2Objectives Describe the hydrogen bonding that occurs in water Explain the high surface tension and low vapor pressure of water in terms of hydrogen bondingAccount for the high heat of vaporization and the high boiling point of water in terms of hydrogen bondingExplain why ice floats on water
3The Water Molecule O-H bonds are highly polar covalent bonds. the O atom has a slightly negative charge. H has a slightly positive charge.Hydrogen bonding- occurs when hydrogen is attracted to a very electronegative element (N, O, and F).
5The Unique Properties of Water High surface tensionLow vapor pressureHigh specific heat capacityHigh heat of vaporizationHigh boiling pointLow density of ice
6Surface propertiesSurface tension: the inward pull that tends to minimize thesurface area of a liquid.Surfactant: surface active agent- surface tension is decreased by detergents (interferes with hydrogen bonding)
13Specific Heat Capacity Water’s high specific heat capacity helps to moderate daily air temperatures around large bodies of water.(Water’s specific heatis more than 4 timesthat of most metals.)
14Water’s high heat of vaporization Because of hydrogen bonding,water absorbs large amountsof heat as it vaporizes.Water releases largeamounts of heat as itcondenses.
15Water’s high boiling point Hydrogen bonding causes water’s high boiling point
16IceIce has an open framework structure, the density of ice is lower than that of water.
17ObjectivesExplain the significance of the statement “like dissolves like”Distinguish between strong electrolytes, weak electrolytes, and nonelectrolytes, giving examples of each
18Solution – homogeneous mixture What is a solution?Solution – homogeneous mixtureSolvent – substance present in largest amount (the dissolving medium)Solutes – other substances in the solutionAqueous solution – water is the solvent
20Solvation… the process that occurs as a solute dissolves. There are two types of solvation:Ionic compounds dissolve by dissociation.Covalent compounds dissolve by molecular solvation.
21Solubility of Ionic Substances: Dissociation The positive and negative ions of a salt come apart (dissociate) as a salt dissolves.
22Dissociation vs. Molecular Solvation NaCl(s) Na +(aq) + Cl -(aq)Note: the ions come apart from each other(electrolytes)Molecular solvation:C6H12O6(s) C6H12O6(aq)Note: no dissociation occurs(nonelectrolytes)
23“Like dissolves like”Polar solutes dissolve in polar solvents (water is polar, so it dissolves polar substances, either ionic or molecular).Nonpolar solutes dissolve in nonpolar solvents (oil dissolves in kerosene).
24Solubility of Polar Substances Ethanol is soluble in water because of the polar OH bond.
25Why is solid sucrose (C12H22O11), table sugar, soluble in water?
26Substances Insoluble in Water Nonpolar oil does not interact with polar water.
27ElectrolytesElectrolytes- conduct an electric current in solution or in molten state.(ionic compounds)Nonelectrolytes- do not conduct an electric current in solution or in molten state.(molecular compounds)
28ElectrolytesStrong electrolytes: solute completely breaks apart in solution[includes soluble salts (such as KCl), inorganic acids (such as HNO3), inorganic bases (such as NaOH)]
29ElectrolytesWeak electrolytes: only a fraction of the solute breaks apart into solution[includes poorly soluble salts (such as PbCl2), organic acids (such as HC2H3O2), and organic bases (such as NH3)]
30ElectrolytesNonelectrolyte – does not conduct when in solution- does not break apart into ions.[includes most organic compounds (such as glucose)]
31Water of hydrationThe water in a crystal is called water of hydration.A hydrate is a compound that includes water of hydration.
32Water of hydrationA hygroscopic substance removes water from the air. These substances are called dessicants.
33Heterogeneous Aqueous Systems Suspensions are mixtures from which particles settle out upon standing. (The particles are much larger than those in a solution.)Colloids are heterogeneous mixtures that contain particles that are intermediate in size between suspensions and true solutions
34Colloidal SystemsColloids exhibit the Tyndall effect, which is the scattering of light in all directions.Colloids include milk, mayonnaise, marshmallows, egg white, blood, and paint.
36Identify factors that determine the rate at which a solute dissolves ObjectivesIdentify factors that determine the rate at which a solute dissolvesIdentify factors that affect the solubility of a solute in solutionCalculate the solubility of a gas in a liquid under various pressure conditions
37Factors affecting the rate of dissolving How could you speed up the dissolving of sugar in a glass of iced tea?Which dissolves faster, table salt or rock salt?
38Factors affecting the rate of dissolving Temperature – increasing the temperature speeds up the rate of dissolvingAgitation – stirring speeds up the rate of dissolvingParticle size – smaller particles dissolve faster than large particles (surface area)
39SolubilityThe solubility- the amount that dissolves in a given quantity of solvent at a given temperature.
40SolubilityA saturated solution contains the maximum amount of solute at a constant temperature.
41SolubilityAn unsaturated solution contains less solute than a saturated solution.A supersaturated solution contains more solute than a saturated solution. (This occurs when a solution is saturated and then allowed to cool but all of the solid remains dissolved. It is an unstable solution, adding a crystal causes precipitation.)
42What would happen……if you added more sugar to a saturated sugar solution and stirred?…if you added more sugar to an unsaturated sugar solution and stirred?
43Factors affecting the solubility of a substance How could you increase the amount of sugar that would eventually dissolve in a glass of tea?
44Factors affecting the solubility of a substance Only two factors affect the amount of solute that can dissolve.Temperature affects solubility of both solids and gases in liquid solvents.Pressure affects solubility of gases in liquid solvents.
45Factors affecting the solubility of a substance The solubility of most solid substances increases as the temperature of the solvent increases.For a few substances, the reverse occurs.
46The Effect of Temperature on the Solubility of Solids
47The Effect of Temperature on Gas Solubility Increasing the temperature of a dissolved gas solution decreases the concentration of the gas.Have you ever tried a hot Dr. Pepper? Heat it in a pan on the stove, pour a cup, and it has no bubbles!Thermal pollution occurs when hot water is added to a lake, the dissolved oxygen levels fall in the water and it kills the fish.
49The Effect of Pressure on Gas Solubility Increasing the pressure of a gas over the surface of a solvent increases the solubility of the gas in the solvent.In a bottled soda, the pressure of CO2 over the liquid is high and when the cap is opened, the pressure is reduced and bubbles begin to come out of the solution.
50The Effect of Pressure on Gas Solubility Henry’s Law: at a given temperature the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid.S1/P1 = S2/P2
51Question:If the solubility of a gas in water is 0.77 g/L at 3.5 atm pressure, what is the solubility (in g/L) at 1.0 atm?(The temperature is held constant at 25oC.)Answer: S1/P1 = S2/P20.77 g/L / 3.5 atm = S2 / 1.0 atmS2 = 0.22 g/L