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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.



From Yahoo Answers

Question:1. Is the ink in your marker a pure substance or a solution? Support your answer with your data. 2. Classify each of these substances as a heterogeneous mixture, homogenous mixture or a pure substance and explain how you can tell. a) Chocolate chip cookie - b) Coffee with cream - c) Aluminum foil - d) Potting soil - e) Gold metal -

Answers:1) It must NOT be a pure substance. Reasons? It has some smell, and it has color. The color is still left on whatever you marked when the smell is gone. Hence smell and color must be from two different substances. 2) a) Chocolate chip cookie - a heterogeneous mixture, since Chocolate chips are still visible b) Coffee with cream - a heterogeneous mixture, since cream itself is a heterogeneous mixture of butterfat and other components. Remember that butterfat does not dissolve in water. c) Aluminum foil - a pure substance d) Potting soil - a heterogeneous mixture e) Gold metal - a pure substance, or a homogeneous mixture, depends on the purity of gold.

Question:im having trouble understand this. both compounds and heterogenous mixtures have two or more different elements/atoms. so what is the difference? i know that elements are from pure substances and hetrogenous mixtures are from Mixtures, but what is the difference if they both are actually mixtures?

Answers:compounds and heterogeneous mixtures both have two or more different elements/atoms, yes, that is true. however, compound have these elements combined together in consistent and fixed ratios; which means that CO2 will always be CO2, whether it is made in america or in antarctica. however, a heterogeneous mixture, such as air, is a mixture of different elements/compounds that are not combined (or mixed) in fixed ratios. for example, air is composed of nitrogen, oxygen and carbon dioxide. but if i were to get some from china and compare it to some from switzerland, i would see a vast difference in compositions.

Question:In my chemistry book, a pure substance is defined as "matter with distinct properties and composition that doesn't vary from sample to sample." A homogenous mixture is "a mixture uniform throughout." It later says that if matter is uniform throughout it's homogenous, if it DOES have variable composition, it is a homogenous mixture (or a solution), and if it DOES NOT have variable composition, it's a pure substance. I'm not seeing how this makes sense... help?!

Answers:Think of it as a pure substance is like an element, the element is always the same. Every time, Carbon is going to have the same properties. A homogeneous mixture is when two things are combined and you can not see any difference. The example i like is water and sand. When you put the sand in the water, it doesn't mix so the mixture is heterogeneous. If you mix water and sugar; however, the end product is still aqueous and appears uniform. It will be this way until you get into over saturation.

Question:I have a paper to finish and i need to know if these are a substance or a mixture and if they are homogeneous or heterogeneous: chlorine water soil sugar water oxygen carbon dioxide rocky road ice cream alcohol pure air iron for example: chlorine;substance;element thanks and do it asap please?!?!?

Answers:To avoid semantics, let's define homogeneous as having the same composition throughout...if you take large or small samples at random, each will be the same. chlorine: element, homogeneous water: compound, homogeneous if pure. soil: mixture, heterogeneous. sugar water: mixture, homogeneous. oxygen: element, homogeneous. carbon dioxide: compound, homogeneous. RRIC: mixture, heterogeneous. alcohol: compound, homogeneous. pure air: mixture (of gases), more or less homogeneous...but some samples will contain varying amounts of CO2, H2O, etc, which will still be 'pure' air...so perhaps heterogeneous is more apt. iron: element, homogeneous...unless you want to differentiate the various crystal forms which may be present. So there may be some ambiguity in the homogeniety of pure air and iron...depends upon the scale of your sampling. (elements and compounds are 'substances')

From Youtube

Differentiate Between Pure Substances and Mixtures :Learn how to differentiate between pure substances and mixtures

GCSEPod Chemistry - Mixtures :**This is a short sample from GCSEPod Chemistry - Mixtures. The full title is 18 minutes long and includes 4 Chapters. ** Solid, liquid and gas are the three states of matter, and mixtures of them can be formed in a variety of ways. The simplest kind of mixture is a solution. The solid disappears because it is broken up into particles that are too small to be seen. We can measure how much solid dissolves in a certain mass of liquid. This is called the solubility. In a suspension, the particles are small enough so that they don't settle out as sediment but are just large enough to be seen. A suspension is one kind of colloid. Colloids are substances that have mixtures of states. A jelly has some properties like a solid and some like a liquid. Some very useful materials are mixtures. These include emulsions, solutions and alloys. We will consider the various types of mixtures in this title. Visit www.gcsepod.co.uk for more.