Chemistry: Post your doubts here!

[smartangel]

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
Q34..after 20 mins rxn is complete..mass of mg used is same so how can sukfuric acid produce more gas? statement 3 is correct according to ms..how?

 

[samwickz]

http://www.xtremepapers.com/CIE/International A And AS Level/9701 - Chemistry/9701_s07_qp_1.pdf
Q no 1 that mass spectro thingy any 1 who could help me pretty plz

 

[smartangel]

Use of the Data Booklet is relevant for this question.
In an organic synthesis, a 62% yield of product is achieved.
Which of these conversions are consistent with this information?
1 74.00g of butan-2-ol → 44.64g of butanone
2 74.00g of butan-1-ol → 54.56g of butanoic acid
3 74.00g of 2-methylpropan-1-ol → 54.56g of 2-methylpropanoic acid
plz do working for this one..all 3 statements are correct!

 

[Casablanca]

The standard enthalpy changes of formation of iron(II) oxide, FeO(s), and aluminium oxide,
Al2O3(s), are –266kJmol–1 and –1676kJmol–1 respectively.
What is the enthalpy change under standard conditions for the following reaction?
3FeO(s) + 2Al(s)
3Fe(s) + Al 2O3(s)
A +878kJ B –878kJ C –1942kJ D –2474kJ

i get the opposite charges alwayss..... how do i get it right?

I got B. Is that the correct answer?

 

[angelicsuccubus]

Hey guys... Is there anyone willing to come online and do a past paper with me? I haven't done any chem all year long and I can't seem to answer shit! Freaking out here >.<

 

[Casablanca]

Hey guys... Is there anyone willing to come online and do a past paper with me? I haven't done any chem all year long and I can't seem to answer shit! Freaking out here >.<

There's two guys already doing that. The thread all the way at the bottom of the page.

 

[lavanyamane]

What is a dimer?

2 molecules of the same compound. Eg: Al3Cl6 is a dimer of AlCl3

 

[umarashraf]

2 molecules of the same compound. Eg: Al3Cl6 is a dimer of AlCl3

you really confirm...???

 

[lavanyamane]

you really confirm...???

Yes

 

[00tanveer]

Can anyone please solve O/N 09 no.21???? Would be very grateful...

 

[umarashraf]

Yes

waoo.. i knew from ages that al2cl6 is a dimer.. but never knew why...

 

[saudha]

I got B. Is that the correct answer?

yah but hw did u do it?

 

[samwickz]

Use of the Data Booklet is relevant to this question.
Oxides of nitrogen are pollutant gases which are emitted from car exhausts.
In urban traffic, when a car travels one kilometre, it releases 0.23 g of an oxide of nitrogen NxOy, which occupies 120cm3.
What are the values of x and y?
(Assume 1 mol of gas molecules occupies 24.0dm3.)

A x = 1, y = 1
B x = 1, y = 2
C x = 2, y = 1
D x = 2, y = 4

so is it correct if i do the sum lyk this

n=(120*10^-3)/24
=5*10^-3

(5*10^-3)=0.23/mr
mr=46

(14*1)+(16*2)=46

am i ryt or is there a diff way 2 get it done?

 

[Osake]

Can someone help me do Question 24 on the winter 2005 paper 1 question? , What the easiest way to approach this question? I got how to do it , but similar questions always come , Whats the deal with teritiary alcohols , can they only form 2 different alkenes or what?

 

[umarashraf]

The standard enthalpy changes of formation of iron(II) oxide, FeO(s), and aluminium oxide,
Al2O3(s), are –266kJmol–1 and –1676kJmol–1 respectively.
What is the enthalpy change under standard conditions for the following reaction?
3FeO(s) + 2Al(s)
3Fe(s) + Al 2O3(s)
A +878kJ B –878kJ C –1942kJ D –2474kJ

i get the opposite charges alwayss..... how do i get it right?

you still have this problem or its solved now...???

 

[Casablanca]

yah but hw did u do it?

3FeO + 2Al -> 3Fe + Al2O3

Enthalpy change of formation of FeO: -266
Enthalpy change of formation of Al2O3: -1676

-Since FeO is breaking, not forming, you flip the sign. So it becomes +266. And since it's 3 molecules of FeO, you multiply it by 3, so it's +798.
-Al2O3 is forming, so it is -1676.

-1676 + 798 = -878

Therefore, the answer is B.

 

[KurayamiKimmi]

Q2) First of all, we know CS2 is the limiting reactant
So 10 cm3 CS2 needs 30 cm3 O2 (See molar ratio)
That means 50 - 30 = 20 cm3 O2 is left after the reaction
Further,
10 cm3 CO2 and 20 cm3 SO2 are produced (See molar ratio)
So total volume of gases left after burning = 20 cm3 O2 + 10 cm3 CO2 + 20 cm3 SO2 = 50 cm3

The answer must be either C or D

Adding NaOH will neutralise (or remove) acidic gases
It will remove 10 cm3 CO2 and 20 cm3 SO2 = 30 cm3 acidic gases
Gas left after NaOH is added = 50 - 30 = 20 cm3

So, C is correct!

Q4) you have add the atomic number of hydrogen carbonate (HCO3-)
H= 1, C=6, O=8
So number of electron of anion = 1+6+(8*3)+1 = 32
The extra 1 is because the anion has a one extra electron that's the reason it has an overall charge of -1 so you have to add that too.
Option C is correct

Q14)View attachment 8889

Thank you so much! ^_^

 

[lavanyamane]

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_s10_qp_11.pdf
Q.5, Q.11 please?

 

[KurayamiKimmi]

What is a dimer?

from wikipedia

A dimer is a chemical entity consisting of two structurally similar monomers joined by bonds that can be either strong or weak, covalent or intermolecular.

lemme expain:
example of a dimer is Al2Cl6
its a dimer of AlCl3
so you can think of a dimer as two same molecules bonded to each other for ex AlCl3+AlCl3=al2cl6

 

[KurayamiKimmi]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_ms_1.pdf

does anyone know how to get answers to q no 3O and 38??
any help will be GREATLY appreciated ^_^