Metals, Non-metals, Electrolysis and Organic Chemistry
Metals, Non-metals, Electrolysis and Organic Chemistry combines reactivity, electrochemical cells and the first rules of carbon chemistry. Questions often ask you to predict a displacement reaction, identify electrode products or name a hydrocarbon.
Metals and non-metals
- Metals are generally lustrous, malleable, ductile and good conductors; non-metals are usually brittle and poor conductors.
- The reactivity series orders metals by tendency to lose electrons. A more reactive metal displaces a less reactive metal from its salt solution.
- Metal oxides are generally basic; non-metal oxides are generally acidic.
Electrolysis
- Electrolysis uses electrical energy to drive a non-spontaneous chemical change. The cathode is the negative electrode where reduction occurs; the anode is positive where oxidation occurs.
- In acidified water, hydrogen is released at the cathode and oxygen at the anode in a 2:1 volume ratio.
- In copper sulfate solution with copper electrodes, copper is deposited at the cathode and dissolves from the anode.
Organic chemistry
- Carbon is tetravalent and forms chains and rings by catenation. Alkanes are CnH(2n+2), alkenes CnH2n, alkynes CnH(2n-2).
- Functional groups include -OH (alcohol), -CHO (aldehyde) and -COOH (carboxylic acid).
Worked example
In electrolysis of acidified water, 44.8 L of hydrogen is collected at STP. Find the volume of oxygen. The reaction gives 2 volumes of hydrogen for 1 volume of oxygen, so oxygen volume = 44.8/2 = 22.4 L at STP. At the cathode, 2H+ + 2e- gives H2; at the anode, hydroxide ions release oxygen.
Traps
- Reversing cathode and anode products.
- Forgetting the 2:1 hydrogen-to-oxygen volume ratio.
- Using the reactivity series backwards in displacement questions.
- Mixing alkane and alkene general formulae.