Solutions Aim: SWBAT identify what solutions are and how they work

SolutionsAim: SWBAT identify what solutions are and how they

work.

Ms. Katwaru

Chemistry

St. Agnes HS

Solution vs. Suspension

Solution – homogeneous mixture

dissolving = physical change

(not a chemical change)

Dissolved particles (atoms, ions or molecules) are extremely small and solutions cannot be separated by filtering.

Suspension – heterogeneous mixture where some particles settle out upon standing ex. muddy water (clay & silt)

Tyndall EffectLight beam is passed through a liquid containing particles in suspension; these particles scatters the light rays. The path of the light rays through the liquid becomes visible in a suspension, having the appearance of a bright cone in the liquid.

Ex. Fog – suspended water droplets

Tyndall Effect – car headlights in fog

- spotlight in smoke or dust

Solutions can be dilute (weak) or more concentrated.

Molarity (M) = expression of Concentration

M = # moles of solute Liters of Solution

If 2.0 moles are dissolved in 4.0 Liters…

Molarity = 2.0 moles / 4.0 L = 0.50 M

Making Molar Solutions

Na 1x23 = 23g

Cl 1x35 = 35g

1 mole = 58 g

Fill to

Line

Calculate Molarity: Given 450 g NaCl (GFM = 58g) in 3.0 Liter.

M = # moles of solute

Liters of Solution1) Find # moles (for numerator). Convert grams to

moles using GFM.

2) Solve for Molarity.

M =

Aqueous Solutions

• Solution - a homogenous mixture mixed molecule by molecule.

• Solvent - the “stuff” that does the dissolving; larger amount than solute.

• Solute - the “stuff” that is dissolved.

• Exist in all phases – most common solid (solute) in liquid (solvent).

• Aqueous solution (aq) - a solution with water as the solvent.

Solutions

Polar Water Molecules with Hydrogen Bonds = surface

tension.

• One water molecule H-bonds to another.

• Other H-bonds to water molecules all around.

Dissolution & Hydration

Water is a Polar Molecule

Hydration of Ions & Orientation of Polar Water

Molecule

Factors Affecting Rate of Solution (Dissolving)

(Rate = how much over time)• Amount of Solute and Solvent

– closer to max. limit = slower rate

• Temperature – higher temp. = faster

• Stirring – faster with stirring

• Particle Size – smaller = faster

Factors Affecting Solubility (max. amount

dissolved)• Nature of Solute and Solvent

(“Like dissolves Like”) e.g., Polar solvents dissolve polar

solutes.

• Temperature – Solids - more soluble @ high Temp.– Gases - less soluble @ high Temp.

• Pressure– Gases more soluble @ high Pressure

“Like Dissolves Like”• Polar solvents dissolve polar & ionic

solutes. Water (polar) dissolves ionic solids and

polar covalent solids. Salts (NaCl, KCl) are ionic & form aqueous solutions.

• Non-polar dissolves non-polar. Oil (non-polar) and water (polar) don’t

mix = immiscible.

• Alcohols – dissolve polar & non-polar solutes; but not ionic solutes.Tinctures – alcohol is solvent.

Solutions

Solubility Curves… show max. limit of solute dissolved for a given temp. and vol. of water.

Supersaturated = above line

Saturated = on the line

Unsaturated = below; under the line

Temp.

Solubility Curves

max. amount dissolved in100g = 100mL of water

Supersaturated = above lineSaturated = on the lineUnsaturated = below; under the line

1) How much KNO3 will dissolve in 100mL @ 50oC?

2) … in 200mL?

3) If 70g of HCl is dissolved @ 50oC in 100g H2O, is this Supersat., Sat. or Unsat.?

Exceptions:

• As temperature rises, the solubility curve of GASES decrease.

Solutions of Ionic Compounds conduct electricity = Electrolytes

Electrolytes – ions (charged particles) in solution.

NiCl2(aq) + KMnO4(aq)

Electrolytes - to conduct electricity in Liquid Phase, mobile (dissolved) ions are requiredGreater number (#) ions in

solution… = greater electrical conductivity

= stronger electrolyte.

Solutions3 Types of Electrolyte Compounds Salts (ionic compounds), acids(H+) & bases(OH-)

Salts = ionic = metal & non-metal K + (aq) & Cl - (aq)

Acetic = weak acid H + & CH3COO -

Covalent = no ions

bright dim dark

KCl CH3COOH C6H12O6

Solutions

; Release OH- (aq)

Salt (aq) Metal +(aq) + Non-Metal – (aq)

Acids, Bases & Salts

Colligative Properties

Properties that depend on the

number of solute particles in solution;

not the nature of the particles

Best example:

Boiling Pt. Elevation

Freezing Pt. Depression

B.P.

F.P.

100 C

0 C

Electrolytes – form ions in solution

KCl (aq) 1 K+1 + 1 Cl –1

(1 mole) (2 moles particles)

CaCl2 (aq) 1 Ca+2 + 2 Cl –1

(1 mole) (3 moles of particles)

Nonelectrolytes – exist as dissolved molecules (do not form ions)ex. Glucose C6H12O6 (aq) (1 mole)

Another Colligative Property

Solute Effect on Vapor Pressure

Vapor Pressure (V.P.) = pressure exerted by a vapor in equilibrium with its liquid (or solid)

Volatile – substance has some V.P.Non-Volatile – V.P. = zero

Dissolved particles (solute = gray)occupy/prevent solvent particles from entering vapor phase.

Greater # particles in solution = Greater effect for…

- B.P. Elevation- F.P. Depression- Lower Vapor Press.

Colligative Properties Summary

Which has the greater # particles …

1) NaCl (aq) 2) CaCO3 (aq) 3) KCl (aq) 4) Fe2O3 (aq)

Hint: Write a balanced dissociation reaction

___ NaCl (s) ___ Na +1 (aq) + ___ Cl –1

(aq)

Coefficients = # moles = # particles (aq)

Which has the greater # particles …

1) NaCl (aq) 2) CaCO3 (aq) 3) KCl (aq) 4) Fe2O3 (aq)

Hint: Write a balanced dissociation reaction ___ NaCl (s) ___ Na +1 + ___ Cl –1

___ CaCO3 (s) ___ Ca +2 + ___ CO3 –2

___ KCl (s) ___ K +1 + ___ Cl –1

___ Fe2O3 (s) ___ Fe +3 + ___ O –2

Which has the greater # particles …

1) NaCl (aq) 2) CaCO3 (aq) Total # Moles of 3) KCl (aq) 4) Fe2O3 (aq) Particles; Ions

_1_ NaCl (s) 1 Na +1(aq) + 1 Cl –1

(aq) 2

_1_ CaCO3 (s) 1 Ca +2 (aq) + 1 CO3 –2

(aq) 2

_1_ KCl (s) 1 K +1(aq) + 1 Cl –1

(aq) 2

_1_ Fe2O3 (s) 2 Fe +2 (aq) + 3 O –2

(aq) 5

Which has the greater Boiling Point (BP), lower Freezing Point (FP) and lower Vapor Pressure?

1) NaCl (aq) 2) CaCO3 (aq) 3) KCl (aq) 4) Fe2O3 (aq)

Because…_________________________________

_________________________________________

Which has the greater Boiling Point (BP), lower Freezing Point (FP) and lower Vapor Pressure?

1) NaCl (aq) 2) CaCO3 (aq) 3) KCl (aq) 4) Fe2O3 (aq)

Because… greatest # moles of particles are formed in solution when it dissolves.

Fe2O3 (aq) 2 Fe +3 (aq) + 3 O3 –2

(aq) 5 moles

Vaporization vs. Condensation (opposing phase

changes)

• Liquid to Gas (evap.)

• Open Container• Liquid evaporates

completely = unlimited vaporiz.

• No significant condensation.

Evap.Evap.

Physical Equilibrium

• Closed Container• Rate of Evap. = Rate of Condensat.• Dynamic Equilibrium between

the 2 phases; exchange occurs in both directions equally (no net change).

• Water level remains unchanged (no net change).

Physical Equilibrium of Saturated Solution

Solid = Precipitate

Equilibrium

Rate of Precipitation = Rate of Dissolving

(equal opposing rates)Sat.

Dissolved Particles

1) What kind of ratio does “percent” mean?

For example, if a compound consists of 35% oxygen by mass, what does 35% represent (as a ratio)?

1) What kind of ratio does “percent” mean?

35 % = 35

100

This is a ratio … X out of 100.

Percent Composition by Mass (Ref. Table T)

% Comp. = mass of part x 100 mass of whole

Given 20.0 g of solute in 2000. g of solution; Calculate % Comp.

% Comp. = mass of part x 100 mass of whole

Given 20.0 g of solute in 2000. g of solution; Calculate % Comp.

% Comp. = 20 g solute x 100 = 0.01 x 100

2000 g solution

% Comp. = 2 g solute x 100 200 g solution

% Comp. = 1 g solute x 100 = 1.00 % 100 g solution

Percent is ratio parts per hundred. % = How many parts out of 100.

2 = 20 = 20 % 10 100

Very small values such as 0.02 % are awkward. Use a smaller ratio, parts per million (ppm).

ppm = How many parts out of 1,000,000 .002 = .02 = .02 %

10 100 = 200 = 200 ppm

1,000,000

Parts Per Million (ppm) (Table T)

PPM is used for low concen.

ppm = grams of solute x 1,000,000 grams of solution

Given 0.025 g of solute in 2800. g of solution; Calculate concen. in ppm.

Parts Per Million (ppm)ppm = grams of solute x

1,000,000 grams of solutionGiven 0.025 g of solute in 2800. g

of solution; Calculate concen. in ppm

ppm = 0.025 g solute x 1,000,000 2800 g solution

= 8.9 ppm

Ref. Table F

Soluble

Soluble Not-Soluble

Not-Soluble

= Single Replacement

Ref. J

*** Elements higher on Ref. J replace lower elements.