Question

(i) Name the other ion formed when ammonia dissolves in water.
(ii) Give one test that can be used to detect the presence of the ion produced.

Answer 1

Hint: First we have to know that an ion is a particle, atom or molecule with a net electrical charge. The two types of positive ions are positive ions and negative ions. \[A{l^{ + 3}},C{a^{ + 2}}\] , …etc are examples of positive ions and \[C{l^ - },B{r^ - }\] , …etc are examples of negative ions.
 The charge of the electron is considered negative by convention. We know that the negative charge of an ion is equal and opposite to the charged proton considered positive by convention. For the detection of the ions, we use the scientific acidic or basic tests.

Complete answer: (I)
Ammonia readily dissolves in water with the liberation of heat. The ions which are formed are ammonium ions and hydroxyl ions (\[O{H^ - }\]). The aqueous solution of ammonia is ammonium hydroxide.
The chemical reaction is given by
\[N{H_3} + {H_2}O \rightleftharpoons N{H_4} + O{H^ - }\].
Hence the other ion formed when ammonia dissolves in water is \[O{H^ - }\].
(ii)
We can test for positive ions by adding sodium hydroxide solution and noting the colour of the precipitate. As we know that ammonium ions give off ammonia gas when we heat them with sodium hydroxide solution. Some metal ions also give coloured lights when we heat them in a Bunsen flame. The flame colour produced indicates which alkali metal ion is present in the compound.
So, litmus paper or indicators can be used to detect the presence of ions in the solution which results as, red litmus turns blue and Phenolphthalein turns colourless.
Hence, we use the red litmus paper test which turns blue, methyl orange or yellow to test the presence of ions produced.

Note:
We know that ions in solution are called electrolytes. All soluble ionic compounds are strong electrolytes. If we have to find the ionic charge of the element, we need to see the Periodic table. The metals, which are positive see on the left side of the periodic table and which are negative see on the right side of the periodic table.