OCR B F334 - Chemistry of Materials - 19th June 2012

Why does [Fe(H2O)]3+ have a 3+ charge? :s-smilie:

Reply 181

ocr_61495_pp_11_jan_gce_f334.pdf325.0KB

Original post by tania<3

I was just doing that paper :tongue:

Basically the question asks you to compare their properties whilst at room temperature - this is roughly 25C. The polymer with Tg value below 25 would therefore be flexible; and the polymer with it's Tg value above 25 would be brittle.

The polymer that has a low Tg value would have enough energy for the chains to slide over each other, therefore it would be flexible; the polymer with a high Tg value would not have enough energy for it's chains to move, so it's brittle. :smile:

Also remember if force is applied to the brittle molecule it will shatter (chains cannot slide over each other). Does not have enough energy.

Reply 182

kishenp

For question 5 on the Jan 2011 paper
I dont how the mark scheme got to that answer as i got the equation to be the other way round
As for the cadium, it has a minus electrode potential so it will be wanting to loose electrons and form ions therefore the equation goes from the right to left
and the nickel has positive electrode potential there it would want to form a stable compound
So i got Cd + Ni02+2h20=> Ni(OH)2+ Cd(OH)2
That is what i got the mark scheme got different
can anyone help =/
Thanks
Its Q5(iii)

ocr_62004_ms_11_gce_f334.pdf248.3KB

Reply 183

hash007

15

Original post by Bi0logical

Why does [Fe(H2O)]3+ have a 3+ charge? :s-smilie:

Water is neutral, it has no charge. So the overall charge is +3 due to the oxidation state of Iron (Fe). Also I think it's [Fe(H2O)6]3+

Reply 184

matt1107

Original post by Bi0logical

Why does [Fe(H2O)]3+ have a 3+ charge? :s-smilie:

H = +1, and O = -2, Therefore each water molecule has an overall charge of 0, and iron(Fe) can have an oxidation state of +2 or +3.

Reply 185

tania<3

15

This is my only afternoon exam... thankgod, means I do last minute markscheme-cramming in the morning :tongue:

good luck everyone!

Reply 186

Original post by tania<3

I was just doing that paper :tongue:

Basically the question asks you to compare their properties whilst at room temperature - this is roughly 25C. The polymer with Tg value below 25 would therefore be flexible; and the polymer with it's Tg value above 25 would be brittle.

The polymer that has a low Tg value would have enough energy for the chains to slide over each other, therefore it would be flexible; the polymer with a high Tg value would not have enough energy for it's chains to move, so it's brittle. :smile:

so the higher the Tg value, the more rigid/brittle it is, the higher the Tm, the more liquid it is?

Reply 187

Original post by Iepnauy

I think the question helps by giving you the Acid-Base equation in the question, and what happens when E300 is mixed with a base (Water).
So the ion you have is

Which will react with Ca2+

ahh I see.
wow that's sneaky.

Thanks :biggrin:

Reply 188

With the c2h4, how would you work out it's a bidentate ligand?

questiiiiioonn.jpg34.3KB

Reply 189

Original post by kishenp

For question 5 on the Jan 2011 paper
I dont how the mark scheme got to that answer as i got the equation to be the other way round
As for the cadium, it has a minus electrode potential so it will be wanting to loose electrons and form ions therefore the equation goes from the right to left
and the nickel has positive electrode potential there it would want to form a stable compound
So i got Cd + Ni02+2h20=> Ni(OH)2+ Cd(OH)2
That is what i got the mark scheme got different
can anyone help =/
Thanks
Its Q5(iii)

I got what you got too :/

would like to know why it's the other way round tooo....

Reply 190

does each (C00-)2 - ethanedioate ion form 2 bonds or does each (C00-) produce two dative bonds so (C00-)2 would produce 4 and be tetrahdral?

Reply 191

tania<3

15

Original post by Cleoleo

so the higher the Tg value, the more rigid/brittle it is, the higher the Tm, the more liquid it is?

It really depends on what temperature you are comparing it against. I think just generally say that at room temperature, polymers with higher than RT Tg values are more brittle and vice versa.

You go from the glass phase (Tg), to flexible, to liquid (Tm) - this diagram is pretty good

Tm is more like a melting point, so no. At room temperature, a polymer with a high Tm value means there is more energy required to separate the chains and turn it into a liquid, so the higher the Tm value (melting point) the more solid it will be

(edited 11 years ago)

Reply 192

what complexes and colours do we need to know??

Reply 193

Immi :)

Original post by Cleoleo

I got what you got too :/

would like to know why it's the other way round tooo....

just did this paper today, if you look in the question it says that it can be recharged by reversing the reaction, so you write it the opposite way to you would expect, meaning that its

Cd(OH)2 + Ni(OH)2 --> Cd + NiO2 + 2H20

hope that helps, i got stuck at first too!

Reply 194

nosh1994

does anyone know what the answer to this question would be. i thought the acid it reacted with was hcl?

Reply 195

mortaz786

jan 11 2b ii)

i never understand how you get the orders? can someone explain please. would be much appreciated

Reply 196

When an amino acid (containing an COOH group and NH2 group) reacts with HCL, How come only the NH2 gains the hydrogen from HCL. Why is the COOH group not affected in any way?

Reply 197

mortaz786

Original post by Bi0logical

When an amino acid (containing an COOH group and NH2 group) reacts with HCL, How come only the NH2 gains the hydrogen from HCL. Why is the COOH group not affected in any way?

i think its to do with if it reacts with acid then the acid is a proton donor so donates a hydrogen to the lone pair on the nitrogen.

but if it was Na OH then the COOH would become COO- as now the COOH is the acid and the NoOH is a base.... you just need to see if its an alkali reactant or an acid

any help on my question few posts back? :smile:

Reply 198