Question

We can detect $B{r^ - }$ and ${I^ - }$ by ‘Layer Test’ if present together. Select true or false.

Answer 1

The layer test is associated with halogens. The halogen elements are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In a layer test bromine shows orange yellow colour and iodine shows violet colour whereas chlorine is almost colourless.

Complete step by step answer:
The layer test is a qualitative test involving redox reactions among halides. This type of test is used to detect the presence of iodide and bromide ions in a solution.
The decreasing order of the reactivity of the halide ions is ${I^ - } > B{r^ - } > C{l^ - } > {F^ - }$. The salts can be oxidized in water.
In this case, if we add chlorine water and chloroform to the mixture of bromide ion and iodide ion, the following redox reactions take place:
$2{I^ - } + C{l_2} \to {I_2} + 2C{l^ - }$
$2B{r^ - } + C{l_2} \to B{r_2} + 2C{l^ - }$
At first Iodide ion is oxidized by chlorine (and bromine) and forms iodine. Here the chloroform layer will show violet colour due to the presence of iodine.
Now we will extract the aqueous layer which contains bromide ion and repeat the addition of chlorine water and chloroform. In this case the chloroform layer will show orange yellow colour due to the presence of bromine.

Therefore, we can detect $B{r^ - }$and ${I^ - }$by ‘Layer Test’ if present together. Hence the correct option is True.

Note: Remember that bromine and iodine are much soluble in organic solvents than in water. Since we are using chlorine as an oxidant, chloride ions are negated here. Chlorine is almost colourless and it will be invisible in the chlorinated solvents as it is a gas.