Equilibria, Energetics and Elements (F325) - June 2011 Exam.

Can someone help me with Q9 of the practice questions on P225 I'm stuck :frown:

okay so to get the moles of NaS2O3 used you do 0.02015x0.2 = 0.00403 (n=c x v)
as you can see, the ratio of thiosulfate:iodine is 2:1, but the ratio in the first equation of iodine:Cu2+ is 1:2, so the moles you've just calculated are the moles in 25cm3
times 0.00403 by 10, so you have the moles in 250cm3
c = n/v so 0.0403/0.25 = 0.1612 mol dm3

Reply 701

cws121

Can anyone explain how you know if a complex ion is tetrahedral or square planar?
e.g. (CuCl4)2- is tetrahedral
but (NiCl4) 2- is square planar
how would you know if its what as they both have a coordination number of 4?
plus whats the bond angle or tetrahedral and square planar?

Reply 702

smoozth

Original post by wilsea05

okay so to get the moles of NaS2O3 used you do 0.02015x0.2 = 0.00403 (n=c x v)
as you can see, the ratio of thiosulfate:iodine is 2:1, but the ratio in the first equation of iodine:Cu2+ is 1:2, so the moles you've just calculated are the moles in 25cm3
times 0.00403 by 10, so you have the moles in 250cm3
c = n/v so 0.0403/0.25 = 0.1612 mol dm3

Thanks

Reply 703

science rules! :)

Original post by Schoolio93

Hi can someone exactly tell me what we need to know about neutralisation? Do we need to know how to calculate the enthalpy of dissociation?

We need to be able to define the enthalpy change of neutralisation which is the enthalpy change which accompanies the addition of aqueous base to neutralise aqueous acid, to form 1 mole of water.
We then need to be able to use the equation Q= mc^T (had to use ^ to represent triangle!) to work out enthalpy changes- which was also covered at AS.

Reply 704

science rules! :)

Original post by cws121

Can anyone explain how you know if a complex ion is tetrahedral or square planar?
e.g. (CuCl4)2- is tetrahedral
but (NiCl4) 2- is square planar
how would you know if its what as they both have a coordination number of 4?
plus whats the bond angle or tetrahedral and square planar?

At A level I think that we are surposed to assume that apart from cis-platin (NiCl2(NH3)2) which is teh drug we need to know about is the complex ion has a co-ordination number of 4 it has a tetrahedral shape.

Tetrahedral shape = 109.5
Square planar= 90 :smile:

Reply 705

monkeyDace

start doing the last two modules of unit 2 on monday afternoon and
expecting to get 90%...........what are the chances???
I havent even looked at it since January...it's just the last two, the first one
I know it inside out....awwwr it F215 on monday

Reply 706

hey-hey-hey

10

Can someone help me with this :
FeO4 2- + H+ -------> O2 + H20 + Fe 3+
Q asks to balance this? I think they use oxidation numbers for this: the answer is :
4FeO4 2- + 20H+ ------->3 O2 + 10H20 + 4Fe 3+

How did they do this??? I could just balance it when looking at the nunber of oxygens, hydrogens etc but i get different answer, Can someone please please help me out... :smile:

Reply 707

sportycricketer

Original post by wilsea05

..

Sorry for the inverted image but here it is :s-smilie:

The questions are:

1. State the energy for the first electron affinity of chlorine

2. Calculate the enthalpy formation of MgCl2

(edited 12 years ago)

Photo on 2011-06-10 at 18.19 18-30-24.jpg64.1KB

Reply 708

KateSW

Original post by hey-hey-hey

Can someone help me with this :
FeO4 2- + H+ -------> O2 + H20 + Fe 3+
Q asks to balance this? I think they use oxidation numbers for this: the answer is :
4FeO4 2- + 20H+ ------->3 O2 + 10H20 + 4Fe 3+

How did they do this??? I could just balance it when looking at the nunber of oxygens, hydrogens etc but i get different answer, Can someone please please help me out... :smile:

I think that you not only have to balance the numbers, but also the charges.
So looking at their answer the charge on either side of the equation = +12
This wouldn't be the case if you balanced only using oxidation numbers.
I hope this makes sense, let me know if i'm not being clear!

Reply 709

wilsea05

1

Original post by sportycricketer

Sorry for the inverted image but here it is :s-smilie:

The questions are:

1. State the energy for the first electron affinity of chlorine

2. Calculate the enthalpy formation of MgCl2

1) -698 (E)
2) that pictures really blurry but add (2xE) and F together, then take away (2xD), C and B from it, to get A (enthalpy change of formation)

Reply 710

KateSW

Original post by cws121

Can anyone explain how you know if a complex ion is tetrahedral or square planar?
e.g. (CuCl4)2- is tetrahedral
but (NiCl4) 2- is square planar
how would you know if its what as they both have a coordination number of 4?
plus whats the bond angle or tetrahedral and square planar?

Original post by science rules! :)

At A level I think that we are surposed to assume that apart from cis-platin (NiCl2(NH3)2) which is teh drug we need to know about is the complex ion has a co-ordination number of 4 it has a tetrahedral shape.

Tetrahedral shape = 109.5
Square planar= 90 :smile:

This is right, but also i've been looking at mark schemes, and if there is four co-ordinate bonds in a complex ion they give marks for either tetrahedral or square planar - regardless of which is right.

Reply 711

sportycricketer

Original post by wilsea05

1) -698 (E)
2) that pictures really blurry but add (2xE) and F together, then take away (2xD), C and B from it, to get A (enthalpy change of formation)

1) why dont you multiply by 2? cos 2 moles of Cl have electron affinity?

2) Isn't G enthalpy change of formation? I know the diagram is blurr but can you see and let me know?

The values are:

A = 148
B = 736
C = 1450
D = 244
E = -698
F = -2522

Reply 712

cws121

How come when a system increases in entropy, it becomes energetically more stable?
I thought if entropy increased, T(DeltaS) would increase, and that means that (Delta)G<0 which means the reaction is spontanoeous?? Or am i just overcomplicating things

Reply 713

wilsea05

1

Original post by sportycricketer

1) why dont you multiply by 2? cos 2 moles of Cl have electron affinity?

2) Isn't G enthalpy change of formation? I know the diagram is blurr but can you see and let me know?

The values are:

A = 148
B = 736
C = 1450
D = 244
E = -698
F = -2522

sorry yeah, thats laid out differently to how im used to.
-2522-2x698=-3918 +148+736+1450+2x244 =-1096 kJ mol -1

Reply 714

sportycricketer

Original post by wilsea05

sorry yeah, thats laid out differently to how im used to.
-2522-2x698=-3918 +148+736+1450+2x244 =-1096 kJ mol -1

Alright thanks mate, thats what I got as well :biggrin:

Just wanted to verify if the answer in the book was wrong!
Last qs, so you have to multiply 2 by -698 right to work out the electron affinity? because its 2 moles?

Reply 715

Princess_perfect786

1

how would i do the following question? i've tried everything but keep getting the wrong answers:

1. 25.00cm^3 of an aqueous solution of ethanedioic acid reacted exactly with 15.0cm^3 of 0.0200 mol dm^-3 Manganate (VII) ions. Calculate the concentration of the solution of ethanedioic acid.

The equation involved is:

2MnO4^- + 5(COOH)2 + 6H+ ---> 2Mn2+ + 8H2O + 10CO2

Reply 716

182blink

Has anhyone got exam cafe answers for this unittt ???

:frown:

Reply 717

wilsea05

1

Original post by Princess_perfect786

how would i do the following question? i've tried everything but keep getting the wrong answers:

1. 25.00cm^3 of an aqueous solution of ethanedioic acid reacted exactly with 15.0cm^3 of 0.0200 mol dm^-3 Manganate (VII) ions. Calculate the concentration of the solution of ethanedioic acid.

The equation involved is:

2MnO4^- + 5(COOH)2 + 6H+ ---> 2Mn2+ + 8H2O + 10CO2