In chemistry, a mixture is a material system made up by two or more different substances which are (mixed) together but are not combined chemically. Mixture refers to the physical combination of two or more substances the identities of which are retained. The molecules of two or more different substances are mixed in the form of alloys, solutions, suspensions, and colloids.

Mixtures are the product of a mechanical blending or mixing of chemical substances like elements and compounds, without chemical bonding or other chemical change, so that each ingredient substance retains its own chemical properties and makeup. Nonetheless, despite there are no chemical changes to its constituents, the physical properties of a mixture, such as its melting point, may differ from those of the components. Some mixtures can be separated into their components by physical (mechanical or thermal) means. Azeotropes can be considered as a kind of mixture which usually pose considerable difficulties regarding the separation processes required to obtain their constituents (physical or chemical processes or, even a blend of them).

Mixtures can be either homogeneous or heterogeneous. A homogeneous mixture is a type of mixture in which the composition is uniform. A heterogeneous mixture is a type of mixture in which the composition can easily be identified, as there are two or more phases present. Air is a homogeneous mixture of the gaseous substances nitrogen, oxygen, and smaller amounts of other substances. Salt, sugar, and many other substances dissolve in water to form homogeneous mixtures. A homogeneous mixture in which there is both a solute and solvent present is also a solution.

The following table shows the main properties of the three families of mixtures.

The following table shows examples of the three types of mixtures.

Physics and Chemistry

A heterogeneous mixture is a mixture of two or more compounds. Examples are: mixtures of sand and water or sand and iron filings, a conglomerate rock, water and oil, a salad, trail mix, and concrete (not cement). Gy's sampling theory quantitatively defines the heterogeneity of a particle as:

h_i = \frac{(c_i - c_\text{batch})m_i}{c_\text{batch} m_\text{aver}} .

where h_i, c_i, c_\text{batch}, m_i, and m_\text{aver} are respectively: the heterogeneity of the ith particle of the population, the mass concentration of the property of interest in the ith particle of the population, the mass concentration of the property of interest in the population, the mass of the ith particle in the population, and the average mass of a particle in the population.

During the sampling of heterogeneous mixtures of particles, the variance of the sampling error is generally non-zero.

Pierre Gy derived, from the Poisson sampling model, the following formula for the variance of the sampling error in the mass concentration in a sample:

V = \frac{1}{(\sum_{i=1}^N q_i m_i)^2} \sum_{i=1}^N q_i(1-q_i) m_{i}^{2} \left(a_i - \frac{\sum_{j=1}^N q_j a_j m_j}{\sum_{j=1}^N q_j m_j}\right)^2 .

in which V is the variance of the sampling error, N is the number of particles in the population (before the sample was taken), q_ i is the probability of including the ith particle of the population in the sample (i.e. the first-order inclusion probability of the ith particle), m_ i is the mass of the ith particle of the population and a_ i is the mass concentration of the property of interest in the ith particle of the population.

It must be noted that the above equation for the variance of the sampling error is an approximation based on a linearization of the mass concentration in a sample.

In the theory of Gy, correct sampling is defined as a sampling scenario in which all particles have the same probability of being included in the sample. This implies that q_ i no longer depends on i, and can therefore be replaced by the symbol q. Gy's equation for the variance of the sampling error becomes:

V = \frac{1-q}{q M_\text{batch}^2} \sum_{i=1}^N m_{i}^{2} \left(a_i - a_\text{batch} \right)^2 .

where a_batch is the concentration of the property of interest in the population from which the sample is to be drawn and M_batch is the mass of the population from which the sample is to be drawn.

For the video game character, seeWild Arms 5

The Dean-Stark apparatus or Dean-Stark receiver or distilling trap is a piece of laboratory glassware used in synthetic chemistry to collect water (or occasionally other liquid) from a reactor. It is used in combination with a reflux condenser and a batch reactor for continuous removal of the water that is produced during a chemical reaction performed at refluxtemperature. It was invented by E. W. Dean and D. D. Stark in 1920 for determination of the water content in petroleum.

Function

Two types of Dean-Stark traps exist – one for use with solvents with a density less than water (shown in the figure on the left) and one for use with solvents with a density greater than water.

The Dean-Stark apparatus in the laboratory typically consists of vertical cylindrical piece of glass (the trap, above part 9), often with a volumetric graduation on its full length and a precision tap on the bottom very much like a burette. The top of the cylinder is a fit with the bottom of the reflux condenser (5). Protruding from the top the cylinder has a side-arm sloping toward the reaction flask (2). At the end the side-arm makes a sharp turn so that the end of the side arm (3) is vertical as well. This end connects with the reactor.

During the reaction in (2), vapors containing the reaction solvent and the component to be removed travel out of reaction flask up into the condenser (5), and then drip into the distilling trap (above 9). Here, immiscible liquids separate into layers. When the top (less dense) layer reaches the level of the side-arm it can flow back to the reactor, while the bottom layer remains in the trap. The trap is at full capacity when the lower level reaches the level of the side-arm--beyond this point, the lower layer would start to flow back into the reactor as well. It is therefore important to syphon or drain the lower layer from the Dean-Stark apparatus as much as needed.

More rarely encountered is the model for solvents with a density greater than water. This type has a tube at the bottom of the side-arm to allow the organic solvent at the bottom to flow back into the reaction vessel. The water generated during the reaction floats on top of the organic phase.

This piece of equipment is usually used in azeotropic distillations. A common example is the removal of water generated during a reaction in boiling toluene. An azeotropic mixture of toluene and water distills out of the reaction, but only the toluene (density=0.865 g/ml) returns, since it floats on top of the water (density=0.998 g/cm³), which collects in the trap. The Dean-Stark method is commonly used to measure moisture content of items such as bread in the food industry.

This equipment can be used in cases other than simple removal of water. One example is the esterification of butanol with acetic acid catalyzed by sulfuric acid. The vapor contains 63% ester, 24% water and 8% alcohol at reflux temperature and the organic layer in the trap contains 86% ester, 11% alcohol and 3% water which is reintroduced. The water layer is 97% pure.

Another example is the esterification of benzoic acid and n-butanol where the ester product is trapped and the butanol, immiscible with the ester flows back into the reactor. Removing water in the course of these esterifications shifts the chemical equilibrium in favour of ester formation.

Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation. Generally the component parts boil at less than 25 Â°C from each other under a pressure of one atmosphere (atm). If the difference in boiling points is greater than 25 Â°C, a simple distillation is used.

Laboratory setup

Fractional distillation in a laboratory makes use of common laboratory glassware and apparatuses, typically including a Bunsen burner, a round-bottomed flask and a condenser, as well as the single-purpose fractionating column.

Apparatus

• heat source, such as a hot plate with a bath, and ideally with a magnetic stirrer.
• distilling flask, typically a round-bottom flask
• receiving flask, often also a round-bottom flask
• fractionating column
• distillation head
• thermometer and adapter if needed
• condenser, such as a Liebig condenser, Graham condenser or Allihn condenser
• vacuum adapter (not used in image to the right)
• boiling chips, also known as anti-bumping granules
• Standard laboratory glassware with ground glass joints, e.g. quickfit apparatus.

Discussion

As an example, consider the distillation of a mixture of water and ethanol. Ethanol boils at 78.4 Â°C while water boils at 100 Â°C. So, by gently heating the mixture, the most volatile component will concentrate to a greater degree in the vapor leaving the liquid. Some mixtures form azeotropes, where the mixture boils at a lower temperature than either component. In this example, a mixture of 96% ethanol and 4% water boils at 78.2 °C, being more volatile than pure ethanol. For this reason, ethanol cannot be completely purified by direct fractional distillation of ethanol-water mixtures.

The apparatus is assembled as in the diagram. (The diagram represents a batch apparatus, as opposed to a continuous apparatus.) The mixture is put into the round bottomed flask along with a few anti-bumping granules (or a Teflon coated magnetic stirrer bar if using magnetic stirring), and the fractionating column is fitted into the top. As the mixture boils, vapor rises up the column. The vapor condenses on the glass platforms, known as trays, inside the column, and runs back down into the liquid below, refluxing distillate. The column is heated from the bottom. The efficiency in terms of the amount of heating and time required to get fractionation can be improved by insulating the outside of the column in an insulator such as wool, aluminium foil or preferably a vacuum jacket. The hottest tray is at the bottom and the coolest is at the top. At steady state conditions, the vapor and liquid on each tray are at equilibrium. Only the most volatile of the vapors stays ingaseous form all the way to the top. The vapor at the top of the column, then passes into the condenser, which cools it down until it liquefies. The separation is more pure with the addition of more trays (to a practical limitation of heat, flow, etc.) The condensate that was initially very close to the azeotrope composition becomes gradually richer in water. The process continues until all the ethanol boils out of the mixture. This point can be recognized by the sharp rise in temperature shown on the thermometer.

Typically the example above now only reflects the theoretical way fractionation works. Normal laboratory fractionation columns will be simple glass tubes (often vacuum jacketed, and sometimes internally silvered) filled with a packing, often small glass helices of 4 to 7 mm diameter. Such a column can be calibrated by the distillation of a known mixture system to quantify the column in terms of number of theoretical plates. To improve fractionation the apparatus is set up to return condensate to the column by the use of some sort of reflux splitter (reflux wire, gago, Magnetic swinging bucket, etc.) - a typical careful fractionation would employ a reflux ratio of around 10:1 (10 parts returned condensate to 1 part condensate take off).

In laboratory distillation, several types of condensers are commonly found. The Liebig condenser is simply a straight tube within a water jacket, and is the simplest (and relatively least expensive) form of condenser. The Graham condenser is a spiral tube within a water jacket, and the Allihn condenser has a series of large and small constrictions on the inside tube, each increasing the surface area upon which the vapor co

Neutral grain spirit (also called pure grain alcohol (PGA) or grain neutral spirit (GNS)) is a clear, colorless, flammable liquid that is distilled from grain and has a very high ethanol content. The term neutral refers to the fact that it lacks any flavor derived from the mash used to distill it, nor does it have any flavor added to it after distillation (as is done, for example, with gin). The grain from which it is produced can be any of the common cereal grains. Other kinds of spirits, such as whisky, are distilled at lower alcohol percentages in order to preserve the flavor of the mash.

Generally, any distilled spirit of 170 proof or higher that does not contain any added flavoring is considered to be neutral alcohol.

The purity of neutral grain spirit has a practical limit of 190 proof because a mixture of ethanol and water becomes an azeotrope at 95.6% ABV (191.2 proof).

Neutral grain spirit is only one type of neutral spirit (also called neutral alcohol). Neutral alcohol can also be produced from grapes, sugar beets, sugarcane, or other fermented plant material. In particular, large quantities of neutral alcohol are distilled from wine, a product that is referred to as vinous alcohol.

Neutral grain spirit is used in the production of blended whiskey, cut brandy, some liqueurs, and some bitters. As a consumer good, it is almost always mixed with other beverages to create such drinks as punch and various cocktails, or to produce homemade liqueurs.

Availability in market areas

Because of its high alcohol content, neutral grain spirit is illegal, unavailable, or difficult to find in many areas.

Canada

• In Canada, The Luxco product Everclear is only sold in the province of Alberta. In British Columbia, one can purchase neutral grain spirits only with a permit for medical, research, or industrial use. Neutral grain spirits are also sold in Quebec from the producer Alcool Global.

United States

Everclear, Golden Grain Alcohol, and Gem Clear are three brands of neutral grain spirit sold in the United States.

• It is illegal to sell the 190-proof variety of neutral grain spirit (i.e., Everclear, Golden Grain Alcohol, or Gem Clear) in some states of the United States— California, Florida, Hawaii, Maine, Massachusetts, Michigan, Minnesota, Nevada, North Carolina, Pennsylvania, and Washington. In some of these states, the 151-proof variety of Everclear may be sold.
• In the U.S. Commonwealth of Virginia, grain alcohol lacking distinctive color, odor, and flavor, while not illegal, is not sold at any liquor stores owned by the State (compare, for example, that beverages such as Southern Comfort, a flavored liqueur that has grain alcohol as its base, are sold). Because Virginia has a self-legislated monopoly on the sale of hard liquor, independent liquor stores are illegal, and the product is thus mostly unavailable. In some cases, however, liquor stores on U.S. military bases in the Commonwealth do sell grain alcohol, and small quantities may be imported on one’s person from nearby states.

Europe

In Europe, neutral alcohol is sold in some countries. Since it is usually distilled from grain, it is in fact neutral grain spirit. This product contains 95%–95.6% ABV (190–191.2 proof) and is much used for making homemade liqueurs. In Germany, neutral alcohol is called Neutralalkohol or (colloquially) Primasprit. Primasprit is sold in stores and is most often used for making homemade liqueurs; other uses are rare.

There are several Polish companies that sell neutral grain spirit. Most of these are part of a state-owned monopoly called Polmos, which is now being privatized.

Japan

In Japan, neutral grain spirit is sold in the same manner as other common liquors. It may be purchased by anyone over the age of 20 in both bars and retail stores, or on Internet shopping sites, provided that the retailer possesses a license issued by the National Tax Agency. Handling or storing more than 400 litres (105.7 US gallons) also requires a license.

Neutral grain spirit is classified as a hazardous material in Japan due