Question

What happens when ${\text{S}}{{\text{O}}_2}$ is passed through acidified ${{\text{K}}_2}{\text{C}}{{\text{r}}_2}{{\text{O}}_7}$ solution?

Answer 1

Hint- Here, we will proceed by giving some details about sulfur dioxide and potassium dichromate. Then, we will be writing down the balanced chemical reaction involved in which potassium dichromate behaves as a strong oxidising agent.

Complete answer:
Sulfur dioxide is a poisonous gas and is responsible for the scent of matches burned. It is naturally emitted by volcanic activity and is created as a by-product of copper extraction and the burning of sulfur-contaminated fossil fuels. In appearance, this gas is colourless.
Potassium dichromate solution (${{\text{K}}_2}{\text{C}}{{\text{r}}_2}{{\text{O}}_7}$) is an inorganic, orange to red coloured compound that releases poisonous fumes of chromium when heated. Potassium dichromate is highly corrosive, and is a strong oxidizer. This material is used in wood preservatives, in pigment manufacturing and in photomechanical processes, but is substituted primarily by sodium dichromate.
When sulfur dioxide (${\text{S}}{{\text{O}}_2}$) is passed through acidified (in the presence of sulphuric acid i.e., ${{\text{H}}_2}{\text{S}}{{\text{O}}_4}$) potassium dichromate solution (${{\text{K}}_2}{\text{C}}{{\text{r}}_2}{{\text{O}}_7}$), potassium sulfate (${{\text{K}}_2}{\text{S}}{{\text{O}}_4}$) and chromium sulphate (${\text{C}}{{\text{r}}_2}{\left( {{\text{S}}{{\text{O}}_4}} \right)_3}$) are formed along with water molecules. The balanced chemical reaction of this process is shown below.
${\text{3S}}{{\text{O}}_2} + {{\text{K}}_2}{\text{C}}{{\text{r}}_2}{{\text{O}}_7} + {{\text{H}}_2}{\text{S}}{{\text{O}}_4} \to {{\text{K}}_2}{\text{S}}{{\text{O}}_4} + {\text{C}}{{\text{r}}_2}{\left( {{\text{S}}{{\text{O}}_4}} \right)_3} + {{\text{H}}_2}{\text{O}}$
Potassium dichromate (${{\text{K}}_2}{\text{C}}{{\text{r}}_2}{{\text{O}}_7}$) is a strong oxidising agent and hence the sulfur dioxide (${\text{S}}{{\text{O}}_2}$) gets oxidised to sulfate (${\text{S}}{{\text{O}}_4}^{2 - }$), the ${\text{C}}{{\text{r}}^{ + 6}}$ in potassium dichromate (orange coloured) gets reduced to ${\text{C}}{{\text{r}}^{ + 3}}$ in chromium sulphate (${\text{C}}{{\text{r}}_2}{\left( {{\text{S}}{{\text{O}}_4}} \right)_3}$) which is green coloured compound.
Potassium sulfate is a potassium source that is moderately water and acid soluble for use consistent with sulfates. Sulfate compounds are sulfuric acid salts or esters formed by substituting one or both of the hydrogens with the metal. In uses such as water treatment, most metal sulfate compounds are readily soluble in water, unlike the fluorides and oxides that appear to be insoluble. Organometallic forms are soluble in organic solutions, and in aqueous and organic solutions at times.
Chromium sulfate typically refers to inorganic compounds that are known commercially as chromium sulfate base.

Note- Chromium sulfate is used in paints, inks, ceramics and garment dyeing processes. They are non-combustible. In this particular problem, the oxidation number of chromium in ${{\text{K}}_2}{\text{C}}{{\text{r}}_2}{{\text{O}}_7}$ is given by $2\left( { + 1} \right) + 2x + 7\left( { - 2} \right) = 0 \Rightarrow 2x = 14 - 2 \Rightarrow x = 6$ and in ${\text{C}}{{\text{r}}_2}{\left( {{\text{S}}{{\text{O}}_4}} \right)_3}$ is given by $2y + 3\left( { - 2} \right) = 0 \Rightarrow 2y = 6 \Rightarrow y = 3$.