Melting Points of Alkali Metals

1. Melting Points of Alkali Metals Form the element in Group 1 excepthydrogen. Soft silvery metals with low melting points and density: Typically stored under oil because it reacts with air (both oxygen and water vapour)

2. Ionization Energies of Alkali Metals Forms one cation (+1) Has only one valence electron, ns1 => low first ionization energy Excellent reducing agent i.e. good at losing electrons so that other elements can be reduced

3. Reaction of Alkali Metals with Water How can I distinguish between the alkali metals? Flame test. All of the alkali metals give positive flame tests. Reactivity with water. All of the alkali metals react exothermically with water to give the corresponding hydroxide and hydrogen gas. IIn Lab *Video: http://www.youtube.com/watch?v=Ft4E1eCUItI&mode=related&search=

4. Exercise A 3 mm cube of sodium metal is added to 100 mL of distilled water in a beaker. Determine the concentration of the resulting sodium hydroxide solution?

5. Reaction with Air Reaction with the oxygen in air: Lithium reacts with excess oxygen to give lithium oxide: Sodium reacts with excess oxygen to give sodium peroxide: Potassium, rubidium and cesium all react with excess oxygen to give the corresponding superoxide: If we limit the amount of oxygen available, we can force sodium to stop at sodium oxide. Potassium, rubidium and cesium cannot be stopped at the oxide – only at the peroxide.

6. Reaction with Halides Alkali metals also react vigorously with halogens: In each of these reactions of alkali metals, the alkali metal has formed an ionic compound. In fact, pure alkali metals are so reactive that they do not exist in nature. Alkali metals are only found naturally in ionic compounds (aka salts). Video: http://www.angelo.edu/faculty/kboudrea/demos/sodium_chlorine/sodium_chlorine.htm

7. Production of Alkali Metals How are they made? • Sodium: Electrolysis of NaCl in a Downs cell. 1)Requires a significant input of (electrical) energy. Industrially this is accomplished by the application of an electric potential to “force” the reaction to go in the unfavourable direction. 2) Reaction is done in molten NaCl?? As H+ is more easily reduced than Na+, there can be no water present in the electrolysis. NaOH melts at 318 °C; NaCl melts at 808 °C; By adding BaCl2 or CaCl2lthe melting point of NaCl can belowered to ~600 °C. As Ba2+ and Ca2+ are more difficult to reduce than Na+ they does not interfere as water does. 3) Sodium is insoluble in molten NaCl and less dense than it. As such, it readily be removed from the cell. • Lithium: Electrolysis of LiCl.

8. Downs Cell

9. Electrolysis of Aqueous NaCl What if NaCl is electrolyzed in solution? NaOHis obtained instead of sodium metal! Main method of Industrial production of sodium hydroxide and chlorine gas much like the Downs Cell: Anode Reaction: Cathode Reaction: Why is NaOH formed? NaOH and chlorine gas are kept separate, otherwise they form bleach (NaOCl):

10. Electrolysis of Aqueous NaCl

11. Production of K, Rb, Cs Potassium: is made by reaction of KCl with sodium metal. K cannot beelectrolyzed like sodium as it is soluble in molten KCl, and thus not easily be removed from the cell. K can be distilled from a mixture of sodium and potassium. Potassium boiling point is 774 °Cvs883 °C for sodium. KCl is added to molten sodium at 850oC : Potassium evaporates and pushes the reaction “forward” by constantly trying to restore equilibrium. Rubidium and Cesium: Similar fashion to K by reduction of a salt by a reducing agent