AQA - Unit 5 - Energetics, Redox and Inorganic Chemistry

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can anyone explain this to me
why larger ligands result in smaller co-ordination numbers?

Larger ligands don't have as much space to fit around the transition metal ion, so where you could have 6 H20 fitting around Cu2+, you can only have 4 Cl-.

Reply 681

angel1992

Original post by usmana

can anyone explain this to me
why larger ligands result in smaller co-ordination numbers?

this is because less ligands can fit around the t metal ion so there is a lower coordination number which represents the number of bond- i.e. number of ligand bonds

Reply 682

angel1992

ey does anyone know what the equation is for fe(h2o)4(oh)2 when it oxidises in air, i know the product is fe(h20)3(oh)3

Reply 683

IFondledAGibbon

Original post by Raimu

Depends on the question and what stats they give you, but when you have something like 1/2Cl2 --> Cl, you need to double it because that's only the atomisation of one mole, and in some haber cycles you need 2 Cl's fully atomised.

ahhh, thanks.

Reply 684

angel1992

can someone also explain why the melting point of aluminium oxide is lower than magnesium oxide, this seems strange, in the book it says that it has cov bonding and ionic bonding but doesnt the extra cov bonding make it stronger?

Reply 685

rrelish

When writing the conventional cell rep. e.g in JAN 10 question 3C
http://store.aqa.org.uk/qual/gce/pdf/AQA-CHEM5-W-QP-JAN10.PDF

How do you know if to write the OH- before the H2O or H2O before the OH- ? or does it not matter

In the mark scheme it says h20 not needed, but still....

Thank you

(edited 12 years ago)

Reply 686

Luke0011

Original post by angel1992

You don't need to know at this point. It's the way ions are arranged, but it's beyond our level at the moment.

Reply 687

rrelish

Original post by angel1992

Hey me and my friend was confused about this too
I think its because MgO, the electronegativities bethween the 2 are greater than the Al203 and so great strength of ionic bonding in Mgo
I think this is a bigger factor than havind add. covalent bonding....

Any other views...

Reply 688

angel1992

Original post by Luke0011

You don't need to know at this point. It's the way ions are arranged, but it's beyond our level at the moment.

thanx i thought so, and i too didnt get into medicine this year :frown:

gutted to be honest but was very competitive, am doing medical microbio for a year at leicster transfer med course and reapplying at the same time,

Reply 689

angel1992

Original post by rrelish

hey thanx what about fe(h20)4(oh)2 reacting with oxygen equation i know the product jus stuck on the equation

Reply 690

Wish I Could Change This

Original post by Sparkly-Star

Reactions with HCl only concerns Cu2+ and Co2+ :smile:

In the AQA book what page does it talk about Co2+ reacting with HCl?

Thanks

Reply 691

starburst92

Do we need to know the equations for fuel cells in alkali conditions? If we do what are they? thanks :smile:

Reply 692

Luke0011

Original post by Wish I Could Change This

In the AQA book what page does it talk about Co2+ reacting with HCl?

Thanks

Page 80, look at the example. :smile:

Reply 693

BethBeth

Original post by Raimu

Again, do we need to know the redox titration equations? I've learnt all of the other reactions in the book apart from these ones because there's half equations to learn as well which take forever.

I believe we need to know about dichromate and manganate redox titrations. I have come across titration calculations for both in past papers. I always find writing out the equations help with the calculations.

(edited 12 years ago)

Reply 694

Tiger_Lilly92

Original post by jimmy303

You multiply by 10 because the sample of H2O2 is 25cm3 from a solution of 250cm3.

you work out how many moles are in 25cm3, then multiply it by 10 to get the number of moles in the whole thing.

It's like working out how much fat it in a slice of cake which amounts to a sixth of the cake and multiplying it by 6 to finding out how much fat is in the whole thing.

You then have to work out the concentration of the original solution. Remember that concentration = moles / volume. Volume must be in dm3 but starts in cm3 so it becomes concentration = moles / (volume/1000).

Now for the tricky part. It doesn't ask for the concentration in 250cm3. It asks for the concentration from 5cm3. What you've got to realise is that the number of moles doesn't change when you dilute a substance.

So if you have 1.14 x 10^(-2 in 5cm3 and add 245cm3 to make 250cm3, the number of moles is still 1.14 x 10^(-2. Only the concentration is affected.

It's like having a spoonful of sugar in a glass of water compared to a spoonful of sugar in a bucket of water. The amount of sugar is the same but it is sweeter in the glass of water because it is more concentrated.

Then you just plug it into the calculation of concentration = moles / (volume / 1000)

= 1.14 x 10^(-2 / (5/1000)
= 2.28 moldm-3

Hope this helps :smile:

Hey how did you work out the equation for this question?

Reply 695

Raimu

Original post by BethBeth

Ah okay, I do you know if the half equations also have to be learnt? I can manage just two equations if that's all it is.

Reply 696

BethBeth

Original post by Raimu

Ah okay, I do you know if the half equations also have to be learnt? I can manage just two equations if that's all it is.

I think it's probably better to know them.. I don't know what the specification says on this, but they may ask a one mark question on it? :confused:

If you know the full equations you will probably be able to split it up in the exam if needed. :smile:

Luckily they just seem to stick in my head :tongue:

Wish the rest would though :rolleyes:

Reply 697

teddyWS

could someone please help me label the following steps in the BH cycle:
1)Na(s) -->Na(g)
2) 1/2 Cl2 (g)--> Cl (g)

Reply 698

SashaLuLu

Original post by angel1992

ionic bonds are always stronger than covalent bonds. this is due to the strong electrostatic forces between oppositely charged ions. It is easier to break the covalent bonds. It will only be incredulity strong if it is macromolecular. Silicon dioxide is macromolecular.

Reply 699

Gertius Maximus

how hard do people think these exams are marked? do you think you have to put exactly what the mark scheme says or does that jus apply for underlined words?