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8th Grade- Chapter 11 Notes

Chapter 11, Lesson 1 Notes

*A pure substance is a single kind of matter that has a specific makeup, or composition.

*The two types of pure substances are elements and compounds.

*A mixture occurs whenever two substances are physically blended, but not chemically bonded.

*Pure substances cannot be separated easily or sometimes, at all.  But, mixtures can be physically separated.

*Because a substance becomes a part of a mixture as soon as it is physically combined with another substance, pure substances are rare in nature.

*Biologists, chemists, and medical researchers have to use special techniques to isolate pure substances from mixtures to run their experiments.

*Mixtures are more common than pure substances in everyday situations.

*Two types of mixtures are heterogeneous mixtures and homogeneous mixtures.

*Heterogeneous mixtures are mixtures in which you can clearly observe the different parts.  Examples of heterogeneous mixtures include beach sand and trail mix.  Because the different parts of the mixture are easy to see, it is also easier to separate the parts.

*Homogeneous mixtures are mixtures that have very well blended parts.  The parts of a homogeneous mixture are so evenly mixed that you can’t see the individual parts of the mixture simply by looking at it.  Examples of homogeneous mixtures include lemonade and ketchup.

*Mixtures can easily be separated because each of the individual parts in a mixture retains its physical properties.

*Physical properties such as state of matter, boiling point, freezing point, and magnetic properties can be used to separate the parts of a mixture.

*Scientists use evaporation, distillation, filtration, and magnetic attraction to isolate the individual parts of a mixture.

Chapter 11, Lesson 2 Notes

*There are different types of mixtures. A mixture is classified as a solution, colloid, or suspension based on the size of its largest particles.

*A solution is a mixture that contains a solvent and at least one solute and has the same properties throughout.

*The solvent is part of a solution usually present in the greatest amount.  It dissolves the other substances.

*The solute is the substance that is dissolved by the solvent.

*The particles of solute in a solution are molecules or ions, and thus cannot be seen with the unaided eye.

*Solutes can be solids, liquids, or gases, as can solutions.

*In many common solutions, the solvent is water.  Water dissolves so many substances that it is often called the “universal solvent”.

*A colloid is a mixture that contains small, undissolved particles that do not settle out.

*Colloid particles are too small to be seen without a microscope, yet they are large enough to scatter a beam of light.

*A suspension is a mixture in which particles can be seen and easily separated by settling or filtration.

*Unlike a solution, a suspension does not have the same properties throughout.  It contains visible particles that are larger than the particles in solutions or colloids.

*A solution forms when particles of the solute separate from each other and become surrounded by particles of the solvent.

*Solutes are either ionic or molecular in nature.  When an ionic solid is mixed with water, the positive and negative ions of the solute are attracted to the partially charged water molecules.  The water molecules will eventually surround all of the ions and the solid crystal will be completely dissolved.

*If the solute is a molecular compound, it will break up into individual neutral molecules when added to water.

*The polar water molecules will attract the polar molecules of the solute.

*The solute molecules will move away from each other.  The covalent bonds within the molecules remain unbroken.

Chapter 11, Lesson 3 Notes

*Recall that a solution is a mixture containing a solvent and at least one solute and has the same properties throughout.

*A mixture that has only a little solute dissolved in a certain amount of solvent is called a dilute solution.  As you add more solute to the solvent, the solution becomes increasingly concentrated.

*A concentrated solution is a mixture that has a lot of solute dissolved in the solvent.  If you keep adding solute to the solvent, the solution will reach a point at which no more solute will dissolve in the solvent.

*Solubility is a measure of how much solute can dissolve in a solvent at a given temperature.

*Factors that can affect the solubility of a substance include pressure, the type of solvent, and temperature.

*A saturated solution is one in which the maximum amount of solute has been dissolved at a given temperature.  No more solute will dissolve.

*An unsaturated solution is one in which more solute will dissolve. 

*Solubility is a characteristic property of matter and can be used to identify a substance.

*By changing certain conditions, you can change a substance’s solubility.

*The solubility of a gas solute in a liquid solvent increases as the pressure of the gas over the solution increases.

*For liquid solutions, ionic and polar compounds will usually dissolve in polar solvents.

*Nonpolar compounds usually do not dissolve in very polar solvents, but they will dissolve in nonpolar solvents.

*For most solid solutes, solubility increases with an increase in temperature.

*A supersaturated solution is formed by cooling a heated saturated solution and letting it remain undisturbed so that the excess solute remains in solution.

*If a supersaturated solution is disturbed, the excess solute will come out of solution. 

*Unlike most solids, gases become less soluble when the temperature increases.

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