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Solutions Aim: 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) - PowerPoint PPT Presentation
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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.