Question

Sodium hydroxide is:
A.A base
B.An acid
C.An alkali
D.Both acid as well as alkali

Answer 1

Hint:We know that sodium hydroxide or caustic soda is an inorganic compound. It is an ionic compound that contains sodium cations $\left( {N{a^ + }} \right)$ and hydroxide anions $\left( {O{H^ - }} \right).$ it is a white solid with molar mass of $40\,g/mol.$

Complete step by step answer:
Now, let us define an acid.
A substance that donates protons (or) hydrogen ions is called an acid. Most acids are hydrogen atoms, which dissociate to form cation and anion in water.
Let us define a base.
A base is a substance, which neutralizes an acid. Base has the ability to accept a proton from an acid. Some of the bases such as metal hydroxides and metal oxide form neutral products on reaction with acids. Base is insoluble in water. Salts and water are produced when the base reacts with acids. They have a bitter taste and are slippery. There are two types of bases, strong and weak bases.
Let us define an alkali.
An alkali is a base that is water-soluble. All alkalis are base but not all bases are alkalis. A basic salt of alkali earth metal or alkali metal is an alkali.
When we add alkali to acid, there is an increase in pH of the solution, whereas when an acid is added to alkali, the pH of the solution because of the removal of base.
We shall identify what is sodium hydroxide.
Sodium hydroxide is both base as well as alkali because it is water-soluble and forms 50% saturated solution with water.
Sodium hydroxide is a strong base that dissociates into sodium ions and hydroxide ion in water. We can write the dissociation reaction of sodium hydroxide as,
$NaOH\xrightarrow{{}}N{a^ + } + O{H^ - }$
The liberation of hydroxide ions in aqueous solution reasons out for its basicity. It has a pH of 12 and is highly alkaline. It liberates a large amount of hydroxide ion, and the degree of dissociation is high. Therefore, it is a strong alkali.
Hence option (D) is correct.

Note:
The other name of sodium hydroxide is lye. We can use it in the manufacture of pulp and paper, soaps, detergents, drinking water etc. It has low solubility in ethanol, methanol and is insoluble in ether and non-polar solvents. It reacts with protic acid to form water and corresponding salts.