Chapter 7

 A heterogeneous mixture is a nonuniform blend of 2 or more substances  Examples of heterogeneous mixtures:  fruit salad  salsa  granite (quartz, black mica and feldspar  orange juice

 A suspension is a mixture in which particles of a material are more or less evenly distributed throughout a liquid of gas. Particles can be settled out or filtered  Examples of suspensions:  Snow globe  Chocolate milk  Water from a muddy creek or river

 Substances like vinegar and oil can be shaken together but will separate into two immiscible liquids  Decanting: the process of pouring a lighter liquid off of a heavier liquid or solid

 A colloid is a mixture consisting of tiny particles that are intermediate in size between those in solutions and those in suspensions and that are suspended in a liquid, solid, or gas  Examples of colloids  Jello  Egg white  Blood Plasma  Whipped cream  Marshmallows  Fog  Smoke

 When light is passed through a colloid, the light is scattered by the invisible particles

 An emulsion is any mixture of two or more immiscible liquids in which one liquid is dispersed in the other  Examples of emulsions  Mayonnaise  Cream

 A solution is a homogeneous mixture of two or more substances uniformly dispersed throughout a single phase  Solute: the substance that dissolves  Solvent: the substance in which the solute dissolves

 Solutions that are solids dissolved in liquids  Salt water  Sugar water  Tea  Solutions that are gases dissolved in liquids  Soda  Water with O2

 Solutions that are liquids dissolved in liquids  Crude oil/petroleum  Ethanol  Distillation: Method of separating components of a mixture based on boiling point

 Solutions that are solids dissolved in solids  Brass (copper and zinc)  Bronze (copper and tin)  Gold  Alloy: A homogeneous mixture that is composed of two or more metals

 Water has a bent structure  The oxygen atom has a partial + charge  The hydrogen atom has a partial – charge  This makes water a polar molecule  Water molecules attract both the positive and negative ions in an ionic compound

 pWo pWo

 Solutes whose water molecules conduct an electric current are classified as electrolytes

 Many ionic compounds dissolve in water, but not all ionic compounds dissolve in water  In order to dissolve, the molecules of the solvent (often water) must exert a greater force on the molecules of the solute than the forces that hold the solute molecules together

 The hydrogen atoms in a water molecule are attracted to oxygen atoms in other molecules, resulting in the formation of hydrogen bonds (hydrogen bonds can also form from the attraction of hydrogen to flourine and nitrogen)  Sugar, for example, is a molecular compound. The –OH groups found in sugar are attracted to water molecules through the formation of hydrogen bonds. As a result, water is able to “pull” sugar molecules into a solution

 Molecular compounds that dissolve in water do not conduct an electric current.

 Polar substances dissolve polar substances. Polar molecular have partial positive and partial negative charges that attract each other and dissolve.  Examples  Salt and water  Sugar and water

 Nonpolar substances only dissolve in nonpolar substances.  Vinegar and oil do not mix. Vinegar is a polar substance and oil is nonpolar.  Oil based paints (nonpolar) cannot be cleaned with water (polar). Turpentine (nonpolar) must be used.

 Solutes with large surface areas dissolve faster  Stirring or shaking a solution helps the solute dissolve faster  Solutes dissolve faster when the solvent is hot EXCEPT gases, which dissolve better when the solvent is cold.

 Solutes RAISE the boiling point of a solution  Solutes LOWER the freezing point of a solution

 Solubility is the maximum amount of a solute that will dissolve in a given quantity of solvent at a given temperature and pressure.  Soluble: Dissolves easily in the solvent (usually water)  Insoluble: Does not dissolve in the solvent

 Concentration is the amount of a particular substance in a given quantity of a mixture, solution, or ore  Concentration is the quantity of solute dissolved in a given volume of solvent  Concentrated refers to a large amount of solute dissolved in the solvent  Weak refers to small amount of solute dissolved in the solvent.

 An unsaturated solution is a solution that contains less solute than a saturated solution does and is able to dissolve additional solute.

 A saturated solution is a solution that cannot dissolve any more solute under the given conditions.

 A supersaturated solution holds more solute that it should at a given temperature and pressure.  A supersaturated solution is formed by heating a saturated solution until all the solute dissolves. The solution is then cooled.  Adding additional solute to a supersaturated solution will cause the excess solute to crystallize.

 The solubility of gases increases as the temperature decreases  The solubility of gases increases as the amount of pressure increases

 Molarity is a measurement of concentration  Molarity = moles of solute = mol  liters of solution L

 Calculate the molarity of sodium carbonate  (Na 2 CO 3 ) in a solution of 38.6 g in L  of solution.  1. List the given  Mass of Na 2 CO 3 = 38.6 g  Volume of solution = L 

 2. Find the moles of Na 2 CO 3  Molar Mass of Na 2 CO 3 = 106 g  Molar of Na 2 CO 3 = Mass of Na 2 CO 3  Molar Mass of Na 2 CO 3  = 38.6 g  106 g/mol  = moles 

 3. Find the molarity  Molarity = Moles  Liter  = mol Na 2 CO 3  L solution  = M

 Concentration can also be given as mass per cent, which is the grams of solute per 100 g of solution.  How would you make a 5% sodium chloride solution?  Dissolve 5 grams of sodium chloride in 100 g of water

 Solute concentration can also be expressed as parts per million (ppm) or parts per billion  (ppb).  Example  The US Environmental Protection Agency has set the maximum safe level for lead in drinking water as 15 ppb.