Chemistry: Post your doubts here!

[nehaoscar]

Copper is oxidized by concentrated nitric acid, HNO3, to produce Cu2+ ions; the nitric acid is reduced to nitrogen dioxide, a poisonous brown gas with an irritating odor. The question says brown gas is formed so here i win.

What I'm saying is why can't it be this equation too:
NO3- + 2H+ + Cu = NO2 + H2O + Cu+
Here NO2 is also formed...

So can't it be either or equations?
---> 2NO3- + 4H+ + Cu = 2NO2 + 2H2O + Cu2+
---> NO3- + 2H+ + Cu = NO2 + H2O + Cu+

why can't we use Cu+ instead of Cu2+ ?

I think I got it
We can't use Cu+ because the voltage would give 0.29 and for a reaction to take place it should be greater than 0.30V
so Cu2+ should be used I guess...

 

[holoholo]

in 2002 october november
An aqueous solution of iron(III) chloride is used to dissolve the excess of copper metal from printed-circuit boards
the mark scheme allowed both Cu2+ and Cu+ despite the voltage being less than 0.3 V ,when using Cu+ .

 

[holoholo]

the idea of a reaction occurring if it's more than 0.3 V is if is under non-standard conditions. However, this was not mentioned in the question for nitric acid and copper

 

[HumptyR]

in 2002 october november
An aqueous solution of iron(III) chloride is used to dissolve the excess of copper metal from printed-circuit boards
the mark scheme allowed both Cu2+ and Cu+ despite the voltage being less than 0.3 V ,when using Cu+ .

Is this A2 stuff lol ? :3 I'm an A's student

 

[nehaoscar]

in 2002 october november
An aqueous solution of iron(III) chloride is used to dissolve the excess of copper metal from printed-circuit boards
the mark scheme allowed both Cu2+ and Cu+ despite the voltage being less than 0.3 V ,when using Cu+ .

Hmmm... Winter 13 they haven't allowed Cu+

 

[nehaoscar]

the idea of a reaction occurring if it's more than 0.3 V is if is under non-standard conditions. However, this was not mentioned in the question for nitric acid and copper

This is the examiner report... they don't mention why Cu+ is technically incorrect though...

 

[nehaoscar]

Is this A2 stuff lol ? :3 I'm an A's student

Yeah this is A2

 

[nehaoscar]

How to do question 2.a.ii
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s13_qp_41.pdf
Summer 13 P41
Is there any formula which says how to do it??
The ms is confusing and I can't see anything in text book :/
Metanoia
Someone please help!

 

[HumptyR]

Yeah this is A2

Well sorry to piss you off then

 

[holoholo]

how do you solve this ?

 

[The Sarcastic Retard]

c

 

[krishnapatelzz]

Hpo
How to find the value of atomisation of chlorine??

 

[nehaoscar]

how do you solve this ?
View attachment 58622

It's no longer part of the syllabus so you don't need to know this.
DNA fingerprinting is removed from the syllabus

 

[Metanoia]

How to do question 2.a.ii
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s13_qp_41.pdf
Summer 13 P41
Is there any formula which says how to do it??
The ms is confusing and I can't see anything in text book :/
Metanoia
Someone please help!

To show that the reaction is first order with respect to the reactant in the y-axis. Draw lines to figure out the half-lives (duration for a concentration to drop to half its value).

The convenient ones I've chosen for this question is the time taken to drop from 0.2 M to o.1M, and time taken to drop from 0.1 M to 0.05 M.

For 1st order, the durations should be the same.

 

[Metanoia]

HpoView attachment 58624
How to find the value of atomisation of chlorine??

Look for the Bond energy data in the data booklet

Cl2 (g) --> 2Cl (g)

Divide that value by 2 to get the atomization of chlorine

1/2Cl(g) --> Cl (g)

 

[Metanoia]

View attachment 58623
c

CaMg(CO3)2 (s) --> CaO (s) + MgO (s) + 2CO2 (g)

Original Mr of CaMg(CO3)2 = 184

Mr "lost" = 2 x Mr of CO2 = 88

% lost in mass = (88/184) x 100%

 

[nehaoscar]

To show that the reaction is first order with respect to the reactant in the y-axis. Draw lines to figure out the half-lives (duration for a concentration to drop to half its value).

The convenient ones I've chosen for this question is the time taken to drop from 0.2 M to o.1M, and time taken to drop from 0.1 M to 0.05 M.

For 1st order, the durationsView attachment 58655 should be the same.

Thanks!
And what about the next part? - part 2.a.iii
How to find the order wrt HCl?

 

[Metanoia]

Thanks!
And what about the next part? - part 2.a.iii
How to find the order wrt HCl?

You will need both graphs for this.

Draw the tangents to both graphs at time = 0

For example..

If the gradient of tangent at double the concentration is TWICE the gradient of the other tangent; then its first order wrt to HCl.

 

[nehaoscar]

You will need both graphs for this.

Draw the tangents to both graphs at time = 0

For example..

If the gradient of tangent at double the concentration is TWICE the gradient of the other tangent; then its first order wrt to HCl.

Ok thanks!
can you give the formula for all orders using this method?
Like if it's twice then it's first order
then when is it zero and second order?

 

[My Name]

Hey guys,
Am an AS student! I am done with the inorganic part of the book (ch1-ch13), so today I will start with the organic part, everyone is freaking about organic chemistry, so can you advice me on how to study this part of the book, inorder to be able to score a high A in my AS?

Thanks in advance

I am sorry if I made you feel OC is tough. XD You'll do great.In sha Allah.
One thing is just even though it may feel hard just keep going.You'll get the hang of it eventually.
Be sure to keep revising the mechanism,conditions and reagents.Keep reading them over and over again.
Solve past paper with patience.