When mercury(II) oxide (HgO) is heated, what color change is observed?

• A. Red to metallic silver
• B. Orange to black
• C. Blue to white
• D. Yellow to green

Answer: (A)

Verified step by step guidance

1. Identify the chemical reaction involved: Heating mercury(II) oxide (HgO) causes it to decompose into mercury (Hg) and oxygen gas (O\_2). The reaction is: \$2 \mathrm{HgO} (s) \rightarrow 2 \mathrm{Hg} (l) + \mathrm{O}_2 (g)$.
2. Recall the physical appearance of the reactant and products: Mercury(II) oxide is typically a red or orange solid, while elemental mercury is a shiny, metallic silver liquid at room temperature.
3. Understand that the color change observed is due to the transformation of the red/orange solid HgO into liquid metallic mercury, which has a silver color.
4. Note that the oxygen gas produced is colorless and does not affect the color change observed in the solid/liquid phase.
5. Conclude that the color change observed when heating HgO is from red (or orange) to metallic silver, corresponding to the decomposition of HgO into elemental mercury.