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From Wikipedia

Mixture

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 abatch is the concentration of the property of interest in the population from which the sample is to be drawn and Mbatch is the mass of the population from which the sample is to be drawn.


Mixture

In chemistry, a mixture is a material system made up by two or more different substances which are ( mix ed) 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

Homogeneous (chemistry)

A substance that is uniform in composition is a definition of homogeneous (IPA: /həmɔ�dʒɪnʌs, ho�modʒi�niʌs/) in Chemistry. This is in contrast to a substance that is heterogeneous. The definition of homogeneous strongly depends on the context used. In Chemistry, a homogeneous suspension of material means that when dividing the volume in half, the same amount of material is suspended in both halves of the substance. However, it might be possible to see the particles under a microscope. In Chemistry, another homogeneous substance is air. It is equally suspended, and the particles and gases and liquids cannot be analyzed separately or pulled apart.

Homogeneity of mixtures

In Chemistry, some mixtures are homogeneous. In other words, mixtures have the same proportions throughout a given sample or multiple samples of different proportion to create a consistent mixture. However, two homogeneous mixtures of the same pair of substances may differ widely from each other and can be homogenized to make a constant. Mixtures can be characterized by being separable by mechanical means e.g. heat, filtration, gravitational sorting, etc.

Solutions

A solution is a special type of homogeneous mixture. Solutions are homogeneous because, the ratio of solute to solvent remains the same throughout the solution even if homogenized with multiple sources, and stable because, the solute will not settle out, no matter how long the solution sits, and it cannot be removed by a filter or a centrifuge. This type of mixture is very stable, i.e., its particles do not settle, or separate. As homogeneous mixture, a solution has one phase (liquid) although the solute and solvent can vary: for example, salt water. In chemistry, a mixture is a substance containing two or more elements or compounds that are not chemically bound to each other but retain their own chemical and physical identities; - a substance which has two or more constituent chemical substances. Mixtures, in the broader sense, are two or more substances physically in the same place, but these are not chemically combined, and therefore ratios are not necessarily considered.



From Yahoo Answers

Question:Ok I need a little help with my homework... I did it all so don't tell me to go do it myself because I'm stuck on this question, I can't find a clear answer anywhere in my textbook or online and I'm determined to understand this. Describe what you would do to form: a) a heterogeneous mixture of sugar and salt crystals b) a homogeneous mixture of the same substances answer & explain please i don't really understand my chem teacher...

Answers:Heterogeneous means that there are discrete particles of each substance present in the mixture. To make this kind, just mix salt and sugar. The result is a mix of grains of both. In a homogeneous mixture, OTOH, there are no separate particles (beyond individual atoms or molecules, at least). The only kind of truly homogeneous mixture is a solution, in which atoms or molecules of one substance are simply in the spaces between the atoms or molecules of the other. To make a homogeneous mixture of only sugar and salt (with no water involved) you'd have to dissolve the salt in the sugar. It's conceivable that you could dissolve a limited amount of salt in melted sugar to get a solution. If you did, that would be a homogeneous mixture. If water is allowed, you could dissolve both the salt and the sugar in water. In that case, although the mixture (solution) is homogeneous, water is the solvent and the salt and sugar are solutes so there are actually three substances involved (a homogeneous mixture of salt, sugar, and water). It's therefore not strictly a homogeneous mixture of just salt and sugar.

Question:This is just my guess. Could you please correct me if I'm wrong. Compound, homogeneous mixture, or heterogeneous mixture: Soil: homogeneous mixture. Sugar water: homogeneous mixture. Rocky road icecream: heterogeneous mixture. Alcohol: compound. Pure air: homogeneous mixture.

Answers:Soil is heterogeneous (not all the parts are the same, and there are many different parts) everything else is right :)

Question:can you help me on this. can you tell me if this is a pure substance or mixture? if a pure substance; is it an element or compound. if its a mixture; is it an homogeneous or heterogeneous mixture? air styrofoam sugar fat free milk copper sulfate zinc develop gel marble granite foam baking power vitamin d copper sodium chromite crystal garden karo syrup thanks in advance=]

Answers:mixture-hetero mixture-homo pure substance- compound pure sub (ps) -compoumnd ps - compounmd ps- element mixture-homo mixture-hetero mixture-hetero mixture-homo mixture-homo ps-compound ps-element ps-compound mixture-hetero mixture-homo

Question:What is an example of homogenous mixture?

Answers:*homogenous mixture: If it is a liquid it is called a solution. If it is a mixture of two metals it is called an alloy. *A glass of water, the air in a closed room (at equilibrium and without heat sources) are examples of homogeneous substances. -A common example would be a solid dissolving into a liquid (i.e. salt or sugar dissolving in water or gold into mercury). Liquids dissolve into one another, and sometimes liquids dissolve into gases, for example water vapor and the atmosphere. Common examples include fountain drinks, where carbon dioxide is trapped in the liquid through carbonation. Several solution properties collectively called colligative properties change as a function of solute concentration. -Colloids are another type of homogeneous mixture in which the particles of one or more components have at least one dimension in the range of 1 to 1000nm, larger than those in a solution but smaller than those in a suspension. In general, a colloid or colloidal dispersion is a substance with components of one or two phases. It creates the Tyndall effect when light passes through it. A colloid will not settle if left to sit. Jelly, milk, blood, paint, fog, and glue are examples of colloid dispersions.

From Youtube

homogenous mixture :

Heterogeneous and Homogeneous Mixture :Making strawberry milk (homogeneous mixture) and bowl of M&Ms (heterogeneous mixture).