POLL: How did you do in your EDEXCEL A2 Chemistry Practicals: Watch

Poll: How did you do in the practicals?
Very Good (A) (52)
60.47%
Good (B) (15)
17.44%
Average (C or D) (8)
9.3%
Bad (E) (2)
2.33%
Fail (F) (9)
10.47%
bhut
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#81
Report 12 years ago
#81
I totally flopped it , but i agree that the paper was reasonable, it was only me the dumbo going to fail! oh, well......i lost hope! anyone wants to go through the paper?
i got 77 for bp but not sure whether its correct.
Abbas, for the silver morror test- u dont have to heat it...like in my one i saw the result straight away even i didnot need to put it in warm water!
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bhut
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#82
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#82
oh yes, many thanks to the people (esp grp1) who gave the hints/suggestions for Grp 2 practical, it was real help .
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mambojambo
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#83
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#83
Question 1
You are given two inorganic compounds F and G, containing one cation and one anion each

(a)Dissolve F in water
Obs: Pink solid forms pink solution
Inf: Transition metal ions present

(b)Add NaOH to F until no further change
Obs: Blue ppte, turns pink on standing
Inf: Co2+ present

(c)Add BaCl2 followed by HCl to F
Obs: white ppte formed, insoluble in HCl
Inf: Ppte is BaSO4, SO4 present

(d)Identify compound F
F is CoSO4

(e)Add HNO3 + AgNO3 to G
Obs: Yellow ppte formed
Inf: Yellow ppte is AgI, I- present

(f)Add dilute HCl + H2O2, followed by starch to G
Obs: Brown solution formed. Black colouration upon adding starch
Inf: Brown solution is Iodine. I- oxidised to I2. I- confirmed present.

(g)Conduct flame test on G
Obs: Orange flame
Inf: Na+ present

(h)Identify compound G
G is NaI


Question 2
You are given two organic compounds H and J that contain only C, H & O.

(a)Add 2,4 DNPH to H
Obs: Yellow ppte formed
Inf: Carbonyl group present

(b)Add ammonical AgNO3 to H
Obs: Silver mirror
Inf: H is an aldehye

(c)The following diagram is the mass spectroscopy for H.
m/e: 58
Structure: CH3CH2COH+

(d)Add concentrated H2SO4 + ethanoic acid to J. Warm and then pour solution into NaCO3. Smell the product carefully.
Obs: Glue smell
Inf: An ester is formed, J is an alcohol

(e)Add dilute H2SO4 + K2Cr2O7 to J. Warm. State the type of reaction
Obs: Orange dichromate turns to green
Inf: J is a primary or secondary alcohol. Oxidation occured.

(f)Given that J has same number of carbons as H, draw two isomers of J
Isomer 1: Propanol
Isomer 2: Propan-2-ol

(i)Name reagents to distinguish between both isomers
NaOH and Iodine

(ii)Describe the observations for each isomer
Isomer 1: No change
Isomer 2: Yellow ppte formed

Question 3
Measure boiling point of organic compound

(a)Temperatures (to nearest degree)
Up: 80C Down:78C
BP is 79C

(b)State which ester is the compound
77C - ethyl ethanoate
79C - methyl propanoate
81C - propyl methanoate

Therefore ester is Methyl propanoate

(c)State the uncertainity in determining which ester is the compound
Boiling temperatures of the three esters given are too close

(d)State ONE reason why BP obtained is not accurate and one improvement to it
Water is poor heat conductor. So use heating block.

Question 4
Part A
You are given four unlabelled colourless aqueous solutions which are AgNO3, Pb(NO3)2, NH3. With only NaCl available to you and no other chemicals or test papers, describe a simple procedure to identify the three solutions.

1. Add NaCl to all three, the one that does not liberate ppte is NH3
2. Add NH3 to remaining two solutions.
3. AgNO3 forms brown ppte with NH3 (Ag2O)
4. Pb(NO3)2 forms white ppte with NH3 (Pb(OH)2)

Part B
You are given a solution containing a mixture of Pb(NO3)2 and AgNO3, using only NH3 and NaCl, describe a procedure to seperate the cations, in which Ag+ is the only cation in the solution. The Ag+ can be in the form of complex ions.

1. Add NH3 to the mixture
2. Brown ppte formed (Ag2O)
3. Add NH3 in excess. Ag2O dissolves to colourless solution.
4. Remaining white ppte is Pb(OH)2
5. Filter off the white ppte
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arxtra
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#84
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#84
i don't think you're supposed to average the rising and falling temperatures?
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Mustard-man
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#85
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#85
(Original post by myzt1kal)
i don't think you're supposed to average the rising and falling temperatures?
We do, it says so in one of the past mark schemes
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bhut
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#86
Report 12 years ago
#86
I knew most of the answers but something was wrong with me in the exam today…….i couldn’t answer them, I will probably get 6/7 out of the total…….
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RMIM
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#87
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#87
(Original post by kingalan)
you oxidise the alcohols with acidified potassium dichromate...then add 2,4-DNP..then do silver mirror test....this is a correct way.......but they only gave us one line....i thought it musta bin sumthin short...and i ran outta time to write it...
I had the same idea in the test.
But what has 2,4-DNP got to do with this.

We know we have a primary and secondary alcohol. We want to know which is which.

1. So we oxidise them with acidified potassium dichromate.
One will now become an Aldehyde, the other a Keytone
2. Ammoniacal silver nitrate

result
silver mirror = aldehyde, must have come from primary
no result= keytone, must have come from secondary.

DNP??

I think the iodo test is what they wanted us to write though.
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Mustard-man
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#88
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#88
(Original post by RMIM)
I had the same idea in the test.
But what has 2,4-DNP got to do with this.

We know we have a primary and secondary alcohol. We want to know which is which.

1. So we oxidise them with acidified potassium dichromate.
One will now become an Aldehyde, the other a Keytone
2. Ammoniacal silver nitrate

result
silver mirror = aldehyde, must have come from primary
no result= keytone, must have come from secondary.

DNP??

I think the iodo test is what they wanted us to write though.
but that would have to be distilled and we would have to know the bp of it, otherwise it would oxidise straight to a carboxylic acid. Which can still be tested with PCl5.

This question was weird - only one mark for the reagents?
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RMIM
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#89
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#89
(Original post by Mustard-man)
but that would have to be distilled and we would have to know the bp of it, otherwise it would oxidise straight to a carboxylic acid. Which can still be tested with PCl5.


This question was weird - only one mark for the reagents?
It's not something I got from brain but rather edexcels revision book.

'To distinguish between primary and secondary repeat the experiment (referring to warm with dil H2SO4 and potassium dicromate(VI)) but distil the product into ammonical silver nitrate solution'

But u r right about the word distil.
Anyway Im sure they were after the iodoform test. But hopefully I will still get some marks.
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ArVi
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#90
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#90
(Original post by RMIM)
It's not something I got from brain but rather edexcels revision book.

'To distinguish between primary and secondary repeat the experiment (referring to warm with dil H2SO4 and potassium dicromate(VI)) but distil the product into ammonical silver nitrate solution'

But u r right about the word distil.
Anyway Im sure they were after the iodoform test. But hopefully I will still get some marks.
The iodoform test is probably the easiest way to do it, but I can't see why your method won't get you the marks...
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"Hurricane"
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#91
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#91
Im glad the exam went smooth for group 2 people, I knew it would be the same as I said before. Im glad I was of help.
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"Hurricane"
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#92
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#92
60% A's till now. That's impressive!!!!
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Smashingdude
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#93
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#93
I am glad that gp2 ppl did well. Wish the same for gp3. And its also good to hear that most of the pattern was similar to gp1. Hope u had some help from our(gp1 ppl) posts.
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"Hurricane"
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#94
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#94
Mambojambo, thanks!! you are great for putting all this effort to help others!! I guess you voted an A, as I went through your answers, and I guess the're all correct. By the way, Im group 1. I hope this thread has helped everyone. Thanks everyone for voting and posting your comments.
Start working on those reps
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"Hurricane"
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#95
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#95
14% failed!!!!!:eek:
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mambojambo
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#96
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#96
(Original post by Aburumman)
Mambojambo, thanks!! you are great for putting all this effort to help others!! I guess you voted an A, as I went through your answers, and I guess the're all correct. By the way, Im group 1. I hope this thread has helped everyone. Thanks everyone for voting and posting your comments.
Start working on those reps
Haha, I spend my last 5 minutes of the paper copying down all the compounds and chemical tests into my book so I won't forget when I come back to this forum. I hope they help you guys in the discussion, at least the full thing is here if you wanna compare!
Thanks aburumman too.. you helped alot before my Group2 pract. Thanksss!!!!
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AamerX
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#97
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#97
for the boiling point determination, i jus made up the results and guessed the ester (the one with the bp of 79degrees celcius). I figured I'd get 3/4 marks for that question losing the mark for the accuracy. This also saved me about 10-15 minutes so I had enough time to do the plan and jus sit around and do nothing afterwards.
PsThx 2 everyone who contributed on the a2 practical planning hints.
Pps i think i did rly well in the practical
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mambojambo
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#98
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#98
Haha.. guessing the results. My friends did not even bother to guess the first few questions. For example, for the silver mirror test, all they did was skip that test and when the person sitting opposite them does the test and leaves the test tube in the rack, all they have to do was just take a peep if silver mirror was formed. There, saved 5 minutes from doing the test.
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"Hurricane"
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#99
Report Thread starter 12 years ago
#99
lol, that's really nice.
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Bakalizo
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#100
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#100
hey.. everyone in my school got ethyl ethanoate.. are you sure its methyl ethanoate? and in the test for the dichromate thing.. i didnt write down in the inference that it shows that the alcohol is pimary or secodary.. i just wrote that it confirms that it is an alcohol.. and oxidation tookplace.. will i lose a mark for this? :confused:
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