Question

The balanced net ionic equation for the reaction of aluminium sulphate and sodium hydroxide contains which of the following terms?
(A) 3$A{l}^{+3}$(aq)
(B) $O{H}^{-}$(aq)
(C) 3$O{H}^{-}$(aq)
(D) 2$A{l}^{+3}$(aq)
(E) $2Al{(OH)}_3$(s)

Answer 1

Hint: The net ionic equation is a chemical equation for a reaction that lists only those species participating in the reaction. In other words, the net ionic equation applies to reactions that are strong electrolytes in water.

Complete step by step answer:
Aluminium sulfate is a chemical compound with the formula $A{l}_2{\left(S{O}_4\right)}_3$. It is soluble in water and is mainly used as a coagulating agent (promoting particle collision by neutralizing charge) in the purification of drinking water and wastewater treatment plants, and also in paper manufacturing.
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations $N{a}^{+}$ and hydroxide anions $O{H}^{-}$. Sodium hydroxide is a highly caustic base and alkali that decomposes proteins at ordinary ambient temperatures and may cause severe chemical burns. It is highly soluble in water, and readily absorbs moisture and carbon dioxide from the air.

The unbalanced molecular equation is:
$$A{l}_2{\left(S{O}_4\right)}_3+NaOH\to Al{\left(OH\right)}_3\downarrow +N{a}_{2}S{O}_4$$

The unbalanced complete ionic equation is:
$$A{l}^{3+}+S{O_4}^{2-}+N{a}^{+}+O{H}^{-}\to Al{\left(OH\right)}_3\downarrow +N{a}^{+}+S{O_4}^{2-}$$

The balanced net ionic equation is :
$$A{l}^{3+}+3O{H}^{-}\to Al{\left(OH\right)}_3\downarrow$$
The balanced net ionic equation for the reaction of aluminum sulfate and sodium hydroxide contains term 3 $O{H}^{-}$.
So, the correct answer is “Option C”.

Note: Aluminium sulfate is sometimes called alum or papermaker's alum in certain industries. However, the name "alum" is more commonly and properly used for any double sulfate salt with the generic formula $XAl{\left(S{O}_4\right)}_2\cdot 12H_{2}O$, where X is a monovalent cation such as potassium or ammonium.