2General Properties of Aqueous Solutions Solution = a homogeneous mixture of two or more substances.Solvent =normally the component that is present in greaterquantitySolute =dissolves in the solvent.
3Electrolytes and Nonelectrolytes Electrolyte = a substance that dissolves in water to give an electrically conducting solution.In general ionic solids that dissolves in water are electrolytes.Some molecular substances are also electrolytes. eg. HCl (g)Nonelectrolyte = a substance that dissolves in water to give a nonconducting or very poorly conducting solution.
4Strong and Weak Electrolytes Strong electrolyte an electrolyte that exists in solution almost entirely as ions.Eg. Sodium ChlorideNaCl (s) Na+(aq) + Cl-(aq)H2OWeak electrolyte an electrolyte that dissolves in water to give a relatively small percentage of ions.Eg. ammoniaNH3(aq) + H20(l) NH4+(aq) + OH-(aq)
5However, in the solution we will also find the reverse reaction. NH3(aq) + H20(l) NH4+(aq) + OH-(aq)For this situation we generally write a single equation with a double arrowNH3(aq) + H20(l) NH4+(aq) + OH-(aq)
6Types of Chemical Reactions Precipitation reactionswhen two ionic solutions are mixed and a solid ionic substance (precipitate) formsAcid-base reactionsinvolve the transfer of a protonOxidation-reduction reactionsinvolve the transfer of electrons between reactantsOther reactions
7Precipitation Reactions A precipitation reaction occurs in aqueous solution because one product is insoluble.Solubility RulesSolubility of a substance the amount of substance that can be dissolved in a given quantity of solvent.The solubility of substances varies widely.Precipitate an insoluble compound formed during a chemical reaction.
8Reaction of Potassium iodide solution and lead(II) nitrate solution
9General InterestShellfish form their shells from calcium carbonate. The organism secretes calcium ions from cells in contact with seawater, which contains dissolved carbon dioxide, some of which is present as carbonate ions. The ions combine to give a precipitate of calcium carbonate.
10General InterestKidney stones are generally also insoluble calcium compounds such as calcium carbonate , calcium phosphate or calcium oxalate.
11Acid-Base ReactionsAcids and bases are some of the most important electrolytesAcids taste sourBases taste bitter and feel soapy
12Another property of acids and bases is their ability to cause colour changes in certain dyes. An acid-base indicator is a dye used to distinguish between acidic and basic solutions by means of the color changes it undergoes in these solution.Probably the most important characteristic of acids and bases is how they react with each other.
13Some Common Acids and Bases Name Formula RemarkAcids:Acetic acid HC2H3O2 Found in vinegarAcetylsalicylic acid HC9H7O4 AspirinAscorbic acid H2C6H6O6 Vitamin CCitric acid H3C6H5O7 Found in lemon juiceHydrochloric acid HCl Found in gastric juiceSulfuric acid H2SO4 Battery acidBases:Ammonia NH3 Often found in household cleanersCalcium hydroxide Ca(OH)2 Slaked Lime (used in building industry)Magnesium hydroxide Mg(OH)2 Milk of magnesiaSodium hydroxide NaOH Found in drain and oven cleaners
14Acid and base definitions An acid is the species that donates a proton to another species in a proton-transfer reaction.A base is the species that accepts a proton in a proton-transfer reaction.NH3 (aq) + H2O (l) NH4+ + OH- (aq)
15Reaction of nitric acid with water HNO3(aq) + H2O(l) NO3-(aq) H3O+(aq)Note: the reaction simply involves the
16Strong and Weak Acids and Bases A strong acid is an acid that ionizes completely in water, and is a strong electrolyte.HCl (aq) + H2O (l) H3O+ (aq) + Cl- (aq)A weak acid is an acid that only partially ionizes in water, and is a weak electrolyte.HCN (aq) + H2O (l) H3O+ (aq) + CN- (aq)
17NaOH (s) Na+ (aq) + OH- (aq) A strong base is a base that is present in aqueous solution entirely as ions (one of which is OH-) and is a strong electrolyte.NaOH (s) Na+ (aq) + OH- (aq)H2OA weak base is a base that is only partially ionized in water.NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq)
18Neutralization Reactions One of the main properties of acid and bases is that they neutralize one another.A neutralization reaction is a reaction of an acid and a base that results in an ionic compound and possibly water.The ionic compound that is a product of a neutralization reaction is called a salt.Acid + Base Salt + Water2HCl (aq) + Ca(OH)2 (aq) CaCl2 (aq) + 2H2O (l)
192HCl (aq) + Ca(OH)2 (aq) CaCl2 (aq) + 2H2O (l) To discuss the essential reactions occurring we have to write the reactions as ionic equations.Writing the strong electrolytes in the form of ions gives the following complete ionic equation:H+(aq) + 2Cl-(aq) + Ca2+(aq) + 2OH-(aq) Ca2+(aq) + 2Cl-(aq) + 2H2O(l)Canceling spectator ions and dividing by 2 gives the net ionic equation:H+(aq) + OH-(aq) H2O(l)
20Example Writing an equation for a neutralization rxn Write the molecular equation and the net ionic equation for the neutralization of sulfurous acid by potassium hydroxide.sulfurous acid =potassium hydroxide =Molecular equation:Ionic equation:Net ionic equation:
21Monoprotic acids acids that have only one acidic hydrogen atom per acid molecule eg. HCl and HNO3 Polyprotic acid an acid that yields two or more acidic hydrogens per molecule.Phosphoric acid is an example of a triprotic acid. By reacting it with different amounts of base, a series of salts can be obtained.H3PO4(aq) + NaOH(aq) NaH2PO4(aq) + H2O(l)H3PO4(aq) + 2NaOH(aq) Na2HPO4(aq) + 2H2O(l)H3PO4(aq) + 3NaOH(aq) Na3PO4(aq) + 3H2O(l)
22Acid-Base reactions with Gas Formation Certain salts, notably carbonates, sulfites and sulfides, react with acids to form a gaseous product.Na2CO3(aq) +2HCl(aq) NaCl(aq) + H2O(l) + CO2(g)If we consider this reaction as an exchange, or metathesis reaction, then we obtain the following:Na2CO3(aq) +2HCl(aq) NaCl(aq) + H2CO3(aq)The last product in the above equation is carbonic acid, which is unstable and decomposes to water and carbon dioxide
23Example Writing an equation for a reaction with gas formation. Write the molecular equation and the net ionic equation for the reaction of copper(II)carbonate with hydrochloric acid.Molecular equation:Ionic equation:Net ionic equation:
24Working with Solutions Most chemistry you have encountered to date takes place in solution!In general, reactions involving solids proceed very slowly, if at all.When carrying out reactions in solutions it is very convenient to measure out the reactant by volume.
25Molar ConcentrationConcentration = the quantity or amount of solute in a standard quantity of solution.Eg. Units: mol/L or g/mlWe also use the relative terms : dilute and concentratedA solution is dilute, when the solute concentration is lowA solution is concentrated when the solute concentration is high.
26Molar concentration, or Molarity, M the moles of solute dissolved in one liter of solution.Molarity =moles of soluteliters of solutionUnits: mol.L-1 or M
27Example Calculating molarity from mass and volume. A student prepared a solution by dissolving g of potassium nitrate (KNO3) in enough water to prepare mL of solution. What is the molarity (concentration) of the solution?
28Example Or the other way around!! Calculate the mass of potassium permanganate needed to prepare 250 mL of M KMnO4 (aq) solution.
29DilutionIt is often necessary to reduce the concentration of a solution - that is to dilute it.This can be accomplished by taking a certain volume of the more concentrated solution and then diluting it with additional solvent.NB - during dilution the number of moles of solute remains constant.
30The Dilution Equation For initial solution : C1 x V1 = n1 For final solution :C2 x V2 = n2However n1 = n2therefore : C1 x V1 = C2 x V2or :C1V1 = C2V2
31Example Diluting a solution. Calculate the volume of M HCl that we should use to prepare 100 mL of a 5.23x10-4 M HCl solution.
32Quantitative Analysis The determination of the amount of a substance or species present in a material.
33Volumetric Analysis A B A+B A titration is a procedure for determining the amount of substance A by adding a carefully measured volume of a solution with a known concentration of B until the reaction of A and B is just complete.ABA+B
34Example Calculating the Quantity of a Substance in a Titrated Solution A dilute solution of hydrogen peroxide is sold in pharmacies as a mild antiseptic. A typical solution was analyzed for the percentage of hydrogen peroxide by titrating it with potassium permanganate.5H2O2 + 2KMnO4 + 6H+8H2O + 5O2 + 2K+ + Mn2+What is the mass percentage of H2O2 in a solution if 57.5 g of peroxide solution required 38.9 mL of M KMnO4?Answer : 3.08%