Question

Bromine is prepared in the laboratory:
A.By heating ${\text{KBr}}$ with Conc. ${{\text{H}}_2}{\text{S}}{{\text{O}}_4}$
B.By heating ${\text{KBr}}$ with ${\text{Mn}}{{\text{O}}_2}$ with Conc. ${{\text{H}}_2}{\text{S}}{{\text{O}}_4}$
C.By heating ${\text{KBr}}$ with ${\text{HCl}}$
D.By passing ${{\text{I}}_2}$ vapours through ${\text{KBr}}$ solution.

Answer 1

We can prepare bromine in the laboratory by oxidation of sodium or potassium bromide. It is done in the presence of concentrated acids.

Complete answer:
The element bromine belongs to the group number 17 of the modern periodic table. It is also known as halogens. Naturally bromine occurs as a diatomic molecule. Bromine exists as liquid at room temperature and is also quite reactive just like the other halogens. Bromine is highly soluble in organic solvent and also partially soluble in water. Bromine gas is reddish brown in colour. Commercially we can prepare bromine gas using chlorine gas over the bromide ions. The oxidation of bromide occurs to form bromine gas.
In the laboratory we can simply perform the oxidation of the sodium bromide or potassium bromide using some oxidising agents such as manganese oxide in the presence of concentrated sulphuric acid. It leads to the formation of sodium hydrogen sulphate, manganese sulphate, water and bromine gas is formed. The reaction occurs as:
${\text{NaBr}} + {\text{Mn}}{{\text{O}}_2} + 3{{\text{H}}_2}{\text{S}}{{\text{O}}_4} \to {\text{NaHS}}{{\text{O}}_4} + {\text{MnS}}{{\text{O}}_4} + {{\text{H}}_2}{\text{O}} + {\text{B}}{{\text{r}}_2}$

Thus, the correct option is B.
Note:
As we know that like dissolves like. The more solubility of bromine in organic solvents is due to its non polar nature. In water polar compounds are more soluble. The less polar or non polar solvent are chloroform, carbon tetrachloride, benzene. In the presence of cold alkali bromine forms hypobromite whereas with hot alkali they form hypobromite. It also reacts with metals such as aluminium to form metal bromides. On reaction with hydrogen it forms hydrogen bromide. It is a weaker oxidising agent than chlorine and is also less electronegative than chlorine.