OCR F321 - 23rd May

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Reply 120

voices1

Guys please reply to my messages. They wud do a great deal of help.

Reply 121

voices1

what happens when you add dilute Nh3 to the white precipitate for chlorine??

Reply 122

Eat.Sleep.Row.Repeat.

Original post by voices1

what happens when you add dilute Nh3 to the white precipitate for chlorine??

It dissolves the AgCl :smile:

Reply 123

The medjai

Can someone explain how the oxidation number of Cu(NO3)2 is 5.

Reply 124

intellectual1

Cu is +2 NO3 is - 2 2 x -2 - 6 = -10 / - 2 = + 5 ?

Reply 125

ilovedubstep

Original post by TrampingRampage

Don't you mean increase?

As you move across a period, there are more protons thus there is increased nuclear charge. The increased nuclear charge pulls in the electrons thus the atomic radius is smaller. The extra electrons as you move across a period fill in on the same shell so there is similar shielding. The nuclear attraction experienced by the outer electrons increase and thus more energy is required to remove the electrons.

How does a base neutralise an acid?

The OH- ions react with the H+ ions from the acid forming H20. (I was trying to trick you :smile:

)

Reply 126

TrampingRampage

Original post by The medjai

Can someone explain how the oxidation number of Cu(NO3)2 is 5.

Cu is +2

O is -2 each, and there are 6 there therefore -12.

so that leaves it to +10 for N

there are two N , and each N is +5

Hope it helps!

Reply 127

The medjai

Original post by intellectual1

Cu is +2 NO3 is - 2 2 x -2 - 6 = -10 / - 2 = + 5 ?

I thought Cu is a transition metal therefore it doesn't have a charge.

Reply 128

xI_NICHO_Ix

Cu can have a charge as a transition metal aswell

Reply 129

intellectual1

Remember Sn is +2 and +4 Fe 2+ Fe 3+ Cu+ Cu2+ these are very common, they're in the old papers for Transition Metal Chem in Unit 5 as well. Also the examiners report highlights the difficulties candidates have with Oxidation numbers.

F321 is the Unit that almost every candidate takes at least twice.

Tomorrow is the last paper in the 3 year cycle, the entire specification is now assessed. Meaning that we can probably expect alot of CALCULATIONS. Look at January 2011, there were not that many marks on Calculations at all.

Group 2 and Group 7 Chemistry is a certainty...

Van der Waals foces, polarity, water and Carbon Graphite, Metallic bonding etc has'nt really featured in recent yrs, they have to assess it every few yrs.

Be very careful with lone pairs, in shapes and molecules questions.

(edited 12 years ago)

Reply 130

The medjai

Original post by ilovedubstep

The OH- ions react with the H+ ions from the acid forming H20. (I was trying to trick you :smile:

)

Original post by TrampingRampage

Cu is +2

O is -2 each, and there are 6 there therefore -12.

so that leaves it to +10 for N

there are two N , and each N is +5

Hope it helps!

Original post by xI_NICHO_Ix

Cu can have a charge as a transition metal aswell

Thanks guys, really appreciate it.

Reply 131

TrampingRampage

Original post by ilovedubstep

The OH- ions react with the H+ ions from the acid forming H20. (I was trying to trick you :smile:

)

Haha love it :smile:

. Well it got my brain in gear! :P

Write down the full chemical equation for the formation of bleach and explain why the reaction is a disproportionation.

Reply 132

xI_NICHO_Ix

Cl2 + 2NaOH --> NaClO + NaCl + H20
Disproportion reaction because Cl goes from an oxidation state of 0 in Cl2
to +1 in NaClO which is oxidation
-1 in NaCl which is reduction
So cl has been oxidised and reduced in the same reaction :smile:

Reply 133

The medjai

Original post by TrampingRampage

Haha love it :smile:

. Well it got my brain in gear! :P

Write down the full chemical equation for the formation of bleach and explain why the reaction is a disproportionation.

2NaOH + Cl2 -----> NaClO + NaCl + H20

Disproportionation because chlorine is oxidised and reduced at the same time.

NaClO: +1 - oxidised
NaCl: -1 - reduced

Now can anyone write the formula for this if it is hot.

Reply 134

greenford

is there negative marking for chem.. because I remember my chemistry teacher ( she's an examiner) that there is negative marking... really confused :confused:

Reply 135

voices1

Original post by The medjai

Reply 136

greenford

Original post by broken_glass_heart

Hi i am an A2 student, my overall mark last year was a D and it still is a D as my college wouldn't allow us to resit AS practicals. I just scraped very low C in both my AS exams (1 mark away from a D, so the lowest C available) therefore, my overall grade was a D. I need a B overall AS+A2 to get into my uni course. but at the moment it looks impossible as the A2 exams r very very hard and am resitting F321 tomoro, hoping to get an A (unlikely though). Plus having got 20/40 (low grade E when u convert it out of 60 according to last years boundaries) in A2 practicals doesn't help with pulling the grade up! so my only way is to get an A in every single chemistry exam in AS and A2.. god help me... am so scared for tomoro!! :fight:

Im in same position as you.... got D for my a2 practical.. would you mind telling me what you got for the exam in January..

Reply 137

voices1

Opps, mistake
3lc2 6naoh---> naclo +5nacl 3h20

Reply 138

Eat.Sleep.Row.Repeat.

Original post by The medjai

That is a nasty equation that I found out we have to memorise:

3Cl2 + 6NaOH -> 5NaCl + NaClO3 + 3H2O.

I just remember it because there's 365 days in a year :smile:

Then balance it from there!

What effect does going down group 2 have on the ease of decomposition?

Reply 139

ilovedubstep

Original post by TrampingRampage

Haha love it :smile:

. Well it got my brain in gear! :P

Write down the full chemical equation for the formation of bleach and explain why the reaction is a disproportionation.

Um thuck I hate this one.

2Cl2 + 2Na(OH)2?? => 2NaClO + 2HCL + H20

Cl is both reduced and oxidised. From 0 => -1 (in HCl) and from 0 => +1 in (NaClO)

This was a bit of a guess..