Which of the following statements describes the difference between an alkali and a base? (A) A base produces more OH− ions than an alkali. (B) An alkali accepts H+ ions, whilst a base produces OH− ions. (C) An alkali describes a base that dissolves in water. (D) A base is an alkali that dissolves in water. Or (E) an alkali forms a blue aqueous solution.
To answer this question, we must understand what is meant by the term alkali. An Alkali is a subset of chemicals known as bases. Using the Brønsted–Lowry definition of a base, a base is a substance that does or can gain protons or, in other words, hydrogen ions in a reaction. An alkali is a base that can be easily dissolved in water and in a solution forms hydroxide ions. For example, sodium hydroxide is a strong base as when in a reaction it can take on hydrogen ions. And it is also an alkali as it is easily dissolved in water to form hydroxide ions.
There are some bases that do not dissolve in water or do not form hydroxide ions in solution. Copper(II) oxide or CuO behaves as a base in a reaction but does not dissolve in water. Therefore, a base like copper(II) oxide is a base but not an alkali. All alkalis are bases. However, not all chemicals that fit the Brønsted–Lowry definition of a base are alkalis.
Using this information, let’s have a look at our answer choices. We can see that answer choice (C) states that an alkali is a type of base that dissolves in water, which fits the description for the difference between an alkali and a base. Therefore, the statement that describes the difference between an alkali and a base is answer choice (C). An alkali describes a base that dissolves in water.