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

Edexcel - Chemistry Unit 2 - 4 June 2013

Scroll to see replies

Heat under Reflux apparatus

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

The liberated iodine reacts with thiosulfate ion

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

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

That's what I thought but this is the mark scheme:
ImageUploadedByStudent Room1370330654.417563.jpg

Posted from TSR Mobile

Reply 1221

Gnome :)

Original post by SophieL1996

thanks but that's part a I mean the iionic equations. thank you :smile:

Oops! Sorry!

bi. Well, you know there has to be 2H+ because H2O is formed. In an ionic equation the charges on both sides must balance. Currently you have ClO- + 2H+ --> Cl- + H2O, so the charge on the LHS is +1 but the RHS is -1. So you add 2 electrons to the LHS to get ClO- + 2H+ + 2e- --> Cl- + H2O

It's the same principle for the iodide. You need 2 iodide ions to make 1 iodine molecule, and you need to add 2 electrons to the RHS to make the charges balance

2I- --> I2 + 2e-

ii. You simply check that the number of moles of electrons transferred in each equation is the same (in this case it is, but if it isn't you just multiply one or both equations to get equal moles of electrons) and then add the equations together. You don't need to show the electrons in the final equation.

ClO- + 2H+ + 2I- --> Cl- + H2O + I2

Reply 1222

F1's Finest

Original post by wanna_get_A*

can u send me the jan 13 paper please? :smile:

Posted from TSR Mobile

Here

6CH02_01_rms_20130307.pdf231.8KB

6CH02_01_que_20130116.pdf464.5KB

Reply 1223

airheadbuster

Original post by Matterhorn

That's what I thought but this is the mark scheme:
ImageUploadedByStudent Room1370330654.417563.jpg

Posted from TSR Mobile

Because they asked how you would collect gaseous alkenes. Either you collect it over water or in a syringe. Just make sure there's an open end or else pressure will build up. :cool:

Reply 1224

posthumus

Original post by Matterhorn

That's what I thought but this is the mark scheme:
ImageUploadedByStudent Room1370330654.417563.jpg

Posted from TSR Mobile

Geor was right :eek:

That's nowhere in the book though god damn it :frown:

... what year is this question from ???? Hopefully it doesn't come up :colondollar:

Reply 1225

Matterhorn

Original post by bhowland1994

You heat under reflux

Mark scheme says ignore any use pumice reflux :s

Posted from TSR Mobile

Reply 1226

F1's Finest

Original post by SophieL1996

hi, how did you do q 21 b i and ii? I don't really understand. thanks :smile:

For the first equation, just add two hydrogens on the left hand side to balance, then balance the charge with electrons. So two electrons on the left.

For the second equation, you need 2I- on the left hand side and therefore you need two electrons on the right hand side to balance.

moles of thiosulfate = 24.2*0.05/1000

Then you look at the mole ratio in the equation they give you in the question. Iodine reacts with thiosulfate in a 1:2 ratio, so divide the answer above by two.

Reply 1227

posthumus

Original post by airheadbuster

Because they asked how you would collect gaseous alkenes. Either you collect it over water or in a syringe. Just make sure there's an open end or else pressure will build up. :cool:

Even if it's gaseous alkenes the reflux is meant to condense it back into the mixture :frown:

Reply 1228

Matterhorn

Original post by posthumus

Geor was right :eek:

That's nowhere in the book though god damn it :frown:

... what year is this question from ???? Hopefully it doesn't come up :colondollar:

May 2011

Posted from TSR Mobile

Reply 1229

airheadbuster

Original post by posthumus

Geor was right :eek:

That's nowhere in the book though god damn it :frown:

... what year is this question from ???? Hopefully it doesn't come up :colondollar:

May 2011 17 f)ii) :cool:

Reply 1230

SophieL1996

Original post by James A

ok thanks

Reply 1231

bhowland1994

Original post by Linked

do i have to remember the actual equations - including state symbols?

Just remember the reaction of H2SO4 and the strongest reducing agent KI

So the first reaction is the reduction of H2SO4...

KI + H2SO4 -------> HI + KHSO4 (really simple one)

Now HI can reduce H2SO4 as well

2HI + H2SO4 --------> I2 + SO2 + 2H20

Finally as HI is such a strong reducing agent it can reduce again

6HI + SO2 ------> 3I2 + H2S +2H20

Now all you need to remeber is that KI and KCl only do the first step and KBr does the first and second step :biggrin:

Reply 1232

airheadbuster

Original post by posthumus

Even if it's gaseous alkenes the reflux is meant to condense it back into the mixture :frown:

I don't think butene can condense under normal laboratory conditions. :smile:

Reply 1233

Matterhorn

Original post by posthumus

Even if it's gaseous alkenes the reflux is meant to condense it back into the mixture :frown:

I guess just don't use reflux when you need to collect gaseous mixtures :/

Posted from TSR Mobile

Reply 1234

bhowland1994

Can someone please jot down the names then of alll the equipment set ups we need to know and an example of what reaction they are used for, so distillation, heating under reflux and this new one regarding the collection of gaseous mixtures .....

Reply 1235

posthumus

Original post by airheadbuster

I don't think butene can condense under normal laboratory conditions. :smile:

Original post by Matterhorn

I guess just don't use reflux when you need to collect gaseous mixtures :/

Posted from TSR Mobile

I guess alkenes have a very low boiling temperature, which makes sense !

So does anyone have an image of what the apparatus should look like ? I know geor posted one yesterday :tongue:

Also is Beryllium the only one which has BeO layer, hence it can't react with water ? :smile:

If not, then why is it so unreactive

Reply 1236

upthegunners

this exam is my bitch

Reply 1237

GCSE-help

Guys in the Jan 2012 MS it says Water can form 2 Hydrogen bonds per molecule, but some guys on here seem to think it's four?

Reply 1238

kabOOmm

if i draw a horizontal test tube to collect the gaseous alkenes with the ceramic fibre and everything, do i still need to draw an opening to not build pressure up? if so, where do i put it?