Warm up. What is the main difference between a strong acid and a weak acid?

Transcription

1 Warm up What is the main difference between a strong acid and a weak acid?

2 Warm up How are acids and bases similar? Different? Have out serial dilu;on follow up for a stamp

3 Reac;ons of acids (#5) Unbalanced: Al (s) + H 2 SO 4 (aq) à Al 2 (SO 4 ) 3 (aq) + H 2 (g) Unbalanced: CaCO 3 (s) + 2HBr (aq) à CaBr 2 (aq) + H 2 O (l) + CO 2 (g)

4 K w, ph and poh Essential Questions What are ph and poh?! How are ph and poh related to the ion product constant for water?! How are the ph and poh of aqueous solutions calculated?!

5 Vocabulary Review Equilibrium! ßà! New ion product constant for water! ph! poh!

6 Properties of Acids and Bases The usual solvent for acids and bases is water water produces equal numbers of hydrogen and hydroxide ions in a process called selfionization.! H 2 O(l) + H 2 O(l) H 3 O + (aq) + OH (aq)! The hydronium ion is H 3 O +.! Introduction to Acids and Bases!

7 !! Ion Product Constant for Water Pure water contains equal concentrations of H + and OH ions.! The ion product constant of water is:! K w = [H + ][OH ].! The ion product constant for water is the value of the equilibrium constant expression for the self-ionization of water.!

8 The Brønsted-Lowry Model Hydrogen fluoride a Brønsted-Lowry acid! HF(aq) + H 2 O(l) H 3 O + (aq) + F (aq)! HF = acid, H 2 O = base, H 3 O + = conjugate acid, F = conjugate base! Introduction to Acids and Bases!

9 !! Ion Product Constant for Water [X] represents the concentration of X in moles/l solution! With pure water at 298 K, both [H + ] and [OH ] are equal to M.! K w at 298 K = ! [H + ] [OH ] must equal at 298 K,! as [H + ] goes up, [OH ] must go down.!

10 CALCULATE [H + ] AND [OH ] USING K W Problem! At 298 K, the H + ion concentration in a cup of coffee is M. What is the OH ion concentration in the coffee? Is the coffee acidic, basic, or neutral? KNOWN UNKNOWN [H + ] = M [OH ] =? mol/l K w = A, B or N?

11 ! ph and poh Concentrations of H + ions are often small numbers expressed in scientific notation.! ph is the negative logarithm of the hydrogen ion concentration of a solution.!! ph = log [H + ]! Remember H + and H 3 O + are the same and are used interchangeably!

12 Logarithmic scale

13 ! ph and poh poh of a solution is the negative logarithm of the hydroxide ion concentration.! poh = log [OH ]! The sum of ph and poh equals 14.!

14 CALCULATE ph FROM [H+] Use with Example Problem 2.! Problem! What is the ph of a solution with a hydrogen ion concentration of 1.3 x 10-5 at 298 K?!

15 ph and poh For all strong monoprotic acids, the concentration of the acid is the concentration of H + ions.! For all strong bases, the concentration of the OH ions available is the concentration of the base.! Weak acids and weak bases only partially ionize and K a and K b values must be used.! Litmus paper and a ph meter with electrodes can determine the ph of a solution.!

16 CALCULATE poh AND ph FROM [OH ] Use with Example Problem 3.! Problem! A cow is being fed straw and hay that has been treated with ammonia. The addition of ammonia to animal feed promotes protein growth in the animal. Another use of ammonia is as a household cleaner, which is an aqueous solution of ammonia gas. A typical cleaner has a hydroxide-ion concentration of M. Calculate the poh and ph of a cleaner at 298 K.!! KNOWN UNKNOWN [OH ] = M poh =?! ph =?!

17 CALCULATE [H + ] AND [OH ] FROM ph Use with Example Problem 4.! Problem! What are [H + ] and [OH ] in a healthy person s blood that has a ph of 7.40? Assume that the temperature of the blood is 298 K.! KNOWN ph = 7.40! UNKNOWN [H + ] =? mol/l! [OH ] =? mol/l!

18 ! CALCULATE K a FROM ph Use with Example Problem 5.! Problem! Formic acid is used to process latex tapped from rubber trees into natural rubber. The ph of a 0.100M solution of formic acid (HCOOH) is What is K a for HCOOH?! KNOWN ph = 2.38! concentration of the solution = 0.100M! UNKNOWN K a =?!

19 Review Essential Questions What are ph and poh?! How are ph and poh related to the ion product constant for water?! How are the ph and poh of aqueous solutions calculated?! Vocabulary!! ion product constant for water! ph! poh!