Year 12s: what will be the first way you research your future options? >>

AQA CHEM5 A2 Chemistry - 19th June 2013

Scroll to see replies

Hi guys, does anyone know when it asks us to draw the shape of the complex ion do the want us to use dash and wedged arrow or normal arrow?

Reply 1801

lifeisgood2012

Original post by flyylikejetz

anyone ... ?

you blud... in the table it says lattice DISSOCIATION... YOU NEED LATTICE FORMATION SO YOU CHANGE THE + TO A NEGATIVE

Reply 1802

MrMeep2580

Original post by elliewoodheadx

How does Cr(H2O)6^3+ react with NH2CH2CH2NH2? In terms of the equation? Thanks

Posted from TSR Mobile

in the question it stataes that, that molecule reacts like Ammonia. so you would assume that. depends on whether its in xs or not

Reply 1803

marleyxd

How do we know when we're given a bond enthalpy instead of atomisation?? Does it say? I've never seen one on a paper
So is bond enthalpy double the atomisation?

Reply 1804

16dan2life

Original post by elliewoodheadx

How does Cr(H2O)6^3+ react with NH2CH2CH2NH2? In terms of the equation? Thanks

Posted from TSR Mobile

They asked this before with Al(h2o)6 3+, so it must be similar.

2[Cr(H2O)6]3+ + 3H2NCH2CH2NH2 --> 2[Cr(h2o)3(oh)3]+ + 3[3HNCH2CH2NH3]2+

Reply 1805

smileitsfree

Original post by OFoster

Why does Al2O3 has a lower melting point than MgO, even though it is smaller and more highly charged?!

the 3+ ions distort the oxygens electron cloud making the bonds partially covalent

Reply 1806

elliewoodheadx

Original post by MrMeep2580

in the question it stataes that, that molecule reacts like Ammonia. so you would assume that. depends on whether its in xs or not

So it would make Cr(OH)^3- in XS with what products? :s-smilie:

NH3CH2CH2NH3?
Thanks for your help!

Posted from TSR Mobile

Reply 1807

elliewoodheadx

Original post by 16dan2life

They asked this before with Al(h2o)6 3+, so it must be similar.

2[Cr(H2O)6]3+ + 3H2NCH2CH2NH2 --> 2[Cr(h2o)3(oh)3]+ + 3[3HNCH2CH2NH3]2+

Wouldn't it make Cr(OH)6^3- though? :frown:

Posted from TSR Mobile

Reply 1808

16dan2life

Original post by marleyxd

How do we know when we're given a bond enthalpy instead of atomisation?? Does it say? I've never seen one on a paper
So is bond enthalpy double the atomisation?

depends on the compound. Let's say the question is to do with NaCl, we'd expect atomisation to be 1/2Cl2 -> Cl

If they gave us, Cl2 -> 2Cl, then this is bond dissociation, so we need to half this value, to work out the atomisation.

Reply 1809

16dan2life

Original post by elliewoodheadx

Wouldn't it make Cr(OH)6^3- though? :frown:

Posted from TSR Mobile

thats with NaOH, not diaminoethane

Reply 1810

problematic

Hey guys, quick question and sorry if this has already been answered.

I;ve attached a table from june11 paper q 5 and its asking to do a cell representation using the Zn and Ag2o equestions.

I just wanted to know why Pt boundaries are penalised, and what is the general rule when to put the Pt and when not to.

thank you

Capture.PNG33.3KB

Reply 1811

Atz23

hello, can someone explain to me question 3d on Jan 2013 please? it would be a big help....I do not get why you do 70-189.

Reply 1812

nabeel1231

anyone got the june 2013 mark scheme? thanks.

Reply 1813

16dan2life

Original post by problematic

The question does state that a Zinc and Silver electrode are used, if it mentioned no electrode, then I'd expect you write Pt.

Reply 1814

hawraaj313

useful link-

http://www.chemguide.co.uk/inorganic/complexions/shapes.html#top

about shapes of complex metal ions and many others

Reply 1815

popnit

Original post by MrMeep2580

Reaction two occurs when its left in the prescence of oxygen, oxygen oxidises it to Co3+

Or you can use hydrogen perioxide to oxidise Co2+

No i know that, how do you figure out the equation? More specifically the 2 moles of each reactant except H2O2

Reply 1816

problematic

Original post by 16dan2life

The question does state that a Zinc and Silver electrode are used, if it mentioned no electrode, then I'd expect you write Pt.

Ahhh I see, thank you ! :smile:

Reply 1817

MrMeep2580

To cheer everyone up during revision :smile:

Reply 1818

lewiszorz

In the electrochemical cell, where it's like Zn and Cu, how do you know that Zn has more tendency to oxidise to Zn2+ than Cu?

Reply 1819

Melissa.S.

So confused, for lattice enthalpies , when the experimental values in born haber cycles is bigger than the value from theory, it means the bonding is stronger because the ions are polarised, so it contains partial covalent bonding. But then in the periodicity unit Al203 has a lower melting point because it contains covalent bonding??

So does covalent character in ionic bonding make bonds stronger or weaker??