AQA CHEM1: 15th May 2012

(c) 109.5 (tetrahedral angle)

nope 109.5 is correct

How come everyone's saying it's trigonal pyrmidal with a lone pair? How can it have a lone pair?
I got it as being trigonal planar.

Like that.
It was BCl3 the question asked for, right?

Why? Not being rude or anything, just wondering.

FULL (UNOFFICIAL) MARK SCHEME (taken by looking at the paper in front of me!)

If you spot any errors I'll happily change something - we all occasionally make the odd mistake...

1(a) p=37
n=48

(b)(i) e- gun fires high energy e- which knock off an e- from an atom of the sample.

(ii) Rb(g) --> Rb+(g) + e-

(c) Rb has a larger atomic radius / more shielding therfore less energy needed to remove e-

(d)(i) s-block

(ii) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1

(e) 85.6

(f) detector
Ions hit the negatively charged plate which produces a current. The size of the current is proportional to the number of ions hitting the plate.

(g) Sr smaller than Rb
Increased nuclear charge/number of protons. Electrons added to the same energy level.

2(a)(i) CnH2n

(ii) Fractional distillation

(b)(i) but-1-ene

(ii) structure of cyclobutane or methylcyclopropane

(c)(i) C15H32 --> 2 C4H8 + C7H16

(ii) (Thermal) Cracking
High demand for X / more valuable

(iii) To break to the covalent carbon-carbon bonds

(d)(i) H2

(ii) Fuel

(iii) C4H10 + 2.5 O2 --> 4 C + 5 H2O

(iv) SO2
CaO or CaCo3

(v) Fluegasdesulphurisation (or neutralisation?)

(e) Both only have vdw IMF's the strength of which is dependent on size. X and Y are similar size so will have similar vdw forces.

3(a) trigonal pryamid with one lone pair (same as NH3)

(b) dative / co-ordinate
both electrons for the bond come from the P atom.

(c) 109.5 (tetrahedral angle)

(d) The difference in electronegativity between P and H is not great enough to deshield the H atom.

4(a)(i) macromolecular

(ii) delocalised electrons which are free move and carry charge

(iii) many strong covalent bonds must be broken

(b)(i) metallic

(ii) strong electrostatic attraction between titanium cation and delocalised electrons.

(c)(i) the layers of Ti atoms can slide over each other

(ii) same crystal structure and bonding (?)

(d) Ionic
strong electrostatic attractions between oppositely charged ions.

5(a) PV=nRT
P=100,000 V=0.005 R=8.31 T=298
n= PV/RT = (100,000*0.005)/(8.31*298) = 0.201908

moles B2O3 = 0.201908 / 5 = 0.0403816

mass= moles*Mr = 0.403816 * 69.6 = 2.79 grams (3s.f.)

(b) B + 1.5 Cl2 --> BCl3
3 bonding pairs of electrons repel equally

(c)(i) moles BCl3 = mass / Mr = 43.2 / 117.3 = 0.368

moles HCl = moles BCl3 * 3 = 1.10

conc = moles / volume = 1.10 / 0.5 = 2.20 mol/dm3

(ii) H3BO3 + 3 NaOH --> Na3BO3 + 3 H2O

(d) Atom economy = (B)/(3HCl+B) * 100 = (10.8)/(120.3) *100 = 8.98%
Sell the HCl produced as well

(e) EF = BCl2
MF = B2Cl4

The value of 14.1 grams was for the two products together ie. 5 moles (ideal gas equation was for the 5 moles of gas) and we wanted the mass of one mole, so this answer should be divided by 5 to give you 2.82g.

2(b)(i) Give the IUPAC name of the position isomer of X.

(ii) Draw the structure of a functional group isomer of X.

PH4+ has 4 bonding pairs of e- and no lone pairs = hence tetrahedral shape and 109.5

I don't remember the exact numbers, but the ratio was 1:2.5 so i just multiplied one by 2.5 and the other by 1, all divided by the total which was 3.5

I'm sure I got the graphene one wrong. I said that it was macromolecular, but looking back, it's obviously not. Hopefully my reasons for the melting point are still valid.
What did people get for the concentration of HCL near the end of the paper?

Ah snap I got (i) wrong then..misread the question At least I got part (ii) correct And seriously, you're amazing for posting the answers..how did you get hold of the paper btw?

Oh okay cool. I think I thought it was asking about PH3 and answered as if it was that. PH3 had a lone pair, right?

That seams like the kind of thing that would happen to Sheldon Cooper. Maybe this is a good sign? :P