Suppose a teaspoon of magnesium filings and a teaspoon of powdered sulfur are placed together in a metal beaker. Would this constitute a mixture or a pure substance? Suppose the magnesium filings and sulfur are heated so that they react with each other, forming magnesium sulfide. Would this still be a “mixture”? Why or why not?

Initially, we have magnesium filings and powdered sulfur placed together in a beaker. This constitutes a mixture because magnesium and sulfur are not combined chemically, and their individual properties are retained. They are simply placed together, thus forming a mixture.

When magnesium filings and sulfur are heated, they undergo a chemical reaction, resulting in the formation of a compound called magnesium sulfide. In this reaction, magnesium loses two electrons and becomes a cation (Mg^2+), while sulfur gains two electrons and becomes an anion (S^2-). These ions form an ionic compound with the formula MgS. The chemical reaction can be represented as: Mg (s) + S (s) -> MgS (s)

Once the magnesium filings and sulfur react to form magnesium sulfide, we no longer have a mixture. This is because the individual properties of magnesium and sulfur are no longer retained. Magnesium and sulfur have combined chemically to form a new substance with different properties, which is called magnesium sulfide. Magnesium sulfide is considered to be a pure substance, not a mixture, since it consists only of one kind of compound with a fixed composition, and it has a uniform structure throughout. It cannot be separated into its components (magnesium and sulfur) by physical means, such as filtration or evaporation, unlike mixtures. In conclusion, initially, when magnesium filings and powdered sulfur are placed together, it constitutes a mixture. However, when they are heated and react with each other to form magnesium sulfide, the result is a pure substance, not a mixture, because the components combine chemically and no longer retain their initial properties.