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Edexcel - Chemistry Unit 2 - 4 June 2013

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Iodide is the strongest reducing agent because, due to its largest radius, it has the lowest charge density. So the nuclear pull on the extra electron in the iodide ion is weakest, and thus it is easiest to remove. With chloride, for example, the charge density of the chloride ion is much higher and so the extra electron is held more tightly. So it is not easy to oxidise a chloride ion (in other words it is a weak reducing agent). Hope that helps :smile:

Thank you soo much! :biggrin:

Reply 1141

scientific222

Original post by Goods

Yep

In jan 2011 do you know the question about what happens when a tube of HI is inverted in water? The mark scheme isn't clear and I don't know the answer

Posted from TSR Mobile

It dissolves in the water, all hydrogen halides are soluble in water

(edited 10 years ago)

Reply 1142

airheadbuster

Original post by posthumus

So what's the test for HCl (I saw that blue litmus turning red was no accepted in a past paper :s-smilie:

).

Add NH3 ... to form NH4Cl?? Observe white solid/smoke?

HBR also forms white solid with ammonia. Most likely the test it to add HNO3 followed by silver nitrate solution. A white precipitate of AgCl will form which dissolves in dilute ammonia, forming [Ag(NH3)]+

(Not sure though. What does the mark scheme say?)

Reply 1143

airheadbuster

Original post by Goods

Yep

In jan 2011 do you know the question about what happens when a tube of HI is inverted in water? The mark scheme isn't clear and I don't know the answer

Posted from TSR Mobile

HI gas is soluble in water. So, the water will rise up the inverted tube. :smile:

Reply 1144

airheadbuster

Original post by Goods

My brother said it when I was complaining about a mark scheme he studies chem at uni it's not worth worrying over they won't ask about it in that way. The stuff about carbocations is also extra syllabus it's just nice to apply the kinetics to see why trends occur. For the exam you need to know that haloalkanes react faster if the halogen atom is further down the group and that the tertiary carbocation is more stable than a primary carbocation due to having surrounding alkyl groups. :biggrin:

sorry if I was stressing you making you think you didn't know something critical

Posted from TSR Mobile

I know all that. I just don't get how tertiary halogenoalkanes are more reactive than primary halogenoalkanes. It's bugging me :s-smilie:

Reply 1145

scientific222

Original post by airheadbuster

I know all that. I just don't get how tertiary halogenoalkanes are more reactive than primary halogenoalkanes. It's bugging me :s-smilie:

They are more reactive because the carbon attached to the halide has more CH3 groups attached to it. A CH3 group tends to push electrons in the bond away from itself; and encourages the release of the halide.

Reply 1146

airheadbuster

Original post by scientific222

I get it now. :thumbsup:

Edit: :sleepy: Best of luck guys.

(edited 10 years ago)

Reply 1147

thextractor007

this might help you guys revise.

Edexcel AS Chemistry Unit 2.pdf

Reply 1148

Maybenexttime

I'm happy about my knowledge until I come to this thread and all the people's discussions confuse me. xD

Reply 1149

Lillian Collins

Can someone answer the q with the star please

image.jpg525.6KB

Reply 1150

Lillian Collins

Original post by thextractor007

this might help you guys revise.

Edexcel AS Chemistry Unit 2.pdf

Thank you so much :smile:

just what I was looking for , best of luck !

Reply 1151

thextractor007

Original post by Lillian Collins

Thank you so much :smile:

just what I was looking for , best of luck !

You too. My pleasure. This is a summary so just go through it before the exam.

Chemistry Summary Unit 2.pptx

Reply 1152

Juliajuliajulia

This how I d answer it, not saying I'm right i just hope i am...
Answer:C- because all the group 2 metals react with chlorine to form ionic salts (solids) [except for beryllium chloride which is covalent but that's solid too anyway]
Why these are not right:
A- Metal oxides neutralise dilute acid- so an alkaline pH like 10 would make sense (not that I knew the pH was 10)
B- Group II sulfates follow the same solubility trends as carbonates though I'm pretty sure that's not in our spec?
D- Group I metal carbonates except Lithium do not compose but group II do
Hope that's right otherwise I should probably just give up x