The following series of observations is made: (1) a small piece of dry ice \(\left[\mathrm{CO}_{2}(\mathrm{s})\right]\) is added to \(0.005 \mathrm{M}\) \(\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq}) .(2)\) Initially, a white precipitate forms.(3) After a short time the precipitate dissolves. (a) Write chemical equations to explain these observations. (b) If the \(0.005 \mathrm{M} \mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})\) is replaced by 0.005. \(\mathrm{M} \mathrm{CaCl}_{2}(\mathrm{aq}),\) would a precipitate form? Explain. (c) If the \(0.005 \mathrm{M} \mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})\) is replaced by 0.010 \(\mathrm{M} \mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq}),\) a precipitate forms but does not re-dissolve. Explain why.

1. When dry ice \(\left[\mathrm{CO}_{2}(\mathrm{s})\right]\) is added to \(0.005 \mathrm{M}\) calcium hydroxide (\(\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})\)), it forms a white precipitate of calcium carbonate, and water is also produced. This can be represented by the chemical equation\(\mathrm{CO}_{2}(\mathrm{s})+\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq}) \rightarrow \mathrm{CaCO}_{3}(\mathrm{s})+\mathrm{H}_{2}\mathrm{O}\).2. After a short time, the precipitate dissolves because the carbon dioxide reacts with the water to form carbonic acid, which in turn reacts with the calcium carbonate to form calcium bicarbonate that is soluble. The chemical equation for this is \(\mathrm{CaCO}_{3}(\mathrm{s}) + \mathrm{CO}_{2}(\mathrm{g}) + \mathrm{H}_{2}\mathrm{O} \rightarrow \mathrm{Ca}(\mathrm{HCO}_{3})_{2}(\mathrm{aq})\).

If the \(0.005 \mathrm{M} \mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})\) is replaced by \(0.005 \mathrm{M} \mathrm{CaCl}_{2}(\mathrm{aq})\), no precipitate would form. This is because calcium chloride is soluble, and when it reacts with carbon dioxide, no insoluble substance is formed. Thus, no precipitate is observed.

Replacing the \(0.005 \mathrm{M} \mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})\) with \(0.010 \mathrm{M} \mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{aq})\) causes the formation of a precipitate that does not dissolve. This is due to the increased concentration of Calcium ions in the solution that results in exceeding the solubility product of Calcium Carbonate, which is relatively insoluble.