Chemistry Revision, from past papers

Question 1

How is the composition of the atmosphere affected by the burning of fossil fuels?

Answer 1

-Oxygen is removed
-Water vapour and CO2 added

Question 2

Do these graphs provide enough evidence that an increase in co2 is causing the earth’s temperature to rise?
[Graphs shown are from 1960 to 2000. The CO2 concentration graph is a steady line upwards. The temperature goes up and down but by the end of the graph, is at a higher average temperature]

Answer 2

-As concentration of CO2 increases the mean global temperature increases

then, EITHER:
-This does provide enough evidence
-However, it fluctuates, so it does not provide enough evidence
-there is no evidence that the mean global increase is due to CO2 increase and could be due to other factors

Ask Dr. Nickson about this one!

Question 3

Which of these four gases are GHGS?
Water vapour, nitrogen, oxygen, methane

Answer 3

water vapour+methane

Question 4

Describe what would be seen when a piece of calcium is dropped into water

Answer 4

-Hydrogen produced; effervescence
-solid CaOH formed, so cloudy water

also…
-calciuim decreases in

-Ca moves

Question 5

State in terms of electronic configuration why calcium is more reacive than magnesium [2]

Answer 5

-Calcium has more electrons so the outermost electrons are further away from the nucleus and experience greater shielding
- so less attraction between nucleus and electrons
- electrons easier to remove

Question 6

explain how ethene is produced using the apparatus in figure 4
[Figure 4 shows a tube being heated. It has ceramic wool soaked in decane at one end in middle “porous pot”. from the porous pot side, a tube goes into a tube above a bowl of water, where “gas containing ethene” ends up]
[3 marks]

Answer 6

-decane vaporises when heated
-decane breaks down when touching the pot
-large decane molecules produce smaller ones eg ethene

Question 7

What type of reaction takes place between butene and steam? [1]

Answer 7

Addition

Question 8

A sample of each of 3 hydrocarbons X,Y and Z was shaken with bromine water.
Bromine water is orange coloured.
X and Y became colourless
Z stayed orange
Comment on rhe structures of the hydrocarbons

Answer 8

X and Y are both unsaturated and contain double bonds/is an alkene {Therefore could react?}
Z contains no double bonds/is an alkane {Therefore could not react?}

Question 9

A student carries out a test on an unknown solid.
A red flame is seen.
They conclude it is lithium carbonate
explain why this conclusion is not justified

Answer 9

Flame test only confirms presence of lithium ions
But another test is required to confirm the identity of the anion

Question 10

A substance containing two ions was tested
a flame test produced a yellow coloue
dilute HCl was added, followed by a few drops of barium chloride
was is the substance’s formula?

Answer 10

Na2SO4

Question 11

The test for chloride ions is carried out
dilute nitric acid was added, followed by a few drops of silver nitrate
why is it necessary to add the dilute nitric acid?

Answer 11

To make sure no carbonate ions are present

Question 12

sodium hydroxide solution is warmed with a solution of ammonium ions
ammonia gas ia given off
describe a test to show the gas is ammonia [2]

Answer 12

Test gas with moist red litmus paper
turns blue

Question 13

Suggest why a given mass of silver is more effective as a catalyst when used as nanoparticles rather than in a powder form [3]

Answer 13

Silver nanoparticles have a greater SA:V ratio than powder
bc reactions take place on the surface of the catalyst
there will be more frequent collisions and a faster rate of reaction

Question 14

During a reaction, reactants are used up and the rate of reaction decreases.
Explain in terms of particles why the rate decreases

Answer 14

reactants used up ->fewer particles to react->lower freq of collisions->fewer particles reacting in a given time

Question 15

two gases, x and y, react to give product z
Condition experiment 1 experiment 2
pressure 1 atm 2 atm
temp 30 degrees 20 degrees

explain why it is not possible to predict the rate of experiment 2 compared to experiment 1
[2]

Answer 15

the decrease in temp will cause a decrease in the rate of reaction
the increase in pressure will cause an increase in the rate of reaction
because the two changes have opposite effects it is not possible to tell which would have the greater effect

Question 16

explain how displacement reactions can be used to show the reactivity of bromine, iodine and chlorine
[6]

Answer 16

order of reactivity: chlorine->bromine->iodine
write down all the ionic equations!!

add aqueous chlorine to a KBr solution
solution turns yellow-orange as bromine is produced
so chlorine is more reactive than bromine

add aqueous bromine to a KI solution
solution turns yellow/red/brown
iodine is produced
so bromine is more reactive than iodine

add aqueous chlorine to KI solution
solution turns yellow/red/brown
iodine is produced so chlorine is more reactive than iodine

Question 17

explain the type of reaction bromine atoms undergo when they are converted to bromide ions

Answer 17

bromine ions are reduced
because electrons are gained to form bromide ions

Question 18

explain how the student could modify the experiment to test if water is produced by burning candle wax

Answer 18

reverse the boiling tube / pass gas through the tube in ice water first
if any liquid condenses it must have come from the burning wax, not the limewater

Question 19

explain how different polymers can be formed using chloroethene

Answer 19

write this later

Question 20

when NaOH is neutralised there is a temperature change
a student is given dilute HCL and dilute ethanoic acid of the same concentration in mol/dm^-3
devise a plan to compare the temperature changes produced when NaOH is neutralised with each of these two acids

Answer 20

-measure known volume of NaOH solution
-add same volume of each acid
-stir
-record initial +final temps/temp change