To answer the question regarding the properties of KCl (potassium chloride) after water has evaporated from its aqueous solution, we should consider what happens during the process of dissolving and evaporation. Let's evaluate each statement:
A) The KCl(s) becomes a molecular compound.
- This statement is incorrect. Potassium chloride is an ionic compound whether it is in the solid state or dissolved in water. Evaporating the water only removes the water molecules; it does not change the ionic nature of KCl.
B) The molar mass of the KCl(s) decreases.
- This statement is also incorrect. The molar mass of a compound is determined by the sum of the atomic masses of the constituent elements, which are potassium and chlorine in this case. Evaporating water from the solution does not alter the atomic composition of the KCl molecules, so the molar mass remains the same.
C) The melting point of the KCI(s) is unchanged.
- This statement is correct. The melting point is an intrinsic property of a substance, depending only on the substance itself and not on its amount or the presence of other substances (once those other substances have been removed). Since the KCl solid obtained after evaporation is chemically identical to the solid before it was dissolved, the melting point remains unchanged.
D) The KCI(s) conducts an electric current.
- In the solid state, KCl does not conduct electricity because its ions are fixed in place within a crystal lattice and cannot move freely. KCl can conduct electricity when it is either melted into a liquid or dissolved in water because its ions are free-moving in those states. Since the water has been evaporated and the KCl is back in the solid state, it will not conduct an electric current.
Therefore, the correct answer is:
C) The melting point of the KCI(s) is unchanged.
