Chem 2 (Don't edit this Mum)

Question 1

Explain, in terms of their structures, why C12H26 has a higher boiling point than C8H18

Answer 1

M1 C12H26 has larger molecules/longer chain/ORA
M2 C12H26 has stronger intermolecular forces/ORA
M3 more energy is needed to separate the
molecules/ overcome the forces in C12H26 /ORA

Question 2

Give two characteristics of a homologous series

Answer 2

M1 same general formula
M2 each member differs from the next by CH2
M3 same functional group
M4 similar chemical properties/reactions
M5 trend/steady increase in physical properties

Question 3

When ethanol is heated with potassium dichromate(VI) and one other reagent,
the ethanol is oxidised to ethanoic acid, CH3COOH
(i) Give the formula of the other reagent.

State the colour change that occurs during this oxidation reaction.

Answer 3

H2SO4 (sulfuric acid)

(ii) M1 from orange
M2 to green

Question 4

Answer 4

) A discussion which refers to any six of the following
points:
Advantages of fermentation/disadvantages of
hydration
M1 sugar cane can be re-grown/is renewable
M2 crude oil is finite/cannot be replaced/is nonrenewable
M3 fermentation uses lower temperatures so energy
costs are lower/ hydration uses higher
temperatures, so energy costs are higher
M4 fermentation uses lower pressure so energy costs
are lower/ hydration uses higher pressure, so energy
costs are higher
M5 yeast is a natural substance and not harmful/
phosphoric acid is corrosive
Advantages of hydration/disadvantages of
fermentation
M6 hydration is a faster process/ fermentation is a
slower process
M7 hydration gives pure ethanol/ fermentation gives
impure ethanol
M8 growing sugar cane takes up land which could be
used for growing food/rearing livestock
M9 hydration is a continuous process/fermentation
is a batch process

Question 5

Give a test for chlorine gas.

Answer 5

(damp) blue
litmus turns red and is
bleached

scores M1 and
M2

Question 6

Explain why metals conduct electricity but covalent compounds do not conduct
electricity.

Answer 6

(metals)
M1 contain delocalised electrons
M2 (which) move/flow/are mobile/are free to
move (through the metal structure)
and two from
(covalent compounds)
M3 contain neutral molecules / molecules with no
overall charge
M4 electrons held (tightly) in covalent bonds (so)
M5 no electrons free to move (so do not conduct)

Question 7

) Hydrogen chloride, HCl, is a covalent substance.
When hydrogen chloride is added to water, a solution of dilute hydrochloric acid
is formed.
This solution does conduct electricity.
Name the type of particle in the solution of the dilute hydrochloric acid that
allows it to conduct electricity

Answer 7

ion(s)

Question 8

Give a test for ammonia gas.

Answer 8

M1 moist/damp red litmus paper
M2 turns blue

Question 9

Explain the meaning of the term dynamic equilibrium

Answer 9

M1 forward and backward/reverse reactions are
taking place at same rate
M2 the concentrations of reactants and products
remain constant

Question 10

Explain why potassium is more reactive than sodium.
Refer to the electronic configurations of the atoms in your answer.

Answer 10

M1 electron configuration of sodium is 2,8,1 and
electron configuration of potassium is 2,8,8,1
M2 outer electron less attracted (to the nucleus of
potassium)
M3 therefore (outer shell electron) is more easily
lost

Question 11

Suggest why carbon dioxide gas is also produced at the positive electrode.

Answer 11

M1 electrodes are made of carbon
M2 which reacts with / burns in oxygen

Question 12

This question is about the insoluble salt silver chloride (AgCl).
Silver chloride can be made by the reaction between copper(II) chloride and silver nitrate.
(a) Describe how a student could prepare a pure, dry sample of silver chloride starting
with copper(II) chloride solution and silver nitrate solution.

Answer 12

M1 mix / stir / add (silver nitrate and copper (II)
chloride)
M2 filter (the silver chloride)
M3 wash with (deionised / distilled) water
M4 dry in a warm oven or dry with filter paper or
leave / allow to dry (on a windowsill) or dry in a
desiccator

Question 13

Explain how oxides of nitrogen form in a car engine.

Answer 13

M1 nitrogen (from the air) reacts / combines with
oxygen (from the air)
M2 at high temperatures (in the car engine)

Question 14

Explain why bitumen is collected at the bottom of the fractionating column
and gasoline is collected near the top of the fractionating column.

Answer 14

M1 column is cooler near the top than at the bottom
ORA
M2 gasoline has a lower boiling point than bitumen
(so is collected nearer the top) ORA

Question 15

Suggest why universal indicator is never used in a titration.

Answer 15

There is no clear (colour change at the) end point/
difficult to determine which shade of green is pH 7
OWTTE

Question 16

The student finds that 21.50cm3
of hydrochloric acid is needed to neutralise
25.0cm3
of sodium hydroxide solution.
(i) Describe what the student should do next to prepare a pure solution of
sodium chloride

Answer 16

M1 add 21.5 cm3 of hydrochloric acid
M2 to 25 cm3 of sodium hydroxide solution

Question 17

Describe how the student could obtain dry crystals of sodium chloride from
the pure sodium chloride solution.

Answer 17

heat to remove some water
leave to cool
filter with filter paper
leave to dry and let crystals form

Question 18

Explain which method should be used to obtain lead from lead(II) oxide, PbO
Include an equation for the formation of lead in your ans

Answer 18

M1 Method 1/ heating the metal oxide/lead(II)
oxide with carbon
M2 (because) lead is less reactive than iron (and
iron is obtained from iron oxide by carbon
extraction)
M3 2PbO + C  2Pb + CO2

Question 19

) Explain why fermentation process is carried out in the absence of air and at a temperature
below 40°C.

Answer 19

M1 fermentation/reaction/respiration needs to be
anaerobic
M2 because in air / aerobic conditions ethanol not
produced
M3 because in air / aerobic conditions CO2 and H2O
are produced
M4 (if temperature above 40 ℃/too high) enzymes
(in yeast) become denatured/lose their structure

M5 causing fermentation/reaction to slow down
/stop

Question 20

concentrated sulfuric acid is also used.
(i) State the purpose of the acid

Answer 20

(acid acts as) a catalyst/to speed up reaction

Question 21

Esters have particular uses that depend on their properties.
Give a use

Answer 21

Property:) distinctive/sweet/fruity smell ALLOW volatile

M2 used in perfumes/flavourings

Question 22

Describe a test to show that solution X contains sulfate ions.

Answer 22

M1 add barium chloride/BaCl2
M2 white ppt forms

Question 23

Explain why Box 5 represents a compound

Answer 23

(box 5 shows) two (different) elements bonded together

Question 24

Acidified silver nitrate solution is used to test for chloride ions.
Give a reason why hydrochloric acid is not used to acidify silver nitrate solution.

Answer 24

Any one from:
M1 (hydrochloric acid/it) contains chloride ions
M2 (hydrochloric acid/it) produces a (white)
precipitate with silver nitrate
M3 (hydrochloric acid/it) reacts with silver nitrate

Question 25

Explain why increasing the pressure increases the rate of this reaction

Answer 25

particles/molecules are closer together M2 therefore more (successful) collisions per unit time

Question 26

When the equilibrium mixture is heated, the yield of ethanol decreases. Explain whether the forward reaction is exothermic or endothermic

Answer 26

M1 an increase in temperature shifts the (position of) equilibrium in the endothermic direction (so backwards reaction is endothermic) M2 so forward reaction is exothermic

Question 27

Indicators can be used to test for carboxylic acids. Describe a different chemical test for a carboxylic acid.

Answer 27

M1 add a named carbonate or hydrogencarbonate M2 effervescence/bubbles/fizzing OR M1 add a suitable named metal e.g. magnesium, aluminium, zinc, iron M2 effervescence/bubbles/fizzing OR M1 add a named alcohol (and some concentrated sulfuric acid and warm) M2 sweet smell (of an ester)

Question 28

Explain why it is necessary to convert long‑chain alkanes into shorter‑chain alkanes

Answer 28

M1 greater demand for short chain alkanes (than long chain alkanes) M2 more long-chain alkanes than are needed / too great a supply of /surplus of long-chain alkanes OR not enough short chain alkanes to meet demands

Question 29

Describe how a pure, dry sample of the insoluble salt, barium sulfate, could be made from the two solids sodium sulfate and barium chloride.

Answer 29

M1 dissolve each of the solids in water/make a solution of each of the solids M2 mix/add (the two solutions together) M3 filter (the mixture) M4 wash the precipitate/solid/barium sulfate /salt/residue (with water) M5 suitable method of drying the solid