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Chapter 13 Water and Its Solutions
Section 13.2 Solutions and Their Properties
Submicroscopic interactions between water and solutes determines how much solute it dissolves
Ionic substances are soluble in water Electrical conductivity is observed when ionic
compounds are dissolved in waterEx: Salt
Solubility
The process by which charged particles in an ionic solid separate from one another
Water molecules are polar- have a positive and negative end
Water molecules are attracted to ionic compounds that
have dissociated into both positive and negative charged ions
Examples: H20
NaCl(s) → Na+ (aq) + Cl- (aq) H20
SrCl2(s) → Sr+ (aq) + 2Cl- (aq)
DISSOCIATION (ionic compounds)
Water is also good at dissolving covalent compounds
Ex: Sucrose (table sugar)
The molecules are simply separated by water molecules, No dissociation occurs
Water dissolves both ionic and covalent substances, however, it does NOT dissolve
everything
Covalent Compounds
Dissolving occurs when similarities exist between the solvent and the
solute
Examples: Water can dissolve salt because water is polar and it tends to dissolve ionic substances
Water can dissolve sugar because water has hydrogen bonding and tends to dissolve substances that are polar Oil and water are an example of two substance that do not mix Oil is a mixture of nonpolar covalent compounds
“Like dissolves Like”
See guidelines and answer the following…
1)Which is insoluble? LiCl, NaCl, AgCl or KCl2)Which is soluble? Barium Sulfate or Potassium Sulfate3)Which is insoluble? Potassium Carbonate or Zinc Carbonate4)Which is soluble? Ammonium hydroxide or magnesium hydroxide
Solubility Guidelines
Relative amount of solute and solvent
Represented by [ ]
Solution concentration
Concentrated- large amount dissolved in water (high concentration)
Dilute- little amount dissolved in water (low concentration)
Concentrated versus Dilute
UNSATURATED SOLUTION- amount of solute dissolved is less than the max that could be dissolved in the solution
SATURATED SOLUTION- solution which holds the max amount of solute per amount of the solution under the given conditions
Unsaturated versus Saturated
SUPERSATURATED SOLUTION contain more solute than the usual max amount Unstable- cannot permanently hold the excess solute in solution and may release it suddenly Usually created at elevated temperatures (higher solubility), then slowly cooled Produce a large amount of crystalline solid if a small amount of solute is added (ex. Fudge)http://education-portal.com/academy/lesson/solubility-and-solubility-curves.html#lesson
Unsaturated versus Saturated
Solubility CurveBelow the linesoln is unsaturated On or above the linesoln is saturatedSupersaturated?
Example - How many grams of KCl can dissolve in 100g of water at 30C?
Temp has a significant effect on solubility The solubilities of MOST solutes increase with
increasing temperature
Unsaturated versus Saturated
Heat taken in or released in dissolving process For most solutes, the process of dissolving is an endothermic process – heat is written as a reactant
Example: NH4NO3
However, the dissolving of some solutes is exothermic – process releases heat
Example: CaCl2
HEAT OF SOLUTION
Molarity = moles of solute/ liter of solutionM = moles / liter or mol/L
Concentration example:0.15 M NaCl = 0.15 moles of sodium chloride
per liter of solution
Concentration Unit
Need to know three things:1) Concentration2) Amount of solute3) Total volume of solution needed
http://education-portal.com/academy/lesson/calculating-molarity-and-molality-concentration.html#lesson
To make a quantitative aqueous solution
1. Weigh the solute2. Transfer solute to a volumetric flask3. Add enough water to dissolve solute (mix). 4. Bring the solution volume up to the calibration mark on the flask5. Solution is shaken, stored and labeled
Steps to Quantitative Solution Preparation
#7) How would you prepare 1.00 L of a 0.400 M solution of CuSO4?
Cu = 63.5 g/molS = 32.1 g/mol
4 O = 16 x 4 = 64.0 g/mol
CuSO4 = 159.6 g/mol
1.00 L soln x 0.400 m CuSO4 x 159.6 g CuSO4 1 L solution 1 mol CuSO4
= 63.8 g CuSO4
dissolve 63.8 g CuSO4 in 1.00 L solution
Sample Solution Preparation Practice Problems p. 462
#8) How would you prepare 2.50 L of a 0.800 M solution of KNO3?
K = 39.098 g/molN = 14.007 g/mol
3 O = 15.999 x 3 = 47.997 g/mol
KNO3 = 101.102 g/mol
2.50 L soln x 0.800 mol KNO3 x 101.102 g KNO3 1 L solution 1 mol KNO3
= 202.2 g KNO3
dissolve 202.2 g KNO3 in 2.50 L solution
Sample Solution Preparation Practice Problems p. 462
12) What is the molarity of a soln that contains 14 g Na2SO4 dissolved in 1.6 L soln?
Na = 2 x 22.990 g/mol= 45.98S = 32.066 g/mol
4 O = 15.999 x 4 = 63.996 g/mol
Na2SO4 = 142.042 g/mol
14 g Na2SO4 x 1 mol Na2SO4 = 0.062 mol Na2SO4/ L
1.6 L soln 142.04 g Na2SO4
or 0.062 M Na2SO4
Calculating Molarity Practice Problem p. 463
#13) What is the molarity of a soln that contains 7.4 g NH4Cl dissolved in 820 mL soln?
N = 14.007 g/mol
4 H = 4 x 1.008 = 4.032 g/mol Cl = 35.453 g/mol
NH4Cl = 53.492 g/mol
7.4 g NH4Cl x 1 mol = 0.17 mol NH4Cl/ L
0.820 L soln 53.492 g NH4Cl
or 0.17 M NH4Cl
Calculating Molarity Practice Problem
A solution has a lower FP than the corresponding pure solvent (less than 0ºC)
The amount that the FP is depressed relative to 0ºC
depends on the concentration of the solute An ionic solute produces greater depression of FP
than a covalent one because it dissociates into ions (more ions to interfere with the freezing process)
Ex: Ice cream, salt on sidewalks in winter
Freezing-Point Depression
BP of a solution is higher than the BP of a corresponding pure solvent (greater than 100ºC)
Solute interferes with the ability of the solvent particles to escape the liquid state – higher temperature is required to allow boiling
The higher the concentration of solute particles,
the greater the boiling-point elevation
Ex. Anti-freeze
Boiling-Point Elevation
The flow of solvent molecules through a selectively permeable membrane (higher solute to lower solute concentration)
Selectively permeable – allows certain
materials to pass through them
OSMOSIS
The solubility of a gas in a liquid depends on the pressure of the gas pushing down on the liquid
The higher the pressure, the more soluble the gas
For solns of gases in liquids, gas solubility
decreases as temp. increases (soda fizzes more when warm)
Solutions of Gases in Water
Mixtures that are between true solutions and heterogeneous mixtures
Contain particles that are evenly distributed through a medium and remain distributed over time – do not settle out
Colloid particles are 10-100x larger than typical
ions or molecules dissolved in solutions
COLLOIDS
Light moving through a colloid is partially scattered and reflected by the dispersed particles- light scattering effect is called TYNDALL EFFECT
The light becomes visible and broadens.
This occurs because colloid particles are about the same size as the wavelength of visible light (400 to 700 nm)
COLLOIDS
Name ColorSolubility
CuCO3 blu/grn Insol Na2SO4 colorless Sol NaNO3 colorless Sol PbCO3 wht Insol BaCO3 wht Insol CuI brn/wht insol I2 brn Insol PbI2 yellow
insol BaI2 colorless sol PbSO4 wht insol BaSO4 wht insol