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==>> For more on Mixtures (Solutions, Suspensions, Emulsions, Colloids )

A solution is a mixture of one substance dissolved in another so the properties are the same throughout. A solution is composed of a solute and the solvent. The solute is the substance being dissolved and the solvent is the part of the solution that does the dissolving. The solute is of molecular size.

Examples of Solutions:

 GasOxygen and other gases in nitrogen (air)
Water vapor in air (humidity)
The odor of a solid -- molecules of that solid being dissolved in the air
LiquidCarbon dioxide in water (carbonated water)Ethanol (common alcohol) in water; various hydrocarbons in each other (petroleum) *Sucrose (table sugar) in water; sodium chloride (table salt) in water
SolidHydrogen dissolved to palladiumWater in activated charcoalSteel, Brass, other metal alloys

* Two liquids that are soluble are said to be miscible in one another.


Strength of Solutions

The solubility is the amount of solute that be be dissolved in a given amount of solvent at any one temperature. A solution is said to be unsaturated as long as more solute can be dissolved.

Dilute or Weak Solution - only a small amount of solute compared to solvent.

Concentrated Solution - A relatively large amount of solute to solvent.

Saturated Solution --At this point, the concentration of the solute in solution is the maximum possible under the existing conditions (temperature and pressure). A solution is saturated when no more solute can be dissolved at the current temperature. A saturated solution is one in which the dissolved and undissolved solutes are in equilibrium.

Supersaturated Solution -- a solution that contains more dissolved substance than does a saturated solution; the solution is not in equilibrium with the pure substance. Examples of supersaturated solutions are carbonated water,

Water is the Universal Solvent

Although water is sometimes called the universal solvent, there are many things it cannot dissolve. For example water and oil do not mix. We say oil is immiscible in water.

What makes water such a good solvent?

Water is a good solvent due to its polarity. The solvent properties of water are vital in biology, because many biochemical reactions take place only within aqueous solutions

When an ionic or polar compound enters water, it is surrounded by water molecules. The relatively small size of water molecules typically allows many water molecules to surround one molecule of solute. The partially negative dipoles of the water are attracted to positively charged components of the solute, and vice versa for the positive dipoles. For more on this topic see: Why is water such a good solvent?

Assessment Questions:

Multiple Choice Questions

1. In a solution the substance that does the dissolving is called ___
a) soluble
b) the solute
c) the solvent
d) an ion

2. Water is a good solvent because
a) Water is a good solvent because it is a negatively charged ion.
Water is such a good solvent because it repels most molecules
c) Water is such a good solvent because it is such a small molecule
d) Water is a good solvent due to its polarity and small molecular size

3. A solution that cannot hold any more solute at room temperature would be ___
a) a dilute solution
b) a concentrated solution
c) a saturated solution
d) a supersaturated solution

4. Ethanol dissolved in water would be an example of ___
a) a solution between two miscible liquids
b) a solution between a solid and liquid
c) a suspension between two liquids
d) ethanol and water do not form a solution

5. To form a supersaturated solution requires
a) reducing the amount of solute
b) increasing the amount of solute in a solution
c) increasing the temperature of a saturated solution so more solute can be added
d) none of the above


==>> For more on Mixtures (Solutions, Suspensions, Emulsions, Colloids )

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