Solution

A solution is a homogeneous mixture of two or more substances. The term homogeneous means "the same throughout." For example, suppose that you make a solution of sugar in water. If you were to take a drop of the sugar solution from anywhere in the solution, it would always have the same composition.

Terminology

A number of specialized terms are used in talking about solutions. The solvent in a solution is the substance that does the dissolving. The solute is the substance that is dissolved. In the sugar solution described above, the water is the solvent and the sugar is the solute.

Although that definition is neat, it does not always make a lot of sense. For example, one can make a solution of two gases. In fact, the air around us is a solution consisting of oxygen, nitrogen, argon, carbon dioxide, and other gases. In this case, it is difficult to say which gas "does the dissolving" and which gas (or gases) "is dissolved."

An alternative method of defining solvent and solute is to say that the component of the solution present in the largest amount is the solvent while the components present in lesser amounts are solute. According to that definition, nitrogen is the solvent in atmospheric air because it is present in the largest amount. Oxygen, argon, carbon dioxide, and other gases, then, are the solutes.

The term miscible is often used to describe how well two substances—generally, two liquids—mix with each other. For example, if you try to mix oil with water, you will find that the two do not mix very well at all. They are said to be immiscible—incapable of mixing. In contrast, ethyl alcohol and water are completely miscible because they mix with each other in all proportions.

Words to Know

Concentration: The amount of a substance (solute) present in a given volume of solvent or solution.

Homogeneous: The same throughout.

Miscibility: The extent to which some substance will mix with some other substance.

Saturated: In referring to solutions, a solution that contains the maximum amount of solute for a given amount of solvent at a given temperature.

Solubility: The tendency of a substance to dissolve in some other substance.

Solute: The substance that is "dissolved" or that exists in the least amount in a solution.

Solvent: The substance that "does the dissolving" or that exists in the largest amount in a solution.

Supersaturated: In referring to solutions, a solution that contains more than the maximum amount of solvent that can normally be dissolved in a given amount of solvent at a given temperature.

Unsaturated: In referring to solutions, a solution that contains less than the maximum amount of solvent that can be dissolved in a given amount of solvent at a given temperature.

Solubility is a term similar to miscibility but more exact. The solubility of a substance is the amount of the substance that will dissolve in a given amount of solvent. For example, the solubility of sugar in water is approximately 90 grams of sugar per 100 grams of water. That statement means that one can dissolve up to 90 grams of sugar in 100 grams of water.

The solubility of a substance is dependent on the temperature. The statement in the previous paragraph, for example, should have been that 90 grams of sugar will dissolve in 100 grams of water at some specific temperature. That temperature happens to be 0°C.

Generally speaking, the solubility of substances increases with temperature. The graph in Figure 1 illustrates this point. Notice that the solubility of sugar increases to a little over 100 grams per 100 grams of water at 25°C and to 130 grams per 100 grams of water at 50°C.

An important exception to this rule concerns gases. All gases become less soluble in water as the temperature increases.

Concentration of solutions

Solutions are mixtures whose composition can vary widely. One can make a water solution of sodium chloride by dissolving 1 gram of sodium chloride in 100 grams of water; 5 grams in 100 grams of water; 10 grams in 100 grams of water; and so on. The amount of solute for any given amount of solvent is defined as the concentration of the solution.

One way of expressing the concentration of a solution is with the terms dilute and concentrated. These terms are not very specific. For example, a solution containing 1 gram of sodium chloride in 100 grams of water and a second solution containing 2 grams of sodium chloride in 100 grams of water are both dilute. But the term is appropriate because, at room temperature, nearly 40 grams of sodium chloride can be dissolved in 100 grams of water. Thus, a solution containing 35 grams of sodium chloride in 100 grams of water could be called a concentrated solution.

Solutions can also be classified as saturated, unsaturated, or supersaturated. A saturated solution is one that holds all the solute it possibly can at any given temperature. For example, the solubility of sodium chloride in water is 37 grams per 100 grams of water. If you make a solution containing 37 grams of sodium chloride in 100 grams of water, the solution is said to be saturated; it can't hold any more sodium chloride.

Any solution containing less than the maximum possible amount of solute is said to be unsaturated. A solution with 5 grams of sodium chloride (or 10 grams or 20 grams or 30 grams) in 100 grams of water is unsaturated.

Finally, supersaturated solutions are also possible. As bizarre as it sounds, a supersaturated solution is one that holds more solute than is possible at some given temperature. The way to make a supersaturated solution is to make a saturated solution at some higher temperature and then let the solution cool very carefully.

For example, one could make a saturated solution of sugar in water at 50°C by adding 130 grams of sugar to 100 grams of water. That solution would be saturated. But then, one could allow the solution to cool down very slowly. Under those circumstances, it might happen that all of the sugar would remain in solution even at a temperature of 25°C. But at that temperature, the solubility of sugar is normally a little over 100 grams per 100 grams of water. Therefore, the cooled solution would be supersaturated. Supersaturated solutions are normally very unstable. The slightest movement in the solution, such as simply shaking it, can cause the excess solute to settle out of the solution.

Solution

A solution, in chemistry, is a homogenous (uniform throughout) mixture, on a molecular level, of two or more substances. It is formed when one or more substances are dissolved in one or more other substances and completely dispersed (distributed so as to disappear). Simply, it is a mixture of a solvent and a solute. The scientific nature of solutions is a relatively recent discovery, though people throughout history have used solutions in one form or another. The word solution is derived from the Latin solvere, to dissolve or to release.

The substances (solids, liquids, or gasses) in a solution make up two phases, the solvent and the solute. The solvent is the substance that typically determines the physical state of the solution (solid, liquid, or gas). The solute is the substance that is dissolved by the solvent. For example, in a solution of salt and water, water is the solvent and salt is the solute.

Solutions are formed because the molecules of the solute are attracted to the molecules of the solvent. When the attractive forces of the solvent are greater than the molecular forces holding the solute together, the solute dissolves. There are no rules that will determine whether substances will dissolve, however the cardinal rule of solubility is “like dissolves like.” Oil and water do not mix, but oil in oil does.

The substances that make up a solution can be either solids, liquids, gasses, or a combination of any of these. Brass is a solution of solid copper and zinc. Gasoline is a complex solution of liquids. Air is a solution of gases. Soda pop is a solution of solid sugar, liquid water, and carbon dioxide gas. The properties of solutions are best understood by studying solutions with liquid solvents.

When water is the solvent, the solutions are called aqueous solutions. In aqueous solutions, dissolved material often separates into charged components called ions. For example, salt (NaCl) ionizes into Na⁺ ions and Cl^- ions in water. The ionic nature of liquid solutions was first identified by Swedish physical chemist Svante August Arrhenius (1859–1927) who, in the early 1880s, studied the way electricity passed through a solution. His ionic theory states that charged particles in a solution will conduct electricity. At the time, his theory was controversial and scorned by the majority of scientists. In the late 1890s, however, when scientists discovered that atoms contain charges, the ionic theory was accepted. He was awarded the Nobel prize in 1903 for his work in understanding the nature of solutions.

Because of molecular interaction, the physical properties of a solution are often different from the properties of the pure substances of which they are composed. For example, water freezes at 32°F (0°C), but a solution of water and salt freezes below 32°F. This is why salt melts ice off the roads and sidewalks in the cold winter months.

Unlike pure substances, solutions do not have a definite composition. Their composition is dependent on the amount of solute dissolved in the solvent. Concentrated solutions have relatively high amounts of solute dissolved in the solvent while dilute solutions have relatively low amounts. The concentration of a solution is typically expressed in terms of grams of solute per liter of solvent. The concentration of a solution of 0.2 oz (5 g) of sugar dissolved in 3.5 oz (100 g) of water is 0.05 or 5%.

Every solute has a certain degree of solubility in a solvent. Solubility is a number that indicates the normal concentration, at a certain temperature, in which no more dissolving will take place. For example, if a teaspoon of sugar is added to a glass of water, it dissolves, and an unsaturated solution is created. However, if more and more sugar is added, it eventually forms a pile of undissolved sugar on the bottom of the glass. At this point, the normal maximum concentration is exceeded and a saturated solution is created.

The solubility of a solute in a solvent is affected by various factors. Molecular structure, pressure, and temperature all affect the solubility of a system. Heating a solution can increase or decrease solubility. Increasing pressure has a similar effect.

If a solution and solvent or two solutions of different strength are separated by a semi-permeable membrane, osmosis can occur. Osmosis is the passage of water from a weak solution to a strong solution through a semi-permeable membrane. The net effect of osmosis is the averaging out of the concentration between the two solutions. A solution can have the solute removed (that is, it can be purified) by reverse osmosis. In one of its many roles, reverse osmosis is used to prepare drinking water from seawater.

If large particles of material are placed into a liquid, they may not dissolve. For example, fine clay in water will merely settle to the bottom of the container due to the action of gravity. The dispersed particles of a solution are of molecular size. Between these two extremes, there are particles that are larger than molecules but not so large that they will settle out due to the action of gravity. The solution containing particles of this size is termed a colloidal solution, or often just a colloid. Many examples of colloids using different phases are commonly encountered and many of their properties are similar to those of normal, molecular solutions.

A solution of two gases generally has each gas acting as if the other component were not present. This property is due to the large intermolecular distances encountered between gas molecules. This result is most obviously encountered when the pressure of the gas solution is modified. This concept is covered by Dalton’s law of partial pressure, which states that the total pressure of a mixture of gases equals the sum of the pressures that each gas would exert if it was present by itself. The pressure exerted by one gas in a mixture of gases is the partial pressure of that individual gas. Dalton’s law assumes that the gases do not react with each other, but that each gas is a separate component of the system.

A solution is an important form of matter and is the basis of many of the products chemists use everyday. From glues to shampoos, soda pops to medicines, solutions will undoubtedly be used by people in the future.

See also Mixture, chemical; Solubility.

Solution

A solution is a homogenous (uniform throughout) mixture, on a molecular level, of two or more substances. It is formed when one or more substances are dissolved in one or more other substances. The scientific nature of solutions is a relatively recent discovery, though solutions in one form or another have been used by people throughout history.

The substances (solids, liquids, or gasses) in a solution make up two phases, the solvent and the solute. The solvent is the substance which typically determines the physical state of the solution (solid, liquid or gas). The solute is the substance which is dissolved by the solvent. For example, in a solution of salt and water , water is the solvent and salt is the solute.

Solutions are formed because the molecules of the solute are attracted to the molecules of the solvent. When the attractive forces of the solvent are greater than the molecular forces holding the solute together, the solute dissolves. There are no rules which will determine whether substances will dissolve however, the cardinal rule of solubility is "like dissolves like." Oil and water don't mix, but oil in oil does.

The substances which make up a solution can be either solids, liquids, gasses, or a combination of any of these. Brass is a solution of solid copper and zinc. Gasoline is a complex solution of liquids. Air is a solution of gasses. Soda pop is a solution of solid sugar, liquid water and carbon dioxide gas. The properties of solutions are best understood by studying solutions with liquid solvents.

When water is the solvent, the solutions are called aqueous solutions. In aqueous solutions, dissolved material often separates into charged components called ions. For example, salt (NaCl) ionizes into Na+ ions and Cl-ions in water. The ionic nature of liquid solutions was first identified by Svante Arrhenius (1859-1927) who, in the early 1880s, studied the way electricity passed through a solution. His ionic theory states that charged particles in a solution will conduct electricity. At the time, his theory was controversial and scorned by the majority of scientists. In the late 1890s, however, when scientists discovered that atoms contained charges, the ionic theory was accepted. He was awarded the Nobel prize in 1903 for his work in understanding the nature of solutions.

Because of molecular interaction, the physical properties of a solution are often different from the properties of the pure substances of which they are composed. For example, water freezes at 32°F (0°C), but a solution of water and salt freezes below 32°F. This is why salt melts ice .

Unlike pure substances, solutions do not have a definite composition. Their composition is dependent on the amount of solute dissolved in the solvent. Concentrated solutions have relatively high amounts of solute dissolved in the solvent while dilute solutions have relatively low amounts. The concentration of a solution is typically expressed in terms of grams of solute per liter of solvent. The concentration of a solution of 0.2 oz (5 g) of sugar dissolved in 3.5 oz (100 g) of water is 0.05 or 5%.

Every solute has a certain degree of solubility in a solvent. Solubility is a number which indicates the normal concentration, at a certain temperature , in which no more dissolving will take place. For example, if a teaspoon of sugar is added to a glass of water, it dissolves, and an unsaturated solution is created. However, if more and more sugar is added, it eventually forms a pile of undissolved sugar on the bottom of the glass. At this point, the normal maximum concentration is exceeded and a saturated solution is created.

The solubility of a solute in a solvent is affected by various factors. Molecular structure, pressure , and temperature all affect the solubility of a system. Heating a solution can increase or decrease solubility. Increasing pressure has a similar effect.

A solution is an important form of matter and is the basis of many of the products we use everyday. From glues to shampoos, soda pops to medicines, solutions will undoubtedly be used by people forever.

See also Mixture, chemical; Solubility.

so·lu·tion / səˈloōshən/ • n. 1. a means of solving a problem or dealing with a difficult situation: there are no easy solutions to financial and marital problems. ∎  the correct answer to a puzzle: the solution to this month's crossword.2. a liquid mixture in which the minor component (the solute) is uniformly distributed within the major component (the solvent). ∎  the process or state of being dissolved in a solvent.3. archaic the action of separating or breaking down; dissolution: the solution of British supremacy in South Africa.

solution
1. A physically homogeneous mixture of two or more substances in which solid, liquid, or gaseous phases may combine in one of those phases. A constituent of a solution can be separated out by changing its phase, e.g. boiling, condensing, or freezing. Where a solution is formed by dissolving a quantity of one substance in a larger quantity of another, the smaller quantity is called the ‘solute’, the larger quantity, the ‘solvent’. Compare COLLOID.

2. A weathering process by which weakly bonded ionic components of minerals are detached through the attraction of water molecules (which carry a positive electrical charge at one end and a negative charge at the other, although they are neutral overall), and then carried away from the weathering environment. Halites and the sulphates and carbonates of magnesium and calcium are especially vulnerable. Solution is usually the first stage of chemical weathering.