Transcript Solutions - Clayton State University

Chem 1151: Ch. 7
Solutions and Colloids
Physical States of Solutions
Solutions: Homogeneous mixtures of two or more substances
Particles uniformly distributed and transparent (clear)
Particles in constant motion (KE), don’t settle under influence of gravity
Solution = Solvent + Dissolved Solute
Solvent is most abundant substance comprising solution
Solute(s) is/are other substance(s) that are not the solvent
Solutions usually liquids but may be gases or solids
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011; http://en.wikipedia.org/;
http://www.medfinity.com/index.php?cPath=704_737
Solubility
Soluble substances: Dissolve completely in solvent
Insoluble substances: Do not dissolve in solvent
Immiscible: Liquid solute that does not dissolve in a liquid solvent
The extent of solubility can vary
 Isopropyl alcohol and water are completely soluble in any proportion
 Limit on how much sugar will dissolve
 Oil and water form distinct, separate layers
Saturated solution: Solution with max amount of dissolved solute
Supersaturated solution: Solutions where amount of solute dissolved is greater than
solute solubility
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Calcium carbonate
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Supersaturation
Preparation of a Supersaturated solution
1. Form a nearly saturated solution at high temp (higher solubility)
• Cool solution to lower temperature (lower solubility)
2. “Seed” the solution with some solid solute  excess solute (above saturation)
crystallizes
3. The remaining solution is saturated
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
;http://www.myrecipes.com/recipe/rock-candy-10000001176193/
Effects of Pressure and Temperature on Gas Solubility
 Solubility of gases in water decreases as temp increases
 CO2 is less soluble in warm soda than cold soda
 Gas solubility is directly proportional to gas pressure
 If gas pressure is doubled, solubility is doubled
Ex.1 Why your champagne is bubbly
 Cold champagne (wine) is saturated with CO2,
sealed under pressure
 Pressure is relieved when bottle opened
Ex.2 The bends
 Divers breath air under pressure that causes N2 to
be more soluble in blood than occurs at 1 atm
 If divers swims to surface too fast, N2 bubbles form
in blood and joints
 Joint pain
 Paralysis
 Death
http://www.knightsbridgeinvest.com/realestateblog/scuba-diving-panama/
Formation of Solutions
 When solid, ionic compounds placed in water, polar water molecules orient
themselves by charge along surface of solid
 Produces a shielding effect, allows water to remove ions from matrix (i.e., ions
become hydrated)
 Hydrated ions become evenly distributed throughout solution
 Process continues until
number of ions in solution
results in saturation.
 Ions begin to reform solid 
equilibrium.
 Similar results are observed
with polar, non-ionic solids
(e.g., sugar)
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Formation of a Solution
Two reasons why solute won’t dissolve in solvent:
1. Forces between solute particles stronger than solvent particles
2. Solvent particles more attractive to each other than solute particles
“Like dissolves like”
 Polar molecules dissolve in polar solvents (e.g., water)
 Non-polar molecules dissolve in non-polar solvents (e.g., CCl4)
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Predicting Solubility
Predict the solubility of the following:
1. NH3 in water
2. O2 in water
3. Ca(NO3)2 in water
4. Mg3(PO4)2 in water
5. Paraffin wax (nonpolar) in CCl4
6. BaCO3 in water
7. Li3PO4 in water
1.
2.
3.
4.
5.
6.
7.
Soluble, NH3 is polar
Insoluble, O2 is nonpolar
Soluble
Insoluble
Soluble
Insoluble
Soluble
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Rate of Solubility
Insoluble compounds may be soluble over long periods of time (chemical
weathering)
Normally soluble solutes may dissolve slowly (rock candy dissolves slower than
granulated sugar)
Dissolving rate may be increased
1. Crushing or grinding solute (increases surface area exposure)
2. Heating solvent (molecules move faster, more collisions)
3. Stirring or agitating
Heat of Solubility
Heat is usually absorbed or released when solute dissolves in solvent
1. In endothermic processes, heat is absorbed by interaction between solute
and solvent molecules
 Removes heat from bulk solvent
2. In exothermic processes, heat is release by interaction between solute and
solvent molecules
 Adds heat to bulk solvent
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Solution Concentrations
Concentration: How much solute is in a solvent
Molarity
Percentage
% w/w
% w/v
% v/v
Calculating Solution Concentrations (Molarity)
Molarity
2.00 L of solution contains 1.50 mol of solute.
150 mL of solution contains 0.210 mol of solute.
315 mL of solution contains 10.3 g of C3H7OH.
Calculating Solution Concentrations
A solution contains 100 g of water and 1.20 g of solute. What is the %(w/w)
concentration?
% w/w
A solution is made by mixing 90.0 mL of alcohol with enough water to give 250.0
mL of solution. What is the %(v/v) concentration of alcohol in the solution?
Calculating Solution Concentrations
A 150.0 mL sample of saltwater is evaporated to dryness. A residue of salt
weighing 27.9 g is left behind. Calculate the % (w/v) of the original saltwater.
A solution is made by dissolving 0.900 g of salt in 100.0 mL of water. Assume that
1.0 mL of water weighs 1.00 g, and the final solution volume is 100.0 mL. Calculate
the %(w/w) and %(w/v) for the solution.
Solution Preparation
Method 1: Mix solute and solvent
Method 2: Dilute a concentrated solution with solvent
Measurements may be volumetric, gravimetric or
both, depending on your concentration objective
Mass may be converted by volume based on
density, so that volume can be measured, not mass
Volume not as accurate as mass
Moles/L
%(w/w)
%(v/v)
%(w/v)
D = m/V
Solution Preparation
Describe how to prepare 1.00 L of 1.50 M CoCl2 solution
Describe how to prepare 1.50 L of 0.50 M CoCl2 solution
Describe how to prepare 200 mL of 0.200 M CoCl2 solution
Describe how to prepare 500 mL of 1.6 × 10-4 M Pb(NO3)2 solution
Solution Preparation
Describe how to prepare 250 mL of 0.900% (w/v) NaCl solution
Describe how to prepare 100 mL of 12.0% (w/v) MgCl2 solution
Solution Preparation - Dilution
This equation works for any form of concentration based on volume
Describe how to prepare 250 mL of 0.100 M NaCl solution from
2.00 M NaCl
Describe how to prepare 500 mL of 0.250 M NaOH solution
from 6.00 M NaOH
Solution Stoichiometry
 Stoichiometry deals with relative quantities of reactants and products in
balanced chemical equation
 We can now apply everything learned about mass, moles,
concentrations and balancing equations to solutions
Ex. 01: What volume of 0.200 M NaOH solution is needed to exactly react
with 0.150 moles of HCl?
We need 0.150 moles of NaOH for 0.150 moles of HCl (1:1 stoichiometry)
NaOH solution is 0.200 M (moles/L)
Solution Stoichiometry
Ex. 01: What volume of 0.185 M NaOH solution is needed to exactly react
with 25.0 mL of 0.255 M HCl?
We need to figure out moles in 25.0 mL of 0.255 M HCl
Now we can find volume of of 0.185 M NaOH from moles HCl and
stoichiometry
Solution Properties – Electrical Conductivity
Electrolytes: Solutes that form water solutions capable of conducting electricity
 Solutes dissociate to form ions
Strong Electrolytes (e.g., HCl) dissociate completely, strong conductors
Weak Electrolytes (e.g., Acetic acid) dissociate slightly, weak conductors
Electrolytes maintain precise osmotic
gradients at the cellular level.
These regulate body hydration and blood pH,
and are critical for nerve and muscle function.
http://healthic.net/supplements/electrolytes-drink-enabling-transmission-of-nutrients-in-body/
Colligative Properties
Depend only on concentration of solute particles present, not identity of
solute
 Solutions containing 1 mol sugar and 1 mol salt would have identical
colligative properties
 Closely-related colligative properties include:
 Vapor pressure
 Boiling point (BP)
 Freezing point (FP)
Colligative properties differ between solutions and pure solvents:
 Vapor pressure of water (solvent) above solution is lower than vapor
pressure of pure water
 Causes higher BP and lower FP of solutions, compared with pure solvent
 These differences can be calculated with the following equations:
m = solution molality (same as molarity for dilute solutions)
K = Derived constant (°C/M) related to BP or FP of solvent
n = number solute moles in solution when 1 mol solute
dissolves
Colligative Property: Osmotic Pressure
 Water can pass through membrane but sugar cannot
 Net flow into sugar side to increase vapor pressure
 Continues until osmotic pressure balances tendency of water to flow to
sugar side (until equilibrium)
 In general, net flow of solvent through semipermeable membranes is always
from more dilute solution into more concentrated solution
 Osmotic pressure can be calculated with the following:
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Colloids
 Similar to solutions
 Homogeneous mixtures of 2 or more components
 More of one component than others
 Colloids defined by:
 Dispersing medium: Like solvent
 Dispersed phase: Like solute
 Main differences:
 Colloids have much larger particles (up to 10X larger) than solutions
 Gives them cloudy appearance
 Colloids:
 Glues
 Gels (shaving cream)
 Cheese