You are hiking in the mountains and find a shiny gold nugget. It might be the element gold, or it might be “fool’s gold,” which is a nickname for iron pyrite, FeS₂. Which of the following physical properties do you think would help determine if the shiny nugget is really gold—appearance, melting point, density, or physical state?

Key Concepts

Physical Properties

Physical properties are characteristics of a substance that can be observed or measured without changing its chemical identity. These include appearance, melting point, density, and physical state. Understanding these properties is crucial for distinguishing between substances, such as gold and iron pyrite, as they exhibit different physical characteristics.

Density

Density is defined as mass per unit volume and is a key physical property used to identify substances. Gold has a significantly higher density (approximately 19.32 g/cm³) compared to iron pyrite (about 5.0 g/cm³). By measuring the density of the nugget, one can effectively differentiate between gold and fool's gold.

Melting Point

The melting point is the temperature at which a solid becomes a liquid. Gold has a melting point of 1,064 °C, while iron pyrite melts at a much higher temperature, around 1,177 °C. Knowing the melting points of these substances can help in identifying the nugget, as it can be tested under controlled conditions to observe its behavior when heated.