TEST 9: Review Notes on Solutions:
1. A solution is a homogeneous mixture, consisting of two components.
o The solute is the substance being dissolved.
o The solvent is the substance doing the dissolving
o (aq) is used to represent a water solution. For example NaCl(aq) the solute is NaCl and the solvent is water
2. Factors that affect solubility
o Nature of the solute and solvent: Polar solutes are soluble in polar solvents (ex: Water), while nonpolar solutes are soluble in nonpolar solvents. Remember the phrase “Like dissolves like”
o Temperature: For solids as the temperature increases the solubility increases, while for gases the solubility will decrease.
o Pressure: Pressure has no effect on the solubility of a solid, but for a gas as the pressure increases the solubility increases.
3. Solubility Curves (Table G)
o A saturated solution has all the solute it can possibly hold at a given temperature. (A point on the curve)
o An unsaturated solution holds less solute than it can possibly hold at a given temperature. (A point below the curve)
o A supersaturated solution holds less solute than it can normally hold at a given temperature. (A point above the curve)
4. Solubility Guidelines (Table F)
o This table is used to tell if an ionic compound is soluble or insoluble in water. (insoluble on this table means only a minute amount would dissolve at room temperature)
o If a substance is insoluble a precipitate is produced. If it is produced as a result of a double replacement reaction, the reaction is said to go to completion)
5. Solution Concentration
o Qualitatively you can use the terms dilute (a small amount of solute) or concentrated ( large amount of solute)
o Quantitatively there are several ways to express concentration.
a. Percent by mass: commonly used to express the concentration of household items. % by mass= grams of solute/grams of solution x 100
b. Percent by volume: commonly used when two liquids are mixed together.
% by volume = volume of solute/ volume of solution x 100
Note: Any percent is always part/whole x 100
A solution is always the solute and solvent combined
c. Parts per Million (ppm): is used for very dilute solutions.
ppm = grams of solute/grams of solution X 1 000 000 (Table T)
d. Molarity: M= moles of solute/liter of solution (Table T)
For example: How many grams of NaOH are used to prepare 250 ml of a 2.0M solution. Ans: M=moles/liter 2.0=x/.250 liters x = .50 moles NaOH
Moles=g/gfm .50 = x/40.0 x = 20.0 grams
e. Dilution: to dilute a solution use M1V1= M2V2, where 1 are the initial values and
2 are the final values.
f. molality: m=moles of solute/kg of solvent
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6. Colligative properties: properties that depend on the number of particles rather than on the nature of particles.
o The addition of a nonvolatile solute (salts, sugars and alcohol) to water will lower the freezing point and raise the boiling point).
o The addition of an electrolyte will lower the freezing point and raise the boiling point more. The more particles produced the greater the change will be.
o Boiling Point elevation: 1 mole of a nonelectrolyte raises the boiling point of 1 kg of water by 0.520C. change in boiling point= m x d.f. x .52 where m is the molality (moles/kg) and d.f. is the dissociation factor (number of particles, use 1 for nonelectrolytes)
o Freezing Point Depression: 1 mole of a nonelectrolyte lowers the freezing point of 1 kg of water by 1.86 . change in freezing point= m x d.f x 1.86