C6 Electrolysis Flashcards
Electrolysis
Using electricity to break down electrolytes to form elements
Describe electrolysis in terms of movement of ions
Passing an electric current through electrolytes causes the ions to move to the electrodes
Why electrolysis can only occur when an ionic compound is molten or in aqueous solution
Ionic compounds only conduct electricity when molten or in aqueous solution
Word equation to describe the electrolysis of a molten ionic compound
Ionic compound ——> metal + non-metal
Describe electrolysis with half equations at the electrodes of 2NaCl ——> 2Na + Cl2
Cathode (reduction) - Na+ + e- ——> Na
Anode (oxidation) 2Cl- —–> Cl2 + 2e-
How to predict the products at each electrode for the electrolysis of a molten ionic compound
A metal forms at the cathode and a non-metal forms at the anode
How to explain the classification of the reactions at each electrode as oxidation or reduction
Reduction happens at the negative cathode as this is where positive ions gain electrons
Oxidation happens at the positive anode as this is where negative ions lose electrons
What would be produced at the anode when some solutions are electrolysed
Oxygen
Describe electrolysis of solutions in terms of movement of ions
Positively charged ions move to the negative electrode (the cathode)
Negatively charged ions move to the positive electrode (the anode)
How hydrogen ions and hydroxide ions can be present in solutions
Hydroxide ions float around in solution
Hydrogen ions transferred directly to a neighboring water molecule to form hydronium ions
What can be produced at the anode when some solutions are electrolysed
Hydrogen
Word equation to describe electrolysis of a lead bromide
Lead bromide + electricity → lead + bromine
How can aluminum be extracted from aluminum oxide
Using electrolysis
Describe the electrolysis of aluminium oxide
Positively charged aluminium ions gain electrons from the cathode and form molten aluminium
Oxide ions lose electrons at the anode, and form oxygen molecules
Why electrolysis is used to extract aluminium from compound
The temperatures needed are too high to be economic
Word equation to describe the electrolysis of aluminium oxide
Aluminum oxide ——-> aluminum + oxygen
Why electrolysis is an expensive metal extraction method
Cost of electricity for electrical energy
Specialized equipment can be expensive
Electrode material costs
High temperature requirements
Why extraction of aluminum is expensive
High temperature
Energy intensive
Electrode consuption
Why cryolite is added to aluminium oxide in the industrial extraction of aluminium
Reduces melting point of aluminum oxide from 2050°C to 950°C
Enhances electrical conductivity of molten mixture
Improves fluidity of mixture
State the products of the electrolysis of brine and a use for each
Sodium hydroxide and hydrogen
How to electrolyse brine in terms of ions moving
Sodium and hydrogen ions go to anode
Chlorine and hydroxide ions go to cathode
What are ionic compounds made from
Positive and negative ions
Industrial uses of electrolysis
Extract reactive metals
Electrolysis of brine
Purifying copper
Why hydrogen is produced at the negative electrode and not sodium
Hydrogen is less reactive than sodium
Which ion gave pH of 1
Hydrogen ions
Name the type of bond between the hydrogen and the chlorine atoms in a molecule of hydrogen chloride
Covalent
What happens to the concentration of the sulphuric acid as the electricity is passed
through it
Concentration increases
Phytomining/phytoextraction
Uses plants to absorb metal compounds from the ground through their roots
Bioleaching
Use bacteria to break down low-grade ores to produce acidic solution
Polyatomic ion
Group of covalently bonded atoms that carries a net charge
Electrolyte
Liquid or solution that contains ions and can conduct electricity
Why do solid ionic compounds not conduct electricity
Ions cannot move
What products are always formed at the anode
OH- and negative element like Cl-
What products are always formed at the cathode
H+ and positive element like Na+
Cathode
Negative electrode
Anode
Positive electrode
Where are metals formed
Cathode
Where are non-metals formed
Anode
How can ionic substances be electrolysed
By melting or dissolving
Why can solid ionic substances not be electrolysed
They don’t conduct electricity (ions can’t move)
In electrolysis of solutions, when is the metal not produced at the cathode
When the metal is more reactive than hydrogen
In the electrolysis of a metal halide solution, what is produced at the anode?
Halogen
In the electrolysis of a metal sulfate solution, what is produced at the anode?
Oxygen
Half equation for ionisation of water
H2O —–> H+ + OH-
What metals are extracted from ionic compounds by using electrolysis
Metals that are more reactive than carbon
In the electrolysis of aluminum oxide what are the anodes made of
Graphite
In the electrolysis of aluminum oxide why do the anodes need to be replaced
They react with oxygen being formed
What 3 products formed from electrolysis of sodium chloride solution
Chlorine
Hydrogen
Sodium hydroxide
How is chloride formed from electrolysis
Cl- attracted to anode where they get oxidised
How is hydrogen formed
Hydrogen attracted to cathode where they reduced
How is sodium hydroxide formed
Sodium and hydroxide ions electrostatically attact to form sodium hydroxide
Two factors that affect the amount of a substance produced during electrolysis
Increase voltage/current increase flow of charges
Increase number of charges increase rate of electrolysis
One disadvantage of plating iron with tin
Tim costs more and is less abudnant in Earth’s crust
Reactivity series least reactive 5
Hydrogen
Copper
Silver
Gold
Platinum
Reactivity series less reactive than carbon
From more reactive to less reactive
Carbon
Zinc
Iron
Tin
Lead
Reactivity series top 5 most reactive
Potassium
Sodium
Calcium
Magnesium
Aluminium
