Chapter 4 - Electrolysis Flashcards
What does an electrolytic cell do?
Turns electrical energy into chemical energy.
Why do the substances in an electrolytic cell not have to be separated?
Because they are non-spontaneous reactions and therefore won’t react by themselves.
when drawing a power pack the positive electrode connects to the
larger stick
when drawing a power pack the negative electrode connects to the
smaller stick
ALWAYS
anions are attracted to the
anode
ALWAYS
cations are attracted to the
cathode
how do we predict which reaction will occur?
We first circle the possible reacting species. If something is not in the P.R.S we cannot circle that side of the equation.
Then We look at the electrochemical series and pick the highest on the left and lowest on the right.
We draw a line to check if it is galvanic or electrolytic.
What is electroplating?
Where an object is used as the cathode in an electrolytic cell and is plated with metal ions undergoing reduction.
GOLDEN RULE OF ELECTROLYTIC CELLS
THE CATHODE CAN NEVER TAKE PART IN A REACTION AS ELECTRONS ARE BEING FORCED ONTO IT AND THUS IT ALWAYS UNDERGOES REDUCTION.
What is faraday’s first law
electric charge depends on current and time
Q=It
Q is electric charge in coulombs
I is current in amperes
t is time in seconds
What is faraday’s second law
charge on an ion can be calculated from electric charge.
n(e-) = Q/F
F is faradays constant = 96500
Relationship between a faraday and a mole of electrons
1 faraday = 1 mole of electrons
What is a discharge reaction
this is a galvanic reaction that occurs in a secondary cell. The discharge is the products formed. The discharge must stay in contact with the electrodes for a cell to be recharged.
What is a recharge reaction
this is an electrolytic reaction that occurs in a secondary cell. The discharge products are converted back into the original reactants.
How to find the discharge and recharge equation
First we find one and then the other is just the same equation but flipped
Describe the electrolysis of Brine
A high concentrated solution of NaCl can change the order of the electrochemical series. It allows Cl- to be a prefer reductant and so Cl- reacts with water to produce Cl2, H2 and OH-. Once all of the solution has been electrolysed, Na is left behind. it passes through the semi-permeable membrane and forms NaOH.
What does a semi-permeable membrane do?
Isolates electrodes.
Why does a brine solution need a semi-permeable membrane?
As the products formed at each electrode, Na+ and Cl- could come together and form NaCl in an explosive manner.
When asking about why this salt bridge could not be used, we look for…
If the ions would be preferably oxidised or reduced rather than the originally intended reactants.
If a precipitate will form with another reactant.
