steps to take a slow whether it is a pure substance or a homogeneous mixture?

Answer 1

All matter can be separated into two categories by asking the question "Is only one chemical substance present in the sample being considered?"


YES - Pure Substance
NO - Mixture

A mixture is one in which two or more pure substances retain their chemical identity. For example, if you dissolve some sugar into water, the sugar molecules and water molecules remain as sugar and water, it is just that the two are now dispersed in each other. Another definition of mixture: a dispersion of two or more pure substances that can be separated using physical means only.

All mixtures have two parts, the "dispersing medium" and the "dispersed phase." Generally speaking, the dispersed phase is in the smaller amount and is spread throughout the dispersing medium. In most cases, the dispersed phase is quite small in amount compared to the amount of the dispersing medium. Only sometimes, in our studies in this class, will the two amounts become near to equal.

IIa. Pure Substances

Question #2: All pure substances can be separated into two categories by asking the question "Can the sample be further decomposed by chemical means?"


YES - Compound
NO - Element

The definitions of element and compound, as well as examples, are found in Section 2.2: Elements and Compounds.

First Historical Note: our concept of an element is due to Robert Boyle (1627-1691). His definition was experimentally-based: an element could not be broken down into simpler substances. This meant that all element identifications were tenative, since better techniques meant that a compound, mistakenly thought to be an element, might be shown to be an element.

Misindentifications of compounds as elements continued to be problems through the 1800's. Not only problems associated with methods, but with getting everybody to agree to use the same definitions. In our era, these problems have been resolved.

One story: hydrogen is the lightest element known. Up until 1913, it was a possibility that there could be lighter elements and there was even an occasional announcement of such a discovery. However, in 1913, work done by Henry Moseley (which you will learn about later) forever shut the door to the possibilty of elements lighter than hydrogen.

Second Historical Note: another important idea at that time was the immutability of atoms. An atom of copper has always been copper and always will be copper. Nothing can change it. This idea has been shown to be wrong by the modern discoveries of radioactivity, fission and fusion. These topics overlap between physics and chemistry and will be studied later in the school year.

IIb. Mixtures

Question #3: All mixtures can be separated into two categories based on the question "Is the sample of constant composition?"


YES - Homogeneous mixture
NO - Heterogeneous mixture

Constant composition means that all parts of the mixture are the same. For example, dissolve sugar in water and mix it completely. Now take several samples from random areas. They will be the same, therefore this is a homogeneous mixture. Take some sand and some water and mix it up well. Take some samples and MAYBE they are the same. Allow the water to stand undisturbed and then sample it. One portion will be more sand than water and another will be more water than sand. This is heterogeneous.

Generally speaking, heterogeneous mixtures can be separated by allowing them to stand undisturbed, letting the "formed portion" (the solids) to settle out. However, filtering or centrifuging may be required. For example, not all the solid components of blood will settle out simply by standing. The blood sample must be placed in a centrifuge and spun at several times the force of gravity. The ribosomes in a cell can be separated from the cell in an ultracentrifuge, a device which can produce 50,000 to 100,000 times the force of gravity.

The technical name for a heterogeneous mixture is a suspension. The solid pieces which are dispersed in the suspension are sometimes able to be seen with the naked eye and can definitly be seen under a light microscope. (Homogeneous mixtures will be divided into two types -- solution and colloid. In both cases the dispersed phase cannot be seen under a microscope.)

In chemistry, homogeneous mixtures are more often found, so we will pretty much end our heterogeneous mixture discussion at this point.

III. Homogeneous Mixtures

Homogeneous mixtures do not settle out upon standing undisturbed and they cannot be separated by filtering or centrifuging. There are two broad categories of homogeneous mixtures.

Question #4: All homogeneous mixtures can be separated into two categories based on the question "Are the constituents of the sample at a molecular or ionic level?"


YES - Solution
NO - Colloid

Solutions: these are, by far, the most important homogeneous mixture in chemistry. Only in more advanced classes will you start to study the characteristics of colloids.

Solutions are made up of a solute and a solvent. The solvent (usually liquid water) is the dispersing medium (component present in greater amount) and the solute (usually, but not always, a solid) is the dispersed phase (component present in the lesser amount). In solutions, the solute is present either as individual ions or individual molecules. There is no "clumping" into pieces made of many ions or molecules.

The word homogeneous is important: the solue is dispersed in an equal manner throughout the solvent. If you sampled two equal-sized regions of the solution, they would contain identical amounts of solute.

Answer 2

carbonated beverage - homogeneous mixture, answer till you may locate the bubbles of CO2 after which you will argue that it incredibly is a heterogeneous mixture chrome metallic - homogeneous mixture sugar - organic substance, a compound gasoline - a homogeneous mixture A organic substance has a single chemical composition, mutually as a mixture has a variable composition.

Answer 3

I assume you mean steps to show.

If it is a solid, I would see if it has a clear melting point. A pure substance will have a sharp melting point, a mixture will seperate as one item melts out.

If the substance is a liquid, do the same but with boiling. A pure substance will fully boil at one temperature. A mixture will fractionate and the components will boil off at different temperatures.

Answer 4

steps to take a slow???

Answer 5

Huh?