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What are Mixtures and Solutions? A MIXTURE is a combination of two or more substances that are not chemically united and do not exist in fixed proportions to each other. Most natural substances are mixtures.In the graphic on the left there are four substances - water, alcohol, oil, and food color dye.
Colloid and suspension In contrast a suspension is a heterogeneous mixture of larger particles. These particles are visible and will settle out on standing. Examples of suspensions are: fine sand or silt in water or tomato juice. A colloid is a homogeneous solution with intermediate particle size between a solution and a suspension. Colloid particles may be seen in a beam of light such as dust in air in a "shaft" of sunlight. Milk, fog, and jello are examples of colloids.
SOLUTIONS SOLUTIONS are homogeneous mixtures. A solution is a mixture of two or more substances in a single phase. At least two substances must be mixed in order to have a solution. The substance in the smallest amount and the one that dissolves or disperses is called the SOLUTE. The substance in the larger amount is called the SOLVENT. In most common instances water is the solvent. The gases, liquids, or solids dissolved in water are the solutes.In the graphic, the blue bottle is a homogeneous solution mixture of water, KOH, glucose, oxygen gas dissolved, and methylene blue - an indicator. Since solutions are mixtures, their compositions may vary over a very wide range. The concentrations may be expressed using a variety of measures. The non-specific terms concentrated and dilute are sometimes used. A concentrated solution has a relatively large (but non-specific) amount of solute dissolved in a solvent. A dilute solution has a smaller quantity of solute dissolved.
Density • Example • In a mixture of oil, water, and sand the density of oil < the density water < the density sand
Particle Size • Example • In a mixture of clay, sand, and pebble the particle size of clay < the particle size of sand < the particle size of pebble.
Particle Size • Example • In a mixture of sand and water the sand can be filtered out.
Filtration This is good for separating an insoluble solid from a liquid (an insoluble substance does not dissolve in water). For example, sand can be separated from a mixture of sand and water using filtration.
Molecular polarity Molecules that are polar attracts one another and other polar molecules. Those attractions are called intermolecular forces. Molecular polarity ranges from none to high. The higher the molecular polarity the stronger the intermolecular force is.
Molecular polarity Example
Boiling and freezing points Distillation is the process of separating substances from a mixture according to their respective boiling points.
Boiling and freezing points • Example • In a mixture of alcohol and water the alcohol will boil first since it has a lower boiling point than water. The alcohol vapor is then condensed and collected
Fractional distillation This is good for separating two or more liquids from each other. For example, ethanol (alcohol) can be separated from a mixture of ethanol and water by fractional distillation. This method works because the two liquids have different boiling points.
Simple distillation This is good for separating a liquid from a solution. For example, water can be separated from salty water by simple distillation. This method works because the liquid evaporates from the solution, but is then cooled and condensed into a separate container. The salt does not evaporate and so it stays behind.
Boiling and freezing points • Example • Petroleum contains gasoline, kerosene, fuel oil, and many useful other substances. When petroleum is heated different substances evaporate at different temperature, therefore each substance can be collected according to its boiling point. This process is called fractional distillation.
Evaporation This is good for separating a soluble solid from a liquid (a soluble substance dissolves in water to form a solution). For example, copper sulphate crystals can be separated from copper sulphate solution using evaporation. Remember that it is the water that evaporates away, not the solution.
Solubility Example Sodium chloride NaCl(s) is soluble in water while calcium carbonate, CaCO3(s) is not. If a mixture of both is made water can be added to separate the two substances then the insoluble substance is filtered out of the mixture.
chromatography chromatography is the process of separating substances from a mixture that rely on the differential affinities of substances for a gas or liquid mobile medium and for a stationary adsorbing medium through which they pass, such as paper, gelatin, or magnesia. Example Paper chromatography When the end of a piece of paper is dipped into water the water molecules keep finding new places (polar regions) to stick to and so the water molecules climb up the paper being replaced by new water molecules below. Other molecules which might be dissolved in the water will also be carried along up the paper.
chromatography A spot of dye is placed on the paper above the level of the water. As the water moves up, the dye molecules will move with it if they are more strongly attracted to the water molecules than to the paper molecules. If the dye molecules are more strongly attracted to the paper than to the water, they will move more slowly than the water or even not at all. What if the dye is a mixture? If two or more dyes have been mixed to form an ink, then they may move at different rates as the water moves up the paper. If this happens, they will separate and we can identify them.
Chromatography This is good for separating dissolved substances that have different colours, such as inks and plant dyes. It works because some of the coloured substances dissolve in the liquid better than others, so they travel further up the paper.
TEST YOUR UNDERSTANDING Which mixture can be separated by using the equipment shown below? (1) NaCl(aq) and SiO2(s) (2) NaCl(aq) and C6H12O6(aq) (3) CO2(aq) and NaCl(aq) (4) CO2(aq) and C6H12O6(aq)
TEST YOUR UNDERSTANDING When a mixture of water, sand, and salt is filtered, what passes through the filter paper? (1) water, only (2) water and sand,only (3) water and salt, only (4) water, sand, and salt Which physical property makes it possible to separate the components of crude oil by means of distillation? (1) melting point (2) conductivity (3) solubility (4) boiling point
TEST YOUR UNDERSTANDING At equilibrium, nitrogen, hydrogen, and ammonia gases form a mixture in a sealed container. The data table below gives some characteristics of these substances. Describe how to separate ammonia from hydrogen and nitrogen.
