Ocr f321 23 may 2013~official discussion thread

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Reply 1180

daisyrchds

aaaand does anyone have the paper by any chance?!

Reply 1181

Funtry

Original post by Freddy-Francis

He got mixed up with the questions :biggrin:

Phew!

Reply 1182

LH78

Original post by Nermin Hayek

did he say anything about the intermolecular forces in PH3 cos I think I got that one wrong
also I'm guessing 49/50 out of 60 because it was quite hard but grade boundaries in chem are usually high

I think he said that was permanent dipole-dipole. I put VdW and then went on to explain why VdW is weaker than H-Bonding and he said I might get ECF (error carried forward)

(edited 10 years ago)

Reply 1183

xcharis18

Anyone working on an unofficial mark scheme? I thought this paper was lovely! And hopefully that means I've done better than the two C's I've got thus far haha

Reply 1184

Nermin Hayek

Original post by LH78

I think he said that was induced dipole-dipole. I put VdW and then went on to explain why VdW is weaker than H-Bonding and he said I might get ECF (error carried forward)

Yh I did the same as you the second part was only one mark right?

Reply 1185

Crabbiey

Sorry, can someone quote the question that gave 360cm3 please? I honestly can't remember any of my answers being that, though I answered all the questions and I think my mind may have just blocked that question.

(Stupid time pressure - couldn't find Si in the Periodic Table for ages!XD)

Reply 1186

Funtry

For everybody saying about the PH₃ question, I'd say it's permanent dipoles, as the lone pair on the P makes the molecule non-symmetrical, and so the dipoles make the molecule polar. VDW forces are always present though.

Reply 1187

Zakee

Original post by Nermin Hayek

Yh I did the same as you the second part was only one mark right?

I think they mean permanent dipole-dipole, as Induced Dipoles are Van Der Waals' forces.

Reply 1188

Ferrari_1996

Original post by sesrugeda

I thought that mol x avagadro constant = number of atoms, not number of molecules?

Posted from TSR Mobile

You might be right. Did the question ask for the number of molecules? And how many marks was the question worth? If it was worth 3 marks, you're probably right because I don't think you'd get 3 marks just for working out the number of moles and multiplying by avagadro's constant. You probably had to divide the answer by 5 to get the number of molecules (if that's what the question asked for).

What did you get as your answer?

Reply 1189

LH78

Original post by Nermin Hayek

Yh I did the same as you the second part was only one mark right?

Yeah.

Reply 1190

Nermin Hayek

Original post by Zakee

I think they mean permanent dipole-dipole, as Induced Dipoles are Van Der Waals' forces.

Yh permanent dipole to dipole

Reply 1191

Funtry

Original post by Ferrari_1996

There were 0.05(?) moles SiCl₄ irregardless of the number of atoms, so the number of molecules will be n x N_A.

Reply 1192

Funtry

Original post by Nermin Hayek

Yh permanent dipole to dipole

PH₃ bonds intermolecularly by permanent dipole-dipole interactions due to it's asymmetric shape and polar bonds, and so is a polar molecule.

Reply 1193

Ferrari_1996

Original post by Funtry

There were 0.05(?) moles SiCl₄ irregardless of the number of atoms, so the number of molecules will be n x N_A.

Multiplying the number of moles by avagadro's constant gives you the right answer? If so, that's good, because that's what I did :smile:

Reply 1194

Zakee

Original post by Funtry

There were 0.05(?) moles SiCl₄ irregardless of the number of atoms, so the number of molecules will be n x N_A.

The question was testing your understanding that you can have moles of anything (in response to the previous poster before you).

I think, (from memory), you had something like this:

Number of moles = m/RMM

Number of moles = 0.05 moles.

0.05 x 6.02 x 10^23 = 3.01 x 10^22 molecules.

Reply 1195

Funtry

Original post by Ferrari_1996

Multiplying the number of moles by avagadro's constant gives you the right answer? If so, that's good, because that's what I did :smile:

Yes, as you can almost treat the molecules as atoms if you like. If you had 1 mole of Helium atoms, it would be the same number of molecules as 1 mole of O₂ molecules and yet twice the number of atoms. It asked for the number of molecules not atoms.

Reply 1196

Nermin Hayek

Original post by Funtry

PH₃ bonds intermolecularly by permanent dipole-dipole interactions due to it's asymmetric shape and polar bonds, and so is a polar molecule.

Ahh thank you i definitely got that wrong

Reply 1197

Funtry

Original post by Zakee

That's what I got :smile:

Seemed too little for 3 marks!

Reply 1198

Funtry

Original post by Nermin Hayek

Ahh thank you i definitely got that wrong

No problem, you may have gotten a mark for VDW forces, as everything technically has slight VDW forces between them, but I'd doubt you'd get full marks. Was it a 1 or 2 mark question?

Reply 1199

Zakee

Original post by Funtry

That's what I got :smile:

Seemed too little for 3 marks!

I think one mark was for n = m/RMM, one mark was for multiplying by avagadro's, and also one mark was to show whether or not you realized what a mole actually was an you didn't need to multiply by 4. :smile: