Edexcel - Chemistry Unit 2 - 4 June 2013

Why is ethanol a polar molecule.
and why is propane a non polar molecule?

Reply 1282

airheadbuster

2

Original post by James A

They don't even form H bonds at all. Fluoroalkanes cannot hydrogen bond.

Oh ya, the electronegativity difference between F and C is not high enough to make Fluorine sufficiently delta-. :biggrin:

Reply 1283

Mimi85

h

Original post by posthumus

Heat under Reflux apparatus

oh okay

At most you'll just need to know this really:

The liberated iodine reacts with thiosulfate ion (after adding KI to your solution being tested)

I2 + 2S2O3^2- ----> 2I- + S4O6^2-

They give you this stuff anyway usually, it's calculations you should be most concerned with :smile:

oh okay , what abt how to prepare ki

Reply 1284

Original post by posthumus

Hey goods could you explain to me why beryllium is so unreactive ? :frown:

[possibly with reference to BeO layer]

also any observations to be made about the group 2 oxides, are they white too solids too ?

Beryllium is very reactive but it forms strong insoluble oxides and hydroxides that form a layer that prevents further reaction.

Just make generic observations like solid sodium melts and disappears gas/effervescence/fizzing

Melt burns and a white powder is formed

Posted from TSR Mobile

Reply 1285

daniya12

Heading off now :P
Good luck everyone!! Do your best, all will be fine :smile:

Reply 1286

Original post by Mimi85

h
oh okay , what abt how to prepare ki

Heat potassium with iodine :biggrin:

Posted from TSR Mobile

Reply 1287

Original post by Hi, How are you ?

Why is ethanol a polar molecule.
and why is propane a non polar molecule?

Anyone ?

Reply 1288

Original post by Hi, How are you ?

Why is ethanol a polar molecule.
and why is propane a non polar molecule?

Ethanol has polar bond and is non symmetrical hence net polar

Propane is symmetrical and so any tiny dipoles in c-h bonds cancel out hence non polar

Posted from TSR Mobile

Reply 1289

posthumus

OP

20

Original post by Mimi85

h
oh okay , what abt how to prepare ki

It's a reagent, you don't need to know how to prepared it.

Original post by Goods

Beryllium is very reactive but it forms strong insoluble oxides and hydroxides that form a layer that prevents further reaction.

Just make generic observations like solid sodium melts and disappears gas/effervescence/fizzing

Melt burns and a white powder is formed

Posted from TSR Mobile

Oh okay thanks :biggrin:

I guess you meant unreactive there.... so group 2 oxides are all white

therefore when group 2 nitrates decompose you can observe white precipitates + brown fumes ?

Reply 1290

Why are Chlorine free radicals and nitrogen monoxides and dioxides described as catalyst, (I know they speed up the depletion of the ozone layer, but why though). Tanks =)

Reply 1291

Matterhorn

Original post by Gnome :)

Yes, the overall percentage error would be 0.48%, however look at the answers; the answers already have the +/- sign, so you don't have to double it because the +/- is already accounted for. Make sense?

Yeah thanks I didn't see that!

Posted from TSR Mobile

Reply 1292

Matterhorn

Original post by bhowland1994

Rookie error, you have multiplied your uncertainty by two .... Why?, your using a pipette not a burette :P

Cause it was plus or minus so I thought double it as it can go either way but as I was shown, the answers take the plus or minus into account

Posted from TSR Mobile

Reply 1293

Gnome :)

2

Original post by Hi, How are you ?

Why are Chlorine free radicals and nitrogen monoxides and dioxides described as catalyst, (I know they speed up the depletion of the ozone layer, but why though). Tanks =)

Because they react , and then the free radical is regenerated in further reactions.

They speed up the depletion because one free radical can result in the formation of thousands of free radicals, and each of those can form more free radicals etc.

Reply 1294

GCSE-help

6

Guys let's end this once and for all, is a C-H bond polar or not? :s-smilie:

I thought Ethane wasn't a polar molecule simply because there is not difference in electronegativity between Carbon and Hydrogen (or an insignificant difference)

Reply 1295

Original post by posthumus

It's a reagent, you don't need to know how to prepared it.

Oh okay thanks :biggrin:

I guess you meant unreactive there.... so group 2 oxides are all white

therefore when group 2 nitrates decompose you can observe white precipitates + brown fumes ?

Beryllium metal is very reactive but it reacts to form very stable insoluble compounds(oxides hydroxides) that form a layer that prevents further reaction hence the reactions stop.

Group 2 and lithium give off no2 and O2
No2 is brown so you can compare thermal stability by comparisons the times until brown gas is produced. The nitrate is already white so you can observe a change. Just say it also produces a gas that relights a glowing splint(O2)

Posted from TSR Mobile

Reply 1296

Original post by GCSE-help

Guys let's end this once and for all, is a C-H bond polar or not? :s-smilie:

I thought Ethane wasn't a polar molecule simply because there is not difference in electronegativity between Carbon and Hydrogen (or an insignificant difference)

It's insignificant :smile:

Posted from TSR Mobile

Reply 1297

bhowland1994

Original post by Matterhorn

Cause it was plus or minus so I thought double it as it can go either way but as I was shown, the answers take the plus or minus into account

Posted from TSR Mobile

No, the reason we double is because we are taking two readings from the same piece of equipment, therefore are uncertatinity in the overall reading doubles. The +/- are just there to represent the fact that your actual value can be either side of the predicted value

Reply 1298