Chemistry C3 Part 7

Based on the Edexcel Textbook

pg 134-135 The Alkali Metals

When the first periodic table was written (1800) the white solid compounds Soda and Potash were thought to be elements because no one had managed to split them up. Humphry Davy in 1807 succeeded in carrying out electrolysis on moltan potash and potash just moist enough to conduct electricity. He was the first person to see potassium metal. A week later he did a similar experiment to extract sodium. Davy had converted potassium ions into potassium metal like this

K+(aq) + e- ---> K(s)

The alkali metals do have some transition metal properties but they are generally softer with lower melting points. They are found in Group one of the periodic table with one electron in their outside shell. They are very reactive; when you put them in water they react vigerously to produce hydrogen gas and a metal hydroxide. This makes them hard to use safely but they can be used in some forms eg Lithium ions are used in rechargable batteries, Potassium ions are used in fertiliser and sodium vapour is used in street lamps because it glows orange.

pg 136-137 Glass

Many compounds of Alkali metals are useful. One of which is sodium carbonate used in the manufacture of glass. The raw material in glass manufacture is sand (silicon dioxide) the problem with this is that it has a very strong structure so it melts at high temperatures of around 2000'C. Adding sodium carbonate reduces the temperature needed to about 1000'C. This make the glass weak but adding calcium oxide (lime) improves the strength. Soda Lime Glass is the most common type of glass.

Different compounds can be added to glass to give it different 'effects' (transition metals give glass colour:

• Pottassium oxide and lead oxide make 'crystal' glass 'sparkle'
• Boron makes glass heat resistant (Pyrex)
• Iron(II) oxide and chromium make glass dark green
• Copper oxide makes it turquoise
• Colbalt makes it blue
• Copper or Gold makes it red

Sand is non-renewable but supplies are…