1. Unit 3 Solutions Chemistry
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2. Can it be physically separated?
Matter Flowchart
MATTER
yes no
Can it be physically separated?
MIXTURE
PURE SUBSTANCE
Is the composition uniform? no
yes
Can it be chemically decomposed? no
yes
Homogeneous Mixture
(solution)
Heterogeneous Mixture
Compound
Element
Colloids
Suspensions
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Pure Substances
A pure substance has a definite composition.
Pure substances can be
elements or compounds
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Mixtures
Combination of 2 or more pure substances.
Heterogeneous
Not uniform throughout
Homogeneous
Uniform throughout
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5. IPC-Solutions-Borders
Solutions, in chemistry, are homogeneous mixtures of two or more substances.
The substance present in largest quantity usually is called the solvent. The solvent can be either a liquid or a solid.
The substance that is present in smallest quantity is said to be dissolved and is called the solute. The solute can be either a gas, a liquid, or a solid.
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6. IPC-Solutions-Borders
Concept Check
Coke lists as its ingredients as: “carbonated water, high fructose corn syrup and/or sucrose, caramel color, phosphoric acid, natural flavors, caffeine”.
What is the solvent?
What are the solutes?
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Types of Solutions
Gaseous solutions – air
Liquid solutions – drinks
Solid solutions – steel or other alloys
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Miscible liquids can easily dissolve in one another.
Immiscible liquids are not soluble in each other.
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9. Miscible and Immiscible Liquids
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10. Heterogeneous Mixtures
Suspensions-contain large particles that “settle out” unless constantly stirred or agitated
Colloids-contain intermediate particles between those in solutions and suspensions
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Suspensions
Heterogeneous Mixture in which the particles in the solvent are so large that they settle out unless the mixture is constantly stirred.
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13. IPC-Solutions-Borders
How does a solid dissolve into a liquid?
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14. How Does a Solution Form?
Solvent molecules are attracted to surface ions.
Each ion is surrounded by solvent molecules.
Ionic solid dissolving in water
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15. Dissolution vs reaction
dry
Ni(s) + HCl(aq)
NiCl2(aq) + H2(g)
NiCl2(s)
Dissolution is a physical change—you can get back the original solute by evaporating the solvent.
If you can’t, the substance didn’t dissolve, it reacted.
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16. Factors Affecting Solubility
Chemists use the saying “like dissolves like”:
Polar substances tend to dissolve in polar solvents.
Nonpolar substances tend to dissolve in nonpolar solvents.
Oil is nonpolar while water is polar.
They are immiscible.
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Rate of Dissolution
There are several factors that affect the rate or “how quickly” dissolving occurs.
Heating
Agitating
Increasing Surface Area
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Saturation
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Saturation Types
saturated
solution containing undissolved solute in equilibrium with the solution
unsaturated
solution containing less than the maximum amount of solute
supersaturated
solution containing more solute than is normally allowed
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Degree of saturation
Unsaturated Solution
Less than the maximum amount of solute for that temperature is dissolved in the solvent.
No solid remains in flask.
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Degree of saturation
Saturated solution
Solvent holds as much solute as is possible at that temperature.
Undissolved solid remains in flask.
Dissolved solute is in dynamic equilibrium with solid solute particles.
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Saturated Solution
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Degree of saturation
Supersaturated Solution
Solvent holds more solute than is normally possible at that temperature.
These solutions are unstable; crystallization can often be caused by adding a “seed crystal” or scratching the side of the flask.
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A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature.
An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature.
A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature.
Sodium acetate crystals rapidly form when a seed crystal is
added to a supersaturated solution of sodium acetate.
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Solubility
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Solubility of Gases
In general, the solubility of gases in water increases with increasing mass.
Why?
Larger molecules have stronger dispersion forces.
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Gases in Solution
The solubility of liquids and solids does not change appreciably with pressure.
But, the solubility of a gas in a liquid is directly proportional to its pressure.
Increasing pressure above solution forces more gas to dissolve.
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Temperature
Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature.
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Temperature
The opposite is true of gases. Higher temperature drives gases out of solution.
Carbonated soft drinks are more “bubbly” if stored in the refrigerator.
Warm lakes have less O2 dissolved in them than cool lakes.
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Temperature and Solubility
Solid solubility and temperature
solubility increases with increasing temperature
solubility decreases with increasing temperature
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Temperature and Solubility
Gas solubility and temperature
solubility usually decreases with increasing temperature
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Electrolytes
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Electrolyte
Electrolyte: a substance that dissolves in water to give a solution that conducts electric current
Any soluble ionic compound is an electrolyte
Strong acids are electrolytes
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