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F321 Updated Unofficial Mark Scheme

An updated version of the F321 mark scheme ~ Friday 21st May 2010

F321 ~ Unofficial Mark Scheme (Updated version)

Answers to Question 1:

a) 50 68 50 ~ proton, neutrons and electrons of Tin (Sn) [1]

b) The weighted mean mass; of an atom of an element compared; to 1/12th of the carbon-12 isotope; [3]

c) 120 Sn has 2 more neutrons than 118 Sn [1]

d) 2.08kg = 2080/118.7 =17.52
17.52 x 6.02 x 10^23 =1.05 x10^25 [2]

e) 78.8% of Sn and 21.2% O2; therefore SnO2 [2]

Answers to Question 2:

a) H+ and SO4 2- [2]

b) bubbles/fizzing of gas (CO2); solid carbonate dissolves;

K2CO3 + H2SO4 = K2SO4 + CO2 + H2O; [3]

c) 2.47 x 10^-3 [1]

d) 4.94 x 10^-3 [1]

e) Since 2.00g of soda was used to make a 250cm^3 solution; then 25cm^3 was titrated against 24.70cm^3 of 0.100mol dm^3 H2SO4;

The calculation for the % mass was:

moles of NaOH ~ n= 2.00/40 = 0.05mol
moles of the amount titrated ~ n= (24.7 x 0.1)/1000 = 2.47 x 10^-3

2:1 reaction, hence; 4.94 x 10^-3 moles used in 25cm^-3
Therefore x10 gives 250cm^-3 = 0.0494

Then; 0.0494/0.05 = 0.988

0.988 x 100 = 98.8% [3]

Answers to Question 3:

a) 4s then 3d [1]

b) Orbital~ where two electrons 'spin'; opposite directions; eq [1]

c) 11 electrons in p-orbitals [1]

d) Ca 2+ = 18 electrons [1]

e) 2nd, 3rd, 10th and 11th [2]

f) Al (2+) (g) = Al (3+) (g) + e- [2]

Answers to Question 4:

a) purple/violet; orange [2]

b) displacement between Br and I; eq [1]

c) Cl simultanously oxidised and reduced;

From 0 to +1 in HClO;
From 0 to -1 in HCl; [3]

ii) Cl kills bacteria; eq [1]

d) thermal decomposition [1]

e) Calculation involving a carbonate; find volume of CO2;

I cannot really remember what my answer was; something like 17.4dm3 [2]

f) Thermal stability increases down the group; eq [1]

Answers to Question 5:

a) Lithium has giant metallic structure; diagram etc;

Fixed cations; surrounded by delocalised electrons; tightly packed/strong attractions; eq ~ high boiling point [3]

b) Fluorine covalently bonded; 8 electrons for each one [ 3 x lone pair]; one shared pair; eq [1]

c) LiF ~ Ionic structure ~ Li electron in outer shell completes the incomplete shell to leave Li with a full shell; and a + charge []; F with a full shell (show by dots and crosses); and a - charge []; eq [2]

d) Fails to conduct when solid; ions are fixed; conducts when molten; ions are delocalised; [2]

e) 2B + 3[F2] = 2[BF3] [1]

f) Trigonal planar; 120 degrees; 3 bonded pairs and no lone pairs; eq ~ repulsion theory explained; eq [4]

g) Permeanent dipoles arise due to difference in electronegativity; F very electronegative; electrons pulled closer; eq [3]

h) Atomic radii decrease across period 2; increased proton number; therefore increased nuclear charge; electrons added to same shell; similar shielding; hence atomic radii decrease; shells/electrons pulled closer/more strongly to nucleus; ionisation increases; eq [4]

Scroll to see replies

Reply 1
Avatar for BAPURAMT
BAPURAMT
wow thats gr8!
Reply 2
Avatar for FoOtYdUdE
FoOtYdUdE
9
Cheers dude.
Reply 3
Avatar for student53
student53
do you have the mark scheme or answers to the F332 Jan 2010 paper?....natural resources...thanks
Reply 4
Avatar for Jawanda
Jawanda
Hi...Mr van der waals, i think u might have missed a few questions out or it could just be me.....the one where you had to write another displacement reaction, the actual thermal decomposition equation of magnesium carbonate, and what use is chlorate ions...i think! thank youu!
Hey you know Q1 part c.
What did the question ask?
I dont remember getting 118 etc, I swear it asked to compare two forms of sn, and one had 2 more neutrons :?
write back ppl x thanks
Reply 6
Avatar for codedmaster
codedmaster
What was the question about NF3 again as I don't remember the question about Lone pairs and bonded pairs.
codedmaster
What was the question about NF3 again as I don't remember the question about Lone pairs and bonded pairs.

Hey codedmaster. the question asked 'why does NF3 have a permanent dipole?' This question was straight after the BF3 question which asked you to write about bond angles etc.

I thought it was hard :/ I messed up ALL the calculations and I'm worrying :'(
Reply 8
Avatar for Dr WestwooDD
Dr WestwooDD
OP
4
baby-angel-x
Hey you know Q1 part c.
What did the question ask?
I dont remember getting 118 etc, I swear it asked to compare two forms of sn, and one had 2 more neutrons :?
write back ppl x thanks

Hi...Mr van der waals, i think u might have missed a few questions out or it could just be me.....the one where you had to write another displacement reaction, the actual thermal decomposition equation of magnesium carbonate, and what use is chlorate ions...i think! thank youu!


Yeah your both right; I did put this together from memory so there is bound to be a few mistakes;

I shall edit the mistakes asap! :cool:

Thanks for your help! :smile:
Reply 9
Avatar for student53
student53
anyone have the mark scheme to natural resoucres jan 2010 ocr salters b?
Fantastic. Thanks alot. I agree with all the marks there actually (well almost) so should be good. :smile:
Mr van der WAALs
An updated version of the F321 mark scheme ~ Friday 21st May 2010


3a) 4s then 3d [1]


Isn't the answer 3d 4p (As 4s was already there?)
Reply 12
Avatar for Dr WestwooDD
Dr WestwooDD
OP
4
BradfordCityJoss
Isn't the answer 3d 4p (As 4s was already there?)


Maybe I cannot quite remember; but I thought it was trying to test if candidates knew the filling of shells order; 4s fills before 3d, I thought the last shell they put was 3p, then we had to put 4s then 3d. :confused:
Reply 13
Avatar for FoOtYdUdE
FoOtYdUdE
9
Mr van der WAALs
Maybe I cannot quite remember; but I thought it was trying to test if candidates knew the filling of shells order; 4s fills before 3d, I thought the last shell they put was 3p, then we had to put 4s then 3d. :confused:

3d and then 4p was ansa if i remb cr3ectly
FoOtYdUdE
3d and then 4p was ansa if i remb cr3ectly


I agree, they were being kind. 4s was the last one, so I put down 3d 4p (this still shows if the candidate was 1) paying attention and spotted 4s 2) showing that they know 3d comes after 4s (but it does it with a prompt which is why I thought it was a kind question.
BradfordCityJoss
I agree, they were being kind. 4s was the last one, so I put down 3d 4p (this still shows if the candidate was 1) paying attention and spotted 4s 2) showing that they know 3d comes after 4s (but it does it with a prompt which is why I thought it was a kind question.

Are you SURE 4s was the last one.
I swear it went like 1s 2s 3s 3p then there were 2 gaps so i put 4s then 3d.

im screwed if i misread the table...lol i neva read Q's properly :/ x
Mr van der WAALs
Yeah your both right; I did put this together from memory so there is bound to be a few mistakes;

I shall edit the mistakes asap! :cool:

Thanks for your help! :smile:

hey mr van der waals
errmm..oh yh you know, the Q about why NF3 has a permanent dipole, I believe this question was worth 2 marks and NOT 3. ??
But thanks anywayy..goodjob :biggrin:
baby-angel-x
Are you SURE 4s was the last one.
I swear it went like 1s 2s 3s 3p then there were 2 gaps so i put 4s then 3d.

im screwed if i misread the table...lol i neva read Q's properly :/ x


I'm afraid so, I was happy becuase I remember thinking, do they want it in order of energy levels or just in order? then I saw 4s and saw they'd made the desicion for me. :smile:
Reply 18
Avatar for BA1
BA1
6
Paper uploaded here:

http://rapidshare.com/files/391528080/f321.pdf
BA1


Thanks for the share.

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