CHM1046 Final Exam Study Guide Chapter 15 Acids and Bases React with certain metals to produce hydrogen gas React with carbonates and bicarbonates to produce carbon dioxide gas Acids Bases Feel slippery Many soaps contain bases Bronsted Acids Bases Bronsted acid is a proton donor Bronsted base is a proton acceptor Conjugate Acid Base Pair An acid and its conjugate base or a base and its conjugate acid o Conjugate base of a Bronsted acid the species that remains when one proton has been removed from the acid o Conjugate acid of a Bronsted base results from the addition of a proton to a Bronsted base acid Every Bronsted acid has a conjugate base every Bronsted base has a conjugate The atom in the Bronsted base that accepts a H ion must have a lone pair A conjugate base always has one fewer H atom and one more negative charge or one fewer positive charge than the formula of the corresponding acid The proton in aqueous solution can be represented as either H or H3O o H better for calculations involving hydrogen ion concentrations equilibrium constants o H3O better for discussions of Bronsted acid base properties Practice Problem 15 1 1 CHM1046 Final Exam Study Guide o Identify the conjugate acid base pairs in the reaction between ammonia and hydrofluoric acid in aqueous solution NH3 aq HF aq NH4 aq F aq NH3 base NH4 F base HF acid acid Acid Base Properties of Water Water a unique solvent Can act as an acid or a base o Functions as a base in reactions with acids like HCl CH3COOH o Functions as an acid in reactions with bases like NH3 Water is a very weak electrolyte but does ionize to a small extent The reaction is sometimes called the autoionization of water o H2O l H aq OH aq o H2O H2O H3O OH H2O acid OH base H3O acid H2O base The Ion Product of Water H indicates the acidity or basicity of the solution Ion Product Constant Kw The product of the molar concentrations of H and OH ions at a particular temperature 1 0 x 10 14 o In pure water at 25 C concentration of H OH ions are equal o Kw H OH o Kw 1 0 x 10 7 1 0 x 10 7 1 0 x 10 14 Concentrations of H or OH can be changed in practice but they cannot be varied independently Concentrations Solution is H OH H OH H OH Neutral Acidic Basic 2 Practice Problem 15 2 CHM1046 Final Exam Study Guide o The concentration of OH ions in a certain household ammonia cleaning solution is 0 0025 M Calculate the concentration of H ions pH A Measure of Acidity H 4 x 10 12 pH The negative logarithm of the hydrogen ion concentration in mol L pH has no units The pH of concentrated acid solutions can be negative As pH increases H concentration decreases As pH decreases H concentration increases o More basic o More acidic Solution is Neutral Acidic Basic H OH H OH H OH At 25 C H 1 0 x 10 7 H 1 0 x 10 7 H 1 0 x 10 7 pH 7 pH 7 pH 7 H 10 pH OH 10 pOH Practice Problem 15 3 o The concentration of H ions in a bottle of table wine was 3 2 x 10 4 M right after the cork was removed Only half of the wine was consumed The other half after it had been standing open to the air for a month was found to have a hydrogen ion concentration equal to 1 0 x 10 3 M Calculate the pH of the wine on these two occasions pH 3 49 pH 3 00 3 CHM1046 Final Exam Study Guide Practice Problem 15 4 o The pH of rainwater collected in a certain region of the northeastern United States on a particular day was 4 82 Calculate the H ion concentration of the rainwater H 1 51 x 10 5 M Practice Problem 15 5 Strength of Acids and Bases pH 10 46 Strong Electrolytes 100 dissociation o In a NaOH solution OH is 2 9 x 10 4 M Calculate the pH of the solution Weak Electrolytes Not completely dissociated Strong Acids Strong electrolytes that are assumed to ionize completely in water o At equilibrium solutions of strong acids will not contain any non ionized acid molecules Strong Acids 6 Formula HClO4 HClO3 HI HBr HCl H2SO4 HNO3 Name Perchloric acid Chloric acid Hydroiodic acid Hydrobromic acid Hydrochloric acid Sulfuric acid Nitric acid Weak Acids Weak electrolytes that ionize only to a limited extent in water o Most acids are weak acids o At equilibrium aqueous solutions of weak acids contain a mixture of non ionized acid molecules H3O ions and the conjugate base o Examples of weak acids Hydrofluoric acid HF 4 CHM1046 Final Exam Study Guide Acetic acid CH3COOH Ammonium ion NH4 Strong Bases Strong electrolytes that ionize completely in water o Hydroxides of alkali metals certain alkaline earth metals strong bases o All alkali metal hydroxides are soluble o Ca OH 2 Sr OH 2 are slightly soluble o Ba OH 2 is soluble o The OH ion of these metal hydroxides is the actual Bronsted base can accept a proton Strong Bases 8 Formula NaOH KOH LiOH RbOH CsOH Ca OH 2 Ba OH 2 Sr OH 2 Name Sodium hydroxide Potassium hydroxide Lithium hydroxide Rubidium hydroxide Cesium hydroxide Calcium hydroxide Barium hydroxide Strontium hydroxide Weak Bases Weak electrolytes that ionize to a very limited extent in water o Conjugate Acid Base Pairs 5 CHM1046 Final Exam Study Guide The conjugate base of a strong acid has no measurable strength o Ex In HCl the Cl ion conjugate base of strong acid HCl is an extremely H3O is the strongest acid that can exist in aqueous solution o Acids stronger than H3O react with water to produce H3O their weak base conjugate bases HCl aq H2O l H3O aq Cl aq o Acids weaker than H3O react with water to a smaller extent to produce H3O and their conjugate bases HF aq H2O l H3O aq F aq OH ion is the strongest base that can exist in aqueous solution o Bases stronger than OH react with water to produce OH and their conjugate acids O2 aq H2O l 2OH aq The OH ion is the strongest base that can exist in aqueous solution 6 CHM1046 Final Exam Study Guide Practice Problem 15 6 o Calculate the pH of a A 1 0 x 10 3 M HCl solution B 0 020 M Ba OH 2 solution pH 3 pH 12 6 Practice Problem 15 7 o Predict the direction of the following reaction in aqueous solution HNO2 aq CN aq HCN aq NO2 aq From left to right HNO2 is a stronger acid than HCN is a better proton donor CN is a better proton acceptor than NO2 Weak Acids HA and Acid Ionization Constants Acid Ionization Constant Ka The equilibrium constant for the ionization of an acid o The larger the …
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