Chapter 4 Flashcards
Electrolysis
The breakdown of an ionic compound, molten or in an aqueous solution, by the passage of electricity
Anode
Positive electrode -> attracts negative ions and provides electrons, which then flow alomg metallic conductor back towards cathode
Cathode
Negative electrode -> attracts positive ions and removes electrons from circuit
Electrolyte
Molten or a aqueous substance that undergoes electrolysis
Electrodes
Solid that conducts, electricity, and is submerged in electrolyte
. Ions move towards the electrodes, were they react and the compound decomposes
Electrolysis of molten ionic solids
. And ionic solid can’t be electrolysed because Its in fixed in position and can’t move.
-> molten ionic compounds can be electrolysed, because the ions can move freely and conduct, electricity
. The metal ion (positive) move to the cathode and the nonmetal (negative) ion will move to the anode
. Electrodes made of inert material, such as platinum or carbon, so they don’t react with the electrolyte
Electrolysis of aqueous solutions
. Ions from the ionic compound, hydrogen ions, and hydroxide ions will be present
. Either a metal or hydrogen will form at the negative electrode (cathode)
. A nonmetal will form at the positive electrode (anode). This will either be a substance formed from the nonmetal ions in salt solution, or oxygen formed from the OH- ions in the water
Aqueous electrolysis of dilute sulphuric acid: products at cathode and observations
. Hydrogen
. Colourless bubbles
Aqueous electrolysis of dilute sulphuric acid: product at anode & observations
. Oxygen
. Colourless bubbles
Aqueous electrolysis of concentrated aqueous sodium chloride: product at cathode & observations
. Hydrogen
. Colourless bubbles
Aqueous electrolysis of concentrated aqueous sodium chloride: product at anode & observations
. Chlorine.
. Pale green bubbles
Predicting the products of aqueous electrolysis: at cathode
. H+ always wins EXCEPT:
. Platinum.
. Gold
. Silver
. Copper
Predicting the products of aqueous electrolysis: anode
. OH- always wins EXCEPT
. Group 7 nonmetals
. Flourine, chlorine, bromine etc
Electrolysis of copper sulphate with inert electrodes -> produces oxygen
- When you electrolyse copper sulphate solution with inert carbon electrodes:
- Copper is more reactive than hydrogen, so copper metal is produced at the cathode you’ll see a coating of copper on the electrode
- At anode, oxygen and water produced from the hydroxide ions in the solution. You’ll see bubbles of oxygen gas forming
Electrolysis using non-Inert electrodes
. And if you use copper electrodes in a solution of copper sulphate, instead of inert electrodes, the result is different. Copper metal is still produced at the cathode, but the anode will now release copper ions into the solution
-> mass of anode will decrease and mass of cathode will increase
Electrolysis to purify copper
- Impure copper anode loses electrons, dissolving into the electrolyte to form copper
- The copper ions gain electrons, add the pure copper cathode, and add to it as a layer of pure copper
- Any impurities from the impure copper anode sink to the bottom of the cell, forming a sludge
Electroplating
. Coating the surface of a metal with another metal using electrolysis
-> cathode is the object you are going to electroplate
. Electrolytes is a solution containing the metal ions of the metal your plating
-> anode is often a bar of metal you’re using for plating. Use to maintain concentration of metal ions in the electrolyte
Why do we use electroplating?
. Four household objects like cutlery and cooking utensils -> to stop them corroding
- Metals used for protection are unreactive and don’t corrode easily
. Jewellery and decorative items often electroplated with metals, like gold or silver
-> improves appearance
Hydrogen/oxygen fuel cells
. Used to generate electricity, produces only water.
Hydrogen/oxygen fuel cells: advantages
. More efficient than car engines
. Difficult for energy to be lost as heat
. Energy isn’t lost through friction
. They only produce water and heat, no greenhouse gases are released
Hydrogen/oxygen fuel cells: disadvantages
. Hydrogen needs much more space to store the liquid fuels such as gasoline
. Hydrogen is also explosive, so it’s difficult to store and transport safely.
. Hydrogen fuel often made either from hydrocarbons, which come from fossil fuels or by electrolysis of water, which often uses electricity is generated using fossil fuels
Extraction of aluminium
. Ore for aluminium is bauxite
. Cryolite is used as it decreases melting points and increases conductivity -> less energy needed + cheaper
. Anodes have to be replaced regularly -> they are made from graphite which easily reacts with oxygen to form carbon dioxide
Ore
A rock from which a metal can be extracted from economically
