[mandy9008]

i know how to do them, it just takes me such a long time.
i have been practicing and practicing to try to increase my speed, but i have a quiz coming up and its timed and im afraid that i will run out of time taking it.
if anyone has any tips on how to increase my speed, with accuracy and confidence, they will be greatly appreciated!
thanks
+M

[cliverlong]

i know how to do them, it just takes me such a long time.
i have been practicing and practicing to try to increase my speed, but i have a quiz coming up and its timed and im afraid that i will run out of time taking it.
if anyone has any tips on how to increase my speed, with accuracy and confidence, they will be greatly appreciated!
thanks
+M

Give two examples of questions you attempted plus what you tried so we can see clearly where you are going wrong. We may only need to correct a small fault - rather than trying to impose a completely different, alien method on you.

Clive

[mandy9008]

FU: Zn(s) + AgNO₃(aq)  Zn(NO₃)₂(aq) + Ag(s)

total ionic:  Zn + Ag⁺ + NO₃^-  Zn²⁺ + 2NO₃^- + Ag

net ionic: (take out spectators)   Zn + Ag⁺  Zn²⁺ + Ag

oxidation: Zn Zn²⁺ + 2e^-
              0       2+
                       0
reduction: [1 e^- + Ag⁺  Ag]2
                         1+         0
                         0

balanced net: Zn + 2Ag⁺ Zn²⁺ + 2Ag

balanced FU: Zn(s) + 2AgNO₃(a1)  Zn(NO₃)₂(aq) + 2Ag(s)

[mandy9008]

one that i am having trouble identifying the oxidation and reduction for:

Mn²⁺ + PbO₂ + H⁺  MnO₄^- + Pb<sup>2+ + H₂O

i recognized the oxidation as :
Mn2+  MnO₄- + 2e-

for the reduction: i dont think that it is the Pb because the oxidation numbers are the same, 2+, and im not sure if the reduction can be with the H+ and H₂O</sup>

[cliverlong]

FU: Zn(s) + AgNO₃(aq)  Zn(NO₃)₂(aq) + Ag(s)

<< snip rest >>

Aha !

An application of Mitch rule number 1.

Do you have a balanced equation? Hint: How many nitrates on each side?

Once you correct that then the rest of your method looks very clear - so reapply it and see what happens

Clive

[cliverlong]

Mn²⁺ + PbO₂ + H⁺  MnO₄^- + Pb^{2+ + H₂O}

Again, this equation is not balanced. For example, look at hydrogen and oxygen on each side of the equation.

Clive

[Las]

one that i am having trouble identifying the oxidation and reduction for:

Mn²⁺ + PbO₂ + H⁺  MnO₄^- + Pb<sup>2+ + H₂O

i recognized the oxidation as :
Mn2+  MnO₄- + 2e-

for the reduction: i dont think that it is the Pb because the oxidation numbers are the same, 2+, and im not sure if the reduction can be with the H+ and H₂O</sup>

I think Pd is reduced in it..from +4 to +2 oxygen is -2.

[Las]

Its not H that's reduced.. Its Pb...from +4 to +2...Oxygen is -2..

[cliverlong]

Balanced equation anyone?

[Las]

Its

2Mn2+  +  5PbO2   +  4H+  -------->5Pb2+   +   2MnO4-  +2H2O


right?

so Pb :  +4 ---> +2 reduction

Mn : +2 -----> +7  Oxidation

[cliverlong]

Its

2Mn²⁺  +  5PbO₂   +  4H⁺  -------->5Pb²⁺   +   2MnO₄^-  +2H₂O


right?

so Pb :  +4 ---> +2 reduction

Mn : +2 -----> +7  Oxidation

Mandy9008,

Las has correctly balanced the original equation. Can you now split it up to show the half equations and confirm the change of oxidation states that Las has written?



Las,

Can you use the "sup" and "sub" buttons when writing an equation as that makes it a bit easier to determine if


MnO4-  means MnO₄^- or MnO^4-

Regards

Clive

[Las]

oh..lol..sure..I didnt really notice it..thanks

Las

[super_kaka1402]

Aha !

An application of Mitch rule number 1.

Do you have a balanced equation? Hint: How many nitrates on each side?

Once you correct that then the rest of your method looks very clear - so reapply it and see what happens

Clive
[/quote]

Sr, can you tell me what is the Mitch rule ?
thanks !

[Borek]

Look for Mitch posts on the forum and read his signature