WJEC Chemistry Practical

How did everybody find that? I got butanoic acid for the acid we were given, positive dichromate test, positive iodoform test (I made this up as I assumed it was supposed to be positive), negative halide ion test.
When we had to suggest a structure I put CH3CH(OH)CH2COOH

(edited 5 years ago)

Reply 5

Original post by nathanwjec

How did everybody find that? I got butanoic acid for the acid we were given, positive dichromate test, positive iodoform test (I made this up as I assumed it was supposed to be positive), negative halide ion test.
When we had to suggest a structure I put CH3CH(OH)CH2COOH

Almost certain you’re right. I got negative iodoform three times but idk something just wasn’t right. Others said iodoform and got the same structure as you.
Only difference for mine was OH was on the end - since I had negative iodoform test

Reply 6

How many marks do you reckon I’d lose for getting the wrong result for iodoform, and hence a slightly wrong structure? (OH one to the left of where it should be). I’d hope not many personally aha

Reply 7

cowseatmilk

10

I got that the spectrum was correct for the last one. Anyone else?

Reply 8

cowseatmilk

10

Original post by jaisuf

How many marks do you reckon I’d lose for getting the wrong result for iodoform, and hence a slightly wrong structure? (OH one to the left of where it should be). I’d hope not many personally aha

I'd imagine 2. One for the incorrect observation and 1 for the incorrect structure

Reply 9

Original post by cowseatmilk

I'd imagine 2. One for the incorrect observation and 1 for the incorrect structure

Yeah, hopefully no more than that. Although I do wonder if it’s possible for my structure to lose no marks, since it’s accurate to my observation.
I’m not a fan of iodoform tests tbh, I did mine literally 3 times and it was completely clear every time. Also technicians realised one of the water baths was off for most of the exam, so my original iodoform would have been wrong anyway (still got clear afterwards tho)
Grim

Reply 10

cowseatmilk

10

Original post by jaisuf

Yeah, hopefully no more than that. Although I do wonder if it’s possible for my structure to lose no marks, since it’s accurate to my observation.
I’m not a fan of iodoform tests tbh, I did mine literally 3 times and it was completely clear every time. Also technicians realised one of the water baths was off for most of the exam, so my original iodoform would have been wrong anyway (still got clear afterwards tho)
Grim

Yeah. The practical can be horrible in that sense. It's just nice to get it out of the way

Reply 11

Original post by jaisuf

How many marks do you reckon I’d lose for getting the wrong result for iodoform, and hence a slightly wrong structure? (OH one to the left of where it should be). I’d hope not many personally aha

Honestly, with the massive divide in people who got positive and negative iodoform tests, I would imaime the mark scheme will cater to both results; i.e. You get the mark either way, as long as you explain what your result says about the structure

Reply 12

Akire

1

How many marks do you think I will lose if my results are not concordant to that of the teacher

Reply 13

Original post by Akire

How many marks do you think I will lose if my results are not concordant to that of the teacher

I can’t remember exactly how many marks the titration readings are worth. I’m pretty sure it’s 5 marks for each titration.
Generally this is how the marks are given, based on how close your value was to your teachers value:
Within 0.2cm3 - 5 marks
0.3cm3 - 4 marks
0.4cm3 - 3 marks
0.5cm3 - 2 marks
0.6cm3 - 1 mark
So, if you didn’t get within 0.6cm3 then you would get 0 for that titration

Reply 14

science234

1

Does anybody have last year's prac analysis paper which they can put on here?

Reply 15

Original post by nathanwjec

I can’t remember exactly how many marks the titration readings are worth. I’m pretty sure it’s 5 marks for each titration.
Generally this is how the marks are given, based on how close your value was to your teachers value:
Within 0.2cm3 - 5 marks
0.3cm3 - 4 marks
0.4cm3 - 3 marks
0.5cm3 - 2 marks
0.6cm3 - 1 mark
So, if you didn’t get within 0.6cm3 then you would get 0 for that titration

that close huh? that's a bit worrying actually, seeing as their value could have been anything... the Mr I ended up with was ~89, which makes me afraid that my tirations were too far off now, seeing as I didn't get 88 exactly

Reply 16

YellowCurryNinja

4

Original post by nathanwjec

How did everybody find that? I got butanoic acid for the acid we were given, positive dichromate test, positive iodoform test (I made this up as I assumed it was supposed to be positive), negative halide ion test.
When we had to suggest a structure I put CH3CH(OH)CH2COOH

I had Ethanoic Acid for the acid given because I messed up my calculation (did the method right, but inserted the volume of NaOH instead of Volume of acid, because I'm an idiot). My Mr was 59.01 as a result of that (rounded to 60 for Ethanoic Acid). I had the same as you for the suggested structure, but it was HEAVILY disputed between people that it was either CH3CH(OH)CH2COOH or CH3CH(OH)COOH (5 of the smartest people in our year who had straight A's last year, had the latter value, whereas a lot of others had the former).

I had the same as you for the tests, but the dichromate in our school messed up so it went from orange to blue lmao.

Reply 17

Original post by YellowCurryNinja

I had Ethanoic Acid for the acid given because I messed up my calculation (did the method right, but inserted the volume of NaOH instead of Volume of acid, because I'm an idiot). My Mr was 59.01 as a result of that (rounded to 60 for Ethanoic Acid). I had the same as you for the suggested structure, but it was HEAVILY disputed between people that it was either CH3CH(OH)CH2COOH or CH3CH(OH)COOH (5 of the smartest people in our year who had straight A's last year, had the latter value, whereas a lot of others had the former).

I had the same as you for the tests, but the dichromate in our school messed up so it went from orange to blue lmao.

Haha! Blue dichromate is fine, basically a greenish-blue colour is positive.

As for the structure: as long as your structure matches up with your data you will be fine!

Also if you looked at the nmr spectrum, it couldn’t have been the 3 carbon compound, it had 4 or 5 readings can’t remember; 4/5 hydrogen environments and in the stem it stated it was only PART of the spectrum

(edited 5 years ago)

Reply 18

Good luck to everyone for tomorrow!

Reply 19