Na & K, Mg & Br Zephan and Tae

Alkali Metals Most reactive elements – Ionic in nature (solid or aqueous) – Kept under special conditions to prevent contact with air. Na + and K + dominate alkali metals

Sodium Primarily NaCl or halite. Major production from mining salt deposits formed from millions of years of evaporation. Also produced by the evaporation of concentrated salt solutions called Brines.

Brines After evaporation, the solid is melted to use in an electrolytic cell called the Down’s cell. Molten Na and Ca forms at the cathode. – Calcium used to lower the boiling point of the sodium chloride. Na is siphoned off by a collection pipe at the cathode and Cl collected at the anode. Sodium and Chlorine are kept separate by an Iron screen to prevent explosive recombining.

Potassium Most potassium comes from sylvite, KCl. – Too soluble to be produced by the same methods as sodium. Instead liquid sodium is used to reduce K +. – Na (l) + K + (l) -> Na + (l) + K (g) – This works because the sodium atom is smaller than the potassium atom so it has greater electron affinity and electronegativity. – This reaction is raised to 850 O C, beyond the boiling point of potassium. to push the reaction to products. – K (g) is then collected, which pushes the reaction even more to products to make this an efficient reaction.

Potassium (saltpeter, KNO 3 ) in gunpowder and fireworks

Jet Engines Not really. Sodium and Lead were once used to make antiknock additives in gasoline to increase the fuel’s octane rating. – Example: Tetraethyl lead or leaded gas. – 4C 2 H 5 Cl (g) + 4Na (s) -> (C2H5) 4 Pb (l) + 4NaCl (s) Because of the toxicity of lead and its’ effects on the environment, leaded fuels are now only used in piston-based aircraft engines.

Nuclear Reactors Sodium can be used in a type of nuclear reactor called a breeder reactor. – Breeder reactor means it creates more usable material than it consumes. Low melting point, high viscosity, thermal conductivity, and heat capacity make sodium perfect for cooling reactors. Potassium is also used in chemical and nuclear reactors as an alloy with sodium to be used as a heat exchanger. – Chemical reactors are containers designed to increase the efficiency of a reaction by applying or removing heat, pressure, agitation, etc.

References

Mining the sea: Mg and Br Magnesium(Mg) - The eighth most abundant element found on the Earth ( About 0.13% of MgCl 2 is present in seawater) - Strong reducing agent (Can not be obtained by chemical reduction method)

Extraction of Mg - Many methods are available from its ores - Dow process (the most widely used method from seawater)

Dow process SeashellSeawater Mg(OH) 2 Setting tank Filters MgCl 2 Evaporation Dryer MgCl 2 *nH 2 O Electrolysis Mg(s)Cl 2 (g) 1. Mining -Intake of Seawater (Mg 2+ ) - Ca(OH) 2 from seashells Seashells(CaCO 3 ) decomposed with heat to CaO and mixed with water  Ca(OH) 2 2. Converting to mineral Ca(OH) 2 (aq) + Mg 2+ (aq)  Mg(OH) 2 (s) + Ca 2+ (aq) 3. Converting to compound Mg(OH) 2 (s) + 2HCl(aq)  MgCl 2 (aq) + 2H 2 O(l) 4. Evaporation 5. Electrochemical redox MgCl 2 (l)  Mg(l) +Cl 2 (g) (heating above 700 ℃) HCl

Uses of Magnesium - In the manufacture of light and high-tensile alloys as form of alloy - Sacrificial anodes - In the metallurgical extraction of other metals ( Be, Ti, Zr and U)

Bromine (Br) -A member of the halogen group -Liquid nonmetalic element -The largest source of Br is the oceans as Br - (at concentration of 0.065g/L) - Readily oxidized to Br 2 with Cl 2 (aq) at standard state 2Br - (aq) + Cl 2 (aq)  Br 2 (l) +2Cl - (aq), ∆G o = -61.5KJ

Also Small amounts of bromine can be made through the reaction with Sulphuric acid (H 2 SO 4 ) NaBr (s) + H 2 SO 4 (l)  HBr (g) + NaH 2 SO 4 (s) 2HBr (g) + H 2 SO 4 (l)  Br 2 (g) + SO 2 (g) + 2H 2 O (l)

Uses of Bromine - In making fire retardant chemicals - In water purification as a disinfectant - In photography film (inorganic bromine)  AgBr - In medicines - As a petrol additive to prevent lead being deposited in the cylinders (Anti-knock agent)