AQA - Unit 5 - Energetics, Redox and Inorganic Chemistry

Original post by hahaff

did anyone get 53.7 for the percentage for the dichromate question

i got 70% :s. i know its wrong cuz i got my ratios muddled up..

Reply 1741

Original post by hahaff

i think i did but i cant really remember
u knw for the first question was it out of 7 marks

i think i got -51..

u had to change the sign for the lattice formation because you need to dissociate the lattice before we can hydrate (or put it on solution) it...

Reply 1742

For the first question, it asked enthalpy of LATTICE formation, not just formation right?

Reply 1743

artykid23

Original post by Betsss

For the first question, it asked enthalpy of LATTICE formation, not just formation right?

yeah lattice :smile:

Reply 1744

Latice enthalpy forms a SOLID IONIC LATTICE. Think u cant just put compound.

Ur definition of hydration is actually the definition of the enthalpy of solution?

Does a H-F bond experience hydrogen bonding?

(edited 12 years ago)

Reply 1745

Original post by Zakir

so enthalpy of lattice formation: enthalpy change when one mole of the ionic solid, calcium fluoride, is formed from its gaseous ions?
and enthalpy of hydration: enthalpy change when one mole of separated gaseous fluoride ions are dissolved in water, forming a mole of aqueous fluoride ions?

Reply 1746

Yh thats right...jus realised i forgot to mention calcium and fluorine in the hydration one!

Reply 1747

Original post by kabolin

i wrote zn2+??????????????????

I think it is Zn as it can be oxidised to Zn2+ and so is the reducing agent effectively :smile:

Reply 1748

Original post by Zakir

Yh thats right...jus realised i forgot to mention calcium and fluorine in the hydration one!

i dont think it matters, just one mark, so they're just looking for gaseous ions to aqueous ions :smile:

Reply 1749

Original post by Liron Ingleby

yes i got +33.6 orsomethingand KJmol^-1 where is this 20.5 coming from?

thought it was mixed ok in parts hard in others. i think i messed up the whole fuel cell question and made silly mistakes but i only need 89 UMS for an A

Yeah pretty much the same as you :smile:

What do you mean by the 20.5? And I need a high c :smile:

Reply 1750

ceeebs

Original post by Betsss

Well, i also put hydrogen bonding, and according to chemguide, it seems to be right :smile:

This is from chemguide:

The hydration of negative ions

When an ionic substance dissolves in water, water molecules cluster around the separated ions. This process is called hydration.

Water frequently attaches to positive ions by co-ordinate (dative covalent) bonds. It bonds to negative ions using hydrogen bonds.

I'm hoping that's what the markscheme wants though!

nooo! i wrote about H bonds at first, then i crossed it out and wrote something else urgh!

Reply 1751

Original post by Zakir

i think i got -51..

u had to change the sign for the lattice formation because you need to dissociate the lattice before we can hydrate (or put it on solution) it...

Think i got this

Reply 1752

l4ith

No fluoride ions don't act as a Lewis Base, it doesn't form coordinate bonds with the water. I was under the impression the attraction was electrostatic in nature.

Reply 1753

Can anyone put the paper up?

Reply 1754

lou12

Original post by Willyg11

Can anyone put the paper up?

someone said y-day that they do have the paper but they dont have a scanner :frown:

Reply 1755

Original post by l4ith

No fluoride ions don't act as a Lewis Base, it doesn't form coordinate bonds with the water. I was under the impression the attraction was electrostatic in nature.

What did you put for: why did sodium oxide dissolve to give an alkaline solution? :smile:

and how would you test that Al2O3 had ions?
:smile:

Reply 1756

loukas2993

Original post by Betsss

What did you put for: why did sodium oxide dissolve to give an alkaline solution? :smile:

and how would you test that Al2O3 had ions?
:smile:

For "why did sodium oxide dissolve to give an alkaline solution?" i put that sodium oxide dissociates in water to form a solution containing 2Na+ + 2OH- ions according to the equation: Na2O + H2O (goes to) 2Na+ + 2OH- . The OH- ions formed contribute to the alkalinity of the resulting sodium hydroxide solution, which has a pH of 14.

Reply 1757