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Home :Glossary

Glossary: Solutions

activity. (a)
An effective concentration used in thermodynamic calculations in place of the actual concentration to allow equations developed for ideal solutions* to be used to treat real solutions.

aeration. aerate.
Preparation of a saturated solution* of air gases by either spraying the solution in air or by bubbling air through it.

aerosol. Compare with colloid*.
A colloid* in which solid particles or liquid droplets are suspended in a gas. Smoke is an example of a solid aerosol; fog is an example of a liquid aerosol.

A sample of precisely determined amount taken from a material.

aqueous. (aq) aqueous solution.
A substance dissolved in water.

azeotrope. azeotropic mixture; azeotropy.
A solution that does not change composition when distilled. For example, if a 95% (w/w) ethanol solution in water is boilled, the vapor produced also is 95% ethanol- and it is not possible to obtain higher percentages of ethanol by distillation.

Conversion of liquid into gas as bubbles of gas that form within the liquid. Boiling begins at the temperature where the vapor pressure* of a liquid would be equal to the external pressure on the liquid.

boiling point. (bp) standard boiling point; normal boiling point.
The temperature at which the vapor pressure* of a liquid would be equal to the external pressure on the liquid. The standard boiling point is the temperature at which the vapor pressure of a liquid equals standard pressure*.

boiling point elevation.
The boiling point of a solution is higher than the boiling point of the pure solvent. Boiling point elevation is a colligative property*.

colligative property. colligative; colligative properties.
Properties of a solution that depend on the number of solute molecules present, but not on the nature of the solute. Osmotic pressure*, vapor pressure*, freezing point depression*, and boiling point elevation* are examples of colligative properties.

A colloid is a heterogeneous mixture* composed of tiny particles suspended in another material. The particles are larger than molecules but less than 1 µm in diameter. Particles this small do not settle out and pass right through filter paper. Milk is an example of a colloid. The particles can be solid, tiny droplets of liquid, or tiny bubbles of gas; the suspending medium can be a solid, liquid, or gas (although gas-gas colloids aren't possible).

Adding solvent to a solution to lower its concentration.

ebulliometry. ebulliometric.
Determination of average molecular weight of a dissolved substance from the boiling point elevation* of the solution.

emulsion. Compare with colloid*.
A colloid* formed from tiny liquid droplets suspended in another, immiscible* liquid. Milk is an example of an emulsion.

enthalpy of hydration. (DeltaHhyd) hydration enthalpy; heat of hydration.
The change in enthalpy* for the process


where the concentration of A in the aqueous solution approaches zero. Enthalpies of hydration for ions are always negative because strong ion-water attractions are formed when the gas-phase ion is surrounded by water.

equivalent. Compare with normality*.
1. The amount of substance that gains or loses one mole of electrons in a redox reaction. 2. The amount of substances that releases or accepts one mole of hydrogen ions in a neutralization reaction. 3. The amount of electrolyte that carries one mole of positive or negative charge, for example, 1 mole of Ba2+(aq) is 2 equivalents of Ba2+(aq).

eutectic mixture.
A mixture of two or more substances with melting point* lower than that for any other mixture of the same substances.

foam. Compare with colloid*.
A colloid* in which bubbles of gas are suspended in a solid or liquid. Aerogel (solid smoke) and Styrafoam are examples of solid foams; whipped cream is an example of a liquid foam.

fractional distillation. Compare with distillation*.
A technique for separation of liquid mixtures by distillation* that uses a tower attached to a flask containing the mixture to perform multiple distillations. Vapor moving up the column condenses on packing material inside the column, trickles down the column, and again vaporises. The more volatile* component can then be drawn off at the top of the component, while the less volatile component remains at the bottom.

freezing point depression. (DeltaTfp)
The freezing point of a solution is always lower than the freezing point of the pure solvent. The freezing point depression is roughly proportional to the molality* of solute particles in the solution. Freezing point depression is an example of a colligative property* of a solution.

gel. Compare with colloid*.
A gell is a sol* in which the solid particles fuse or entangle to produce a rigid or semirigid mixture. For example, gelatin dissolved in water produces a sol of protein molecules. When the gelatin is cooked, the protein chains entangle and crosslink, forming a gel which is a mesh of solid protein with trapped pockets of liquid inside. Fruit jellies are also gels

Henry's Law. Henry's law constant.
Henry's law predicts that the solubility (C) of a gas or volatile substance in a liquid is proportional to the partial pressure (P) of the substance over the liquid:

P = k C

where k is called the Henry's law constant and is characteristic of the solvent and the solute.

hydrophilic. hydrophilicity; hydrophilic group.
A polar molecule or group that can form strong hydrogen bonds* with water.

hydrophobic. hydrophobicity; hydrophobic group.
A nonpolar molecule or group that has little affinity for water. Hydrophobic groups on molecules in solution tend to turn in on themselves or clump together with other hydrophobic groups because they are unable to disrupt the network of strong hydrogen bonds in the water around them.

hypertonic. Compare with osmotic pressure*.
Describes a solution which has higher osmotic pressure than some other solution (usually, higher osmotic pressure than cell or body fluids). Freshwater fish die if placed in seawater because the seawater is hypertonic, and causes water to leave the cells in fish's body.

hypotonic. Compare with osmotic pressure*.
Describes a solution which has lower osmotic pressure than some other solution (usually, lower osmotic pressure than cell or body fluids). Washing your contact lenses with distilled water rather than saline is painful because distilled water is hypotonic; it causes water to move into cells, and they swell and burst.

ideal solution.
All molecules in an "ideal solution" interact in exactly the same way; the solvent-solvent, solvent-solute, and solute-solute intermolecular forces are all equivalent. Ideal solutions obey Raoult's law* exactly. Real solutions behave ideally only when they are very dilute.

mass percentage. ((w/w)%)
Mass percentages express the concentration of a component in a mixture or an element in a compound. For example, household bleach is 5.25% NaOCl by mass, meaning that every 100 g of bleach contains 5.25 g of NaOCl. Mass percentage can be calculated as 100% times the mass of a component divided by the mass of the mixture containing the component.

molality. (m) Compare with molarity*.
Concentration measured as moles of solute per kilogram of solvent. For example, a 1 m NaCl solution contains 1 mole of NaCl per kilogram of water. Molalities are preferred over molarities in experiments that involve temperature changes of solutions, e. g. calorimetry and freezing point depression experiments.

1. Of or pertaining to moles*. 2. An synonym for molarity*; for example, a "six molar solution of hydrochloric acid" contains 6 moles of HCl per liter of solution.

molarity. (M) molar concentration.
Concentration of a solution measured as the number of moles of solute per liter of solution. For example, a 6 M HCl solution contains 6 moles of HCl per liter of solution.

mole fraction.
Concentration of a substance in a mixture measured as moles of the substance per mole of mixture. For example, the mole fraction of oxygen in air is about 0.21, which means that 1 mol of air contains about 0.21 mol O2.

normality. (N) normal. Compare with molarity* and equivalent*.
A measure of solution concentration, defined as the number of equivalents* of solute per liter of solution.

osmometry. Compare with osmosis*.
Determination of the average molecular weight of a dissolved substance from measurements of osmotic pressure*.

osmosis. Compare with reverse osmosis*.
Passage of solvent molecules from a dilute solution through a semipermeable membrane* to a more concentrated solution.

osmotic pressure.
Pressure which must be applied to a solution to prevent water from flowing in via a semipermeable membrane*.

parts per million. (ppm)
Concentration expressed as parts of solute per million parts of solution. Usually refers to parts per million by mass. For example, a 10 ppm NaCl solution can be written as: 10 mg NaCl/kg solution, 10 µg NaCl/g solution, 10 ng NaCl/mg solution. In very dilute aqueous solutions, ppm is approximately equal to mg solute per liter of solution.

Raoult's law.
The vapor pressure* of a solvent in an ideal solution* equals the mole fraction of the solvent times the vapor pressure of the pure solvent.

reverse osmosis. Compare with osmosis*.
Solvent molecules flow spontaneously from a dilute solution through a semipermeable membrane* to a more concentrated solution (osmosis). In reverse osmosis, pressure is applied to the more concentrated solution to force the flow of solvent to go from more concentrated to more dilute solution. Reverse osmosis is used to produce fresh water from sea water.

saturated solution. Compare with supersaturated solution*.
A solution which does not dissolve any more solute. When a saturated solution is placed in contact with additional solute, solute neither dissolves nor is deposited from a saturated solution.

semipermeable membrane.
A membrane that allows some but not all of the components in a mixture to pass through it. Semipermeable membranes are used in dialysis*.

A colloid* with solid particles suspended in a liquid. Examples are protoplasm, starch in water, and gels.

solubility. solubilities; equilibrium solubility; solubleness.
The solubility of a substance is its concentration in a saturated solution*. Substances with solubilities much less than 1 g/100 mL of solvent are usually considered insoluble. The solubility is sometimes called "equilibrium solubility" because the rates at which solute dissolves and is deposited out of solution are equal at this concentration.

solubilizing group.
A group or substructure on a molecule that increases the molecule's solubility. Solubilizing groups usually make the molecule they are attached to ionic or polar. For example, hydrocarbon chains can be made water-soluble by attaching a carboxylic acid* group to the molecule.

A substance dissolved in a solvent* to make a solution*.

solution. homogeneous mixture. Compare with heterogeneous mixture*.
A sample of matter consisting of more than one pure substance* with properties that do not vary within the sample. Also called a homogeneous mixture.

The most abundant component in a solution*.

sorption. Compare with adsorption* and absorption*.
Assimilation of molecules of one substance by a material in a different phase. Adsorption (sorption on a surface) and absorption (sorption into bulk material) are two types of sorption phenomena.

specific gravity. specific gravities. Compare with density*.
The mass of a unit volume of a substance relative to the mass of a unit volume of water. Temperature must be specified when reporting specific gravities, since the density of the substance and of water change with temperature. Specific gravities are often reported relative to water at 4°C; at that temperature, water has a density of 1.00000 g/mL and the specific gravity of a substance is equal to its density in g/mL.

standard solution.
A solution of precisely known concentration.

supersaturated solution. supersaturated.
A supersaturated solution has concentration of solute that is higher than its solubility*. A crystal of solute dropped into a supersaturated solution grows; excess solute is deposited out of the solution until the concentration falls to the equilibrium solubility.

Tyndall effect.
Light passing through a colloid* is scattered by suspended particles. The light beam becomes clearly visible; this phenomenon is called the Tyndall effect. For example, car headlight beams can be seen in fog, but the beams are invisible in clear air.

unsaturated compound.
An organic compound with molecules containing one or more double bonds.

vapor pressure lowering. vapour pressure depression; vapor pressure depression.
A colligative property* of solutions. The vapor pressure of a solution is always lower than the vapor pressure of the pure solvent; the ratio of solution to pure solvent vapor pressures is approximately equal to the mole fraction of solvent in the solution.

volume percentage. ((v/v)%)
Volume percentages express the concentration of a component in a mixture or an element in a compound. For example, 95% ethanol by volume contains 95 mL of ethanol in 100 mL of solution (NOT in 100 mL of water!)

General Chemistry Online! Solutions

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