OCR B (Salters) F332 Tuesday 4th June 2013 Exam Discussion (Now Closed)

Yes. Have you done some titration practicals?

Think about it. If I have an original solution of 1000cm³, it won't be wise for me to use all of it for my titrations. So I'll have to scale the volume down, and we do this by diluting it to a lower value of around 20 to 30 cm³ in most cases. This will obviously change the number of moles, so after finishing this modified practical, I'll have to scale it back up to my original volume.

Practice the calculations, it'll help a lot

I just cant get my head around it
So in any question referring to titrations after i find out the number of moles of the solution its asking i then find out how many moles there would be in 100cm3? Is this the same for all titration molarity Q's? Sorry to be such a pain btw i know the calculations aren't hard i'm just having a hard time understanding why

It's not necessarily the shape of the molecule, even if you have a tetrahedral molecule, you still can have a polar molecule. For example, trichlorofluromethane is polar:


Because fluorine is more electronegative than chlorine, the charges will be unbalanced across the molecule and will not cancel out. Thus, it's important you know how electronegativity values can effect the overall charge of a shape.

If there's a symmetrical molecule, like tetrachloromethane, then that is non-polar. This is because all the negative charge can be cancelled down, as there is an equal electronegative difference between carbon and the chlorine atoms around the molecule.

In this exam, they'll mainly focus on more simple molecule shapes, such as tetrahedral, bent, triangle planers so it'll be obvious if the charges can get canceled down or not. Try some past paper questions, it has been asked quite a few times. Hope that helped!

Yeah it's on the specification:

(v) describe and explain the principal stages in the
purification of an organic liquid product:
(i) shaking with sodium hydrogencarbonate solution to
remove acidic impurities,
(ii) separating from other immiscible liquids using a
separating funnel,
(iii) drying with anhydrous sodium sulfate,
(iv) simple distillation to allow collection of the pure
product

to produce a aldehyde, do you do reflux then distil but for carboxylic acid, do you reflux, distil and reflux or just reflux? (obviously with acidified potasium dichromate)

Ahhh, right! That makes sense...thanks a lot! just one more question....so for argument's sake if the molecule was symmetrical which shapes would mean that the molecule is polar....bent....? Thank you so much!

okay so im stuck on a question... about atom economy.... so...
C2H4 + 0.5O2 ---> C2H40 (epoxyethane)
-In one reaction, 5.6kg of ethene produced 1.32kg of epoxyethane. Calculate the % yield for this reaction....help would be much appreciated I know the answer but just not the correct method to get to it

What's the answer? (Don't wanna give you the wrong solution)

What's the answer? (Don't wanna give you the wrong solution)

The molecule has E/Z isomers because of the carbon double bond on the right. It can't be the one on the left because there isn't 2 different groups on each carbon of the carbon double bond. You can swap the methyl groups because they are bonded to different carbon double bonds.
It may help to draw out the full structural formula to understand it better.


Posted from TSR Mobile

Thanks mate I think I get it now, but also does this mean stereoisomerism can be between functional groups as well as side chains?

Posted from TSR Mobile

Stereoisomerism can occur on any chain that has a double C to C bond and two different groups (not functional groups) on each carbon atom, regardless on how long or short the chain is.
The double bond can be anywhere on the chain.

Posted from TSR Mobile

Q3a)i) Jan 2010 - why is the answer not co polymerisation? I thought it would be because the polymer's made of two difference monomers, so why is it addition?

Co-polymerisation is a type of addition polymer, because only once product is produced.

I don't quite understand ppm calculations? Can somebody help me with that. Like maybe tell me a basic structure/formula I can use to work them out?