Electrolysis Flashcards
What are ionic substances?
Ionic substances contain charged particles called ions.
For example, lead bromide contains positively charged lead ions and negatively charged bromide ions.
What is electrolysis?
Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them.
What does molten mean?
When its reduced to liquid form by heating.
How can you make ions free to move for electrolysis?
Ions are free to move when an ionic substance is dissolved in water or when melted.
What happens during electrolysis?
Positively charged ions move to the negative electrode during electrolysis. They receive electrons and are reduced.
Negatively charged ions move to the positive electrode during electrolysis. They lose electrons and are oxidised.
What is the substance that is broken down by electrolysis called?
The electrolyte
What is an electrolyte?
A substance which will conduct an electric current in solution.
Why is electroplating useful?
It’s useful for coating a cheaper metal with a more expensive one, such as copper or silver.
How does electroplating work?
The negative electrode should be the object that is to be electroplated
The positive electrode should be the metal that you want to coat the object with
The electrolyte should be a solution of the coating metal, such as its metal nitrate or sulfate.
Why is aluminium oxide dissolved in molten cryolite?
Aluminium oxide has a very high melting point so its dissolved in molten cryolite to reduce the energy costs involved in extracting aluminium.
What is cryolite?
An aluminium compound with a lower melting point than aluminium oxide.
Explain the process of extracting aluminium
First its melted so electricity can pass through it,
Both the negative electrode (cathode) and positive electrode (anode) are made of graphite, a form of carbon.
Aluminium metal forms at the negative electrode and sinks to the bottom of the tank, where it is tapped off.
Oxygen forms at the positive electrodes. This oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide, and they gradually burn away.
What is formed at the negative electrode during the electrolysis of aluminium?
Aluminium metal forms at the negative electrode and sinks to the bottom of the tank, where it is tapped off.
What is formed at the positive electrode during the electrolysis of aluminium?
Oxygen forms at the positive electrodes. This oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide, and they gradually burn away.
Why does the positive electrode have to be replaced frequently?
Oxygen forms at the positive electrodes. This oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide, and they gradually burn away. As a result, the positive electrodes have to be replaced frequently. This adds to the cost of the process.
What happens at the negative electrode?
At the negative electrode, positively charged ions gain electrons. This is reduction, and you say that the ions have been reduced.
What happens at the negative electrode, depending on the position of the metal in the reactivity series?
The metal will be produced if it is less reactive than hydrogen
Hydrogen will be produced if the metal is more reactive than hydrogen
What happens at the positive electrode?
At the positive electrode, negatively charged ions lose electrons. This is oxidation, and you say that the ions have been oxidised.
What are the three products of the electrolysis of sodium chloride solution?
Hydrogen ions H+ (from the water) are discharged at the negative electrode as hydrogen gas, H2
Chloride ions Cl– are discharged at the positive electrode as chlorine gas, Cl2
Sodium ions Na+ and hydroxide ions OH– (from the water) stay behind - they form sodium hydroxide solution, NaOH
What are the three products of the electrolysis of concentrated sodium chloride solution used for in chemical industry?
Hydrogen is used as a fuel and for making ammonia
Chlorine is used to kill bacteria in water, and to make bleach and plastics
Sodium hydroxide is used to make soap and bleach
What is a half equation?
A half-equation shows you what happens at one of the electrodes during electrolysis.
