Thermal stability and flame coloursEdexcel International A Level Chemistry: Mind map

Exam questions on Thermal stability and flame colours

1. A technician identifies the metal in unlabelled solid samples by flame tests. She dips a clean nichrome wire into each sample, holds it in the edge of a blue Bunsen flame and records the colour. The samples contain compounds of lithium, potassium, calcium and barium.
   Explain, in terms of electrons, how the heated metal ions produce coloured light.2 marks
2. Samples of magnesium carbonate and barium carbonate are heated strongly in turn in a hard-glass test tube under identical conditions, and any gas given off is passed through limewater. Magnesium carbonate decomposes at a much lower temperature than barium carbonate.
   Explain why barium carbonate decomposes at a higher temperature than magnesium carbonate.2 marks
3. A student heats small samples of sodium nitrate and calcium nitrate in separate dry test tubes. Both tubes give off a colourless gas that relights a glowing splint, but only one of them also gives off a brown gas.
   Write equations for the thermal decomposition of sodium nitrate and of calcium nitrate. State which tube gives the brown gas, naming it and giving its effect on damp blue litmus paper.3 marks