P1C10 - Electrolytic Processes Flashcards
What is electrolysis?
The process that splits ionic compounds into the different elements that they are made of.
What is the electrolyte?
The solution that conducts electricity.
(dissolved ionic compounds)
Whats attracted to the negative cathode?
Positively charged ions
Whats attracted to the positive anode?
Negatively charged ions
If copper ions (Cu2+) are in a solution and a voltage is applied, which electrode will they move towards and what will happen when they touch that electrode?
Copper ions (Cu2+) will move towards the cathode (negative electrode).
When the copper ions (Cu2+) touch the cathode, each ion will gain 2 electrons, forming copper metal:
Cu2+(aq) + 2e- → Cu(s)
What happens when we electrolyse molten copper oxide (CuO)?
Positively charged copper ions (Cu2+) are attracted to the cathode.
A pinkish coat of copper will appear on the cathode.
Negatively charged oxygen ions (O2-) are attracted to the anode.
Oxygen atoms will form at the anode and combine to give O2 gas bubbles
What is the disadvantage of electrolysis?
Lots of energy is needed to:
- Melt the solid ionic compound to allow the ions to flow.
- Produce the electrical current.
It’s expensive
What is formed at the anode?
If there are halide ions present, the respective halogen forms.
If there are no halide ions, oxygen forms.
What is formed at the cathode?
Hydrogen is produced if the metal is higher than hydrogen in the reactivity series.
The metal is produced if the metal is lower than hydrogen in the reactivity series.
What is a halide ion?
A halogen atom bearing a negative charge
What reaction happens at the anode
Oxidation
(Negatively charged ions lose electrons)
What reaction happens at the cathode?
Reduction reactions happen (positively charged ions gain electrons.)
Whats oxidation?
Gain of oxygen, loss of electrons
2Br- → Br2 + 2e-
bromide ions→bromine+electrons
Whats reduction?
Loss of oxygen, gain of electrons
Pb2+ + 2e- → Pb
What are the steps to the purification of copper?
The copper ions (Cu2+) will go into the electrolyte solution of copper sulfate.
The Cu2+ ions will be attracted to the cathode and pure copper will form.
Cu2+(aq) + 2e- → Cu(s)
The impurities of the anode will fall.
When the mass of the cathode is constant, the purification process is complete.
To measure the mass of copper formed on the cathode:
Record the initial mass of the electrodes. The cathode must be cleaned for the copper to stick to it
Use a variable resistor because the current may vary during the process. It should be kept constant.
You should wash electrodes to remove any copper sulfate. You should then dry them.
You should also wash the electrodes with a more volatile solvent to make them dry faster. You could use propanone, for instance.
Equation:
Measure the final mass of the electrodes.
change in mass = final mass - initial mass.
