IS Question2

2009-05-24 8:15 pm

Add acid to a boiling tube contains marble. Then collect the carbon dioxide from the boiling tube by using a rubber stoppers with delivery tube. Let the CO2 goes to another test tube which contains lime water. The lime water turns milky afterwards. But it then turn back to colourless and never turn to milky again. Why does it happen?

回答 (1)

老爺子

2009-05-24 8:55 pm

✔ 最佳答案

Why does lime water turn milky ?
Lime water is the solution of calcium hydroxide. When carbon dioxide is passed through the lime water, carbon dioxide reacts with calcium hydroxide to give a white precipitate of calcium carbonate. The presence of calcium carbonate makes the mixture looks milky.
Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)

Why does the mixture turn back to clear and never to milky again?
In the presence of water, the excess carbon dioxide reacts with the calcium carbonate to give a colourless solution of calcium hydrogencarbonate. Therefore, the calcium carbonate dissolves to give a clear colourless solution.
CaCO3(s) + CO2(g) + H2O(l) → Ca(HCO3)2(aq)
The calcium hydrogencarbonate solution does not have further reaction, and thus the solution never turns to milky again.
=

👍 0 👎 0