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