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# OCR Chemistry F321 Exam. - [Next Tuesday[

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1. (Original post by Pride)
1) yeah, so Mg is oxidised, the equation for that. Then H2O is reduced, the equation for that. Doing the full equation helps.

2)correct.
3)say the same element is both ox and red, not the atom
4 and 5)sounds good.
thanks
So is it mg2+ + o2 to give mgo ?
2. (Original post by Pride)
think about it. an orbital, is a region within an atom that can contain 2 electrons in opposite spin. In aluminium, there are 6 orbitals because 1s2, 2s2, 3s2, are all complete orbitals, and 2p6 is actually 3 orbitals, in one 'sub-shell'. similar question came up in jan 2012
cheers mate so every s2 shell is a full orbital? as theres 3 s'2s theres 6 orbitals? :3
3. (Original post by Pride)
It won't come up...
thanks pride like in Jan 2012 there was this N2H2 can we apply our knowledge to work out the angles and bonding pairs and lone pairs?
4. (Original post by otrivine)
thanks
So is it mg2+ + o2 to give mgo ?
No...

the full equation is
Mg + 2H2O --> Mg(OH)2 +H2

the ionic equations are:
Mg ---> Mg2+ + 2e-
2H2O ---> 2(OH)- +H2
5. (Original post by otrivine)
thanks pride like in Jan 2012 there was this N2H2 can we apply our knowledge to work out the angles and bonding pairs and lone pairs?
yes, I remember that one, hydrazine.

It was easy if you drew it out. Like NH3, around each N atom, was another bonded N, and 2 bonded hydrogens, and a lone pair of electrons. So that's 4 regions of electron density, 109.5 - 2.5 = 107
6. (Original post by Pride)
No...

the full equation is
Mg + 2H2O --> Mg(OH)2 +H2

the ionic equations are:
Mg ---> Mg2+ + 2e-
2H2O ---> 2(OH)- +H2
but they will tell you which one is in aqueous solution right?
7. (Original post by Pride)
yes, I remember that one, hydrazine.

It was easy if you drew it out. Like NH3, around each N atom, was another bonded N, and 2 bonded hydrogens, and a lone pair of electrons. So that's 4 regions of electron density, 109.5 - 2.5 = 107
but NH3 has got 3 bonding pairs and 1 lone pair right but this one had 2 hydrogen with N
?
8. (Original post by Craming Revision)
cheers mate so every s2 shell is a full orbital? as theres 3 s'2s theres 6 orbitals? :3
each filled s sub shell is a full orbital.
each filled p sub shell is 3 full orbitals.

Remember also, sub shells fill one electron to each orbital in the sub shell first.

So next to aluminium, silicon Si (1s2 2s2 2p6 3s2 3p2) still actually only has 6 full orbitals! 3p6 sub shell fills each orbital one electron at a time, then goes back to the first p orbital in the sub shell.

I really hope that makes sense. Keep asking questions if it doesn't, this is good revision for me too.
9. (Original post by otrivine)
but NH3 has got 3 bonding pairs and 1 lone pair right but this one had 2 hydrogen with N
?
don't forget

The N atom is bonded to the N next to it, as well as the 2 Hydrogens. then the lone pairs are there, so 4
10. (Original post by otrivine)
but they will tell you which one is in aqueous solution right?
I don't understand the question
11. (Original post by Pride)
don't forget

The N atom is bonded to the N next to it, as well as the 2 Hydrogens. then the lone pairs are there, so 4
oh yes of course yes now i get it !!! that was hard actually to get in an exam especially when you are under pressure! in an exam room .

So then how can you find oxidation like if they give you Sodium chlorate (7) how can you make it into a formula?
12. (Original post by Pride)
each filled s sub shell is a full orbital.
each filled p sub shell is 3 full orbitals.

Remember also, sub shells fill one electron to each orbital in the sub shell first.

So next to aluminium, silicon Si (1s2 2s2 2p6 3s2 3p2) still actually only has 6 full orbitals! 3p6 sub shell fills each orbital one electron at a time, then goes back to the first p orbital in the sub shell.

I really hope that makes sense. Keep asking questions if it doesn't, this is good revision for me too.
o wow lmfao! amazing thanks lol i got it!! what did you get in jan? seems like your well prepared for tomorow!
13. (Original post by Pride)
I don't understand the question
like to write an equation ionic you need to know which one is aqueous correct like
Mg + HNO3
so HNO3 gives H+ and NO3- correct so the product formed would be Mg2+ cause the NO3- cancels out right?
14. (Original post by otrivine)
oh yes of course yes now i get it !!! that was hard actually to get in an exam especially when you are under pressure! in an exam room .

So then how can you find oxidation like if they give you Sodium chlorate (7) how can you make it into a formula?
good question!

in sodium chlorate, there is Na, Cl and O right?
O is always 2- unless bonded to F or not bonded to anything.
Na is always +1 or 0 if not bonded to anything as it loses one electron.

chlorate 7 means chlorine's oxidation number is 7 (remember chlorine can have different ox numbers)

So +7 + +1 = +8
How many O's would make the charge = 0?
-8.
You need 4 Os then.
So NaClO4
15. (Original post by Pride)
good question!

in sodium chlorate, there is Na, Cl and O right?
O is always 2- unless bonded to F or not bonded to anything.
Na is always +1 or 0 if not bonded to anything as it loses one electron.

chlorate 7 means chlorine's oxidation number is 7 (remember chlorine can have different ox numbers)

So +7 + +1 = +8
How many O's would make the charge = 0?
-8.
You need 4 Os then.
So NaClO4
i get it so you did -8/-2 which gives you 4 oxygens i got it but when oxygen is bonded to F or not bonded to everything is it -2 charge or is it F2O ?
16. (Original post by otrivine)
like to write an equation ionic you need to know which one is aqueous correct like
Mg + HNO3
so HNO3 gives H+ and NO3- correct so the product formed would be Mg2+ cause the NO3- cancels out right?
well you need to know which are important ions and what's just a spectator ion, or where the electrons are going.

Mg + 2HNO3 ---> Mg(NO3)2 + H2

ionic equations would be:
Mg + 2NO3- ---> Mg(NO3)2 +2e-
2H+ +2e- ---> H2
17. (Original post by Pride)
well you need to know which are important ions and what's just a spectator ion, or where the electrons are going.

Mg + 2HNO3 ---> Mg(NO3)2 + H2

ionic equations would be:
Mg + 2NO3- ---> Mg(NO3)2 +2e-
2H+ +2e- ---> H2
yes i got it
18. (Original post by otrivine)
i get it so you did -8/-2 which gives you 4 oxygens i got it but when oxygen is bonded to F or not bonded to everything is it -2 charge or is it F2O ?
in F2O, the oxidation state of O is actually +2. This is because F is the only atom with a higher electronegativity than O, the electrons are pulled closer to the F atom than the O.

but that explanation won't come up, just no that F is the only exception, and F is always -1 oxidation state.
19. (Original post by Pride)
in F2O, the oxidation state of O is actually +2. This is because F is the only atom with a higher electronegativity than O, the electrons are pulled closer to the F atom than the O.

but that explanation won't come up, just no that F is the only exception, and F is always -1 oxidation state.
thanks and if they gave us the formula but had to say it in word sodium chlorate 7 will we have to do the same working?
20. (Original post by otrivine)
thanks and if they gave us the formula but had to say it in word sodium chlorate 7 will we have to do the same working?
yep. It's normally not hard to work out.

What is NaClO3?

Spoiler:
Show
sodium chlorate (V) remember ox number always after the element it's describing, I lost a mark once for saying sodium (V) chlorate

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