Question Papers Marking Instructions

Hints offered by J Coull

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Section 1

Question 1

Hint 1: This is a low wavelength and lower than any in visible spectrum (see colour wheel) so high frequency ... UV

Hint 2: Emission involves electrons moving from higher to lower energy levels

Question 2

Hint 1: look for a substance which has waters of crystallisation displayed in formula. Mass difference after heating solid due to water loss.

Question 3

Hint 1: Requires precipitation of an insoluble magnesium salt by addition of a suitable soluble salt. Check data book solubilities.

Question 4

Hint 1: check the rules for clarification

Question 5

Hint 1: Use VSEPR if you wish, but the greater number of atoms that need to be arranged in space the smaller the angles generally between the bonds

Question 6

Hint 1: Fe³⁺ is d⁵ and Fe²⁺ is d⁶ Check relative stability of these oxidation states

Question 7

Hint 1: look at rules: total charge of ion = sum of all oxidation states taking into account number of 'atoms'

Question 8

Hint 1: Check number of bonds to central metal ion from surrounding atoms

Question 9

Hint 1: find out from your notes which is the only factor to affect the size of the equilibrium constant upon a change.

Hint 2: Endothermic /exothermic directions affected differently by T

Question 10

Hint 1: Feasible when free energy change has a negative value. Check graph for these values and hence work out temperature range

Question 11

Hint 1: Use equation on page 4 of data book to compute table values

Question 12

Hint 1: Condensing means going from higher entropy gas state to lower entropy liquid state. To work out ΔH, think of the change - exo or endo?

Question 13

Hint 1: how does [X] affect rate? Do same for [Y]. For example, as [X] doubles what happens to rate?

Question 14

Hint 1: k here will be for example, Rate/[A]² Now substitute all units into this expression and work out overall unit for k

Question 15

Hint 1: A double bond is made up of one σ bond and one π bond. A triple bond is made up of one σ bond and two π bonds

Question 16

Hint 1: the N atom is taking up place of one C atom. N has valency 3 so no H on it. Carboxyl bearing carbon will not have an H attached.

Question 17

Hint 1: looking for cis/trans isomerism possibility around C=C

Hint 2: looking for cis/trans isomerism. Draw out each only if necessary. Key is......if the =C has two identical atoms or gaps on it - no chance of cis/trans arrangement.

Question 18

Hint 1: skeletal representation. Top groups shown: ethyl, bottom ones methyl. Same side so....? Look for longest chain when naming

Question 19

Hint 1: N-H bond more strongly polar than N-C. What effect does this have on solubility / intermolecular forces and hence boiling point?

Hint 2: Stronger intermolecular interactions with N-H containing molecule and stronger interactions with water molecules

Question 20

Hint 1: Lithium aluminium hydride is a reducing agent (for example it can reduce a carboxylic acid to the aldehyde then primary alcohol)

Question 21

Hint 1: step 1: nitration, with nitro group replacing an H on ring

Hint 2: step 2: nitro to amine (H going in effectively) - oxidation is loss of electrons, loss of H or gain of O

Hint 3: step 3: amine to amide - know your conversions. Awkward looking one but this is condensation. Also, get steps 1 and 2 right then only one correct response possible

Question 22

Hint 1: check your reactions, watch C as you need to be sure what reduction means here

Question 23

Hint 1: draw out structure and circle all possible fragments. Remember molecular ion will be present.

Question 24

Hint 1: Divide each % by relative atomic mass and look for simplest ratio between the three. Check for an x:y:1 ratio first, then go from there if necessary.

Question 25

Hint 1: Focus on the neighbouring C atom. Number of peaks = number of H on it, plus one

Question 26

Hint 1: check definitions of agonist/antagonist and apply

Question 27

Hint 1: 0.03ppm means 0.03mg hydrogen sulfide per litre of air. Calculate total volume of air, then link to mg hydrogen sulfide

Question 28

Hint 1: caffeine is an organic compound. Look at practical techniques and how to purify such a compound from an impure sample

Question 29

Hint 1: Water less dense. Will it sit above or below the dichloroethene?

Hint 2: K = 4, so X is 4 × more soluble in the organic layer than the water (aqueous layer)

Question 30

Hint 1: EDTA can be used to determine metal ion content.

Section 2

Question 1

1a) Hint 1: check out quantum numbers, n = 2 rules out 1s for example.

1b) Hint 2: Use ΔG = ΔH - TΔS, take care with units

1c) Hint 3: rearrange equation for log(K), then compute, and finally take antilog

Question 2

2a) Hint 1: need to specifically focus on participants in rate determining step

2b)i) Hint 2: Look at slowest step. How many participating reacting particles in this step?

2b)ii) Hint 3: Don't forget k. Not K. Both first order. Remember [ ]

2c) Hint 4: Add steps 1, 2 and 3 together. Watch as arrow positions may confuse

Question 3

3a) Hint 1: Dilution factor is 10 so only 1/10 of moles needed. This would be in 50/10 cm³ of original solution

3a) Hint 2: Could do c₁v₁=c₂v₂. i.e., 0.01 × 50 = 0.1 × v₂

3b)i) Hint 3: Think: what well known substance found in the lab would give an absorbance reading of 0?

3b)ii) Hint 4: mark scheme provides clear answer

3b)iii) Hint 5: Use 0.34 to find concentration of Cu²⁺ in the diluted solution = 0.032.

3b)iii) Hint 6: Double this as the solution was halved in concentration.

3b)iii) Hint 7: Use n = cv where the v = 0.25 litre.

3b)iii) Hint 8: Work out mass then %

Question 4

4a)i) Hint 1: See your notes or mark scheme for definition

4a)ii) Hint 2: Look for two species connected by transfer of H⁺ e.g., NH₃ and NH₄⁺

4b) Hint 3: oxygen atom has lone pairs

4c) Hint 4: must describe the relationship clearly and don't stray from this. See marking instructions.

4c)ii)A) Hint 5: Work out GFM from formula in table, then moles then do c = n/v. Watch out as volume in litres needed

4c)ii)B) Hint 6: Must use equation stated in mark scheme. This is a weak acid: its pH must be linked to level of dissociation , Ka, and its concentration, c

4d) Hint 7: Look at key areas here and make sure you use equations to help you describe the theory

4d) Hint 8: Indicators: e.g, are weak acids where acid form and conjugate base forms have different colours,. Buffers have large reservoirs of acid/ conj. base etc

Question 5

5a) Hint 1: This is atomic emission theory. Check notes for excitation method

5b)i) Hint 2: Remember double aa - hexaaqua. Not zincate as this is a positive ion

5b)ii) Hint 3: Remember Zn²⁺ has a d¹⁰ configuration so no d-d transitions. Check periodic table position. 4s electrons lost to form this ion, full set d orbitals

5c)i) Hint 4: Use E = hf. No need for L here as we are not seeking mole quantity

5c)ii) Hint 5: convert answer from part (i) to eV, then compute through to final answer

Question 6

6a) Hint 1: Always 'follow the moles' ... the dichromate solution is reacting with 1/1000 of the ethanol in original 20cm³ sample

6a) Hint 2: Calculate moles of dichromate in 25.0cm³ then subtract from this the moles left unreacted 1(1.65 × 10^-4)

6a) Hint 3: Use moles of dichromate reacted. Multiply by 3/2 to get moles ethanol reacted. Multiply by 1000 to get moles ethanol in the 1 litre volume

6b) Hint 4: see mark scheme

6c) Hint 5: focus on chemicals - impurities or conc

6d) Hint 6: you need to check accuracy of technique so standard solution required

Question 7

7a) Hint 1: see mark scheme

7b)i) Hint 2: have a look over hybridisation ideas in organic chemistry notes then look at sigma bond formation. Crucial point: it's along axis, end-on overlap

7b)ii) Hint 3: mixing of one s orbital with two p orbitals. Theoretically, the p orbital not involved in hybridisation then overlaps with p orbital from neighbouring C atom

7c) Hint 4: this involves movement of electrons from Highest occupied to lowest uncoccupied molecular orbital. Energy absorbed. Colour observed is the complementary colour.

7d)i) Hint 5: link to Higher: look at hydroxyl groups: think about their nature and what the types of bonds/molecular features they will interact well with

7d)ii)A) Hint 6: infrared radiation excites the vibrational modes of molecules: bends, stretch

7d)ii)A) Hint 7: wavenumber is proportional to frequency

7d)ii)B) Hint 8: Check data book for absorptions and look for key functional groups/bonds which are detected in region of 3395 cm^-1

7d)ii)C)i) Hint 9: to get cm you need to work out 1/wavenumber, as stated, then convert to m

7d)ii)C)ii) Hint 10: Use E = Lhf here as we want per mole.

7d)ii)C)ii) Hint 11: Work out f using c = frequency × wavelength

7d)ii)C)ii) Hint 12: or go direct route using. E = Lhc/λ

Question 8

Hint 1: Take each in turn. Compare and contrast. Discuss reagents and products wherever you can. All combust, sooty flames

Hint 2: benzene: electrophilic substitution reactions, substitution on ring, give examples. Resists addition reactions due to destruction of aromaticity etc

Hint 3: cyclohexene: addition. Could possibly show a mechanism for electrophilic addition

Hint 4: cyclohexane: less reactive, substitution on ring, free radical mechanism

Question 9

9a)i) Hint 1: Look for a carbon which has four different groups attached

9a)ii) Hint 2: check notes / mark scheme for definition

9b)i) Hint 3: Look to see what is different about reactant and product molecules

9b)i) Hint 4: Amino takes place of bromine atom. Type of reaction therefore?

9b)ii) Hint 5: in theory 1 mole produces 1 mole

9b)ii) Hint 6: calculate moles of 1-phenylpropanone and the theoretical mass of cathinone which would be produced if 100% yield

9b)ii) Hint 7: use % to calculate actual mass produced. Keep approximations to end

Question 10

10a) Hint 1: look at C-O-C and apply knowledge of organic structures met

10b)i) Hint 2: Check notes and apply knowledge of representing molecules in skeletal form.

10b)ii) Hint 3: split in two around O atom. Smaller segment comes first. 2-methoxy needed to show position of attachment

10c)i) Hint 4: similar to Na + water here

10c)ii) Hint 5: Check notes here and apply theory to this chloralkane

10c)ii) Hint 6: Tertiary so carbocation formation

10c)iii) Hint 7: Check stability of primary/secondary/teriary carbocations - answer lies within this theory. Check steric hindrance meaning too.

10d) Hint 8: Must be an isomer and one C atom must have 4 different groups attached. Draw out all examples in marking scheme to see clearly.

10e) Hint 9: 9 H's in one environment, 3 in another

10e) Hint 10: Check nuclear magnetic resonance (nmr) shifts on p16 data book. Shift displayed corresponds to methyl directly attached to O. (value on page 16 3.9 - 3.5)

10e) Hint 11: Intensity: compare relative numbers of protons in each environment