Question

On passing excess CO2 through lime water, it first turns milky and then becomes 3 colourless. Explain why ? Write the chemical reactions.

Answer 1

On passing co2 through lime water it turns milky because co2 reacts with calcium hydroxide (lime water) to form precipitate of calcium carbonate that is why it turns milky.
But when excess of co2 is passed calcium hydrogencarbonate is formed which is soluble in solution and therefore it becomes colourless.
Hoping it will help you.

Answer 2

We have lime water = Ca(OH)2
And CO2
When we pass CO2 through lime water it forms CaCO3 calcium carbonate.
The reaction is
Ca(OH)2+CO2-----> CaCO3+H2O
Thus as CaCO3 is formed the solution appears milky white.

And on passing excess CO2 we get
CaCO3+H2O+CO2----->Ca(HCO3)2

Thus calcium bicarbonate is formed.Normally,
The carbonates form precipitates and forms some crystals in the solution or due to the formation of sodium bicarbonate the milkyness disappears.and the solution becomes colourless.



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