past papers

Question 1

what is a fraction?

Answer 1

a group of hydrocarbons with similar boiling points

Question 2

why does CO2 absorb IR?

Answer 2

C=O bonds vibrate at the same frequency as IR
IR radiation emitted by the earth does not escape (from the
atmosphere)

Question 3

why is aqueous ethanol a suitable solvent when heating coconut oil with KOH?

Answer 3

allow to dissolve both oil and KOH

Question 4

way to improve accuracy of experiment to determine enthalpy value of combustion?

Answer 4

use a wind shield

Question 5

why do chemists aim to design production methods with fewer steps?

Answer 5

less energy used

Question 6

why are reactants added to excess NaHCO3?

Answer 6

to neutralise the acid and stop the reaction

Question 7

why does a graph w a constant gradient show 0 order?

Answer 7

ror doesnt change as conc changes

Question 8

observations of sodium heated in oxyegn

Answer 8

yellow flame
white solid

Question 9

how do you determine melting point of a sample?

Answer 9

using melting point apparatus
heat slowly

Question 10

why does cyclohexene have a shorter retention time than cyclohexanol in column chromatography?

Answer 10

cyclohexene is less polar than cyclohexanol
cyclohexene has greater affinity for the mobile phase

I DONT THINK THIS IS RIGHT

Question 11

example of a change to decrease percentage uncertainty in the use of the same thermometer

Answer 11

increase magnitude of temp change by increasing conc of acid/ alkali

Question 12

pH of barium hydroxide is lower at 50c than 10c

at 50c, 25cm3 is neutralised by 22.45cm3 HCl

what vol of HCl will be needed to neutralise 25cm3 at 10c? why?

Answer 12

22.45cm3
because the concentration of OH- is the same

Question 13

pH of SO2
pH of SO3

Answer 13

2-3
0-1

Question 14

equation for reaction of aluminium oxide with H2SO4

Answer 14

Al2O3 + 3H2SO4 -> Al2(SO4)3 + 3H2O

Question 15

reaction of phosphorus oxide with sodium hydroxide

Answer 15

P4O10 + 12NaOH -> 4Na3PO4 + 6H2O

Question 16

explanation of bond angles

Answer 16

LONE pairs repel to be as far apart as possible

Question 17

why are aq solutions containing [CuCL4]2- ions yellow?

Answer 17

visible light is absorbed
only yellow light is reflected

Question 18

define mean bond enthalpy

Answer 18

avg energy required to break 1 mol of a certain type of bond over a range of compounds

Question 19

equation for electrospray ionisation

Answer 19

X + H+ -> XH+

Question 20

state the meaning of the term periodicity

Answer 20

repeating patterns of chemical/ physical properties

Question 21

role of sulphuric acid when NaCl reacts w conc sulphuric acid

Answer 21

proton donor

Question 22

how to reduce % uncertainty in measurement of vol

Answer 22

use lower conc

Question 23

why is copper iodide white?

Answer 23

full 3d subshell
so no d-d transitions possible

Question 24

why is electrospray ionisation is used instead of electron impact for the ionisation of a protein

Answer 24

the protein (ion) does not break up/fragment

Question 26

observation confirming cyclohexene is dry after adding drying agent

Answer 26

goes clear

Question 27

golf balls are made of polymers they dont biodegrade why?

Answer 27

Carbon Carbon bonds are non polar or (too) strong or not attacked by nucleophiles

Question 28

suggest a suitable reagent for hydrolysis of a protein

Answer 28

concentrated HCl

Question 29

dicarboxylic acid can be identified from 2 diols by high res mass spec despite having same rm of 118 how?

Answer 29

The precise (relative molecular) masses are different

Question 30

meaning of the term complimentary when referring to DNA strands

Answer 30

(Complementary means the two strands must have base sequences) that match (all) A to T and C to G

Question 31

explain why NaBH4 reduces 2-methylbutanal but not 2-methylbut-1-ene

Answer 31

M1 H- ion / nucleophile is attracted to d+ C M2 electron rich C=C M3 H- ion / nucleophile is repelled by C=C OR C=C only attacked by/reacts with electrophiles

Question 32

why doesnt pentane lead to depletion of ozone layer?

Answer 32

doesnt produce cl radicals

Question 33

why is ..... the minor product?

Answer 33

(major) product formed via more stable carbocation OR tertiary carbocation more stable (than primary) Due to electron-releasing character / (positive) inductive effect of three alkyl groups (as opposed to one)

Question 34

A suitable target titre for the titration is 30.0 cm3 of 0.025 mol dm−3 Br2(aq). Justify why a much smaller target titre would not be appropriate.

Answer 34

Smaller titre will increase (%) uncertainty / error

Question 35

State the reason for inverting the flask several times.

Answer 35

To ensure the solution is homogeneous Allow evenly mixed/ distributed OWTTE Uniform solution

Question 36

why does kw increase as temp increases?

Answer 36

M1 Equilibrium is endothermic (in forward direction) 1 M2 Equilibrium shifts to the RHS to minimise/oppose temperature increase Ignore more H+ and OH formed 1

Question 37

which period 4 element has the largest atomic radius? explain

Answer 37

potassium smallest number of protons similar shielding

Question 38

which period 4 element has highest electronegativity

Answer 38

bromine