Chemistry: Post your doubts here!

[omarjaved619]

1- BF3 =
Each F has 7 outer electrons
Each B has 3 outer electrons
So, B forms 3 bonds and hence has 6 electrons (incomplete octet!)

CH3-
Each C has 4 outer electrons
Each H has one outer electron
CH3 has an overall negative charge.

So, C forms 3 bonds and will have 6 electrons.
One electron is left but there is a negative charge so it is gaining an electron. [Well that's what my teacher told me back when I asked him!]

14- 4Al + Ba(NO3)2 -> 2(Al2O3) + Ba + N2

1 mol : 1 mol
0.783/(137+62(2)) = 0.003 mol

1 mol occupies 24dm3
0.003 mol will occupy 0.072dm3
Hence,B

I understood the first question. But I dont really get how you got 137 and 62 for the second question. I understand you took mass/molar mass. Which substance's moles are you tryna find?

 

[AbbbbY]

I understood the first question. But I dont really get how you got 137 and 62 for the second question. I understand you took mass/molar mass. Which substance's moles are you tryna find?

I need the mols of Ba(NO3)2 to deduce how many mols of N2 will be produced.

I didn't have a periodic table but I remember Ba and NO3 values having used them ample times so I simply plugged 137 and 62x2. You could also do 137+2(14+16+16+16) and it'd give you the same thing. (137+62+62 is the Mr of Ba(NO3)2)

Did you get it?

 

[omarjaved619]

I need the mols of Ba(NO3)2 to deduce how many mols of N2 will be produced.

I didn't have a periodic table but I remember Ba and NO3 values having used them ample times so I simply plugged 173 and 62x2. You could also do 173+2(14+16+16+16) and it'd give you the same thing. (137+62+62 is the Mr of Ba(NO3)2)

Did you get it?

I think you're mixing up 173 and 137 lol.
My Periodic Table shows that the Mr of Ba is 39.

 

[AbbbbY]

I think you're mixing up 173 and 137 lol.
My Periodic Table shows that the Mr of Ba is 39.

My bad. Typo.

What sort of period table do you have?
http://www.ptable.com/Images/periodic table.png

 

[omarjaved619]

I think you're mixing up 173 and 137 lol.
My Periodic Table shows that the Mr of Ba is 39.

Gawwwwd I was looking at something else. -__-
Haahaha I get it now. Thanks mate.
Mind if I ask you some more questions?

 

[AbbbbY]

Gawwwwd I was looking at something else. -__-
Haahaha I get it now. Thanks mate.
Mind if I ask you some more questions?

Inorganic and Physical, fire away!

 

[omarjaved619]

Inorganic and Physical, fire away!

s12_qp12
4, 6,

I've got a lot more but sadly all of them are from Inorganic Will have to ask my lousy teacher lol.

 

[AbbbbY]

s12_qp12
4, 6,

I've got a lot more but sadly all of them are from Inorganic Will have to ask my lousy teacher lol.

Oh jeez. Contradiction in 4. I'll text my teacher and ask what the method was.

6- P = nRT/V
=> ((0.96/32)(8.31)(30+273))/7000 * 10^-6
=10791.1 Pa
Hence, C

I do know inorganic.
Just haven't done organic.

 

[omarjaved619]

Oh jeez. Contradiction in 4. I'll text my teacher and ask what the method was.

6- P = nRT/V
=> ((0.96/32)(8.31)(30+273))/7000 * 10^-6
=10791.1 Pa
Hence, C

I do know inorganic.
Just haven't done organic.

Thanks man! Appreciate it.

 

[AbbbbY]

Thanks man! Appreciate it.

For the first question,

we know CH3- is complete

So, CH3+ has to be incomplete as it's losing 2 electrons. It didn't make sense when I first did it because I thought it was CH3- that was listed.

 

[omarjaved619]

For the first question,

we know CH3- is complete

So, CH3+ has to be incomplete as it's losing 2 electrons. It didn't make sense when I first did it because I thought it was CH3- that was listed.

2 electrons? What is actually losing the electrons, the C or the H?

 

[AbbbbY]

2 electrons? What is actually losing the electrons, the C or the H?

The lonepair on Carbon is lost (from CH3-)

 

[omarjaved619]

So, CH3+ has to be incomplete as it's losing 2 electrons

How do you know its losing 2 electrons?

 

[AbbbbY]

So, CH3+ has to be incomplete as it's losing 2 electrons

How do you know its losing 2 electrons?

Because it has a positive charge on top!

 

[omarjaved619]

Because it has a positive charge on top!

Doesnt "2+" mean losing two electrons? Isnt it just +? Wont it lose only 1 e? :S

 

[AbbbbY]

Doesnt "2+" mean losing two electrons? Isnt it just +?

[CH3]- has the complete octet
[CH3] has lost one electron/not gained one electron
[CH3]+ has lost one further electron

Thus, a total of two electrons.

 

[omarjaved619]

[CH3]- has the complete octet
[CH3] has lost one electron/not gained one electron
[CH3]+ has lost one further electron

Thus, a total of two electrons.

Ohhhh I get it nowww. Thanks a ton

 

[saadgujjar]

how GT is calculated for as level.in the GT it is wriiten that total marks for as level is 130 for chemistry but actually it is 140.plz explain

 

[shaista]

*Not allowed*

 

[hela]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s09_qp_1.pdf Q9 A Q20 C

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q7 D

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s10_qp_12.pdf Q9 D Q25 C

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_13.pdf Q22 B Q25 A