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AQA CHEM1 23rd May 2013 : Unofficial MARK SCHEME

Unit: CHEM1 Chemistry: Unit 1 - Foundation Chemistry.
Date: 23rd May 2013 (Morning)
Board: AQA

I've tried to get together as coherent a mark scheme as I can, mainly drawing on contributions to this thread. (Special thanks to Sam, Arjun, Kulraj and NabRoh for the beginnings of a Mark Scheme, and to anyone else who has contributed to the thread.)

I've tried to put short explanations next to one or more difficult and/or controversial questions. I'll add to these as needed. Approximate marks per question are in square brackets after each question. Most questions are paraphrased somewhat; you get the idea!

Any comments and additions are welcomed and appreciated: I can't remember most of the questions so nothing is numbered, but is in a vague order.

Thumbs up as a thanks are always appreciated :smile:

------------------------------------------------

Unofficial Mark Scheme CHEM1 June 13

∙ Define relative atomic mass [2]
The average mass of one atom of an element compared to 1/12 the mass of a carbon-12 atom.

∙ Find the Ar of the sample (from mass spectrum) [3]
72.4

∙ Identity of the ion responsible for the particular peak (73?) [1]
⁷³Ge⁺ ?? Unsure - I actually put ⁷³X⁺

∙ Which is deflected most? + Explanation [2?]
70 got deflected most as it has the lowest mass/charge ration (lightest for the same charge)

∙ Why does ⁷⁰Se have different chemical properties to ⁷⁰X ? [1]
They have different electron configurations (and proton numbers), which is responsible for chemical properties.

∙ Current is proportional to abundance: how is a current produced? [2]
Positively charged ions hitting the metal plate cause delocalised electrons to flow; a current is induced in the detector plate.

∙ Define Structual Isomers [2]
Molecules with the same molecular formula but different structural formula (oe.)

∙ State the position isomer of but-1-ene [1]
But-2-ene

∙ State the chain isomer of but-1-ene [1]
2-methylprop-1-ene or methylpropene (both numbers are redundant as there are no other possible positions. putting numbers in should not be marked wrong, though)

∙ Draw Functional Group Isomer of but-1-ene [1]
Cyclobutane - cyclic hydrocarbon with 4 Carbons arranged in a circle (square!) and 2 hydrogens on each

∙ Equation: but-1-ene incomplete combustion to form a solid product [1]
C₄h₈ + 20₂ = 4C + 4H₂0

∙ Hazard associated with the solid product above [1]
Carbon particulates exacerbate [make worse] asthma and other respiratory conditions and can be carcinogenic [cause cancer]. Debated: smog/pollution - it asks for a hazard, implying not an environmental concern.

∙ Formula of the hydrocarbon that forms ____, ____, ____: [1]
C₁₆H₃₄ .

∙ Use of this hydrocarbon: [1]
Diesel fuel ('Fuel' on its own may or may not get credit.)

∙ Largest atomic radius in Period 2 Carbon to Neon + explanation [2]
Carbon: atomic radius decreases across a period as nuclear charge increases but shielding remains constant.

∙ Trend in first Ionisation energies of Period 2, Deviating element, Explanation [4]
Increase. Oxgyen deviated; doubling up in one of the three 2p orbitals introduces a repulsion on the outermost electron so ionisation energy decreases from nitrogen to oxygen.

∙ Which Period 2 element has the greatest second ionisation energy? + Explanation (No explanation needed?) [2]
Lithium: the second electron is taken from an electron level/shell much closer to the nucleus (level 1).

∙ Equation: Including State Symbols, the first ionisation of Carbon. [1]
C_(g) -----> C⁺_(g) + e^- / C_(g) + e^- ----> C⁺_(g) + 2e^- / C_(g) - e^- -----> C⁺_(g)(Alternatives from previous mark schemes, charge on electrons not always requires but state symbols are essential.)

∙ Tick box: Which ionisation brings Thallium down to [Xe] 5d¹⁰ 6s¹ ? [1]
Second

∙ Formation of Aluminium Chloride from elements. [1]
Al + 1.5Cl₂ ----> AlCl₃ (accept multiples)

∙ Bond in AlCl₄- And how it is formed [3]
Dative Covalent / Coordinate bond. Both electrons in the shared bonding pair are donated by the Cl- ion. (chloride, chlorine may not get credit.)
pair electron donated from chlorine

∙ Molecule with same number of electrons and same shape as AlCl4- [1]
SiCl4 - not any others like BCl4- or NH4- as they don't have the same total number of electrons (Nitrogen has 7 electrons, Aluminium has 13). MgCl4 2- may get credit, but unlikely.

∙ Gas from Aluminium Chloride with Mr = 267. [1]
Al₂Cl₆ (NOT 2AlCl3, as this implies two molecules of a different gas as opposed to one molecule of the required gas).

∙ Strongest type of bonding between ammonia and water [1]
Hydrogen bonding

∙ Why is Phosphene (Ph3) insoluble? [1]
Phosphene doesnt form hydrogen bonds with water, hence the strongest intermolecular forces are Van der Waals ( dispersion / temporarily induced dipole moments) forces which are much weaker than H bonds so molecules aren't held in solution.

∙ Draw 1 molecule of NH3 bonding with 1 molecule of water. [3]
NH3 has one lone pair on the nitrogen; H20 has 2 lone pairs on the oxygen. Delta+ charges on hydrogens (Delta- charges on N, O), Dotted line denoting hydrogen bond goes from LONE PAIR to DELTA- on H.

∙ Empirical formula of graphane [1]
CH only. If you look at the diagram, each carbon is bonded to one hydrogen. C3H and C4H are incorrect; the wording is designed to confuse. Check wikipedia if you disagree!

∙ Name the type of crystal structure in graphane [1]
Macromolecular (giant covalent)

∙ Why does graphane not conduct electricity? [1]
There are no delocalised free electrons or other charged species (e.g. ions) to transmit charge through the material.

∙ How do C-C bonds form? [1]
Each carbon atom donates one electron to form a shared bonding pair in a covalent bond.

∙ Shapes of molecule (boron central with 5 others?) and draw [3?]
Trigonal Bipyramidal

∙ Draw shape of Thallium something (TlCl2?) and Explain shape. [2]
Linear (drawn only, not named). No lone pairs 2 bonding pairs (high electron density regions) equally repel to be as far as possible away from each other.

∙CALCULATION QUESTIONS (6, 7, 8? ) (precise questions appreciated if anyone can remember):
∙ x = 7 [3 marks]
∙ About 8g of one of the Zn compounds formed. 8.18g is most likely correct. (8.18. 8.81, 8.84, 8.83 all suggested) [4 marks]
∙ Zinc metal purity: 90.3% [4 marks]

∙ Type of crystal shown in ZnF2 + Why does it have high melting point. [3]
ZnF2 is giant Ionic crystal. Strong electrostatic attraction between oppositely charged ions (Zn2+ and F-); lots of strong ionic bonds have to be broken to melt the crystal.

∙ Equation: catalytic converter converts octane and NO into nitrogen, CO2 and water. [1]
C₈H₁₈ + 25NO ---> 12.5N₂ + 8CO₂ + 9H₂O (accept multiples)

∙ Catalyst used in this reaction (catalytic converter) [1]
Any of: Platinum, Palladium, Rhodium, Pt, Rh, Pd.

∙ Name branched organic molecule with bromines on [1]
2-bromo, 2,3-Dimethylbutane

∙ General formula of homologous series [1]
C_nH_2n+1Br

∙ Why is the unbranched chain higher boiling point than suggested chain isomer [2]
Larger surface area / Greater contact area therefore stronger Van der Waals (or dispersion / temporarily induced dipole) forces.

∙ Empirical formula of chlorine-containing hydrocarbon given [2]
C2H4Cl

--------------------------------------------------------
Marks: ~ 70 / 70 (I think?!)
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All your contributions are most appreciated!

- Ben

(edited 10 years ago)

Scroll to see replies

Reply 1

A sheesh

The one where O2 deviated. 4 marks

Reply 2

borisjohnson

Thanks a lot man, do you think I would get the marks for car fuel or would it fall into the category as just fuel.
Anyway quite a good paper, hoping for 60+ to reduce the pressure on CHEM2.

Reply 3

ble

Original post by A sheesh

The one where O2 deviated. 4 marks

Right you are, thanks.

Original post by borisjohnson

Thanks a lot man, do you think I would get the marks for car fuel or would it fall into the category as just fuel.
Anyway quite a good paper, hoping for 60+ to reduce the pressure on CHEM2.

Car fuel might be taken as petrol, but its one of those answers that could go either way; fingers crossed!

Yeah, some interesting questions in ways they don't often ask. Not easy, but grade boundaries are likely to be generous.

(edited 10 years ago)

ur a legend!!

I know there are only 60 marks there..... But I can't remember any others :?

Any predictions on grade bounderies. I think I have lost around 10/14 marks....

Reply 6

A sheesh

2nd greatest ionisation energy of lithium
1 mark not 2

Reply 7

alt31

The type of crystal structure shown by graphane (1 mark)
How 2 carbons form carbon-carbon bond (1 mark)
Why graphane doesn't conduct electricity (1 mark)

This is amazing though!

Reply 8

A sheesh

Why doesn't graph end conduct electricity, bonding in graph e- cocovalent and one on why ph3 insoluble in water?

Reply 9

Enn21

You forgot to add about the current being produced

Reply 10

ble

Original post by A sheesh

2nd greatest ionisation energy of lithium
1 mark not 2

Was the explanation not required?

Original post by neji123

ur a legend!!

Reply 11

blueboa

Why does 70Se have different chemical properties to X, or something like that. The answer was about different electronic configurations.

Reply 12

Paulineuh

Original post by ble

Was the explanation not required?

:colondollar:

No, it was just state which element :biggrin:

Reply 13

ble

Original post by alt31

The type of crystal structure shown by graphane (1 mark)
How 2 carbons form carbon-carbon bond (1 mark)
Why graphane doesn't conduct electricity (1 mark)

This is amazing though!

Thankyou!! Took long enough :P
Adding them now.

Original post by A sheesh

Why doesn't graph end conduct electricity, bonding in graph e- cocovalent and one on why ph3 insoluble in water?

On it

Original post by Enn21

You forgot to add about the current being produced

Brill, adding it now

Reply 14

ble

Original post by rugbymad123

for 'Why is the unbranched chain higher boiling point than suggested chain isomer [2]'

wasnt it SMALLER surface area hence stronger VdW forces?

A larger surface contact area produces stronger VdW forces I'm pretty sure

Original post by blueboa

Why does 70Se have different chemical properties to X, or something like that. The answer was about different electronic configurations.

well remembered, thanks

Reply 15

chaddy0101

there was a question about. Explain how a carbon atom bonds to another carbon atom

Reply 16

madmax1234

Original post by rugbymad123

for 'Why is the unbranched chain higher boiling point than suggested chain isomer [2]'

wasnt it SMALLER surface area hence stronger VdW forces?

I'm sure its not surface area though its about contact points

Reply 17

borisjohnson

Original post by rugbymad123

for 'Why is the unbranched chain higher boiling point than suggested chain isomer [2]'

wasnt it SMALLER surface area hence stronger VdW forces?

No; the strength of vdW forces relies on the amount of contact areas, therefore a straight chain can come into contact more than a branched alternative.

Reply 18

connolrj01

Judging by this hopefully 66/70, what do you think boundary for 100UMS is? A lot of people saying this is the hardest paper they've seen, and on a couple of occasions it has been 65/70 for 100UMS.