A-Level Chemistry Atoms Elements and Molecules_5&6

A ​ (a)   is used to represent the reaction that happens at an ​ (b)   during electrolysis. It shows what happens when​ (c)   gain or lose ​ (d)   .

• half equation
• electrode
• ions
• electrons

What are half equations?

So a half equation is an equation that shows us what's happening to only ​ (a)   element in a ​ (b)   , it doesn't include all the ​ (c)   just one. It tells us whether that element is being ​ (d)   ; losing electrons or reduced; ​ (e)   electrons.

• one
• chemical reaction
• elements
• oxidized
• gaining

So we need to remember what ​ (a)   and reduction mean.

We do that using the acronym OIL {Oxidation is the loss of electrons} RIG {Reduction is the gain of electrons}. So this is to help you remember what oxidation and reduction are.

it stands for (oil) oxidation is ​ (b)   ; reduction is ​ (c)   . This is different to the oxidation and reduction in terms of​ (d)   . This is just looking at in terms of ​ (e)   .

• oxidation
• loss of electrons
• gain (rig) of electrons
• oxygen
• electrons

Look at a couple of examples.

So if we start with sodium we've got ​ (a)   forms ​ (b)   +e– ==>​ (c)   . So this e- in the equation represents ​ (d)   .

e for electron and​ (e)   because electrons have a negative charge.

So if you see +e- that means an electron

This half equation tells us that a sodium atom loses one electron.

Now because oxidation is a loss of electrons, that means sodium is being oxidized it's losing an electron

• Na
• Na+
• an electron
• (-)

Look at a couple of examples.

So if we start with sodium we've got ​ Na forms ​Na+ +e– ==>​Na . So this e- in the equation represents ​an electron .

e for electron and​ (-) because electrons have a negative charge.

So if you see ​ (a)   that means an electron

This ​ (b)   tells us that a ​ (c)   loses one electron. Now because ​ (d)   is a loss of electrons, that means sodium is being ​ (e)   it's losing an electron

• +e-
• half equation
• sodium atom
• oxidation
• oxidized

We could also start with an ​ (a)   instead of an atom. So if we start with a ​ (b)   . That half equation tells us that a sodium ion ​ (c)   one electron. Now because reduction is gain of ​ (d)   we could say that Na+ is being ​ (e)   ; whereas, Na in the first equation was being reduced.

• ion
• Na+ +e– ==> makes Na
• gains
• electrons
• reduced

We could also start with an ​ (a)   instead of an atom. So if we start with a ​ (b)   . That half equation tells us that a sodium ion ​ (c)   one electron. Now because reduction is gain of ​ (d)   we could say that Na+ is being ​ (e)   ; whereas, Na in the first equation was being reduced.

• ion
• Na+ +e– ==> makes Na
• gains
• electrons
• reduced

whereas Na in the first equation was being ​ (a)   Na+ is being ​ (b)   , and in the last equation s plus two e minus makes ​ (c)   ; we are starting with a sulfur atom and it's gaining ​ (d)   . this time. So it doesn't just have to be one. Because it's gaining electrons we would say is being ​ (e)   because reduction is gain of electrons.

• oxidized
• reduced
• S + 2e- ===> S2-
• two electrons

A ​ (a)   shows what happens at one of the ​ (b)   during electrolysis.

So we do need to be able to ​ (c)   and ​ (d)   half equations for these reactions.

• half equation
• electrodes
• compute
• balance

Remember that ​ (a)   occurs at the anode and reduction occurs at the ​ (b)   . Let's have a look at a simple redox reaction. A strip of ​ (c)   wire is placed in silver nitrate solution. Over time the solution ​ (d)   from colorless to bright blue. You will also observe silver metal crystal ​ (e)   on what was once copper wire.

• oxidation
• cathode
• copper
• changes color
• deposits