Topic 8 - Electrolysis Flashcards
Cation
Positive ion
Anion
Negative ion
Electrolysis
The breaking down of a compound using electricity.
Electrolyte
Ionic compound that is molten or dissolved in water.
When an ionic substance is melted or dissolved in water this allows the ionic bonds to break. This allows the ions to move freely when a voltage is applied. An ionic compound with free moving ions is called an electrolyte.
What happens during electrolysis?
Electrical energy is transferred to decompose the electrolyte. The ionic compound is broken down into positive cations and negative anions.
Electrode
Positive and negative ‘rods’
Anode
Positive electrode
Cathode
Negative electrode
Are metal ions positive or negative?
Positive
Are non-metal ions positive or negative?
Negative
What happens to cations?
They are attracted to the negative cathode where they gain electrons to become atoms (reduction)
What happens to anions?
They are attracted to the positive anode where they loose electrons to become atoms (oxidation).
What does an ion turn into when it goes to an electrode?
Atoms
What atoms do lead bromide turn into?
Lead + bromine
The negative bromide ions are attracted to the positive anode and turn into bromine atoms.
The positive lead ions are attracted to the negative cathode and turn into lead atoms.
What column on the periodic table requires a 2 in the equation?
Hydrogens
2nd column to the end.
What does molten mean?
Melted
Not with water
What is a solution?
Dissolved
With water
What is produced when a solution is used in electrolysis?
Water
H2O —> H+ + OH-
Hydrogen + Hydroxide
Where does H+ go to?
Cathode
Where does OH- go to?
Anode
What are the rules for producing products in electrolysis at the cathode?
If the metal is less reactive than hydrogen it is made at the cathode.
If the metal is more reactive than hydrogen, hydrogen will be made at the cathode.
What are the rules for producing products in electrolysis at the anode?
If the anion is chloride, bromide or iodide then the halogen will be made.
If the anion is sulphate, nitrate or carbonate then oxygen will be made.
Half equation for oxygen
4OH- —> 2H2O + O2 + 4e-
Half equation for hydrogen
2H+ + 2e- —> H2
Method for the process of electrolysis of copper sulfate solution using copper electrodes?
1) 50.0 cm3 copper sulphate solution.
2) Wash and clean copper electrodes with emery paper.
3) Record mass of copper electrodes.
4) Change variable resistor until ammeter read 0.2A
5) Power pack 4v for 5 minutes
6) Record number of amps
7) Rinse each electrode with propane, dry and record mass.
8) Repeat steps 2 to 7 for different amps.
Results of practical at the cathode?
The higher the current the larger the change in mass of electrodes in 20 minutes.
The cathode gets heavier as copper ions gain electrons (reduced) and form pure copper metal which is deposited on the cathode.
When the current is higher the electrons are provided more quickly.
Results of practical at the anode?
The anode gets lighter as the copper atoms loose electrons (oxidised) and form copper ions which dissolve into the solution.
When the current is higher the electrons are removed more quickly.
Product and half equation at the anode?
Cu —> Cu2+ + 2e-
Product and half equation at the cathode?
Copper
Cu2+ + 2e- —> Cu
Why should you clean electrons at start with emery paper?
To remove impurities.
What is an ammeter used for?
To measure the voltage of the solution.
Why is a variable resistor used?
To change the current.
Why should you measure the time of electrolysis?
So you can compare how much mass is added or lost in the same amount of time.
What do you use to wash and dry electrodes and why?
Acetone because it evaporates.
Why should you dry the electrodes at the end?
The electrolyte will still be on it and it has a big mass so can affect the results.
Which electrode is pure?
Cathode
Which electrode is impure?
Anode
Oxidation
Loss of electrons
Reduction
Gain of electrons.
Method for electrolysis of copper sulfate solution using inert electrodes?
1) 50cm3 of copper sulphate solution
2) Graphite electrodes
3) Power pack 4v for 5 minutes
4) Observe positive electrode
5) Observe negative electrode
Results at positive anode for electrolysis of copper sulfate solution using inert electrodes?
Bubbles
Oxygen made
4PH- —> O2 + 2 H2O + 4e-
Results at negative cathode for electrolysis of copper sulfate solution using inert electrodes?
Orange solid
Copper
Cu2+ + 2e- —> Cu
