Question #65d03

Sep 5, 2015

Option $\left(a\right)$

Explanation:

When carbon dioxide is passed through limewater, you see a milky white precipitate, $C a C {O}_{3} \left(s\right)$. Lime water is saturated $C a {\left(O H\right)}_{2} \left(a q\right)$; $C a {\left(O H\right)}_{2}$ is sparingly soluble in water. $C a C {O}_{3}$, alike with most carbonates, is pretty insoluble stuff; much more so that $C a {\left(O H\right)}_{2}$.

Its reaction with $C {O}_{2} \left(g\right)$ may be represented:

$C a {\left(O H\right)}_{2} \left(a q\right) + C {O}_{2} \left(g\right) \rightarrow C a C {O}_{3} \left(s\right) \downarrow + {H}_{2} O \left(l\right)$

Note that this equation is balanced.

If you keep bubbling $C {O}_{2}$, the white solid should go up. You should form the bicarbonate, $C a {\left(H C {O}_{3}\right)}_{2}$, which is soluble in water, and the reaction is outside the A level syllabus. As a further tip, the best source of carbon dioxide outside of a cylinder, is carbonated water (fizzy water; water supersaturated with $C {O}_{2} \left(g\right)$); you can cheaply pick up litres of this in a supermarket.

None of what I have written here is a substitute for doing the reaction in a laboratory