[lisabella3686]

Hiya everyone,

I'd like to thank everyone who has posted trying to help me!  I almost helped a fellow boarder, but I was thwarted by the speed and efficientcy of Xianxi (sorry if that's not your name, I only went by memory)

anyhooz,

I would like to know how to go about balancing the following redox eqauations:

CuS (s) + O2(g) -> Cu (s) + SO2(g)

thus:
CuS =?
O2= 0
Cu = 0
SO2 = +4/-2(2)

I am not sure of the charge of CuS, nor am I sure about the coefficients to use to balance the equation.


b)

Cl2 (g) + 2BR-(aq) -> Br2(l) +2Cl-(aq)

thus:
CL2 =0
Br= -1
Br2= 0
Cl-=-1

does this mean that equation is already balanced because the charge on both sides of the equation is equal to -1?

[Borek]

I think copper can only ever have one oxidation state (other than 0 of course).

Stop thinking, start learning

[lisabella3686]

I thought that copper could be +2, +3 or 0..is that right?

so then
CuS would be S= 2-, Cu= 2+...

CuS (s) + O2(g) -> Cu (s) + SO2(g)

thus:
CuS =2+, 2-
O2= 0
Cu = 0
SO2 = +4/-2(2)

that woule mean that sulphur is oxidized
so it would be
2CuS + 2O2 -> 2Cu + 2SO2?

[Borek]

I thought that copper could be +2, +3 or 0..is that right?

0, +1, +2, +3 (rare)

unbalanced

CuS (s) + O2(g) -> Cu (s) + SO2(g)

vs balanced

2CuS + 2O2 -> 2Cu + 2SO2?

Compare both equations

[lisabella3686]

the coefficients are all 2, therefore, the ratios are all 1:1. Thus, it was already balanced?

[Donaldson Tan]

redox reaction involve transfer of electrons.

in balancing redox reaction, we not only seek a mass balance, but also electron balance. this reaction involves the oxidation of sulphur and the reduction of copper.

1. Cu²⁺ (s) + 2e => Cu (s)

2. S^2- (s) + O₂ => SO₂ (g) + 2e

combing equations (1) and (2), we arrive at the solution:
CuS + O₂ => Cu + SO₂

[lemonoman]

I just deleted my post where I was wrong about Copper's oxidation state.  And in the process, made Borek look like a fool for quoting some guy who doesn't exist.

It was a rough day yesterday.  It was everybody's fault but mine.

[xiankai]

oh and electrons have a charge of -1, make sure u put that in.