Chemistry Paper2

State two ways of finding the rate of reaction

• mass/volume of the products formed

• mass/volume of the reactant used

State two rates of reactions symbols

cm³/s or g/s

State 2 ways of measuring the quantity of reactant or product

• mass→ use a balance

• volume→ use a gas syringe

A student collects 50cm³ of Co2 in 10 seconds.What is the RofR?

50/10 = 5cm³/s

Is the rate of reacton faster,slower,or the same between 0 and 10s(8cm³ made) than between 30 and 40s(2cm³ made)

• between 0 and 10s

• 4 times more gas was collected

• In the same amount of time

What is meant by activation energy?

• The minimum amount of energy needed to cause colliding particles to react

What is a catalyst?

• A substance which increases the RofR

• without being used up in the reaction

Other than adding a catalyst,give three factors that affect the RofR

• temperature

• surface area

• concentration of reactants

Why does the volume of acid added to a flask containing a strip of magnesium not affect the RofR?

• Only the particles of acid which collide with the magnesium strip will react

• More acid particles does not mean more collisions per second

• so does not change the RofR

Explain how you can tell which line on the graph shows the fastest rate of reaction?

• the faster reaction has a steeper gradient

Explain why both lines on the graph level off at the same point?

• The same amount of product is made

• it is just made in a shorter period of time when the reaction is fast

Explain how catalysts increase the RofR?

• lowers the activation energy needed for the reaction to occur

• and provides an alternative,lower energy pathway

The catalyst for this reaction is chlorophyll, this does not appear in the equation for photosynthesis, why?

• Equations show reactants and products, chlorphyll is neither

Explain how you know which chemcals were catalysts?-From table

• the time taken to collect the gas is less,so reactions are faster

Explain which catalyst gave the fastest reaction.

the time taken to collect the gas was the shortest.

What is a reversible reaction?

Reactants can become products, but then products react and turn back into reactants

If a reaction is endothermic in one direction, what is it in the other direction?

exothermic

What is meant by dynamic equilibrium?

the rate of the forwards reaction is the same as the backwards reaction in a closed system

What happens to the equilibrium position if the temp of a reversible reaction is increased?

• equilibrium shifts in the endothermic direction

What happens to the equilibrium position if the pressure of a reversible reaction is increased?

• equilibrium shifts in the direction where there are fewest molecules to reduce pressure

Crude oil is a finite resource.What does finite mean?

a resource that will run out

What is crude oil?

A mixture of hydrocarbons formed from the remains of ancient biomass

How was crude oil formed

• plankton from millions of years ago died and fell to the sea bed

• they were covered in layers of sediment/mud

• and over millions of years formed crude oil

What is a hydrocarbon?

a compound containing hydrogen and carbon atoms only

What is the general formula of alkanes?

CnH2n+2

Name the first four members of alkanes

• methane CH4

• ethane C2H6

• propane C3H8

• butane C4H10

Explain the trends of the boiling point,viscosity and flammability of the 2 alkanes in the table.(petrol then diesel)

• Diesel has the longest carbon chain.This means that:

• Diesel has a higher B.P than petrol

• Diesel is more viscous than petrol

• Diesel is less flammible than petrol

Describe how crude oil is seperated into fractions.

• Crude oil is heated into a vapour and put into a fractionating column which is hotter at the bottom and cooler at the top

• Each fraction has a different B.P so will condense at the points in the column where the temp matches the B.P (4 MARKS)

• Longer chain hydrocarbons have high B.P so condense at the bottom where it is hotter

• Shorter chain hydrocarbons have lower B.P so condense at the top where it is cooler.

Define the term cracking

The breaking down of a long chain hydrocarbon into shorter chain alkanes and amore useful alkene

Name 2 methods of cracking

• catalytic cracking

• steam cracking

Explain why the cracking of alkanes is carried out

• the supply of long chain hydrocarbons is much higher than the demand as they are not useful.

• short chain alkenes are very useful as fuels

• alkenes are useful as they are used to make polymers

Describe the test which can be carried to determine whether a hydrocarbon is an alkane or an alkene

• add bromine water

• if it stays orange→ alkane

• if it changes colour from orange to colourless then it is an alkene

What is a pure substance

a substance which contains only 1 element or compound

Describe a test to determine whether a sample of a liquid is pure

• boil the liquid and check the temp when it boils

• pure substances boil at an exact temp, not a range of values higher than the B.P

What is a formulaton?

A mixture made from quantities in carefully measured amounts designed for a useful purpose

Give 3 examples of formulations

• drinks

• drugs

• food

Name the 2 phases of chromotography

• mobile

• stationary

Describe how to set up a chromotography experiment to identify the components in an ink sample.

• Draw a baselines in pencil near the bottom of chromothraphy paper

• place a small dot of ink to the baseline using a capillary tube

• place solvents in a beaker below the level of the baseline

• suspend the chromotography paper in the solvent

• add a lid and allow the ink to move up the paper

• Remove from the solvent,mark the position of the solvent front and leave it to dry

• Calculate the rf value of each ink

• Compare these R.f Values with known R.f values of other inks in the same solvent to identify

Explain how chromotography separates the chemicals in each substance

• different chemicals have different solubilities

• chemicals with an affinety to the mobile phase will move a further distance in the same time

• so the chemicals will separate

Chemical has not moved.explain what this shows

it is insoluble in that particular solvent

Chemical Z rose up the paper but did not separate into multiple spots.Explain what this shows

It is a pure substance

What is the gas test for oxygen gas?

• a glowing splint will relight

What is the test for hydrogen

• a lit splint burns with a squeaky pop sound

How would you test for Co2?

bubble the gas through lime water,co2 will turn it cloudy

How do you test for chlorine?

• damp blue litmus paper is bleached white

Name 5 gases in the Earths atmosphere

• Oxygen

• Carbon dioxide

• nitrogen

• water vapour

• methane

Give the proportion of the 2 main gases in the Earths atmosphere today

• nitrogen-80%

• oxygen- 20%

Why is evidence for the Earths atmosphere limited?

• it was formed 4.6 billon years ago

How have we been able to make predictions about what the Earths early atmosphere was like?

we have studied the atmosphere of mars and venus today

Where is the Earths early atmosphere believed to have come from?

From volcano eruptions

Describe the composition of the Earths early atmosphere .

• Mainly Co2

• Some water vapour,nitrogen,methane

• no oxygen

How did oceans form

when the water vapour cooled and condensed

Why did the amount of Carbon dioxide in the earlier atmosphere decrease?

• Co2 dissolved in oceans

• Co2 was taken in by plants and algae for photosynthesis

• sedimentary rocks formed as well as fossil fuels which contained carbon

Why did the amount of oxygen in the early atmosphere increase?

plants and algae carried out photosynthesis which releases oxygen

Name 3 greenhouse gases

Methane,water vapour,Carbon dioxide

Explain how greenhouse gases cause global warming

• short wavelength radiation enters the atmosphere from the sun

• It is absorbed by the Earths surface and re-emmited at longer wavelengths

• This radiation is trapped by greenhouse gases which increases temperature

• which causes global warming

Name human activities which increase the amount of carbon dioxide in the atmosphere

• Combustion of fossil fuels

• Deforestation by burning trees

Name human activities that increase the amount of methane in the atmosphere

• cattle farming

• growing rice in paddy fields

Give three possible effects of climate change

• ice caps melting

• droughts

• loss of biodiversity

What are the 2 main elements in most fuels?

• hydrogen

• carbon

What are the products of the complete combustion of hydrocarbons?

• carbon dioxide

• water vapour

Why does the combustion of fuel in power stations contribute to acid rain formation

• sulfur impurities react with o2 to form sulfur dioxide

• The sulfur dioxide dissolves in clouds and makes the rain water acidic

Why does the combustion of fuels in cars contribute to acid rain formation?

• nitrogen and oxygen from the air combine because of the high temperatures in car engines

  to form nitrous oxides

• this is an acidic gas which causes acid rain

Describe the issues associated with acid rain

• building damage

• killing plants/trees

• acidifying lakes kill fish

Other than water vapour,which other 2 substances could be formed during the incomplete combustion

Carbon, Carbon monoxide

Why is carbon monoxide difficult to detect?

it is oudourless and colourless

Describe the issue associated with carbon monoxide.

• it is a toxic gas and causes death

Describe two effects of particulates in the atmosphere

• global dimming

• health issues

Why is potable water not described as pure water by scientists?

• potable water is water which is safe to drink

• it may have dissolved minerals in it so this means it isnt necessarily pure

What does the method used to produce potable water depend on?

• what water sources are available at a particular location

Describe and explain the method used to produce potable water from fresh water supplies in the UK.

1. filter → remove solid objects e.g twigs/sand

2. Sterilise the water using ozone chlorine or UV light to kill bacteria

Describe the 2 methods which can be used for the desalination of salty water

• distilation

• reverse osmosis

Describe an improvement the student could make to make sure her results are valid

• after 10mins find the mass then reheat checking the mass every minute until the mass no longer changes

• This means all the water is definitely gone

Why would using a smaller sample of water give a less accurate result?

• smaller sample means less solid is dissolved

• any errors would be a larger percentage of the total mass