Classification of Matter Solutions are homogeneous mixtures
Solute A solute is the dissolved substance in a solution. Salt in salt water Sugar in soda drinks Carbon dioxide in soda drinks Solvent A solvent is the dissolving medium in a solution. Water in salt water Water in soda
Saturation of Solutions • A solution that contains the maximum amount of solute that may be dissolved under existing conditions is saturated. • A solution that contains less solute than a saturated solution under existing conditions is unsaturated. • A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated.
Electrolytes vs. Nonelectrolytes The ammeter measures the flow of electrons (current) through the circuit. • If the ammeter measures a current, and the bulb • glows, then the solution conducts. • If the ammeter fails to measure a current, and the • bulb does not glow, the solution is non-conducting.
Definition of Electrolytes and Nonelectrolytes An electrolyte is: • A substance whose aqueous solution conducts • an electric current. A nonelectrolyte is: • A substance whose aqueous solution does not • conduct an electric current. Try to classify the following substances as electrolytes or nonelectrolytes…
Electrolytes? • Pure water • Tap water • Sugar solution • Sodium chloride solution • Hydrochloric acid solution • Lactic acid solution • Ethyl alcohol solution • Pure, solid sodium chloride
Answers… ELECTROLYTES: NONELECTROLYTES: • Tap water (weak) • NaCl solution • HCl solution • Lactate solution (weak) • Pure water • Sugar solution • Ethanol solution • Pure, solid NaCl But why do some compounds conduct electricity in solution while others do not…?
Ionic CompoundsDissociate NaCl(s) Na+(aq) + Cl-(aq) AgNO3(s) Ag+(aq) + NO3-(aq) MgCl2(s) Mg2+(aq) + 2 Cl-(aq) Na2SO4(s) 2 Na+(aq) + SO42-(aq) AlCl3(s) Al3+(aq) + 3 Cl-(aq)
Some covalent compounds IONIZE in solution Covalent acids form ions in solution, with the help of the water molecules. For instance, hydrogen chloride molecules, which are polar, give up their hydrogens to water, forming chloride ions (Cl-) and hydronium ions (H3O+).
Strong acids such as HCl are completelyionized in solution. Other examples of strong acids include: • Sulfuric acid, H2SO4 • Nitric acid, HNO3 • Hydriodic acid, HI • Perchloric acid, HClO4 • Hydrobromic acid, HBr
Weak acids such as lactic acid usually ionize less than 5% of the time. Many of these weaker acids are “organic” acids that contain a “carboxyl” group. The carboxyl group does not easily give up its hydrogen.
Because of the carboxyl group, organic acids aresometimes called “carboxylic acids”. Other organic acids and their sources include: • Citric acid – citrus fruit • Malic acid – apples • Butyric acid – rancid butter • Amino acids – protein • Nucleic acids – DNA and RNA • Ascorbic acid – Vitamin C This is an enormous group of compounds; these are only a few examples.
However, most covalent compounds do not ionizeat all in solution. Sugar (sucrose – C12H22O11), and ethanol (ethyl alcohol – C2H5OH) do not ionize - That is why they are nonelectrolytes!
Molarity The concentration of a solution measured inmoles of solute per liter of solution. mol= M L
Strong Acid and Strong Base • Word Equation Hydrochloric acid reacts with sodium hydroxide • Molecular Equation HCl (aq) + NaOH (aq) H2O(l) + NaCl (aq) • Complete Ionic Equation H+ (aq) + Cl-(aq) +Na+ (aq)+ OH- (aq) H2O(l) + Na+ (aq)+Cl-(aq) • Net Ionic Equation H+ (aq) + OH- (aq) H2O(l)
Weak Acid and Strong Base • Word Equation Acetic acid reacts with sodium hydroxide • Molecular Equation HC2H3O2(aq) + NaOH (aq) H2O(l) + NaC2H3O2(aq) • Complete Ionic Equation—(weak acids stay together). HC2H3O2(aq)+Na+ (aq)+ OH- (aq) H2O(l) + Na+ (aq)+C2H3O2-(aq) • Net Ionic Equation HC2H3O2(aq)+ OH- (aq) H2O(l) + C2H3O2-(aq)
Preparation of Molar Solutions Problem: How many grams of sodium chloride are needed to prepare 1.50 liters of 0.500 M NaCl solution? • Step #1: Ask “How Much?” (What volume to prepare?) • Step #2: Ask “How Strong?” (What molarity?) • Step #3: Ask “What does it weigh?” (Molar mass is?) 1.500 L 0.500 mol 58.44 g = 43.8 g 1 L 1 mol
Serial Dilution It is not practical to keep solutions of many different concentrations on hand, so chemists prepare more dilute solutions from a more concentrated “stock” solution. Problem: What volume of stock (11.6 M) hydrochloric acid is needed to prepare 250. mL of 3.0 M HCl solution? MstockVstock = MdiluteVdilute (11.6 M)(xLiters) = (3.0 M)(0.250 Liters) xLiters= (3.0 M)(0.250 Liters) 11.6 M =0.065 L
Single Replacement Reactions A + BX AX + B BX + Y BY + X Replacement of: • Metals by another metal • Hydrogen in water by a metal • Hydrogen in an acid by a metal • Halogens by more active halogens
The Activity Series of the Metals • Lithium • Potassium • Calcium • Sodium • Magnesium • Aluminum • Zinc • Chromium • Iron • Nickel • Lead • Hydrogen • Bismuth • Copper • Mercury • Silver • Platinum • Gold Metals can replace other metals provided that they are above the metal that they are trying to replace. Metals above hydrogen can replace hydrogen in acids. Metals from sodium upward can replace hydrogen in water
The Activity Series of the Halogens • Fluorine • Chlorine • Bromine • Iodine Halogens can replace other halogens in compounds, provided that they are above the halogen that they are trying to replace. 2NaCl(s) + F2(g) 2NaF(s) + Cl2(g) ??? MgCl2(s) + Br2(g) No Reaction ???
Oxidation and Reduction (Redox) • Electrons are transferred • Spontaneous redox rxns can transfer energy • Electrons (electricity) • Heat • Non-spontaneous redox rxns can be made to happen with electricity
Oxidation and Reduction An old memory device for oxidation and reduction goes like this… LEO says GER LoseElectrons = Oxidation GainElectrons = Reduction
Oxidation Reduction Reactions(Redox) Each sodium atom loses one electron: Each chlorine atom gains one electron:
LEO says GER : Lose Electrons = Oxidation Sodium is oxidized Gain Electrons = Reduction Chlorine is reduced
Rules for Assigning Oxidation NumbersRules 1 & 2 • The oxidation number of any uncombined element is zero 2. The oxidation number of a monatomic ion equals its charge
Rules for Assigning Oxidation NumbersRules 3 & 4 3.The oxidation number of oxygen in compounds is -2 4. The oxidation number of hydrogen in compounds is +1
Rules for Assigning Oxidation Number Rule 5 5. The sum of the oxidation numbers in the formula of a compound is 0 2(+1) + (-2) = 0 H O (+2) + 2(-2) + 2(+1) = 0 Ca O H
Rules for Assigning Oxidation NumbersRule 6 6. The sum of the oxidation numbers in the formula of a polyatomic ion is equal to its charge X + 4(-2) = -2 S O X + 3(-2) = -1 N O X = +5 X = +6
Reducing Agents and Oxidizing Agents • The substance reduced is the oxidizingagent • The substance oxidized is the reducingagent Sodium is oxidized – it is the reducing agent Chlorine is reduced – it is the oxidizing agent
Trends in Oxidation and Reduction • Active metals: • Lose electrons easily • Are easily oxidized • Are strong reducing agents • Active nonmetals: • Gain electrons easily • Are easily reduced • Are strong oxidizing agents
Not All Reactions are Redox Reactions Reactions in which there has been no change in oxidation number are not redox rxns. Examples: