A chemist dissolves 0.10 mol of solid magnesium chloride, MgCl₂(s)
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
A chemist dissolves 0.10 mol of solid magnesium chloride, MgCl₂(s), in enough water to prepare 1.0 L of aqueous solution at 25 °C. Assume the substance is completely soluble.
Use a fixed-volume “particle box” model in which one water molecule is represented by a small, open circle. For every ion you include, you may omit most of the water molecules except those needed to illustrate ion–dipole interactions clearly.
(a) Write the balanced chemical equation that represents the dissociation of MgCl₂ in water.
(b) Calculate the number of moles of each distinct ionic species that are present in the final solution.
(c) Draw a particulate-level diagram for a small portion of the solution that contains exactly four Mg²⁺ ions. Include the corresponding number of Cl⁻ ions and show at least two water molecules properly oriented around ONE Mg²⁺ ion and ONE Cl⁻ ion. Clearly distinguish the different particle types with labels or shading codes.
(d) Explain how your diagram in part (c) satisfies both overall charge balance and stoichiometric consistency with the bulk solution.
(e) Describe the orientation of the water molecules in the hydration shells of Mg²⁺ and Cl⁻, citing the relevant intermolecular force for each case.