OCR chemistry foundation jan 10th 2007

arjang

didnt u have to add the first and second ionisation energy together and then multiply?

for the methane and hcl question i also wrote van der waals but some others said that it was cause hcl had ionic bonds?? which one is it then?

I hope it involved adding them!

I wrote about Van der Waals and ionic bonding. :redface:

Reply 22

Medicallicious

Ah, maybe you're right. Oh well... Anyone know what the grade boundaries for this paper might be? Anyone know what the grade boundaries on past papers were?

Reply 23

yay so i may get half the marks. i wrote that the van der waals were weaker in ch4 cause of fewer electrons and molar mass....??

did anyone get the emperical formula of the hydrated crystalline?

Reply 24

i think this paper was quite harder than any past paper i had done.. there were a few new questions. hope they lower the boundaries, but usually its 77-80% for an A

Reply 25

arjang

i think this paper was quite harder than any past paper i had done.. there were a few new questions. hope they lower the boundaries, but usually its 77-80% for an A

Yeah I thought it was a bit harder than some of the past papers as well.

The June '07 PP seemed harder though.

Reply 26

For the mole calcs in one part, did anyone else get answers like 2.14 and then 1.07... can't remember exactly what the questions were.

Reply 27

not as far as i know. in the first calcs i got sth with 0.000117 or sth.. i just remember i got pretty small decimals :smile:

one of us is probably really wrong

Reply 28

amppatel

is HCL ionically bonded, cause i think they wanted things on the dipoles? or not? :s-smilie:

Reply 29

arjang

not as far as i know. in the first calcs i got sth with 0.000117 or sth.. i just remember i got pretty small decimals :smile:

one of us is probably really wrong

I got a really small answer at first, then crossed it out...

Reply 30

hcl is covalent.............

Reply 31

i can remember it asked for moles on naoh or sumin and i remember that it was 24.45cm3 and something like 0.0100 moldm-3 of conc so u multiply em together

part b you divide the moles by 2

part 3 cant remember wot the question was

Reply 32

amppatel

equinox3o0o

hcl is covalent.............

so that question, what was the answer? was it that HCL had dipoles methane did not?

Reply 33

amppatel

equinox3o0o

i can remember it asked for moles on naoh or sumin and i remember that it was 24.45cm3 and something like 0.0100 moldm-3 of conc so u multiply em together

part b you divide the moles by 2

part 3 cant remember wot the question was

but you have to convert 24.45 to dm3 (0.02445dm3)

Reply 34

Medicallicious

fannyface

I got a really small answer at first, then crossed it out...

Yeah, I got most of my answers to 10^-4.

Reply 35

hcl is covalent but ionic in water, rite?

@equinox: yeah thats the question and even if i calculate it now i get 0.0002445moles.
then divide by 2 and etc..

Reply 36

ok i wrote dat methane has weak van der waals forces thus it has a very low BP
HCL has dipole-dipole forces which are stonger then van der forces which is why it is higher then methane

Reply 37

i think the answer was that HCl had permanent dipole-dipoles while methane has only got van der waals and therefore more energy is needed to break the dipole bonds in HCl, hence the higher bP.

Reply 38

wot do you think the boudary for an A is, im hoping its something like 45-46 cos they had questions they have never used in past exams! e.g. ionisation ca2+ :s-smilie:

Reply 39