1. A student performs a calorimetry experiment with KCl. — Atomic Structure, Calorimetry, Thermodynamics, Solubility Equilibria Chemistry Question

Consider the K⁺ ion in KCl.
i. Write the complete ground-state electron configuration for the potassium ion, K⁺.

ii. Which has the larger radius, the K⁺ ion or the K atom? Explain your reasoning using principles of atomic structure.

The following information applies to parts B, C, D, and E.
A student performs an experiment to determine the enthalpy of solution, ΔHsoln, of KCl. The student places water in a calorimeter, measures the initial temperature, adds KCl(s), and stirs until the KCl dissolves completely. The temperature is continuously monitored during the experiment. Data from the experiment are given in the following table.

Describe how the student can use the temperature readings during the experiment to determine when the dissolution is complete.

Use the data in the table to do the following.
i. Calculate the magnitude of the thermal energy, q, in joules, transferred during the dissolution. Show the work that leads to your answer. (Assume that the solution has a specific heat capacity of 3.95 J/(g·°C).)

ii. Calculate the value of the molar enthalpy of solution, ΔHsoln, in kJ/mol, for KCl given that 0.0912 mol of KCl dissolved. Show the work that leads to your answer. Include the sign with your answer.

The calorimeter is not perfectly insulated. Would this cause the magnitude of ΔHsoln calculated in part C (ii) to be greater than, less than, or equal to the accepted value? Justify your answer.

The student performs a second experiment using the same mass of water but 6.80 g of RbCl(s) instead of 6.80 g of KCl(s). The magnitude of the molar enthalpy of solution, ΔHsoln, of RbCl is approximately equal to that of KCl.
Is the magnitude of ΔT in the RbCl experiment greater than, less than, or equal to that in the KCl experiment? Justify your answer. (Assume that the specific heat capacities of the solutions are equal.)

RbCl has a Ksp of 57 at 20 °C.
i. Write the net ionic equation for the dissolution of RbCl in pure water.

ii. Calculate the molar solubility of RbCl in a saturated solution at 20 °C. Show the work that leads to your answer.

iii. A second saturated solution is prepared by dissolving RbCl(s) in 1.0 M KCl(aq) at 20 °C instead of in pure water. Will the molar solubility of RbCl in 1.0 M KCl(aq) be greater than, less than, or equal to the molar solubility calculated in part F (ii)? Justify your answer.