Problem 104 - Chemistry: The Central Science

Question

(a) One of the alkali metals reacts with oxygen to form a solid white substance. When this substance is dissolved in water, the solution gives a positive test for hydrogen peroxide, \(\mathrm{H}_{2} \mathrm{O}_{2}\). When the solution is tested in a burner flame, a lilac-purple flame is produced. What is the likely identity of the metal? (b) Write a balanced chemical equation for the reaction of the white substance with water.

Step-by-Step Solution

Answer

The alkali metal is likely potassium (K) due to the lilac-purple flame color. The white substance is potassium oxide (K2O). The balanced chemical equation for the reaction of K2O with water is \(K_{2}O + 2H_{2}O \rightarrow 2KOH + H_{2}O_{2}\).

Step 1: Identify the alkali metal based on the flame color

The fact that the substance produces a lilac-purple flame when tested in a burner flame points to the alkali metal being potassium (K). This is because the characteristic flame color of potassium is lilac-purple.

Step 2: Determine the formula of the white substance

The white substance is formed when potassium (K) reacts with oxygen (O). Alkali metals typically form compounds with oxygen in the form of M2O, where M is the alkali metal. So, the white substance is likely potassium oxide (K2O).

Step 3: Write the balanced chemical equation for the reaction of K2O with water

When potassium oxide (K2O) reacts with water (H2O), it forms potassium hydroxide (KOH) and hydrogen peroxide (H2O2). To balance the equation, we need to ensure that the number of atoms of each element on the reactant side is equal to the number of atoms of the same element on the product side. The balanced chemical equation for the reaction of K2O with water is: \(K_{2}O + 2H_{2}O \rightarrow 2KOH + H_{2}O_{2}\)