Question

Which of the following is true about $C{O}_2$?

• A. It is a colourless, odourless and tasteless gas
• B. It dissolves in water to form carbonic acid.
• C. It reduces to CO When passed through red hot coke
• D. It can turn lime water milky

Answer 1

Answer: (A), (B), (C), (D)

The correct options are
A

It is a colourless, odourless and tasteless gas

B

It dissolves in water to form carbonic acid.

C

It reduces to CO When passed through red hot coke

D

It can turn lime water milky

(1) $C{O}_2$ is a colourless, odourless and tasteless gas.

(2) $C{O}_2$ dissolves in water to form carbonic acid (H${}_2$CO${}_3$) in very small amount, and most of the dissolved $C{O}_2$ remains loosely hydrated.
$C{O}_2$, therefore, is also known as carbonic anhydride.

$C{O}_2\left(g\right)+H_{2}O\left(l\right)$ $⟷$$H_2$$C{O}_3\left(l\right)$

(3) When passed through red-hot coke, it is reduced to carbon monoxide, CO.

$C{O}_2\left(g\right)+C\left(s\right)\to CO\left(g\right)$

(4) $C{O}_2$, when bubbled through lime water $Ca(OH{)}_2$, initially turns lime water milky, due to formation of calcium carbonate $CaC{O}_3$. However, when CO${}_2$ is passed in excess, the solution
becomes clear or the milkiness disappears. On heating the clear solution, milkiness reappears. This is explained by the following reactions:

Ca(OH)${}_2$ + CO${}_2$$\to$CaCO${}_3$ $\downarrow$+ H${}_2$O

CaCO${}_3$ + CO${}_2$ + H${}_2$O $\to$ Ca(HCO${}_3$)${}_2$

So, all the options (a), (b) (c) and(d) are True.