Oxidation-Reduction

Oxidation-reduction (redox) reaction

involves a transfer of electrons

Reduction

gain of electrons

half reaction (reduction)

+ e- —> (e- on the reactants side)

oxidation

loss of electrons

half reaction (oxidation)

—> + e- (e- on the products side)

In a redox reaction the # of electrons lost =

$ of electrons gained

What happens to electrons when oxidizing?

Lose electrons

What happens to electrons when reduction?

Gain electrons

Assigning oxidation numbers…

sum of the oxidation #’s = 0

Changes in oxidation numbers indicates that…

oxidation and reduction has occured

An electrochemical cell can either be…

voltaic or electrolytic

In an electrochemical cell: oxidation occurs at the _______, reduction occurs at the ________.

anode, cathode

A voltaic cell _______________ converts…

spontaneously, chemical energy to electrical energy

An electrolytic cell requires…

electrical energy (a battery)

Why does an electrolytic cell require electrical energy?

In order to produce chemical change

Electrolysis

An electrolytic cell requires electrical energy to produce a chemical change.

What does Table J tell us?

If the free element is above the element, it is replacing the reaction will occur

Electrochemical cell (voltaic cell) transfer:

chemical energy —> electrical energy (spontaneous)

Electrolytic cell transfer:

electrical energy —> chemical energy (non spontaneous)

What does the salt bridge do?

Allows the migration of ions

For an Anode, does the mass increase or decrease?

decrease

In an anode, what becomes what?

Atoms becomes ion

For an Cathode, does the mass increase or decrease?

increase

In a cathode, what becomes what?

Ion becomes atom

In terms of electron flow, how does it flow?

Anode to Cathode (more active to least active)

For Voltaic, the anode is…

negative

For electrolytic, the anode is…

positive

To recognize a redox reaction, look…

for a free element

Sum of the oxidation number in compounds is…

zero

Sum of the oxidation numbers in polyatomic ions is…

equal to the charge

Monatomic ions have an oxidation number…

equal to the ionic charge

H is always __, except…

+1, when combined with metals it is -1

O is usually -2, except when combined with…

flourine it is +2 and in peroxides it is -1

Group 1 elements have a charge of ____, group 2 elements have a charge of ____.

+1, +2

Free elements have a charge of…

zero

Flourine is always…

-1

How do you find the number of moles of electrons?

Moles of e- = (change in charge) * (moles in question)