Electrolysis Flashcards
electrolysis definition
the breakdown of an ionic compound, either molten or in aqueous solution, by the passage of electricity
what is an electrolyte?
the liquid that the current is passed through
what is the electric current caused by?
electrons moving in the electrodes + wires of the circuit, and by ions moving in the solution.
what must the electrolyte contain?
ions that are free to move around
what are inert electrodes?
they do not undergo any chemical change in the reaction of electrolysis
what forms during the electrolysis of lead (II) bromide?
the positive lead ions move to the cathode
the negative bromide ions move to the anode
silvery deposits of lead form near the bottom of the dish, and brown bromine gas forms near the anode
what happens during the electrolysis of sodium chloride solution?
at the cathode: two ions, Na plus and H plus move to the cathode but only H plus ions are discharged. the sodium ions remain as ions but the solution turns alkaline because the loss of hydrogen ions leaves a surplus of hydroxide ions
at the anode: two ions, Cl minus and OH minus move to the anode. either ions could be discharged depending on the concentration of the solution. if the solution is concentrated, Cl minus ions are discharged. at intermediate concentrations both ions are discharged, giving a mixture of products
what happens when copper (II) sulfate solution os electrolised?
(uses inert carbon electrodes)
the products are copper and oxygen. the copper forms as a red-brown coating on the carbon cathode and bubbles of a colourless gas, oxygen, are seen next to the anode. the solution will become paler blue as the cooper ions are discharged
(using copper electrodes)
copper is deposited as a red/brown coating at the cathode but there is a difference in the reaction at the anode.
copper (II) sulfate using copper electrodes
cathode becomes thicker, copper is deposited on cathode
at the anode copper atoms lose two electrons and cu two plus ions are formed. the anode slowly dissolves and loses mass
what happens to the concentration in the copper (II) sulfate electrolysis?
the concentration of the cu two plus ions in the solution remains constant because the rate of production of cu two plus ions at the anode is exactly balanced by the rate of removal of cu two plus ions at the cathode
why is this reaction important in refining copper?)
copper is extracted from its ore by reduction with carbon, but the copper produced is not pure enough for its uses (like in electrical cables) was
the metal forms at the _______, and the non metal forms at the _______
cathode
anode
what is the rule for the products in a solution?
only metals below hydrogen in the reactivity series are deposited as the metal on the cathode, metals above hydrogen produce hydrogen gas instead
e.g if magnesium chloride solution is electrolysed, hydrogen, not magnesium, is formed at the cathode
at the anode, the main product depends on the conc. of the solution.
e.g if hydrochloric acid is electrolysed, chlorine is the main product at the anode. if dilute hydrochloric acid is used, oxygen is likely to be the main product
the loss of electrons is _____
the gain of electrons is_____
oxidation
reduction
OILRIG
oxidation is loss
reduction is gain
what is electroplating?
coating an object with a thin film of metal. often this is done for economic reasons, with a fairly cheap metal like nickel being coated with gold or silver or chromium
