Edexcel Chemistry A2 Unit 5 ~ Wednesday 19th June 2013 (Now Closed) Watch

Poll: How pumped up are you for this exam?-(warning)-(bad jokes arene this poll!)
"Titanium-I'm not going to corrode (even at high temperatures)" (A*) (22)
16.67%
"Benzene's my middle name, give me the paper in a week and I'll ace it!" (A) (27)
20.45%
"Yeah, I'm fairly electrophillic (positively charged) about the exam" (B) (27)
20.45%
"I'm in the middle of the salt bridge, but I will pass-eventually" (C) (21)
15.91%
"I'm feeling rather electroNegative about this exam" (D) (18)
13.64%
"Benzene, what's that?" (E) (6)
4.55%
"Chemistry, what's that?" (F) (11)
8.33%
This discussion is closed.
F1's Finest
Badges: 21
Rep:
?
#1181
Report 6 years ago
#1181
(Original post by GeorgeL3)
The sodium carbonate will clearly remove SO2 and HBr since they're acids.
Then it hints that sodium sulphate is a drying agent by telling you that it is anhydrous and so it's not going to affect anything but the water.
This leaves you making an educated guess that Bromine would be removed by the sodium carbonate (like this )so the answer must be D.
As far as I know we don't have to actually learn or remember that sodium sulphate is a drying agent or that sodium carbonate removes bromine, you just have to use the hints they give you to try and work it out.
Remember that when you use a separating funnel, you shake it for a couple of times...... however a build up of gas occurs inside the funnel so you have to release the gas by using the tap of the funnel. This releases the CO2 that causes a build up in pressure.

Further proof that your equation above is correct. That has definitely has to be the reaction that occurs between the sodium carbonate and the impure solution
0
AtomicMan
Badges: 12
Rep:
?
#1182
Report 6 years ago
#1182
(Original post by HarryMWilliams)
I see, in that case, I'd recommend ploughing through ChemGuide, there is a lot of useful information on there which I have personally found helpful.
Thanks
0
swahmad
Badges: 14
Rep:
?
#1183
Report 6 years ago
#1183
Anyone doing unit 4 or can help? I have a few questions.

1. I don't understand drawing titration curves. I get where to start from and and where to end, depending on the acid and base etc. but how do you know what volume the equivalence point vertical section is supposed to be at and how many pH units it's supposed to go vertical for?

2. With buffer solutions is it the anion of the salt and the acid compound that's in excess for acid buffers and the salt cation and the base compound in basic buffers?

3. What criteria does the indicator have to fulfill in order to be suitable, I thought it was the pH range including the starting pH and changing colour just before the end pH?

Thanks
0
GeorgeL3
Badges: 5
Rep:
?
#1184
Report 6 years ago
#1184
(Original post by swahmad)
Anyone doing unit 4 or can help? I have a few questions.

1. I don't understand drawing titration curves. I get where to start from and and where to end, depending on the acid and base etc. but how do you know what volume the equivalence point vertical section is supposed to be at and how many pH units it's supposed to go vertical for?

2. With buffer solutions is it the anion of the salt and the acid compound that's in excess for acid buffers and the salt cation and the base compound in basic buffers?

3. What criteria does the indicator have to fulfill in order to be suitable, I thought it was the pH range including the starting pH and changing colour just before the end pH?

Thanks
I haven't done it for a while but from what I remember and my notes from unit 4:
1. The pH vertical units should be:
SB & SA 4 - 10
WB & SA → 3 - 7.5
SB & WA
→ 6.5 - 11
The equivalence point is where equal proportions of acid and base have been added

2. I think so yes, an acid buffer has a large reservoir of acid and conjugate base whereas a base buffer has a large reservoir of base and conjugate acid.

3. A suitable indicator needs to change colour in the vertical region of the graph. (i.e. a range for colour change that the equivalence point lies in).
1
Brownie12335
Badges: 0
Rep:
?
#1185
Report 6 years ago
#1185
Hey guys. I have no idea which practical apparatus we need to know how to draw? Apart from reflux and distilling. Every now and again something comes up and I have no idea. I asked my teacher for a complete list and she dodged my question. Help please!

Thanks
0
GeorgeL3
Badges: 5
Rep:
?
#1186
Report 6 years ago
#1186
(Original post by Brownie12335)
Hey guys. I have no idea which practical apparatus we need to know how to draw? Apart from reflux and distilling. Every now and again something comes up and I have no idea. I asked my teacher for a complete list and she dodged my question. Help please!

Thanks
I think the most likely ones are:
- Normal distillation
- Steam distillation
- Reflux

But who know's, they could do something obscure like get us to draw the apparatus for preparing chromium (II) ethanoate.
Potentially though they could ask us to draw any diagram since the start of unit 1 though which included things like diagrams for apparatus to collect gas and stuff.
I think though you basically just need to remember:
- Never completely seal the apparatus
- Don't leave gaps between joins unless they're meant to be there
- Water goes in at the bottom of a condenser and comes out at the top
- Label everything including reactants and products
- If you put a thermometer in, remember the bell of the thermometer needs to be at the 'junction' in the still head.
0
JRP95
Badges: 2
Rep:
?
#1187
Report 6 years ago
#1187
(Original post by GeorgeL3)
I think the most likely ones are:
- Normal distillation
- Steam distillation
- Reflux

But who know's, they could do something obscure like get us to draw the apparatus for preparing chromium (II) ethanoate.
Potentially though they could ask us to draw any diagram since the start of unit 1 though which included things like diagrams for apparatus to collect gas and stuff.
I think though you basically just need to remember:
- Never completely seal the apparatus
- Don't leave gaps between joins unless they're meant to be there
- Water goes in at the bottom of a condenser and comes out at the top
- Label everything including reactants and products
- If you put a thermometer in, remember the bell of the thermometer needs to be at the 'junction' in the still head.
Someone's preparing to get an A*...
0
GeorgeL3
Badges: 5
Rep:
?
#1188
Report 6 years ago
#1188
(Original post by JRP95)
Someone's preparing to get an A*...
Why would you aim any lower? haha.
I need an A for my university offer so that's all I want. An A* would be nice though...
0
jojo1995
Badges: 2
Rep:
?
#1189
Report 6 years ago
#1189
Hi guys, could anyone add to my answer please ?
#
why is a reference electrode required:?
- electrode potenials cannot be measured directly
- redox reaction has to take place
- electron donor required
- electron acceptor required

anyone got anything else ? everything would be much appreciated thank you in Ad

EDDIIT!! : does anyone also know why E cell doesnt tell us if a reaction will take place ?
thanks
0
Gnome :)
Badges: 2
Rep:
?
#1190
Report 6 years ago
#1190
(Original post by jojo1995)
EDDIIT!! : does anyone also know why E cell doesnt tell us if a reaction will take place ?
thanks
Because the E cell value only tells us if the reaction is feasible; in reality, the rate may be too slow for us to consider it to be happening under standard conditions
0
swahmad
Badges: 14
Rep:
?
#1191
Report 6 years ago
#1191
(Original post by GeorgeL3)
I haven't done it for a while but from what I remember and my notes from unit 4:
1. The pH vertical units should be:
SB & SA 4 - 10
WB & SA → 3 - 7.5
SB & WA
→ 6.5 - 11
The equivalence point is where equal proportions of acid and base have been added

2. I think so yes, an acid buffer has a large reservoir of acid and conjugate base whereas a base buffer has a large reservoir of base and conjugate acid.

3. A suitable indicator needs to change colour in the vertical region of the graph. (i.e. a range for colour change that the equivalence point lies in).
So if there's 20cm^3 of acid then the equivalence point is when 20cm^3 of alkali has been added? Thanks again
0
posthumus
Badges: 20
Rep:
?
#1192
Report 6 years ago
#1192
(Original post by swahmad)
So if there's 20cm^3 of acid then the equivalence point is when 20cm^3 of alkali has been added? Thanks again
It all depends on the stoichiometry but it's usually 1:1 ratio anyway... so what you say is correct
0
jojo1995
Badges: 2
Rep:
?
#1193
Report 6 years ago
#1193
(Original post by Gnome :))
Because the E cell value only tells us if the reaction is feasible; in reality, the rate may be too slow for us to consider it to be happening under standard conditions

aww that's it... thank you
0
kd964
Badges: 0
Rep:
?
#1194
Report 6 years ago
#1194
Hi,

Would anyone mind helping me out with a unit 4 question? It's Q 11a) here:

http://www.edexcel.com/migrationdocu...e_20110615.pdf

The mark scheme says it's C, but I don't understand why it couldn't be either A or C. Doesn't 2,4 DNP test for C=O. So would it not test positive with propanoic acid and negative with propan-1-ol?
0
Gnome :)
Badges: 2
Rep:
?
#1195
Report 6 years ago
#1195
(Original post by kd964)
Hi,

Would anyone mind helping me out with a unit 4 question? It's Q 11a) here:

http://www.edexcel.com/migrationdocu...e_20110615.pdf

The mark scheme says it's C, but I don't understand why it couldn't be either A or C. Doesn't 2,4 DNP test for C=O. So would it not test positive with propanoic acid and negative with propan-1-ol?
It only works for aldehydes and ketones. Can't remember the reason- sorry! Not sure we need to know why though, but it's definitely only for aldehydes and ketones
1
GeorgeL3
Badges: 5
Rep:
?
#1196
Report 6 years ago
#1196
(Original post by kd964)
Hi,

Would anyone mind helping me out with a unit 4 question? It's Q 11a) here:

http://www.edexcel.com/migrationdocu...e_20110615.pdf

The mark scheme says it's C, but I don't understand why it couldn't be either A or C. Doesn't 2,4 DNP test for C=O. So would it not test positive with propanoic acid and negative with propan-1-ol?
Brady's reagent will only give a positive result with an unmodified carbonyl group which means it has to be a ketone or aldehyde.
Sodium carbonate is always the test for a carboxylic acid group though. It fizzes lots as carbon dioxide is formed because it acts as an acid.
1
swahmad
Badges: 14
Rep:
?
#1197
Report 6 years ago
#1197
(Original post by Gnome :))
It only works for aldehydes and ketones. Can't remember the reason- sorry! Not sure we need to know why though, but it's definitely only for aldehydes and ketones
The lone pair of electrons from the 2 oxygen atoms are delocalised, so the electrons are shared between the OOH bit and so it doesn't really count as a C=O group.
1
kd964
Badges: 0
Rep:
?
#1198
Report 6 years ago
#1198
(Original post by swahmad)
The lone pair of electrons from the 2 oxygen atoms are delocalised, so the electrons are shared between the OOH bit and so it doesn't really count as a C=O group.
Ahh I see... thanks for the help
0
Gnome :)
Badges: 2
Rep:
?
#1199
Report 6 years ago
#1199
(Original post by swahmad)
The lone pair of electrons from the 2 oxygen atoms are delocalised, so the electrons are shared between the OOH bit and so it doesn't really count as a C=O group.
Ah that makes sense- thanks!

Posted from TSR Mobile
0
JoshL123
Badges: 2
Rep:
?
#1200
Report 6 years ago
#1200
(Original post by GeorgeL3)
Brady's reagent will only give a positive result with an unmodified carbonyl group which means it has to be a ketone or aldehyde.
Sodium carbonate is always the test for a carboxylic acid group though. It fizzes lots as carbon dioxide is formed because it acts as an acid.
Isn't sodium carbonate also a test for the OH group of alcohols, though unlike carboxylic acids, does not produce CO2? That what I can remember for practical sessions in chem
0
X
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • Cardiff Metropolitan University
    Undergraduate Open Day - Llandaff Campus Undergraduate
    Sat, 19 Oct '19
  • Coventry University
    Undergraduate Open Day Undergraduate
    Sat, 19 Oct '19
  • University of Birmingham
    Undergraduate Open Day Undergraduate
    Sat, 19 Oct '19

Why wouldn't you turn to teachers if you were being bullied?

They might tell my parents (11)
5.95%
They might tell the bully (19)
10.27%
I don't think they'd understand (32)
17.3%
It might lead to more bullying (70)
37.84%
There's nothing they could do (53)
28.65%

Watched Threads

View All