How can you distinguish between aluminum and aluminum alloy?

Using a 10 percent solution of caustic soda is an effective method for distinguishing between pure aluminum and aluminum alloys. When aluminum reacts with caustic soda, it undergoes a chemical reaction that produces hydrogen gas. However, aluminum alloys, which may contain other elements such as copper, magnesium, or silicon, could react differently due to the presence of those additional metals. This enables the identification of pure aluminum versus its alloys based on the difference in their chemical behavior when exposed to caustic soda.

For instance, pure aluminum tends to show a more vigorous reaction, while some alloys may exhibit either reduced reactivity or a different level of hydrogen gas production, allowing for differentiation between the two. This chemical method is reliable in that it provides a clear observable result based on the material's composition.

Visual inspection might not provide sufficient information as both forms could appear similar to the naked eye, while measuring the density requires precise equipment and may not yield definitive results depending on the alloy’s specific composition. Using a conductivity meter can also be informative since pure aluminum has high electrical conductivity. However, alloys can have varied conductivity, making this method less definitive compared to the chemical reaction with caustic soda.