AS Chemistry OCR A- evaluative task

  • 1 vote

i'm taking my evaluative task for the third time, i got 7 and 8 out of 15 in the first two, so reaally need to do well in this because it's my last go! the practical is about carboxylic acids but that is all i know, has anyone done it or does anyone know more detail?

Posted Mon 30th April, 2012 @ 14:09 by anna

11 Answers

  • 19 votes

I got overall 36/40 and my highest mark in evaluative is 12 so I did this last week to boost my mark up. I can give you some hints on what came :)
1) You need to know about the absorption peaks for the ifrared absorption for carboxylic acid.
2) functional group and structural isomers of carboxylic group 
3) the fact that infrared spectrum an only help identify the functional group in a compound
4) remember calculations for moles: n=cv and n=m/Mr
5) need to know how to change from mol/dm^3 to g/dm^3
6) If the student added more water than they were meant to the number of moles would be affected due to making the solution more dilute therefore decreasing the number of moles in the solution
7) Rinsing the flask to keep all the residue does not affect the number of moles in the solution as overall amount of water would still be the same even though the flask has been rinsed
8) Can increase accuracy by rinsing the flask and stirring the solution to ensure everything is dissolved
9) need to know how to calculate percentage error: (degree of accuracy results were measured)/(amount measured) x 100
eg: if given a value 27.6 g +-0.01 then percentage error is 0.01/27.6 x100
also, you must double the value for the percentage error, as you have measured twice - this is true for titres and for temperature change
10)need to write an equation between a metal hydroxide and carboxylic acid
eg: Ch3OOH + Mg(OH)2 -> (CH3COO)2Mg + H2O
you might have to write equation between carboxylic acid and sodium instead of with magnesium ;) then there would be no 2 on the OH (LHS) or on the CH3Coo (RHS) as this is only a +! metal ion, instead of +2 
11) need to consider moel ratios. eg: if carboxylic acid is replaced by dicarboxylic acid. this means there would be 2 moles of carboxylic acid on the LHS of equation.
12) Know all about reaction of alkenes with bromine water. know also colour change
13) Need to know about reactions of primary and secondary alcohols with dichromate ions. know also colour change
14) Need to know all about E/Z isomers
Hope this helps! =)

Answered Mon 30th April, 2012 @ 14:48 by Skylight
  • 2 votes

This is really good info, thanx a bunch, BTW well done on those grades 

Answered Mon 30th April, 2012 @ 22:14 by AJSarah
  • 2 votes

Thank you so much for putting this on here you have helped so much

Answered Mon 11th March, 2013 @ 13:46 by Catherine
  • 1 vote

for mol dm 3 you do m/mR

for gdm3 you do m X MR

Answered Tue 1st May, 2012 @ 16:51 by Doctor
  • 1 vote

Has anyone done the A2 and AS OCR chemistry practicals this year?

Answered Sat 4th May, 2013 @ 12:33 by Pri 0103
  • 0 votes

hi there i have mine tmrw, and well done on your score thats a very strong grade A

i need to know what exactly comes up , i really need to do well at this please could you help me

Thank you so much

Answered Mon 30th April, 2012 @ 16:51 by Doctor
  • 0 votes

how do you change from mol/dm^3 to g/dm^3 ?

Answered Tue 1st May, 2012 @ 11:05 by anna
  • 0 votes

Catherine, that was last year's ISA?

Answered Mon 11th March, 2013 @ 18:52 by B
  • 0 votes

do you know whats coming up this year?

Answered Tue 30th April, 2013 @ 16:13 by natty
  • -1 votes

sarah i have this task tmrw, just wondering if you have it so we can both revuse together

Answered Mon 30th April, 2012 @ 22:17 by Doctor
  • -1 votes

Thank you!

Answered Sun 13th May, 2012 @ 22:25 by Pri 0103