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

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Good Luck everyone :smile:

Relax remember to watch out for sig figs!
Even if you don't know how to solve a calculation just times and divide a little and get the sig figs for a method mark

Edit: C-Cl is stronger as the atom is smaller, this means electrons are closer to the nucleus, this is why the bond enthalpy for C-Br is lower :smile:

(edited 10 years ago)

Reply 601

issy5038

what would be an ideal 3/4 mark answer for solubility of polymers? i dont really know how to go into detail on it.. :confused:

Reply 602

YA BISH

Original post by TheNote

Edit:

It depends, bond enthalpies:
C-Cl is stronger due to a higher polarity caused by a higher elctronegativity which means the bonding electrons are attracted more strongly to the smaller halogens in C-Halogen bonds.
However when talking about boiling points the larger halogens are easier to boil since their intermolecular bonds are weaker due to less polarity in their bonds.

i understand the first bit but a little confused on the boiling point bit. theres a question on it in the jan 13 paper (question 2d) which has confused me.
thank you for the help btw

Reply 603

Hac

Original post by issy5038

what would be an ideal 3/4 mark answer for solubility of polymers? i dont really know how to go into detail on it.. :confused:

Hydrogen bonding causes solubility. It occurs because oxygen is small and electronegative making it partially negatively charged whereas hydrogen has a partial positive charge; this causes an attraction. -OH groups on the polymer can hydrogen bond to water molecules as the also have OH groups.

Reply 604

TheNote

Original post by issy5038

what would be an ideal 3/4 mark answer for solubility of polymers? i dont really know how to go into detail on it.. :confused:

I can't find many ways to ask you in detail about it, since it's mostly, does it have OH in it? Yes? Does it have lots or little OH in it:
lots: soluble
Little: not soluble

Also ester groups make a polymer soluble, due to the oxygen being able to hydrogen bond.

Reply 605

Hac

Original post by TheNote

Having lots of hydrogen bonds means the hydrogen bonds are too strong between the molecules and therefore cannot break and join with water molecules; it requires a balance for a polymer to be soluble.

Reply 606

TheNote

Original post by YA BISH

i understand the first bit but a little confused on the boiling point bit. theres a question on it in the jan 13 paper (question 2d) which has confused me.
thank you for the help btw

I don't know, either way, the larger the atom and the more of them their are, the larger the boiling point.

Reply 607

TheNote

Original post by Hac

Wouldn't it just slow down the rate at which it dissolves rather than reducing it's solubility? because can't water break covalent bonds in polar molecules?

Reply 608

Davelittle

C-Cl is stronger than C-Br because Cl is smaller and the bonding electrons can get closer to the nucleus. (It has nothing so to with polarity)

However Br2 has a higher boiling point than Cl2 because it is larger and has more electrons so stronger instantaneous dipole-induced dipole bonds which require more energy to break.

Regarding -OH groups and polymer solubility, one OH on the monomer is only slightly soluble but all OH groups means the polymer is more attracted to its other OH groups than the H2O so it is not soluble.

(edited 10 years ago)

Reply 609

Branny101

Original post by Davelittle

What about bond polarity?

Posted from TSR Mobile

Reply 610

TheNote

Original post by Branny101

What about bond polarity?

Posted from TSR Mobile

bond polarity is related to electronegativity, the more electronegative it is, the more polarity it has.

Reply 611

Davelittle

Original post by Branny101

What about bond polarity?

Posted from TSR Mobile

Bond polarity doesn't affect bond strength (there was a question in Jan 2013 on this)

Reply 612

JoshThomas

Original post by Davelittle

Bond polarity doesn't affect bond strength (there was a question in Jan 2013 on this)

So what effects bond strength, it all confuses me im sure polarity plays a part

Posted from TSR Mobile

Reply 613

lollage123

Afternoon exam right?

yes afternoon exam

Original post by JoshThomas

So what effects bond strength, it all confuses me im sure polarity plays a part

Posted from TSR Mobile

Bond reactivity in this term depends on how close the outer shell electron is to the nucleus; the outer shell electron in Bromine is further away than Chlorine, as it's a larger atom; thus there's less nuclear charge, thus less energy is required for Bromine to lose its electron and react.

Bond polarity plays a very small role in the case of halogenoalkanes. Bond reactivity explains why the rate of hydrolysis is faster for bromoalkanes than chloroalkanes, as simply the C-Br is weaker than the C-Cl bond, so it'll take less time to break the C-Br bond and hence react quicker.

There was a question on this in the June 2007 legacy paper, and recently in the Jan 2013 paper. Try doing them, it'll help :smile:

Posted from TSR Mobile

Reply 616

Whostolemycookie

How do we explain the difference in silicon dioxide and carbon dioxide in terms of boiling and melting points?

Also in the Jan 2010 paper is asks you to give the name and full structure of another alkene monomer that is reacted to but-2-ene to get co-polymer A
It says the answers is propene, but I don't understand why?

Also last question, What is the instantaneous-induced forces and van der waals? I understand some of it but not properly

(edited 10 years ago)

Reply 617

krisshP

Original post by Whostolemycookie

SiO2 has a giant lattice structure with covalent bonding. CO2, O=C=O, has a simple molecular structure with covalent bonding. Bonds in SiO2 are stronger than weak intermolecular bonds in CO2.

Reply 618

Whostolemycookie

Original post by krisshP

SiO2 has a giant lattice structure with covalent bonding. CO2, O=C=O, has a simple molecular structure with covalent bonding. Bonds in SiO2 are stronger than weak intermolecular bonds in CO2.