Page 212 - ICSE Chemistry 8

By Heating Metal Carbonates or Metal Hydrogen Carbonates

Metal carbonates and metal hydrogen carbonates when heated produce carbon dioxide.
Heat
CuCO 3 CuO + CO 2
Copper carbonate Copper oxide Carbon dioxide
Heat
2NaHCO 3 Na CO 3 + H O + CO 2
2
2
Sodium hydrogen Sodium carbonate Water Carbon dioxide
carbonate
Tests for Carbon Dioxide

We perform the following tests to check the presence of carbon dioxide.
• On passing carbon dioxide through lime water, lime water turns milky due to the forma on of
calcium carbonate which is insoluble. However, when excess of carbon dioxide is passed through
lime water, the milkiness disappears due to the forma on of calcium bicarbonate which is soluble
in water.

• On pu ng a burning candle or a burning splinter in a jar which contains carbon dioxide, it is
observed that the fl ame gets ex nguished. This shows that carbon dioxide does not support
combus on.

(a) burning splinter (b) carbon dioxide present in a jar causes
extinguishing of fl ame

Fig. 9.12: Carbon dioxide: non-supporter of burning

Activity 9.8

Aim: To show that carbon dioxide is heavier than air and does not support combus on
Materials required: A big glass container, 4–5 candles of diff erent
height, baking soda, vinegar

Procedure
• Fix the diff erent sized candles in the container.

• Add a heaped tablespoon of baking soda in the container.
• Light the candles.
• Now, pour vinegar a tablespoon at a me on the baking
soda.

Observa on: You will no ce that the candle fl ames go out one at
a me, star ng with the shortest.

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