Electrochemistry

[Audaciity]

1.(a) Define reduction (Give three different definitions)

1.(b) Define oxidation (Give three different definitions)

 

15. A dry cell has a limited life. Describe two possible reasons why this may be.

 

For question 1, I believe I know two definitions for both terms: Oxidation is a loss of electrons in a redox reaction; Reduction is a gain of electrons in a redox reaction; Oxidation is the addition of oxygen to a substance; Reduction is the removal of oxygen from a substance. If those are right, I'm confused about the third.

 

Thank you in advance.

Edited October 31, 2009 by Audaciity

[mooeypoo]

Moved to Homework Help so you can get the help you need.

 

Welcome to the forum!

[Fuzzwood]

Oxidation state

[DrP]

For question 1, I believe I know two definitions for both terms: Oxidation is a loss of electrons in a redox reaction; Reduction is a gain of electrons in a redox reaction; Oxidation is the addition of oxygen to a substance; Reduction is the removal of oxygen from a substance. If those are right, I'm confused about the third.

 

 

Loss and gain of Hydrogen? Up to you to work out which way round though!

[Audaciity]

I now have 4 definitions.

 

1. Oxidation is the loss of electrons in a Redox reaction.

1. Reduction is the gain of electrons in a Redox reaction.

 

2. An increase in the oxidation state of an atom is known as oxidation.

2. A decrease in the oxidation state of an atom is known as reduction.

 

3. Oxidation is the addition of oxygen to a substance.

3. Reduction is the removal of oxygen from a substance.

 

4. Oxidation is an increase in oxidation number of an atom.

4. Reduction is a decrease in oxidation number of an atom.

 

--- I couldn't find any evidence of the hydrogen one.

--- 1 and 2 say the same thing, really.

[insane_alien]

3 doesn't hold all the time.

 

redox reactions frequently don't have oxygen involved at all. and example would be reacting sodium with chlorine. the sodium is oxidized and the chlorine is reduced. oxygen wasn't involved at all.

[Audaciity]

I realise 3 is not always appropriate; however, can't I just add something like "If oxygen is involved..." at the start of the definition?

[insane_alien]

it still isn't a good definition, as oxygen can be the thing being oxidised

[Audaciity]

I doubt that, in the exam, they will ask for three definitions. Perhaps, two. Also, they might ask why that definition is bad.

[Mr Skeptic]

DrP has your answer. An H+ transfer is essentially the opposite of an electron transfer. The reason for using these is because lots of acid/base reactions work in this way, though personally I think the Lewis acid and bases are a better description, and likewise for oxidation and reduction.

[Audaciity]

A dry cell has limited life. Name two reasons why this is.

 

1. An electrode could become depleted in the cell, due to........?

2. ?????????????

 

leakage??????? please help, my test is in an hour

[hermanntrude]

i'm sorry I can see only one reason, and that is the first law of thermodynamics.