Acids and bases, salts and solutions.ppt

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1、Acids and bases, salts and solutions,Chapter 10-1 10-9, 11-1 11-4,Key concepts,Compare and contrast the Arrhenius and Brnsted-Lowry theories of acids and bases Describe hydrated protons Properties of acid and base solutions Arrange acids according to acid strength Balance acid-base equations Amphote

2、rism Lewis acid-base theory Molarity calculations in titrations Equivalents,Various properties of acids and bases,Arrhenius theory of acids/bases,Developed in 1884. An acid is a substance containing hydrogen that produces _ in aqueous solution. A base is a substance containing the OH group that prod

3、uces _ in aqueous solution.,Protons are not alone.,Protons combine with water molecules to form _ _.We commonly represent this as the hydronium ion, H3O+(aq), but writing H+(aq) means the same thing.,Brnsted-Lowry theory (1923),An acid is a _ _. A base is a _ _.Bases are no longer restricted to comp

4、ounds that release OH- in solution. For instance, NH3 is a base. What does it look like after reacting with a proton?,Ionization of weak acids/bases,While strong acids dissociate completely, not all reactions are complete and irreversible (in fact, most are not). Rxns with weak acids/bases are rever

5、sible. Example: HF + H2O What is the acid? What is the base? (depends on which side of rxn you look at),Conjugate acid-base pairs,Conjugate acid-base pairs differ in structure by _ _.Some examples of conjugate pairs:,Acid/base strength,The strength of an acid is _ proportional to the strength of its

6、 base.Strong acids have _.Weaker acids have _. As the acid gets weaker and weaker, what happens to the conjugate base? What does this tell you about the amount of ionization taking place?,Amphoterism,Some substances can both give and accept protons. This process is called amphoterism. Water is the p

7、rime example of amphiprotic behavior.2H2O H3O+ + OH-,Acid strength,The hydrohalic acids: HF, HCl, HBr, HI What are the sizes of the halogens? How will this affect the H-X bond?HF bond is very strong vs. the other halogens. F- causes ordering of the H2O molecules (how does that happen?),Leveling solv

8、ents,In aqueous solution, no acid is stronger than H3O+(aq). All other acids completely dissolve in water to form H3O+. Because of this, all strong acids are of equal strength in water.A similar effect is observed for strong bases, which completely dissolve to form OH-.,Ternary acids and bases,What

9、is a ternary acid?Ternary acids are hydroxyl compounds of a _.Ionize to produce H+.,Compare to other hydroxyl compoundsMetal hydroxidesionize to produce _ and are _ in aqueous solution.,Ternary acid strength,H2SO4 vs H2SO3. Whats the difference in acid strength? Compare oxidation number of sulfur in

10、 each.Acid strength increases with _ oxidation number of the central atom.Order the following acids from weakest to strongest:HBrO3, HBrO, HBrO4, HBrO2,important!,When comparing ternary acid strength, make sure the compounds have similar structure. Where are the hydrogens located? (H3PO3 vs H3PO4),N

11、eutralization of Brnsted-Lowry acids/bases,HA + MB HB + MAIn many cases, HB ends up being _. Classic example: strong acid + strong base.What happens in the reaction of hydrochloric acid and sodium hydroxide? What is the net ionic equation?,Weak acid + strong base,General reaction:HxA (aq) + x OH- (a

12、q) A- (aq) + x H2O (l)When does x vary?Examples:,Acid salts,Acid salts are salts of _ acids that still contain _ _.,Lewis theory,The most general of all acid-base theories Discards the proton acceptor/donator all together.A Lewis acid _ a share in an electron pair.A Lewis base _ a share in an electr

13、on pair.Lewis acids and bases are neutralized when a _ _ forms.,Bronsted-Lowry,When is Lewis theory used?,Arrhenius,LEWIS THEORY,Arrhenius or B-L theory a better description for most aqueous solns,Lewis theory a good descriptor for nonaqueous solvents or transition metals,Acid-Base calculations,Mola

14、rity calculations play an important part in acid-base reaction stoichiometry Much of what we will learned in Chapter 3 will be used here.,Molarity,M = mol/L or M = mmol/mLwe can use moles and liters, or millimoles and milliliters, and the molarity is still the same.,Similarities between acid-base an

15、d other reaction calculations,We still compare moles to moles, not volumes to volumes or molarities to molarities. Additionally, knowing the limiting reactant is very important (i.e, what will run out firstacid or base?),Some examples,what volume of 0.800 M NH3 is required to neutralize 22.0 mL of 1

16、2.0 M HCl? 25.0 mL of 0.0500 M Ca(OH)2 added to 10.0 mL of HNO3. Is the solution now acidic or basic? how many moles excess acid or base are in the solution? how much additional Ca(OH)2 or HNO3 soln required to neutralize solution?,TITRATIONS,Combining a known concentration with an unknown concentra

17、tion solution. Titrant: The solution of one reactant (usually of unknown concentration) that is carefully added to the solution of the other reactant until the resulting solution is just neutralized (no excess acid or base). How do we know when to stop?,Titrations (cont),indicators: How to measure t

18、he volume of titrant? Buret: equivalence point: The point where _ _ amounts of acid and base have reacted. end point: The point where the indicator _ _. For accurate work, one wants the end point and equivalence point to coincide with each other.,Primary and secondary standards,Reading on standardiz

19、ation: your text goes over the requirements of a primary standard. You should be familiar with these requirements. Primary standards are used to determine the concentration of solutions, which become secondary standards. Example: KHP and NaOH.,EQUIVALENT WEIGHTS AND NORMALITY,One mole of acid is _ B

20、ut, one equivalent of acid contains _. The equivalent weight, then, corresponds to molar mass/(# of equ./mol),normality,number of equivalents per liter, or N = eq/L = meq/mL N = M eq/mol Lets do a couple of examples,EQUIVALENTS in acid/base reactions,1 eq acid always reacts with 1 eq base.Va Na = Vb Nb,