Calcium chloride has many uses including as an agent to lower the freezing point of water. It is very effective for preventing ice formation on road surfaces and as a deicer.
i)
Define the term ionisation energy
ii)
Explain why the second ionisation energy of calcium is greater than the first ionisation energy
Magnesium chloride supplements are commonly found in tablet and capsule forms and are used to help increase magnesium levels in the body. Magnesium is an important nutrient and is responsible for many processes in the body including regulation of blood sugar and blood pressure.
i)
Define the term enthalpy of hydration in relation to a chloride ion.
ii)
State whether the hydration of a chloride ion is an exothermic or endothermic process. Justify your answer.
Using Section 20 in the Data Booklet, explain why the value for the enthalpy of hydration for the fluoride ion is more negative than that for the chloride ion.
The enthalpy of solution for magnesium chloride was measured in a lab as -73 kJ mol-1 Using Sections 18 and 20 in the Data Booklet and showing your working, determine the enthalpy of hydration of magnesium ions, ΔHθhydMg2+
Calculate the percentage error for your value for the enthalpy of hydration of magnesium ions, ΔHθhydMg2+, and the value given in section 18 in the Data Booklet.
The enthalpy of hydration of anhydrous magnesium sulfate, MgSO4 (s), is difficult to determine experimentally, but can be determined by using a Hess’s Law cycle.
A group of students decided to measure the enthalpy of hydration of anhydrous magnesium sulfate, MgSO4 (s), by dissolving 3.05 g into 50.0 cm3 of water and recording the maximum temperature change. They calculated the value to be -85 kJ mol-1.
The same group of students repeated the experiment using hydrated magnesium sulfate, MgSO4.7H2O (s), and calculated the enthalpy change to be +16 kJ mol-1.
Using the student’s data, draw a Hess’s Law cycle to determine the enthalpy of hydration of solid anhydrous magnesium sulfate, MgSO4 (s).
A student measured the energy change when 1.35 g of zinc was added to 50 cm3 of 0.5 mol dm-3 copper sulfate, CuSO4 (aq), solution. The initial temperature of 21 oC was recorded before the addition of the zinc and a temperature reading was taken every 30 seconds.
Use the graph to determine the overall temperature change for the reaction
Calculate the percentage error between your value for the enthalpy change of reaction and the literature value of -217 kJ mol-1. Give your answer to two significant figures.
