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# Ocr f321 23 may 2013~official discussion thread Watch

1. (Original post by Saif95)
What you you do is you split them up into ions

so you have Na+ and ClO- (Chlorate is ClO)

VII means 7, so this means the oxidation number of chlorine is 7, and the overall charge on ClO is -1.

The oxidation number of oxygen is -2.

Now you have to get the right amount of oxygens.

Lets take 4 oxygens, that will give you -2+-2+-2+-2 which is -8

And 7-8 = -1

That means the formula is NaClO4

Edit: Ahh I was beaten ..lol
Hope you understood and hope I helped
Thanks that really did help, was really clear. +rep
2. (Original post by ii-mohsin-ii)
explain why fluorine has low boiling point?

why does NF3 have a permanent dipole?
Flourine: has a low boiling point because it has a simple molecular structure with weak van der waal forces between molecules.

2nd question:
1) Charge difference across bond

2) Resulting from difference in electronegativities

3) Fluorine is more electronegative

4) has a greater attraction for the bonded pair of electrons/ bonded pair of electron are closer to fluorine
3. (Original post by MathsNerd1)
Sure thing. Define what an isotope is and why some people decide not to add KI to their table salt.

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An isotope is an atom of an element with the same number of protons but different. Number of neutrons

KI is toxic and may lead to health problems
4. (Original post by trrr)
.

2nd question:
1) Charge difference across bond

2) Resulting from difference in electronegativities

3) Fluorine is more electronegative

4) has a greater attraction for the bonded pair of electrons/ bonded pair of electron are closer to fluorine
and it's asymmetrical, they quite often put that in the mark schemes because if it was symmetrical the dipoles would cancel
5. (Original post by jo7777)
Ahhh yes I get it, thanks.

Also, I hate the questions where it states two elements such as Magnesium and chlorine, and then says that magnesium's melting point is higher...
Then it asks you to explain why.
I understand that magnesium has metallic bonding, and chlorine has covalent bonding... but how do I know whether or not it has giant covalent or simple covalent.

And why does the mark scheme say that only the Cl has van der waals? I thought all molecules had van der waals...

Bit confused

Okay, if you have molecules in the group 4 for example they will form giant covalent structures. This is because you can't have a quadruple bond (I dont think you can atleast) therefore the molecule has to get a full shell in another way. So it cannot do it by simple molecules e.g. C2 or C4. So it forms a giant covalent structure. I hope that helps if not I can try explain it better. Where as elements in group 6 or 7 can get their full shell by a covalent or double covalent bond.

Since Magnesium is metallically bonded it means it has delocalised electrons floating around. Van der Waal's forces arise from an uneven distribution of electrons in a molecule. Since the electrons are delocalised, van der Waal's forces can't occur.

Edit: van der Waa's forces do occur in all MOLECULES. But not in giant structures.
6. (Original post by reneetaylor)
Amount of substance is the measure of the amount of entities in a expressed in moles.

A mole is a amount of a substance which contains as many atoms as in 1/12th of carbon 12.

Avogadro's constant is 6.0225 x 10^23
Your mole definition is wrong it's the amount of molecules/atoms in exactly 12g of carbon-12 thus ~ 6.02x10^23 molecules/atoms and 6.02x10^23 is enough significant figures for avogadros constant theres no need for 5sf LOL

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7. (Original post by ii-mohsin-ii)
explain why fluorine has low boiling point?

why does NF3 have a permanent dipole?
Because fluorine has less number of electrons and hence, less van der waals forces so less energy needed to break intermolecular forces

This is because nh3 is asymmetrical
8. (Original post by yodawg321)
Bioling Point Trends group 3??
Yh for example the metallic elements eg Na to Mg you say that Mg is higher because it has more electrons, higher charge , more vanderwaals forces so stronger v walls forces that need lot of energy to be broken
9. Do not understand these reactions with Cl and Hydroxides, why are there so many possibilities?!
And why does the concentration and temperature of the hydroxide change anything?
10. (Original post by Freddy-Francis)
Symmetrical - Dipoles cancel out each other. The molecules are Non-Polar.
asymmetrical - Dipoles dont cancel out but adds together to make a molecule with a larger dipole moment.
No it's
Symmetrical: non polar so dipoles don't cancel out
Asymmetrical : polar so dipoles cancel out

11. (Original post by hassanakhtaruk)
No it's
Symmetrical: non polar so dipoles don't cancel out
Asymmetrical : polar so dipoles cancel out

Nah sorry mate that's wrong. If the molecule is polar, and you just said the dipoles cancel out, how is the molecule polar?
12. (Original post by Freddy-Francis)
oh ok. thanks.
Cruel people
Ha ha you can find it on the back of the yellow data sheet inserted in the booklet
13. I'm just going to wing this exam lol!
14. (Original post by theCreator)
Okay, if you have molecules in the group 4 for example they will form giant covalent structures. This is because you can't have a quadruple bond (I dont think you can atleast) therefore the molecule has to get a full shell in another way. So it cannot do it by simple molecules e.g. C2 or C4. So it forms a giant covalent structure. I hope that helps if not I can try explain it better. Where as elements in group 6 or 7 can get their full shell by a covalent or double covalent bond.

Since Magnesium is metallically bonded it means it has delocalised electrons floating around. Van der Waal's forces arise from an uneven distribution of electrons in a molecule. Since the electrons are delocalised, van der Waal's forces can't occur.

Edit: van der Waa's forces do occur in all MOLECULES. But not in giant structures.
Ahhh thanks that explains so much! Life saver
15. (Original post by theCreator)
Fluorine exists as a simple molecule. So there are only weak van der waal's forces between molecules which are weak and require a small amount of energy to break.

NF3 has permanent dipoles because Fluorine is more electronegative than Nitrogen. So it attracts the shared pair of electrons more creating a permanent dipole. The overall molecule is polar therefore since NF3 has an unsymmetrical shape and the dipoles would not cancel each other out.
cheers
16. Any predictions for tomorrow? Hoping to improve from a C to an A so I can give myself some slack for F322
17. (Original post by jo7777)
Ahhh thanks that explains so much! Life saver
I think we are mainly tested on the first 20 elements. And I just found this, hope it helps:

Giant Metallic Structures: Li, Be, Na, Mg, Al, K and Ca

Giant Covalent Structures: B, C and Si

Covalent Simple Molecules: N, O, F, P, S, Cl, etc.
18. (Original post by Char_lotteee)
Any predictions for tomorrow? Hoping to improve from a C to an A so I can give myself some slack for F322
Definitely think it will be a harder exam than usual. Don't know if you've taken any of these or heard, but all the maths, further maths, biology and physics exams so far have been considerably harder than previous years. We'll see tomorow morning though
19. Just a quick question plz!
What is a Precipitation reaction and how do you tell if it is one?
Good luck everyone
20. (Original post by avoxgirl)
yeah you do, a Cl2 turns the organic solvent layer light green, Br2 turns it orange and I2 turns it purple
So if you had I2 to 2Br- it won't react but with cyclohexane the organic solvent will be purple because of the I2 ??

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