Solutions
What Is A Solution? Recall that a solution is a homogeneous mixture. (the same throughout) Solvent major component of a solution. Dissolves the solute(s). (Usually Water) Solute(s) minor component(s) of a solution. Active ingredients of a solution. (The salt in salt water) Solution = solvent + solute(s)
Some Common Solutions
The Solution Process 3 things happen when a solute dissolves: 1. Solute particles separate. This requires energy to overcome the intermolecular forces holding them together. 2. Solvent molecules separate. This also requires energy. 3. Solvent particles surround solute particles. Known as solvation. Releases energy.
The Solution Process 1. Particles separate from solute. 3. Solvation 2. Solvent molecules move apart to accommodate solute.
Ions in Solution Solvated cation Solvated anion
The Solution Process
Energy Changes in Solutions The formation of a solution always involves a temperature change. Can be a large or small temperature change. Can get warmer or cooler as solute dissolves. H = enthalpy (heat) of solution Energy absorbed or released as a solute dissolves in a solvent. + H = endothermic sol n process. More heat absorbed than released. Temperature decreases as sol n is formed. - H = exothermic sol n process. More heat released than absorbed. Temperature increases as sol n is formed.
Energy Changes in Solutions
Solubility Not all substances dissolve in water. Remember, like dissolves like. Polar solutes tend to dissolve more in polar solvents. Non-polar solutes tend to dissolve more in non-polar solvents. Some (but not all) ionic compounds will dissolve in water. Of those that do, temperature affects how much they dissolve. Solids usually dissolve more in warm water. Gases usually dissolve more in cool water.
Solubility Insoluble less than 0.1 grams of solute will dissolve in 100 grams of solvent. BaSO 4 is insoluble in water. Only 0.0002448 grams of BaSO 4 will dissolve in 100 grams of water. Slightly soluble 0.1 to 1 gram of solute will dissolve in 100 grams of solvent. Ag 2 SO 4 is slightly soluble in water. About 0.8 grams of Ag 2 SO 4 will dissolve in 100 grams of water at 20ºC. Soluble more than 1 gram of solute will dissolve in 100 grams of solvent. NaCl is soluble in water. 35.9 grams of NaCl will dissolve in 100 grams of water at 20ºC.
Solubility Rules Use your list of solubility rules to determine whether each of the following salts is soluble or insoluble in water. NaCl K 2 SO 4 CaCO 3 NH 4 NO 3 Cu 3 (PO 4 ) 2 AgBr NaCl is soluble. K 2 SO 4 is soluble. CaCO 3 is insoluble. NH 4 NO 3 is soluble. Cu 3 (PO 4 ) 2 is insoluble. AgBr is insoluble.
Saturation Saturated solution A sol n containing the max. amt. of solute for a given amt. of solvent at constant temp. and pressure. If additional solute is added it will not dissolve. Unsaturated solution A sol n that does not contain the max. amt. of solute for a given amt. of solvent. Additional solute can dissolve in an unsaturated solution. Supersaturated solution A sol n that contains more solute than it can theoretically hold at a given temperature. Addition of more solute causes the excess solute to precipitate.
Solubility Curves Solubility curve chart compares the solubilities of several compounds in water as a function of temperature. Usually expresses solubility in terms of grams of solute per 100 grams of water.
Solubility Curves How many grams of KNO 3 can dissolve in 100 grams of water at 30ºC? Answer: About 48 grams.
Solubility Curves How many grams of KClO 3 can dissolve in 100 grams of water at 55ºC? Answer: About 25 grams.
Solubility Curves How many grams of NH 4 Cl can be dissolved in 200 grams of water at 40ºC? Answer: About 96 grams.
Solubility Curves A saturated solution of NaNO 3 is prepared at 70ºC in 100 grams of water. If the temperature is lowered to 40ºC, how many grams of NaNO 3 will precipitate? Answer: About 30 grams will precipitate out.
Solubility Curves If 35 grams of NH 4 Cl are dissolved in 100 grams of water at 30ºC, is the solution unsaturated, saturated, or supersaturated? Answer: The solution is unsaturated.
Solubilities of Gases Henry s Law The solubility of a gas in a liquid increases as the pressure above the liquid increases. Explains decompression sickness (the bends ). Nitrogen is forced to dissolve in scuba divers blood by high pressure. If the diver ascends too quickly, the nitrogen bubbles come out of solution and form painful and possibly fatal gas embolisms.