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15 Cards in this Set
- Front
- Back
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what is electrolysis
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electrolysis is the use of electricity to bring about a chemical reaction
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what is an electrolyte
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a compound that can conduct an electric current when molten or dissolved in water, due to the presence of ions in the dissolved state
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what is an electrode
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carries the current in and out of the electrolyte.
inert electrodes: don't react with the electrolyte (eg graphite, platinum) active electrodes: react with the electrolyte ( eg copper, iron) |
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what happens when an electric current is passed through potassium iodide using inert electrodes
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POSITIVE ELECTRODE: oxidation occurs. Water molecules lose electrons 2H20 ---> O2 + 4H+ +4e-
the I- ions lose an electron to from iodine atoms (2I- --> I2 +2e-) NEGATIVE ELECTRODE: H2O molecule gains an electron (2H2O + 2e- ---> H2 +2OH-) pink colour observed when phenolphthalein added H2 gas bubbles given off |
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electrolysis of copper sulphate with active copper electrodes
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POSITIVE ELECTRODE: Cu metal more easily oxidised than SO42- ion (Cu ---> Cu2+ + 2e-) hence electrode gets smaller
NEGATIVE ELECTRODE: Cu2+ ion more easily than H2O (Cu2+ +2e- ---> Cu) hence electrode gets bigger |
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the electrolysis of sodium sulphate solution
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POSITIVE ELECTRODE: oxidation occurs
(2H2O ---> O2 + 4H+ +4e-) H+ ions surround, red colour observed (with universal indicator) NEGATIVE ELECTRODE: reduction occurs (2H2O + 2e- ---> H2 + 2OH-) blue colour (OH- ions) |
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to demonstrate the movement of ions during electrolysis
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electrolyte: copper sulphate and potassium chromate dissolved in ammonia solution. green in colour (Cu2+ is blue and CrO42- is yellow)
solution on filter paper with 2 electrodes. -ve electrode ~ blue is attracted (Cu2+) +ve electrode ~ yellow is attracted (CrO42-) |
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what is electroplating
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a process where electrolysis is used to put a thin layer of one metal on the surface of another.
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electroplating of silver onto a nickel spoon
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ELECTRODES: nickel spoon as negative electrode, silver metal as positive electrode.
ELECTROLYTE: solution of silver nitrate. POSITIVE ELECTRODE:oxidation occurs (Ag -> Ag+ +e-) NEGATIVE ELECTRODE: Ag+ gains electron and coats nickel spoon (Ag ---> Ag+ +e-) |
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what is a galvanic/ voltaic cell
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a cell in which a chemical reaction results in the production of an electrical current is called a galvanic cell or voltaic cell
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what is the salt bridge used for in the galvanic cell?
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to maintain a balance of ions in each part of the fell. It is filter paper that has been soaked in KCl or KNo3-
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what is the hydrogen half cell?
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it is a standard half cell with which all other cells are compared (platinum in solution of H+ ions with H2 gas bubbled in over the platinum)
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what is electrode potential
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the tendency of a metal to be oxidised. It can be measured by connecting the metal's half cell to the hydrogen half cell. The higher the voltage the greater the electrode potential of the metal
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what is the electrochemical series
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it is a list of elements in order of their standard electrode potential
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list the electrochemical series
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Potassium, Calcium, Sodium, Magnesium, Aluminium, Zinc, Iron, Lead, Hydrogen, Copper, Mercury, Silver, Gold
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