AQA - Unit 5 - Energetics, Redox and Inorganic Chemistry

Reply 640

cheeseisnice

Original post by Abdulla

[Al(OH)6]- and [Al(OH)6]3- are both correct.

Do you mean [Al(OH)4]-?
Thanks so much!

Reply 641

Raimu

Do we have to learn the redox titration equations as well? For example the one with MnO4 and Fe.

Reply 642

Sparkly-Star

13

Does anyone know if it is worth learning the equations on page 237 regarding the carbonate ion? I did learn them before but forgotten them, I've just not seen them in exam questions.

Reply 643

jwest

hi guys anyone fancy explaining an answer to question 2b on the specimen paper

using a born haber cycle, a value of -905kJ/mol was determined for the lattice enthalpy of silver chloride. a value for the lattice enthalpy of silver chloride using the ionic model was -833kJ/mol
Explain what a scientist would be able to deduce from a comparison of these values?

Reply 644

AminaJB

hi help needed!

just wondering how this question is calculated.

A chemical company has a waste tank of volume 25 000 dm
3
. The tank is full of
phosphoric acid (H3PO4) solution formed by adding some unwanted phosphorus(V)
oxide to water in the tank.
A 25.0 cm
3
sample of this solution required 21.2 cm
3
of 0.500 mol dm
–3
sodium
hydroxide solution for complete reaction.
Calculate the mass, in kg, of phosphorus(V) oxide that must have been added to the
water in the waste tank. jan 2010 paper

Reply 645

Thisisj

hey has anyone got a cgp revision guide?

Reply 646

strawberry_cake

Original post by Thisisj

hey has anyone got a cgp revision guide?

I do.. How come? :smile:

Reply 647

?!master?!mini?!

16

Original post by Sparkly-Star

Does anyone know if it is worth learning the equations on page 237 regarding the carbonate ion? I did learn them before but forgotten them, I've just not seen them in exam questions.

There was a carbonate one with a 3+ transition metal in Jan 2011

Reply 648

strawberry_cake

Original post by Abdulla

Does anybody have the Jan11 QP they can upload? Thanks :smile:

http://www.a-levelchemistry.co.uk/AQA%20Chemistry/AQA%20A2%20Chemistry/Unit%205/Unit%205%20Past%20Papers%20and%20Revision%20Aids/Unit%205%20summary%20home.htm

:smile:

Reply 649

strawberry_cake

Do we need to know the reactions of period 3 elements with Chlorine? :/

Reply 650

Thisisj

Original post by strawberry_cake

I do.. How come? :smile:

do you like it??
Ive just been looking at a few pages on the cgp website and its soo clear and concise :smile:

I want it but the exam is tomorrow :frown:

Reply 651

jamest92

Original post by strawberry_cake

Do we need to know the reactions of period 3 elements with Chlorine? :/

Nope

Reply 652

OsmosisJones

Original post by jwest

hi guys anyone fancy explaining an answer to question 2b on the specimen paper

using a born haber cycle, a value of -905kJ/mol was determined for the lattice enthalpy of silver chloride. a value for the lattice enthalpy of silver chloride using the ionic model was -833kJ/mol
Explain what a scientist would be able to deduce from a comparison of these values?

The Ag-Cl bond is slightly covalent due to the high difference in electronegativity. The lone pair of electrons are pulled away from the Cl and towards the Ag, thus why the enthalpy change is higher (less negative). The born-haber cycle assumes everything is an ion and there is no covalent.

Reply 653

Somali-Pir8

9

Original post by Thisisj

do you like it??
Ive just been looking at a few pages on the cgp website and its soo clear and concise :smile:

I want it but the exam is tomorrow :frown:

well don't get it then????????? :confused:

Reply 654

jamest92

Original post by AminaJB

hi help needed!

just wondering how this question is calculated.

A chemical company has a waste tank of volume 25 000 dm
3
. The tank is full of
phosphoric acid (H3PO4) solution formed by adding some unwanted phosphorus(V)
oxide to water in the tank.
A 25.0 cm
3
sample of this solution required 21.2 cm
3
of 0.500 mol dm
–3
sodium
hydroxide solution for complete reaction.
Calculate the mass, in kg, of phosphorus(V) oxide that must have been added to the
water in the waste tank. jan 2010 paper

Write an equation for NaOH and H3PO4
3NaOH + H3PO4 ---> Na3PO4 + H320

Calculate the number of moles of NaOH and therefore moles of H3PO4
21.2 x 0.5 / 1000 = 0.0106 moles of NaOH
It reacts 3 : 1 so divide by 3
3.53 x10^-3 moles of H3PO4 in 25 cm^3

Work out the number of moles in 25 dm^3
3.53 x10^-3 x 25000000 = 3533.3 moles of h3PO4

Work out the number of moles of P4010
P4010 + 6H20 ---> 4H3PO4
Reacts 1 : 4 so divide by 4
Therefore 883.3 moles of P4O10

m = n x Mr
m = 883.3 x 284
m = 2508572 g

m = 250.9 kg

Reply 655

strawberry_cake

Original post by Thisisj

do you like it??
Ive just been looking at a few pages on the cgp website and its soo clear and concise :smile:

I want it but the exam is tomorrow :frown:

ohh its really good :biggrin:

hmm I really liked it for mod4, it really helped me learn the stuff because NT was just too confusing,..Anything specific you want? I can copy out some stuff for you if you want? :smile:

Reply 656

lornaa

Original post by Sparkly-Star

No need to know it.

It's Yellow. I have a list of colours off the Chief Examiner since they're obviosly colourblind.. but it's on the list?

Reply 657

Sheldon

7

Original post by AminaJB

hi help needed!

just wondering how this question is calculated.

A chemical company has a waste tank of volume 25 000 dm
3
. The tank is full of
phosphoric acid (H3PO4) solution formed by adding some unwanted phosphorus(V)
oxide to water in the tank.
A 25.0 cm
3
sample of this solution required 21.2 cm
3
of 0.500 mol dm
–3
sodium
hydroxide solution for complete reaction.
Calculate the mass, in kg, of phosphorus(V) oxide that must have been added to the
water in the waste tank. jan 2010 paper

Refer to post 574

Reply 658

Willyg11

Original post by jwest

hi guys anyone fancy explaining an answer to question 2b on the specimen paper

using a born haber cycle, a value of -905kJ/mol was determined for the lattice enthalpy of silver chloride. a value for the lattice enthalpy of silver chloride using the ionic model was -833kJ/mol
Explain what a scientist would be able to deduce from a comparison of these values?

Assuming atoms are perfect spheres, the lower value for the lattice enthalpy shows that silver chloride is not perfectly ionic and shows covalent character. The lattice is partially polarised.

Hope this helps.

Reply 659

strawberry_cake

Can someone pleaseeeeeeeee help me with q8c in the jan10 paper?? :smile:

AQA - Unit 5 - Energetics, Redox and Inorganic Chemistry

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