- solvent: the substance in which a solute dissolves to produce a homogeneous mixture
- solute: the substance that dissolves in a solvent to produce a homogeneous mixture
Many different kinds of solutions exist. For example, a solute can be a gas, a liquid or a solid. Solvents can also be gases, liquids or solids.
The following figures show the microscopic behavior of several different kinds of solutions. Note that in each case, the solute particles are uniformly distributed among the solvent particles.
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| Microscopic view of Br2 gas (solute) dissolved in Ar gas (solvent). | Microscopic view of Ar gas (solute) dissolved in liquid H2O (solvent). |
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| Microscopic view of Br2 liquid (solute) dissolved in liquid H2O (solvent). | Microscopic view of solid NaCl (solute) dissolved in liquid H2O (solvent). Note that the ionic solid, NaCl, produces Na+ ions (blue) and Cl- ions (green) when dissolved in water. |
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| Microscopic view of solid Kr (solute, blue) dissolved in solid Xe (solvent,red). |
Examples of Solutions:
| Gas | Liquid | Solid | ||
|---|---|---|---|---|
| Gas | Oxygen 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 | |
| Liquid | Carbon 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 | |
| Solid | Hydrogen dissolved to palladium | Water in activated charcoal | Steel, 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.
What are colloids?
Colloids are substances in a dispersed phase. A substance can be considered as a colloid when its size was larger than the size of a molecule but smaller than what can be seen by the naked eye. An easy way of determining if a mixture is a colloid is through Tyndall Effect.
Tyndall Effect is the effect of light scattering in many directions in colloidal dispersion. During a Tyndall effect, when the light passed through a colloidal solution, the substance in the dispersed phases scatters the light in all directions making it readily seen.
A common method of classifying colloids is based on the phase of the dispersed substance and what phase it is dispersed in. Colloids have three types: Sol, emulsion, foam and aerosol. Sol is a colloidal suspension with solid particles in the liquid. An example of this are ruby glasses, paints and cell fluids. Emulsion is a dispersion between two liquids. An example of this are pearl, cheese, milk and oil in water. Foam is formed when many gas particles are trapped in a liquid or solid. Soap suds and whipped cream are an example. Aerosol contains small particles of liquid or solid dispersed in gas. Smoke, fog and mist are an example.Brownian movement may be used to distinguish between solutions and colloids. Brownian motion is the random movement of colloidal particles suspended in a liquid or gas, caused by collisions with molecules of the surrounding medium. The particles in solutions and colloids are in constant motion. However colloid particles are large enough to be observed and are small enough to still be affect by the random molecular collisions. Colloid particles resist settling rapidly to the bottom of a vessel due to Brownian motion.
Emulsions are a type of colloid
Emulsions are an example of colloids composed of tiny particles suspended in another immiscible (unmixable) material. An emulsion is a suspension of two liquids that usually do not mix together. These liquids that do not mix are said to be immiscible. An example would be oil and water. If you mix oil and water and shake them a cloudy suspension is formed. Let the mixture rest and the oil and water will separate.
An emulsifying agent (emulsifier) is any substance that keeps the parts of an emulsion mixed together. For example if we mix oil and water a suspension will form that over time separates. But now, if we add a few drops and shake the mixture the oil and water will stay mixed much longer.
Examples of emulsions include butter and margarine, and mayonnaise.
Examples of Colloids
| Dispersed Medium | ||||
|---|---|---|---|---|
| Continuous Medium | Gas | (All gases are soluble) | Liquid Aerosol Examples: Fog, Mist | Solid Aerosol Examples: smoke, dust |
| Liquid | Foam Examples: Whipped cream | Emulsion Examples: Milk, Mayonnaise, hand cream | Sol Examples: Paint, pigmented ink, blood, Milk of Magnesia | |
| Solid | Solid Foam Examples: Aerogel, Styrofoam, pumice | Gel Examples: Gelatin, cheese | Solid Sol Examples: ruby glass | |
the benefits and risks of both solutions and colloids
Solutions and colloids have both benefits and risks to us, humans, and the environment. For example, solution and colloids used for medication. If we are talking about medication, the benefits of solutions are:
- The drug is available to be immediately absorbed after dosage
- Flexible dosing
- Can be designed for any route of administration
- No need to be shaken before dosage
- Facilitates swallowing in difficult cases
- Better than crystalloids at expanding the circulatory volume
- Increases osmotic pressure
Even if these two have benefits to our industry of medication it still also have some risks.
For solutions:
- The drug's stability was often reduced in solution
- Difficult to mask unpleasant tastes
- Bulky and is difficult to transport
- Prone to container breakages
- Some of the drugs are poorly soluble
For colloids:
Can precipitate cardiac failure and pulmonary and peripheral oedema
Can also cause anaphylactic shock
Can lead to a small increase in the rate of death
Some solutions and colloids can be harmful to the environment. Some of these mixtures might cause pollution. For some colloids, it releases some CFC's that contributes to the ozone layer's depletion.
