2.7.1g: describe and carry out the following: (i) experiments to study the thermal decomposition of group 1 and 2 nitrates and carbonates (ii) flame tests on compounds of group 1 and 2 (iii) simple acid-base titrations using a range of indicators, acids and alkalis, to calculate solution concentrations in g dm-3 and mol dm-3, eg measuring the residual alkali present after skinning fruit with potassium hydroxide

THERMAL DECOMPOSITION OF GROUP 1 AND 2 NITRATES AND CARBONATES

All carbonates decompose to the oxide and carbon dioxide on heating, thermal stability increases down the groups

All nitrates decompose to the oxide on heating, thermal stability increases down the groups

FLAME TESTS

1. dip a nichrome or platinum wire (chemically inert) into hydrochloric acid (cleans impurities and chloride ions create a more visible colour change)
2. dip the damp nichrome or platinum wire into a solid sample of the metal
3. hold the metal in a non-luminous Bunsen flame and observe a colour change

ACID-BASE TITRATIONS

Indicators:

• phenolphtalein (pink in alkali, colourless in acid)
• methyl orange (yellow in alkali, red in acid)