CHAPTER 4. First year . Solutions B By Dr. Hisham Ezzat 2011- 2012 . Example 6.
You calculate the molarity!
You do it!
You do it!
Experience tells us that sugar dissolves better in warm water than in cold water.
As temperature increases, solubility of solids generally increases.
Sometimes solubility decreases as temperature increases (e.g., Ce2(SO4)3).
Gases are less soluble at higher temperatures. An environmental application of this is thermal pollution.
Solute + solvent → solution + heat
Solute +solvent + heat → solution
ΔH = H solution - (H solute + H solvent).
ΔH solutionnegative = exothermic
positive. = endothermic,
Since saturated solutions are at equilibrium, LeChatelier’s principle applies to them.
Possible stresses to chemical systems include:
Heating or cooling the system.
Changing the pressure of the system.
Changing the concentrations of reactants or products.Effect of Temperature on Solubility
21 kJ + KI(s) K+ + I-
the solubility of KI increases with increasing temperature.
solubility of lithium iodide decreases with an increase in temperature
LiI (s) Li+ + I- + 71 KJ
equilibrium shifts to the left
(1) using up some of the added heat (and Li and I- ions in solution) and , (2) forming more solid Lil. (We observe the precipitation of some Lil out of solution.)
the solubility of gas decreases with temperature.
Carbonated beverages are bottled under PCO2> 1 atm. As the bottle is opened, PCO2 decreases and the solubility of CO2 decreases. Therefore, bubbles of CO2 escape from solution.
At 740 torr and 20°C, nitrogen has solubility in H2O of 0.018 g /I. At 620 torr and 20°C its solubility is 0.015 g/l.
Do these data show that nitrogen obey Henry's law or not?
At 25°C oxygen gas collected over water at a total pressure of 101 kPa is soluble to the extent of 0.0393 g dm-3. What would its solubility be if its partial pressure over water were 107 kPa?
The vapor pressure of water is 3.0 kPa at 25°C.
P total = PH2O + PO2
PO2 = P total - PH2O = 101-3 = 98 kPa