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SOLUTIONS
Objectives
Describe the unique role of water in chemical and biological processes.
Distinguish between types of solutions such as electrolytes and nonelectrolytes and unsaturated, saturated, and supersaturated solutions.
Develop and use general rules regarding solubility through investigations with aqueous solutions.
Investigate factors that influence solubilities and rates of dissolution such as temperature, agitation, and surface area.
Calculate the concentration of solutions in units of molarity.
Use molarity to calculate the dilutions of solutions.
The Role of Water
Chemical Processes
Polarity
Hydrogen bonding
Surface tension
Capillary action
Specific heat
Three states of matter
Polarity
The oxygen atom is bigger than the hydrogen atoms, the electrons spend more time around the oxygen. This creates a slight charge on each end of the water molecule.
Hydrogen Bonding
The force of attraction between the hydrogen atom of one water molecule to the oxygen atom of another water molecule
Easily done because of water’s bent shape- allowing the hydrogen to bond.
Surface Tension
Attractive force between particles in a liquid that minimizes surface area
Water has a high surface tension due to hydrogen bonds.
Capillary Action
attractive force between the surface of a liquid and the surface of a solid
water mercury
Specific Heat
The amount of heat required to raise the temperature of one gram of a substance by one degree.
Water has a high specific heat meaning it takes a great deal of energy (heat) to raise the temperature
States of Matter
Naturally found in all three (solid, liquid, gas) on Earth
Water cycle
Density of solid form less than liquid
Biological Processes
Because less dense ice floats on liquid water, a beneficial environment is created – many living things stay alive during the winter when lakes and ponds freeze over.
The high specific heat of water also makes it conducive for aquatic life. A large body of water can absorb and store a large amount of heat from the Sun on a hot day with only a small effect on the temperature of the volume of water.
Biological Processes
When water freezes and expands, it has many different impacts. The most important is the weathering of rocks and minerals that produces the soil with minerals necessary for plant growth.
Evaporative cooling, such as from human sweat, is also important to life. Transpiration in plants functions as both a transport and a cooling mechanism.
Biological Processes
The chemical processes of life all happen in cells in water (aqueous solutions). Specifically, proteins function for support, transport, movement, protection, and coordination of organism activities. Carbohydrates necessary for fuel and energy storage are also in water solution.
The Nature of Solutions
Definitions
Solution - homogeneous mixture
Solvent - present in
greater amount
Solute - substance
being dissolved
Solvation
the process of dissolving
solute particles are separated and
pulled into solution
solute particles are surrounded by
solvent particles
Solvation
Dissociation separation of an ionic solid into aqueous ions
Ionization breaking apart of some polar molecules into aqueous
ions
Example
Example
Solvation
Detergents polar “head” with long nonpolar “tail” can dissolve nonpolar grease in polar water
NONPOLAR
NONPOLAR
POLAR
POLAR
“Like Dissolves Like”
Types of Solutions
SATURATED
SOLUTION
no more solute
dissolves
UNSATURATED
SOLUTION
more solute
dissolves
SUPERSATURATED
SOLUTION
becomes unstable,
crystals form
concentration
Concentration
The amount of solute in a solution.
Describing Concentration
% by mass - medicated creams
% by volume - rubbing alcohol
ppm, ppb - water contaminants
molarity - used by chemists
molality - used by chemists
Electrolytes
Strong
Electrolyte
Non-
Electrolyte
solute exists as
ions only
- +
salt
- +
sugar
solute exists as
molecules
only
- +
acetic acid
Weak
Electrolyte
solute exists as
ions and
molecules
Solutions Quiz
Fold your paper into thirds
On front flap-
Describe why water is the universal solvent.
On the inside flaps-
Describe and draw the three types of solutions: unsaturated, saturated and supersaturated
Solutions Quiz
Fold your paper into thirds
On front flap-
Explain polarity, hydrogen bonding and surface tension.
On the inside flaps-
Describe and draw the three types of solutions: unsaturated, saturated and supersaturated
Investigating solubility
Solubility
Solubility
maximum grams of solute that will dissolve in 100 g of solvent at a given temperature
varies with temperature
based on a saturated solution
Rate of Solution
Solids dissolve faster...
more stirring
small particle size (increased surface area)
high temperature
Rate of Solution
Gases dissolve faster...
no shaking or stirring
high pressure
low temperature
Solubility Curve
Solubility Rules
Molarity and dilutions
Molarity
Concentration of a solution.
solution of liters
solute of moles(M)Molarity
total combined volume
substance being dissolved
Preparing Solutions
To prepare a solution:
Know what Molarity you need
Know how much volume you need
Do the calculations, solve for grams
Place the number of grams you calculated into a beaker
Add the amount of volume you need of distilled water
Why distilled water?
Preparing Solutions
500 mL of 1.54M NaCl
• mass 45.0 g of NaCl • add water until total
volume is 500 mL
500 mL mark
500 mL volumetric flask
2211 VMVM
Dilution
Preparation of a desired solution by adding water to a concentrate.
Moles of solute remain the same.
Dilution
What volume of 15.8M HNO3 is required to make 250 mL of a 6.0M solution?
GIVEN:
M1 = 15.8M
V1 = ?
M2 = 6.0M
V2 = 250 mL
WORK:
M1 V1 = M2 V2
(15.8M) V1 = (6.0M)(250mL)
V1 = 95 mL of 15.8M HNO3
Preparing Solutions
250 mL of 6.0M HNO3 by dilution
measure 95 mL of 15.8M HNO3
95 mL of 15.8M HNO3
water for safety
250 mL mark
• combine with water until
total volume is 250 mL
• Safety: “Do as you
oughtta, add the acid to
the watta!”