C2.7 - Electrolysis Flashcards
What is electrolysis?
Electrolysis means “splitting up with electricity”.
Why does electrolysis occur when ionic substances are molten or dissolved?
The ionic substance must be molten or dissolved in solution so the ions are free to move and conduct electricity.
What do the ions break down into during electrolysis?
If an electrical current is passed through an ionic compound that is molten or in solution, it breaks down into the elements it is made of and electrolysis occurs.
What is meant by the “electrolyte”?
The electrolyte is the substance that is broken down under electrolysis.
What is the positive electrode otherwise known as?
The positive electrode is the anode.
What is the negative electrode otherwise known as?
The negative electrode is the cathode.
Where do the different ions move in electrolysis?
In electrolysis, positive ions move to the negative electrode and negative ions move to the positive electrode.
As ions gain or lose electrons, they become atoms or molecules and are released.
Describe reduction.
When positively charged ions reach the negative electrode, they gain electrons to become neutral atoms. This is reduction.
What happens when ions gain 2 electrons?
Ions with a single positive charge gain one electron and those with a 2+ charge gain 2 electrons.
Describe oxidation.
When negatively charged ions reach the positive electrode, they lose electrons to become atoms. This is oxidation.
What is OILRIG?
Oxidation is loss, reduction is gain.
Describe what happens at the negative electrode in the electrolysis of lead bromide.
Positive ions are attracted to the negative electrode. The Pb2+ gains 2 electrons to produce lead. (Reduction).
Describe what happens at the positive electrode in the electrolysis of lead bromide.
Negative ions are attracted to the positive electrode. The Br- lose one electron each to become one bromine molecule (Br2)
What ions does water contain?
Water contains hydrogen ions and hydroxide ions.
In the electrolysis of sodium chloride, why is hydrogen sometimes produced?
When aqueous solutions are electrolysed, hydrogen gas is produced at the negative electrode unless the solution contains ions of a metal that is less reactive than hydrogen.
When is oxygen produced in the electroylsis of sodium chloride?
When aqueous solutions are electrolysed, oxygen gas is produced at the positive electrode unless the solution contains a high concentration of halide ions (Cl-, Br-, I-).
Why do less reactive metals get produced in electrolysis?
The more reactive an element, the keener it is to stay as ions.
What is brine?
When sodium chloride is dissolved in water, it is known as brine.