Question

What is the percentage of ammonium ions in ammonium dichromate?

Answer 1

Ammonium dichromate is a chemical compound with the molecular formula of ${\left( {N{H_4}} \right)_2}C{r_2}{O_7}$ . This compound can dissociate into ammonium ions and chromate ions. Two moles of ammonium ions were obtained. The molar mass of two ammonium ions when divided by the total molar mass of ammonium dichromate gives the percentage of ammonium ions in ammonium dichromate.

Complete answer:
Ammonium ions exist as cations and chromate ions exist as anions. The chemical compound formed from these ions was ammonium dichromate. The molecular formula is ${\left( {N{H_4}} \right)_2}C{r_2}{O_7}$ .
The molar mass of ammonium dichromate is obtained by the sum of all the atoms present in it which will be written as $2\left( {14} \right) + 8\left( 1 \right) + 2\left( {52} \right) + 7\left( {16} \right) = 252gmo{l^{ - 1}}$
Thus, the molar mass of ammonium dichromate is $252gmo{l^{ - 1}}$
Ammonium dichromate dissociates into ammonium ions and chromate ions as follows:
${\left( {N{H_4}} \right)_2}C{r_2}{O_7} \rightleftharpoons 2N{H_4}^ + + C{r_2}{O_7}^{2 - }$
Molar mass of one ammonium ion is $14 + 4 = 18gmo{l^{ - 1}}$
In the above dissociation equation, two moles of ammonium cations were formed. The total molar mass of two ammonium ions will be $2 \times 18gmo{l^{ - 1}} = 36gmo{l^{ - 1}}$
To obtain the percentage of ammonium ions in ammonium dichromate, divide the molar mass of the ammonium ions with the molar mass of ammonium dichromate.
$\%$ of $N{H_4}^ +$ will be $\dfrac{{36}}{{252}} \times 100 = 14.31\%$
Thus, the percentage of ammonium ions in ammonium dichromate is $14.31\%$

Note:
The molar mass of some elements in the periodic table is not exactly equal to the double to the atomic number of elements. Thus, the molar mass should be calculated correctly. The number of moles of ammonium cations obtained in the above equation are two. Thus, the molar mass of ammonium should be multiplied with two.