Chapter 12: Solutions
Principles of Chemistry
A Molecular Approach,1st Ed.
Nivaldo Tro
NaCl soln
Dr. Azra Ghumman
Memorial University of Newfoundland
Chem 1011
Solution
Solution-A homogeneous mixture of two pure
substances.
Solution = solute + solvent
Solute- The solution component in smaller amount
Solvent- The solution component in greater amount
Most homogeneous materials are actually solutions.
e.g. air and seawater (NaCl + H2O)
Nature has a tendency toward spontaneous
mixing.
Generally, uniform mixing is more energetically
favorable.
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Sea Water is a thirsty solution. Why?
Nature’s tendency towards mixing and lower conc. of salt in body
fluids causes a flow of solvent out of body cells into the sea water
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12.2-Types of solutions
Gaseous solution- Gases or vapours are miscible in all
proportions. e.g. Air
Liquid solution-obtained by dissolving a gas, liquid or
solid in water
e.g. soda water (gas-liquid), ethanol water (liquidliquid) salt solution (solid-liquid), and ocean water
Solid-solid solution- e.g. Ag in Hg, (dental filling), Au-Ag
alloy,Jewelry, Brass(Cu&Zn)
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Solubility
Solubility- The amount of the substance that will
dissolve in a given amount of solvent
E.g. Solubility of NaCl in water at 25 °C is 36g NaCl/ 100g
H2O
The solubility of one substance in another depends
on two factors
nature’s tendency towards mixing(Entropy),
the types of IMF’s
The solubility varies with temperature and pressure.
Miscible- Two liquids that are mutually soluble are
said to be miscible
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Mixing and the Solution Process
Entropy
Most processes occur because the end result has
less potential energy
However, a solution formation does not necessarily
lower the potential energy of the system
Entropy-Is a measure of energy randomization or
energy dispersal in a system
When two ideal gases are put into the same
container, they mix spontaneously. Why?
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Solution formation
Process of solution formation depends on IMF’s
between solute and solvent molecules
1. solute–solute attractive forces
2. solvent–solvent attractive forces
Both processes are endothermic.
3. solute–solvent attractions. (exothermic)
A solution will form if
attractive forces between solute and solvent
molecules are stronger than between pure
solvent molecules and pure solute molecules,
A rule of thumb is “like dissolve like”
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Common Laboratory solvents
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Practice Problem
Determine whether each of the following compound
is soluble in hexane (C6H6)
a) H2O
b) Propane(CH3CH2CH3)
c) Ammonia (NH3)
d) Hydrogen chloride (HCl)
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Describing a Solution
Qualitative description
Concentrated solution-contains large quantities of
solute relative to amount of solvent
Dilute solution-contains small quantity of solute
compared to solvent
Saturated A solution that has the maximum amount
of solute dissolved in it
Supersaturated-A solution that has more solute than
saturation
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12.5- Expressing Solution
Concentration
Quantitative description
Concentration- The amount of solute in given
amount of solvent or solution
Molarity(M)- Amount of solute in moles divided by
the volume of solution in liters (mol L-1)
Molarity is temperature dependent
Percent by mass or mass %-
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Solution Concentration
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Solution Concentrations
Mole Fraction, XA
The mole fraction- The fraction of the moles of one
component in the total moles of all the components of
the solution
Sum of all the mole fractions in a solution = 1
unitless
The mole percentage:
mol% = XA × 100%
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Practice problems
1. A solution prepared by mixing 17.2 g of ethylene
glycol(Mm C2H6O2 = 62.07g mol-1 ) with 0.500 kg of
H2O to make 515 mL of solution. Calculate its
a) molarity, b) % by mass c) mol fraction d) mol %
b) 2. How would you prepare 250.0 mL of 19.5% by
mass CaCl2 solution? (d = 1.18 g/mL)
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12.6 Colligative Properties
Colligative properties-Properties whose value
depends only on the number of solute particles, and
not on the type of particles
Consequently, ionic solutes that dissociate in
solution provide higher effective solute
concentration than nonelectrolytes.
Examples include vapour pressure lowering of a volatile solvent
by the addition of nonvolatile solute,
freezing point depression (antifreeze, 0.01mol of
Ethyleneglycol lower the of H2O)
boiling point elevation
osmotic pressure
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Osmosis and Osmotic pressure
Osmosis-The flow of solvent from a solution of low
concentration into a solution of high concentration
through a semipermeable membrane.
A semipermeable membrane allows solvent
molecules to flow through it, but not the solute
osmotic pressure-The amount of pressure needed
to stop osmotic flow from taking place
MRT M is the molar concentration in mol L-1
R, the gas constant = 0.0821 L.atm mol-1.K-1
T is Temperature in Kelvin
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Osmotic Pressure
An osmosis cell-
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Reverse Osmosis
In normal osmosis solvent flows from a dilute solution
through a membrane to a more concentrated solution
Reverse Osmosis- is reversing the osmosis process
by applying greater pressure than osmotic pressure
to the more concentrated solution so that solvent
flows from concentrated solution through a
membrane to the more dilute solution
Desalination- removing salts from seawater to
make it usable for drinking
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Calculating molar mass
What is the molar mass of a protein if 5.87 mg per
10 mL solution gives an osmotic pressure of 2.45
torr at 25°C?
Given: mass of protein 5.87 mg
Vsoln = 0.001L
= 2.45 torr T = 25 °C + 273.15 = 298.15 K
Find: molar mass, g/mol
1. we know
we can calculate M
2. Calculate moles of protein using n = MV
3. Calculate molar mass
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Mm = mass (g)/mol
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Importance of Osmosis
Rising of Sap in a tree trunk- The sap flows upward
to dilute the water solution in the leaves during the
day
Osmosis is important in many biological processes
The solution surrounding the cell must have
osmotic pressure equal (isotonic) to that within
the cell, why?
For intravenous feeding it is necessary that the
nutrient solution have exactly the osmotic pressure
of blood plasma, otherwise the cell may collapse or
burst as a result of osmosis
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The Importance of Osmotic Pressure
to Living cells
Osmosis in a blood cell
Osmotic pressure of
the solution is greater
than that of the cell
(cell collapsed).
Hypertonic solution
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Osmotic pressure of
the solution is equal to
that of the cell
(normal cell)
Isotonic
Chapter 12: Solutions A. Ghumman
Osmotic pressure of
the solution is less
than that of the cell
(bloated shape)
Hypotonic
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