Chemistry: Post your doubts here!

[strangerss]

how does NF3 have 6 bonding pair ?

Bonding pair or you mean bonding electrons?

 

[Aries_95]

ANYONE PLS
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_11.pdf
Q4, Q17,Q23
thanks in advance plz answer

Q.4:
N2+O2--->2NO
180+(-994)+(-494)= 2X
X=655 hence A.

 

[HubbaBubba]

I have a couple of questions I don't really understand, could anybody help?

 

[darkxangel]

Two moles of compound P were placed in a vessel. The compound P was partly decomposed by heating. A dynamic equilibrium between chemicals P, Q and R was established.
At equilibrium, x mol of R were present and the total number of moles present was (2 + x).
What is the equation for this equilibrium?
A P 2Q + R
B 2P 2Q + R
C 2P Q + R
D 2P Q + 2R
I need help in this question as well !

 

[h4rriet]

in that case 8 moles of N2 will react with 24 moles of H2 and 16 moles of NH3 are produced....
so mass of NH3 wud be 16* Mr of NH3 ie 272 :/ please help me out

I'm trying to work it out but I'm not getting any of the options! Wait a bit, I'll post up the answer in a while, after I figure it out.

 

[strangerss]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_11.pdf can some one explain Q11 please??

 

[h4rriet]

Two moles of compound P were placed in a vessel. The compound P was partly decomposed by heating. A dynamic equilibrium between chemicals P, Q and R was established.
At equilibrium, x mol of R were present and the total number of moles present was (2 + x).
What is the equation for this equilibrium?
A P 2Q + R
B 2P 2Q + R
C 2P Q + R
D 2P Q + 2R
I need help in this question as well !

You'll have to draw an ICE chart for the equations in A, B, C and D. Here's the one for B:

 

[strangerss]

hwo come an ideal gas's volume is not inversely proportional to it's pressure??

 

[cute97]

Q.4:
N2+O2--->2NO
180+(-994)+(-494)= 2X
X=655 hence A.

Thank you can u do the other two plz

 

[h4rriet]

I have a couple of questions I don't really understand, could anybody help?

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That's not a couple!
Anyway, for the first: you're taking the Kc for the reverse reaction, so you'll take the reciprocal of the forward reaction. Then, look at reaction II, and you'll see that all the moles have been divided by 2. Therefore you take the square root of the reciprocal of the Kc.
The second: AlCl3 is entirely covalent. MgCl2 is very slightly acidic in solution, so it is covalent to a limited degree.
The 3rd: Ammonium compounds give off ammonia when reacted with a base. You have to recognise D to be ammonium nitrate: NH4NO3. They've just jumbled the atoms in the compound.
The 4th: Perhaps it'll help if you point out which option (1/2/3) you're having trouble with.
5th: Don't look at the 2D shape. Count the bond pairs and lone pairs and write down the angles.

 

[h4rriet]

hwo come an ideal gas's volume is not inversely proportional to it's pressure??

It is.

 

[Dr.MMM]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s12_qp_12.pdf Q28?

 

[Jiyad Ahsan]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
Q4 h4rriet

96 kg hydrogen is left means (120 - 96) = 24 kg was used up

The equation:
3H2 + N2 --> 2NH3

(3 x 2) = 6 kg hydrogen produces (2 x 17) = 34 kg ammonia

1 kg hydrogen would produce (34/6) kg ammonia
24 kg hydrogen would produce
= (34 / 6) x 24
= 136 kg ammonia

That is why answer is C

 

[h4rriet]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_11.pdf can some one explain Q11 please??

For 11, n has to be the number of bonds in the compound. For example, the bond energy of a C-H bond is found by divided the enthalpy of formation of CH4 by 4, because there are 4 C-H bonds in CH4.

 

[HubbaBubba]

That's not a couple!
Anyway, for the first: you're taking the Kc for the reverse reaction, so you'll take the reciprocal of the forward reaction. Then, look at reaction II, and you'll see that all the moles have been divided by 2. Therefore you take the square root of the reciprocal of the Kc.
The second: AlCl3 is entirely covalent. MgCl2 is very slightly acidic in solution, so it is covalent to a limited degree.
The 3rd: Ammonium compounds give off ammonia when reacted with a base. You have to recognise D to be ammonium nitrate: NH4NO3. They've just jumbled the atoms in the compound.
The 4th: Perhaps it'll help if you point out which option (1/2/3) you're having trouble with.
5th: Don't look at the 2D shape. Count the bond pairs and lone pairs and write down the angles.

Thanks for answering all those questions! My main problem in the fourth question is that I don't understand how it can produce two alkenes? I understood the third option though.

 

[Saad (سعد)]

وعليكم السلام
7 and 11:
Draw ICE charts, i.e. initial moles, change in moles and equilibrium moles, for ALL the options (A, B, C and D). Then see which one has x + 2/x for its final moles.
For example, 7 D:

We divide the equilibrium moles by 2 because the question says that the final moles of R are x, so we need to make the final moles of R = x.

Jazak Allah Khayr!

 

[Saad (سعد)]

Question 14, please.

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w11_qp_13.pdf

 

[h4rriet]

Thanks for answering all those questions! My main problem in the fourth question is that I don't understand how it can produce two alkenes? I understood the third option though.

When an alcohol is dehydrated, the -OH is eliminated and an H atom from a neighbouring C atom.

 

[HubbaBubba]

When an alcohol is dehydrated, the -OH is eliminated and an H atom from a neighbouring C atom.

Thank you, it makes much more sense now! If I could like your posts more than once, then I would

 

[h4rriet]

Question 14, please.

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_13.pdf

When you write the equation for the decomposition of a Group II metal nitrate, you see that the mole ratio of the metal nitrate to the metal oxide is 1:1. So n(nitrate)=n(oxide). You have the mass of the nitrate and you can find the mass of the oxide (mass of nitrate minus mass of gases). You can calculate the molecular mass of Group II metal nitrate and oxide knowing the general formulae: M(NO3)2 and MO. M can be x. Cross multiply.