Page 7 - Curriculum Visions Dynamic Book

 The calcium pellet rises up the test tube, buoyed by bubbles of hydrogen gas.
The solution in the
test tube quickly becomes saturated with calcium hydroxide from the reaction. Calcium hydroxide now forms tiny particles (precipitate), making the water appear cloudy.
The hydrogen gas released by the vigorous reaction between the calcium pellet and the water soon fills the test tube.
compound: a chemical consisting of two or more elements chemically bonded together.
precipitate: tiny solid particles formed as a result of a chemical reaction between two liquids or gases.
reaction: the recombination of two substances using parts of each substance to produce new substances.
saturated: a state in which a liquid can hold no more of a substance. If any more of the substance is added, it will not dissolve.
The cloudiness in the water is caused by particles of calcium hydroxide.
 On reaching the surface the bubbles burst and the calcium pellet again sinks down into the beaker. Each time the reaction becomes more violent and the bubbles become bigger. Big bubbles like this can form when the oxide coating has been removed, allowing
the metal to react more rapidly. The reaction also gives out heat. The precipitate of calcium hydroxide is granular, remaining suspended in the water for some time and making it cloudy.
 The calcium bobs
up and down in the water for a while and then stays on the surface because the calcium pellet gets so small it is more and more easily lifted to the surface by bubbles.
The tube fills with hydrogen and all the water is pushed out of the tube. This stops the reaction.
EQUATION: Calcium in water
Calcium + water ➪ hydrogen gas + calcium hydroxide Ca(s) + 2H2O(l) ➪ H2(g) + Ca(OH)2(aq)
(calcium hydroxide solution is also known as limewater)
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