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OCR Chemistry F321~ 23rd May 2014~ AS Chemistry

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Could someone explain the answer to 4c ii please :smile:

http://www.ocr.org.uk/Images/131286-question-paper-unit-f321-atoms-bonds-and-groups.pdf
http://www.ocr.org.uk/Images/135163-mark-scheme-unit-f321-atoms-bonds-and-groups-june.pdf

Reply 81

AsianNoodles

ImageUploadedByStudent Room1400255419.988493.jpg

How do I do iii??? Any help is appreciated

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Reply 82

Aimen_Hassan

You have 8 * 10^-4 moles of Barium Hydroxide in 100cm^3 of water. This is one tenth of 1 dm^3. To work out the amount per 1dm^3, just times 8 * 10^-4 by 10, which gives you 8 * 10^-3.

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Reply 83

georgie20

heyy it's concentration and you're given the volume and you've worked out the number of moles you have so just do moles/volume(dm3) to get the concentration

Reply 84

jo7777

Hey guys,
I've done all the past papers for this unit. I was just wondering does anyone have any extra questions I can do to prepare further? :biggrin:

Reply 85

rosie111

Original post by jo7777

Hey guys,
I've done all the past papers for this unit. I was just wondering does anyone have any extra questions I can do to prepare further? :biggrin:

A-levelchemistry.co.uk has a lot of practice questions

Reply 86

GXO

how much UMS do you need overall to get an A?

Reply 87

bbadonde2

Original post by GXO

how much UMS do you need overall to get an A?

240/300

Reply 88

GXO

Original post by bbadonde2

240/300

thanks, and so if there's 300 ums and 200 raw marks, each mark is worth 1.5 ums? or does what each raw mark is worth depend on how easy/hard the paper was?

Reply 89

lovekitty123

Anyone know how many raw marks is full ums for this unit?

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Reply 90

bbadonde2

Original post by lovekitty123

Anyone know how many raw marks is full ums for this unit?

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Probably 59/60 for this unit, it's not like humanities where 20 marks below full raw marks is full UMS

Reply 91

LaurenLambert

This is probably a really stupid question but does the ionisation energy increase down group 7 due to more electrons thus more van Der Waals as I know it decreases down group 2 but reactivity decreases as group 7 descends?

Reply 92

bbadonde2

Original post by LaurenLambert

They decrease down EVERY group. As the amount of electron shielding and the atomic radii increases down the group, the attraction between the nucleus and outer electrons decrease meaning a an electron can be taken (ionised) more easily.

Reply 93

LaurenLambert

Original post by bbadonde2

Okay thanks why is it that the reactivity decreases down group 7 then if it becomes harder to remove an electron surely the reactivity would increase down the group then?

(edited 9 years ago)

Reply 94

LaurenLambert

Actually don't worry I understand now is it because the electron shielding increases and so effective nuclear charge decreases and the atom becomes less densely charged and so reduces its ability to accept an electron as I they obviously accept the electrons when reacting - sorry just had a 'blonde moment' haha

Reply 95

Mutleybm1996

Original post by LaurenLambert

Do you understand it now? :smile:

This is a place to get questions answered, and no question is stupid! (Despite what some TSR users may like us to believe,*cough*)

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(edited 9 years ago)

Reply 96

LaurenLambert

Original post by Mutleybm1996

Do you understand it now? :smile:

This is a place to get questions answered, and no question is stupid! (Despite what some TSR users may like us to believe,*cough*)

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Yes! Thank you haha

Reply 97

subject1

Guys anyone got the June 2013 Paper and Mark scheme for F321?? Thanks.