AQA CHEM5 A2 Chemistry - 19th June 2013

Hiya...

Sorry if someone else has already answered this question for you.

With 2+ hexa-aqua ions, basically (well my chemistry teacher told me because there is no distinction in the book(s))

Its 3en which forms [M(en)₃]²⁺ + 6H₂O

With 3+ hexa aqua ions it does something different.

en is H₂NCH₂CH₂NH₂

This is the following equation

2[M(H₂O)₆ ]³⁺ + 3H₂NCH₂CH₂NH₂ ----> 2[M(H₂O)₃(OH)₃] + 3H₃NCH₂CH₂NH₃

This is because 3+ ions are slightly more acidic and can donate H⁺ more easily. Think of the reactions between the hexa aqua ions and carbonate ions.

Hope this helps. I was completely muddled by it all initially. There is not actually any distinction in the book (I use Nelson Thornes) at all, but I think you are supposed to apply knowledge of the differences between the reactions betweeen carbonate with 2+ hexa aqua ions and 3+ hexa aqua ions. en is a bidentate ligand, as is the carbonate ion.

thanks alot, cant rep you

Does the value of emf increase if more electrons are released?

it gets more -ve i think but someone confirm this

Emf should always be positive otherwise the spontaneous reaction doesn't occur. I think the emf decreases if more electrons are produced because that would lead to an increase in current in the circuit and as current increases, emf decreases but I'm not entirely sure

Edit: thinking about it though that's more to do with physics and I think it would be unfair to assume everyone would know it so I'm not even sure if that would be tested in the exam. Did it come from a specific question in a past paper?

Sorry to butt in. i didn't know that about 3+ ions with 'en'. But it kinda explains the question about Al3+ reacting with diaminoethane in January 2012 paper. The questtion says diaminoethane behaves like ammonia, So i thought you were meant to think, well Al3+ doesn't undergo substitution with ammonia, so its not going to undergo substitution with this ligand...didn't know there was a rule, thank you for sharing.

Nope i was just wondering.... on some papers... they give you like a table and one of the questions was explain why water reacts with flurorine... and you had to use the ecell values to explain it

Does the value of emf increase if more electrons are released?

Pls could someone explain what you would put for the reasoning..

For question 4b

http://papers.xtremepapers.com/AQA/Chemistry/2004%20Jan/AQA-CHM5-W-QP-JAN04.pdf


If the hydrogen ion concentration is reduced, equilibrium shifts to the left so more e- ions are accepted so EMF should increase? Why does it decrease?

Thanks

Wow, are AQA serious. June 2012, the gradient of the line question is ridiculous. I only noticed the it didn't go exactly through the middle of the box after I'd seen the answer and zoomed in A LOT. No chance of me seeing that, not clear AT ALL. I'd never assume that it didn't pass directly through.

Pls could someone explain what you would put for the reasoning..

Wouldn't it just be 0 and then for a reason just "by definition. The Standard Hydrogen Electrode is a reference point".

The answer is just " by definition "


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What’s the difference between mol and mole?

It is actually ridiculous. I kept getting 0.1 but the markscheme says that it must not be that number unless the students has written 0.997.. Whatever it was. So ridiculous. I actually would not mind such a question but they need to make their graphs more clearm