What happens if water contains a lot of carbon dioxide and you add lime? Would it be more or less expensive to soften a water that has a lot of carbon dioxide in it? Solution Answer:- When calcium hydroxide is allowed to react with carbon dioxide,calcium carbonate is obtained. Ca(OH) + CO—-> CaCO + HO Controlled addition of CO is required to prepare calcium carbonate. Excess CO lead to the formation of calcium hydrogen carbonate ,which is water soluble. Reaction has no harmful effects. CaCO + HO + CO—->Ca(HCO) Enough CO2 added to reduce the pH of water to less than 8.7 Excess corbon di oxide present in water is less expensive for softening of water..