How can you distinguish between aluminum and aluminum alloy?

To distinguish between aluminum and aluminum alloys, testing with a 10 percent solution of caustic soda is effective because aluminum reacts with caustic soda to form sodium aluminate and hydrogen gas, which can be observed as bubbles. Pure aluminum is less reactive and will produce fewer bubbles compared to aluminum alloys, which often contain copper, zinc, or other metals that result in a more vigorous reaction.

In contrast, visual inspection may not provide enough definitive clues since both pure aluminum and its alloys can appear very similar. Using a magnet is ineffective because aluminum, whether pure or alloyed, is non-magnetic. Measuring density could provide some information, but it requires precise calculations and might not be conducive for a quick identification since the density of alloys can vary widely. The reaction with caustic soda is a clear, observable difference that effectively highlights the distinction between the two materials.