve in water
dont ionise completely
weak acids (higher pH)
ester equation
alcohol and carboxylic acid
acid catalyst (e.g. sulfuric acid)
first ester
ethyl ethanoate CH3COOC2H5
condensation polymers
polymers containing different functional groups
monomers form bonds
e.g. polyester
molecule lost during condensation polymerisation
e.g. water
condensation polymer example
number of types of monomers
addition - one monomer type
condensation - two monomer types with diff func groups
or one monomer with 2 functional groups
number of products
addition - 1 product
condensation - 2 products
functional groups involved in polymerisation
addition - c=c double bond
condensation - two reactive groups per monomer
amino acids
amino group + carboxyl group
amino acids form...
polymers called polypeptides via condensation polymerisation
long chains of polypeptides
proteins
natural occurring polymers
DNA
proteins
carbohydrate polymers (e.g. cellulose and starch)
What colour do lithium ions produce in a flame?
Crimson
What colour do sodium ions produce in a flame?
Yellow
What colour do potassium ions produce in a flame?
Lilac
What colour do calcium ions produce in a flame?
Orange-red
What colour do copper ions produce in a flame?
Green
What colour precipitate do calcium ions produce?
White
What colour precipitate do copper ions produce?
Blue
What colour precipitate do iron2 ions produce?
Green
What colour precipitate do iron3 ions produce?
Brown
What colour precipitate do aluminium ions produce?
White at first, the redissolves in excess NaOh to form a colourless solution
What colour precipitate do magnesium ions produce?
White
What is a pure substance?
A substance where nothing has been added to it, so it's in its natural state (contains only one compound or element throughout)
Impure substances will:
1) lower the melting point and increase the melting range of the substance
2) increase the boiling point of the substance
What are formulations?
Useful mixtures with a precise purpose that are made by following a 'formula' (a recipe)
Paint is a formulation. What four components is it composed from?
Pigment, solvent, binder and additives
What industry are formulations important in?
The pharmaceutical industry
What can formulations be found in?
Cleaning products, fuels, cosmetics, fertilisers, metal alloys and even food and drink
What is chromatography?
An analytical method used to separate the substances in a mixture
What are the two phases of chromatography?
1) Mobile phase: where the molecules can move (liquid or gas)
2) Stationary phase: where molecules can't move (solid or really thick liquid)
What forms Whilst the particles are constantly moving between the mobile and stationary phases in chromatography?
An equilibrium
Why might the number of spots formed on the chromatography paper change in different solvents?
The distribution of some chemicals may be the some in some solvents but different in others
How many spots will a pure substance form on chromatography paper?
One, as there is only one substance in the sample
The amount of time the molecules spend in each phase depends on:
1) how soluble the molecules are in the solvent
2) how attracted they are to the paper
Will molecules that have a higher solubility and are less attracted to the paper carry further or shorter up the paper?
Further
What is the formula for Rf values?
Rf value = distance travelled by substance (B) / distance traveled by solvent (A)
What is the test for chlorine?
Placing a piece of damp litmus paper into a test tube containing a gas
What colour will the litmus paper turn if chlorine is present?
White (because chlorine bleaches damp litmus paper) however it may turn red for a moment since the solution of chlorine is acidic
What is the test for oxygen?
Putting a glowing splint into a test tube containing a gas
What will happen if oxygen is present?
The split will relight
What is the test for hydrogen?
Holding a lit splint of the open end of a test tube containing a gas
What will happen if hydrogen is present?
There will be a 'squeaky pop' sound
What is the test for carbon dioxide?
Making a solution of calcium hydroxide in water (called limewater) and bubbling gas through it into the test tube
What will happen to the limewater if carbon dioxide is present?
It will turn cloudy
What are ionic compounds made up of?
Positive ions (cations) and negative ions (anions)
What do flame tests and precipitation reactions test for?
Positive ions
What test can you use to test for negative ions as well as a gas?
The test for carbon dioxide
What happens when a carbonate reacts with a dilute acid?
Produces salt, water and carbon dioxide
What colour precipitate does the negative ion chloride produce when used in the halide test?
White
What colour precipitate does the negative ion bromide produce when used in the halide test?
Cream
What colour precipitate does the negative ion iodide produce when used in the halide test?
Yellow
Why do you have to use nitric acid in the halide ions test and not hydrochloride acid?
Hydrochloride acid would introduce chloride ions to the solution, so a white precipitate would be formed regardless of whether the solution originally contained chloride ions or not
crude oil
A dark liquid that is a mixture of different hydrocarbons.
mixture
A substance containing two or more elements or compounds that are mixed but not joined together.
distillation
A method of separating liquids with different boiling points.
fractional distillation
The process used to separate different hydrocarbons found in crude oil.
boiling point
The temperature at which a liquid turns to a gas or a gas condenses to a liquid.
viscosity
How easily a substance flows.
flammability
How easily a substance will burn.
volatility
The tendency of a liquid to turn into a gas.
fraction
Made up of hydrocarbons with similar boiling points separated from crude oil.
hydrocarbon
A compound that contains hydrogen and carbon only.
alkane
A hydrocarbon containing only single bonds.
alkene
A hydrocarbon containing at least one carbon-carbon double bond (C=C).
general formula of an alkane
general formula of an alkene
CH₄
Methane
C₂H₆
Ethane
C₃H₈
Propane
saturated hydrocarbon
A hydrocarbon that contains as many hydrogens as possible in each molecule.
unsaturated hydrocarbon
A hydrocarbon containing a C=C double bond (and not as many hydrogens as possible).
oxidation
When oxygen is added in a chemical reaction in which oxides are formed.
complete combustion
When a fuel burns in plenty of oxygen to produce only carbon dioxide and water.
incomplete combustion
The process by which a fuel burns in insufficient oxygen to produce some carbon monoxide (CO).
carbon monoxide
A poisonous gas produced during incomplete combustion, a silent killer.
cracking
The process by which large hydrocarbons are broken down into smaller hydrocarbons.
thermal decomposition
A reaction in which a substance is broken down by heating.
orange to colourless
The positive result in the test for unsaturation.
atmosphere evolution phase 1
volcanoes gave out gas
atmosphere evolution phase 2
oceans, algae, and green plants absorbed CO2
atmosphere evolution phase 3
green plants and algae produce oxygen
greenhouse gases
CO2, methane, water vapours
insulate earth
deforestation
less trees to remove CO2 from atmosphere
burning fossil fuels
releases more CO2
agriculture
farm animals produce methane
creating waste - landfills
waste contributes to CO2 build up
climate change consequences
ice caps melt
animals die
weather changes
temp changes
carbon footprints
measure of the amount of greenhouse gases released by something over its lifetime.
air pollution
pollutants:
fossil fuels
incomplete combustion - soot
carbon monoxide
release of sulfur dioxide and oxides of nitrogen
pure substance
a substance made of just one type of substance (either an element or a compound)
fixed points
the melting and boiling points of an element or compound
formulations
a mixture designed to produce a useful product
chromatography
the process whereby small amounts of dissolved substances are separated by running a solvent along a material such as absorbent paper
solvent front
the furthest point reached by the solvent
baseline
the starting point where substances are placed in chromatography
mobile phase
substances travel in this phase (usually a solvent)
stationary phase
substances are adsorbed onto this phase (usually a solid)
Rf
retention factor
Rf =
distance moved by substance ÷ distance moved by solvent
test for hydrogen
a lighted splint 'pops'
test for oxygen
relights a glowing splint
test for carbon dioxide
limewater turns milky
test for chlorine
damp blue litmus paper turns white