[nimbusracing]

Pour some limewater into a beaker and bubble CO2 gas through it. Watch as the limewater becomes cloudy. Get some CO2 and then quickly put the lid on the jar. Add limewater to the jar of CO2, cap, and then shake the jar. Cloudy solution indicates CO2. Sediment forms at the base.

i presume this sediment is calcium carbonate...

how do u write an equation for this reaction?

[xiankai]

given that the reaction is an acid-base reaction, u should know the reactants and products. put them on appropriate sides of the equation, and balance it.