Electrolysis Flashcards
What are acids?
Substances that produces hydrogen ions when they are added to water
What is made when a solution is dissolved in water?
An aqueous solution
What ph do acids have?
Ph values of less than 7
What does the state symbol aq mean?
The ions are in an aqueous solution
Hydrogen ions make solutions ……….
Acidic
What are bases?
Things that react with acids and neutralise them
What are alkalis?
Bases that have dissolved in water to make alkaline solutions
What ions do alkalis produce in the solution?
Hydroxide ions
What is the PH of alkalis?
Values greater than 7
What ph will strong acids have?
Low ph, such as values between 0-2
What ph values will highly alkaline solutions have?
12-14
What do indicators do?
Change colour based on the ph of solutions
Which indicators can tell us the ph of a solution?
Universal indicators or full range indicators
Which metals will acids react with?
Ones above hydrogen in the reactivity series
Why are the reactions of very reactive metals and acids too dangerous to be done safely?
They are too violent
When metals react with an acid what is produced?
A salt and hydrogen gas.
What type of compound are metal oxides and metal hydroxides?
Bases
What happens when an acid reacts with a base?
Neutralisation occurs
What are the products of neutralisation?
Salt and water
What is the formula of hydrochloride acid?
HCL
What is the formula of sulphuric acid?
H2SO4
What is the formula of nitric acid?
HNO3
How is the soluble salt obtained from an base/metal that is insoluble in water + acid reaction?
- metals/base that is insoluble In Water is added little at time til all the acid has reacted
- filter the mixture to remove excess solid reactant leaving a salt solution
- it is left to crystallise leaving the salt
How can soluble salts be made?
By reacting an acid and alkali
How can we represent the reaction between any acid and alkali?
H+(aq) + OH-(aq) ——-> H2O (l)
How can the salt be obtained from a neutralisation reaction?
- the alkali is added little at time til all the acid has
- there is no visible change so indicator must be used to detect when the reactions complete
- the exact measurements of acid and alkali must be recorded
- repeat the experiment without the indicator
- it is left to crystallise leaving the salt
What are ammonium salts used as?
Fertilisers
How can insoluble salts be made?
Mixing solutions of soluble salts
How can the insoluble salts be obtained from the mixture of soluble salt solutions?
Mix the 2 solutions A precipitate forms The solution is filtered Washed And left to dry
What is precipitate!
An insoluble solid formed by a reaction taking place in solution
What are precipitation reactions useful for?
Pollutants such as metal ions can be removed from water
How is precipitation used to remove metal pollutants from water?
The water is treated by adding substances that react with the pollutant metal ions dissolved in the water to form insoluble salts
Zinc carbonate is insoluble in water. What would happen when sodium carbonate solution is added to zinc sulphate solution?
Zinc carbonate would be produced as a precipitate or solid, sodium sulphate would remain in the solution
What is ammonium solution?
An alkali that does not contain metal
What ammonium solution react with acid what is formed?
Ammonium salts such as NH4NO3
What is electrolysis?
The process of breaking substances into smaller substances using electricity
Why can electrolysis not take place on solids?
The ions are not free to move
Which substances can electrolysis take place on?
Molten ionic compounds or a solution containing ions
What is the substance that is broken down by electrolysis called?
Electrolyte
What must happen to ionic compounds before they can be electrolysed?
Melted or dissolved in water
What must the electrodes be made from?
Inert substances that do not react with the products
What happens to the ions in the electrolyte do in electrolysis?
They move to the electrodes where they are discharged to produce elements
Which electrode do positively charged ions go?
Negative electrode, where they form metals or hydrogen depending on the ions in the electrolyte
Which electrode do negatively charged ions go?
Positive electrode where they lose their charge to form non- metallic elements
Molten zinc chloride is electrolysed. Name the substances formed at the positive and negative electrodes
+ chlorine
- zinc
What happens when the positively charged ions reach the negative electrode?
Gain electrons to become neutral atoms
What is reduction?
Gaining electrons
Positive ions are …… In electrolysis
Reduced
Ions with a single positive charge gain …. And those with …. Gain 2 electrons
1
2+
What happens at the positive electrode in electrolysis?
The negative ions lose electrons to become neutral atoms
What is oxidation?
Lose of electrons
What do non-metals Ions form in electrolysis?
Non-metal atoms combine to form molecules
Complete the half equation for the formation of chlorine at a positive electrode
2CL- —–> ….. + …..
CL2 + 2E-
What does water contain?
Hydrogen ions and hydroxide ions
When a solution is electrolysed using water as an electrolyte what may be produced at the negative electrode and when?
If the positive ions in the solution are those of a metal more reactive than hydrogen, hydrogen will be produced
What could be produced at the positive electrode from an aqueous solution?
Oxygen
If a solution contains a reasonably of a halide ion what will be produced at the positive electrode?
A halogen will be produced
What are halide ions?
Chlorine, bromine, iodine
Name the products at the positive and negative when aqueous copper sulphate solution is electrolysed using carbon electrodes.
+ oxygen
- copper
What ph is pure water?
Neutral, ph 7
Why does aluminium have to be extracted from its ore by electrolysis?
It is more reactive than carbon
What does aluminiums ore contain?
Aluminium oxide
Why is aluminium oxide mixed with cryolite?
Means the mixture can be electrolysed at a lower temperature saving energy, making it less expensive
What does the electrolysis of aluminium produce?
Aluminium and oxygen
What happens at the negative electrode in the electrolysis of aluminium?
The aluminium ions are reduced to aluminium atoms by gaining electrons.
What happens at the positive electrode in the electrolysis of aluminium?
The oxide ions are oxidised to oxygen atoms by losing electrons and the oxygen atoms from oxygen molecules
Why do the positive carbon electrodes have to be replaced over time?
At the high temperatures of the cell the oxygen reacts with the carbon electrodes to produce carbon dioxide so they gradually burn away
What is brine?
A solution of sodium chloride in water
What ions does brine contain?
Sodium, chloride, hydrogen and hydroxide ions
When brine is electrolysed what is produced at the negative electrode?
Hydrogen from the hydrogen ions
When brine is electrolysed what is produced at the positive electrode?
Chlorine from the chloride ions
What solution is left after the electrolysis of brine?
Sodium hydroxide, sodium and hydroxide ions
Why is hydrogen produced when sodium chloride solution is electrolysed?
The solution contains hydrogen ions which are discharged in the preference of sodium ions
Half equation at the positive electrode in brine
2cl- —> cl2 + 2e-
Half equation at the negative electrode IN Brine
2H+ + 2e- —-> H2
What is sodium hydroxide used for?
It is a strong alkali and is used for soap, bleaching paper
What is chlorine used for?
Kill bacteria in drinking water and swimming pools
What is hydrogen used to make?
Margarine and hydrochloride acid
Why is the electrolysis of brine important?
It produces 3 useful products
What is electroplating?
Using electrolysis to out a thin coat of metal onto an object
Which metals are often used in plating?
Gold, silver, chromium
Why is electroplating done?
Make it more attractive
Protect metal from corrosion
Increase hardness
Reduce costs by using thin layer instead of pure metal
In electroplating which object is used as the negative electrode?
The object to be plated
In electroplating what object is the positive electrode?
The plating metal
What is the electrolyte like for electroplating?
It’s a solution containing. Ions of the plating metal
What happens at the positive electrode in electroplating?
Atoms of the plating metal lose electrons to form metal atoms which go into the solution
What happens at the negative electrode in electroplating?
Metal ions from the solution gain electrons to form metal atoms which are deposited to the object to be plated
Half equation nickel electroplating positive electrode
Ni —–> Ni2+ + 2e-
Ni2+ + 2e- —–> Ni
Describe how you would silver plate a piece of copper jewellery
Pass electricity through a cell with the item of jewellery as the negative electrode, the positive electrode being silver and containing a solution of a silver salt (eg silver nitrate solution, as the electrolyte)
For writing half equations which elements natural exist in pairs (diatomic molecules)
Hydrogen Chlorine Florine Nitrogen Oxygen Iodine Bromine
What is an electrolyte?
A liquid containing free moving ions The substance that is broken down by electricity in electrolysis
