A student is given four solid samples labeled \(W, X, Y\), and \(Z\). All except \(Z\) have a metallic luster. She is told that the solids could be gold, lead sulfide, quartz \(\left(\mathrm{SiO}_{2}\right),\) and iodine. The results of her investigations are as follows: (a) \(\mathrm{W}\) is a good electrical conductor; \(\mathrm{X}\), \(\mathrm{Y},\) and \(\mathrm{Z}\) are poor electrical conductors. (b) When the solids are hit with a hammer, W flattens out, X shatters into many pieces, \(Y\) is smashed into a powder, and \(Z\) is cracked. (c) When the solids are heated with a Bunsen burner, Y melts with some sublimation, but \(\mathrm{X}, \mathrm{W},\) and \(\mathrm{Z}\) do not melt. (d) In treatment with \(6 \mathrm{M}\) \(\mathrm{HNO}_{3}, \mathrm{X}\) dissolves; there is no effect on \(\mathrm{W}, \mathrm{Y},\) or \(\mathrm{Z}\) On the basis of these test results, identify the solids.

Understanding the electrical conductivity of substances is key when investigating unknown solids in a chemistry lab. Conductivity refers to the ability of a material to allow the flow of electric current. Metals, such as gold, are excellent conductors due to their sea of delocalized electrons that can move freely, facilitating current flow. In contrast, non-metals like iodine and insulating minerals such as quartz have tightly bound electrons and exhibit poor conductivity.

In our exercise, the substance that was identified as a good conductor, sample W, was thus correctly deduced to be a metal, specifically gold. Poor conductivity observed in the other samples would suggest they are non-metals or non-conducting solids. These results can form an initial hypothesis in a lab investigation, guiding further testing to determine the identity of the unknown substances.

The physical properties of solids, such as malleability and reaction to heat, are distinctive characteristics that aid in the identification process. Malleable substances, like metals, can deform under pressure, flattening out when hit with a hammer without breaking. This property confirmed that sample W, which flattened, was indeed a metal such as gold. Crystalline solids like quartz, mentioned as sample X, shatter because their rigid lattice structure cannot absorb the impact – aligning with the observed behavior of sample X shattering into pieces.

Additionally, melting points give insight into a solid's makeup; iodine (Y) sublimates and melts readily under heat, while lead sulfide (Z), a mineral with a high melting point, does not. These findings, tied with a sound understanding of such physical properties, deepen the comprehension of solid-state chemistry and are crucial for diagnosing the nature of the substances in question.

A substance's chemical properties define how it reacts with other materials. Solubility in particular acids, like HNO3 (nitric acid), can be highly revealing. For instance, quartz is soluble in nitric acid, while metals like gold and substances like iodine and lead sulfide are not. The solubility test conveys a wealth of information about the chemical structure and bonding within a substance. Sample X dissolving in HNO3 keyed us into its true identity - quartz - because such a reaction is indicative of non-metallic mineral compounds.

Recognizing the chemical reactivity or inertness of different substances is fundamental in chemistry. Gold's inertness made it unreactive to nitric acid, helping to reinforce the previous identification of sample W as gold. A solid grasp of both chemical reactivity and solubility assists students in not only identifying unknowns but also in predicting how substances will behave in various chemical contexts.