1.9 - Electrolysis Flashcards
What is electrolysis?
Electrolysis is a process that uses an electrical current to split up a substance that contains ions
The substance is broken down by electrolysis is an electrolyte. Electrolytes are made up of ions
When does electrolysis occour?
When an ionic substance is molten or in solution a substance that can be electrolysed is an electrolyte.
What is an electrode and what are its features?
An electrode is a material that carries electricity into and out of the electrolyte. Usually made of graphite.
Which is a good conductor of electricity and inert.
How does electrolysis work?
Positive ions (cations) are attracted to the negative electrode (cathode)
Negative ions ( anions ) are attracted to the positive electrode (anode)
Oxidation is loss
Reduction is gain
At the cathode ( negative electrode ) the cations ( positive ions ) gain electrons and are reduced
At the anode ( positive electrode ) the anions ( negative ions ) lose electrons and are oxidised.
How does electrolysis occour in a molten compound?
Lead (II) Bromide is a binary ionic compound meaning that it is a compound consisting of 2 elements joined together by ionic bonding
When these compounds are heated beyond their melting point, they become molten and can conduct electricity as their ions can move freely and carry the charge
These compounds undergo electrolysis and always produce their corresponding element
To predict the products of any binary molten compound first identify the ions present
The positive ion will migrate towards the cathode and the negative ion will migrate towards the anode
Therefore the cathode product will always be the metal and the product formed at the anode will always be the non-metal
How does electrolysis occour in an aqueous solution?
Aqueous solutions will always have water present
Some water molecules split up into hydrogen and hydroxide ions, H+ and OH–, which participate in the electrolysis reactions
Positive Electrode
OH– ions and non-metal ions are attracted to the positive electrode
Either OH– or non-metal ions will lose electrons and oxygen gas or a non-metal is released e.g. chlorine
The product formed depends on which ion loses electrons more readily
Negative Electrode
H+ ions and metal ions are attracted to the negative electrode but only one will gain electrons
Either hydrogen or a metal will be produced
If the metal is above hydrogen in reactivity series, hydrogen will be produced – bubbling will be seen at the cathode
The apparatus can be modified for the collection of gases by using inverted test tubes over the electrodes
The electrodes are made from graphite which is inert and does not interfere with the electrolysis reactions
What is the method for this experiment?
Add lead(II) bromide into a crucible and heat so it will turn molten, allowing ions to be free to move and conduct an electric charge
Add two graphite rods as the electrodes and connect this to a power pack or battery
Turn on the power pack or battery and allow electrolysis to take place
Negative bromide ions move to the positive electrode (anode) and lose two electrons to form bromine molecules. There is bubbling at the anode as brown bromine gas is given off
Positive lead ions move to the negative electrode (cathode) and gain electrons to form grey lead metal which deposits on the bottom of the electrode
Electrode Products:
Anode: Bromine gas
Cathode: Lead metal
Explain the practical Investigate the electrolysis of Aqueous solution
To electrolyse aqueous solutions of sodium chloride, sulfuric acid and copper(II)sulfate, and to collect and identify the products at each electrode
Add the aqueous solution to a beaker and cover the electrodes with the solution
Invert two small test tubes to collect any gaseous products
Connect the electrodes to a power pack or battery.
Turn on the power pack or battery and allow electrolysis to take place
Observations at each electrode are made
Gases collected in the test tube can be tested and identified
If the gas produced at the cathode burns with a ‘pop’ when a sample is lit with a lighted splint. This shows that the gas is hydrogen
If the gas produced at the anode relights a glowing splint dipped into a sample of the gas. This shows that the gas is oxygen
If the anode gas bleaches of a piece of litmus paper this indicates chlorine is the product
If a solid forms around the electrode, the metal have been formed. The colour can indicate the metal
What is the conclusion for this practical?
Sodium chloride solutions produces hydrogen at the cathode and chlorine at the anode
Dilute sulfuric acid produces hydrogen at the cathode and oxygen at the anode
Copper(II)sulfate solution produces copper at the cathode an oxygen at the anode
