Chemistry: Post your doubts here!

[nehaoscar]

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

What does the ms say? Usually they allow both reactions ...

 

[nehaoscar]

Well, IDK :3 But i guess we can't use Cu+ simply because NO2 and H2O need e- :3

Even Cu+ has e-

 

[HumptyR]

Even Cu+ has e-
View attachment 58619

But according to the eq H2O and NO2 require two e-

 

[nehaoscar]

But according to the eq H2O and NO2 require two e-

Hmm yeah ... But can't you multiply the Cu+ eqn by 2 so to get 2e-?

 

[HumptyR]

Hmm yeah ... But can't you multiply the Cu+ eqn by 2 so to get 2e-?

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.

 

[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+

 

[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.