Chapter 1 Structure and Bonding - faculty.swosu.edu

I. Acid-Base Properties of Salts A) Neutral Salts 1) Salt = ionic compound = one that completely ionizes in water 2) Cations of strong bases have no effect on pH 1) Na+, K+, etc 2) These cations have no affinity for OH- in water 3) Anions of strong acids have no effect on pH 1) Cl-, NO3-, etc 2) These anions have no affinity for H+ in water 4) Solutions of these combined ion salts have pH = 7.00 B. Basic Salts 1) Salts containing the conjugate base of a weak acid produce basic solutions 2) The conjugate base must be strong if the acid is weak, so it must have a strong affinity for H+, which will affect the pH of a solution 3) Sodium Acetate Example NaC2H3O2 Na+ + C2H3O2 C2H3O2- + H2O HC2H3O2 + OH- [HC 2 H 3O 2 ][OH ] Kb ??? [C 2 H 3O 2 ] 4) For any weak acid and its conjugate base, Ka x Kb = KW Kb = KW / Ka = 1 x 10-14 / 1.8 x 10-5 = 5.6 x 10-10 for acetate C. Acidic Salts 1) Salts having the conjugate acid of a weak base produce acidic solutions 2) Ammonium chloride = NH4Cl NH4+ + ClNH4+

NH3 + H+ 3) Since ammonia is a weak base, ammonium is strong acid and will effect pH 4) Highly charged metal ions can also be acidic a) AlCl3 + 6 H2O Al(H2O)63+ + 3 Clb) Al(H2O)63+ + H2O Al(H2O)5(OH)2+ + H3O+ c) The higher the metals charge the more acidic Example: AlCl3 Ka = 1.4 x 10-5 II. Salt Solution Procedure A. Add ~0.5 g of eight different salts to 25 ml water and test with pH paper 1) Use pH = 7 water and graduated cylinder 2) Dont have to be very careful with amount; just seeing if acidic/basic/neutral 3) Hydrolysis Reaction = reaction with water (neutral salt: no hydrolysis) NaF: F- + H2O -------> HF + OH- (pH is basic) B. Carefully add 0.500 g of NH4Cl and NaC2H3O2 to 25 ml water; test with pH meter 1) 2) 3)

Use pH = 7 water and Volumetric Flask Need to know mass to 3 decimal places and pH to 2 decimal places Use ICE tables to calculate theoretical pH of your solutions III. Buffers A. A Buffer is a solution containing a weak acid and the salt of its conjugate base (or a weak base and the salt of its conjugate acid) which resist changes to its pH. 1) Example: Blood stays at pH = 7.4, even when various reactions in the body produce much H+ and OH2) The buffer system in blood is H2CO3/HCO33) Buffer Capacity = amount of H+/OH- a buffer can absorb with only a small pH change B. How a Buffer Works 1) Buffers have a large concentration of both HA and A2) When OH- is added, it reacts with HA and is replaced in solution by A 3) When we add H+, it is used up by reaction with A- and replaced in solution by HA 4) HA H + + A- [H ][A- ] [HA] Ka [H ] K a [HA] [A - ] pH depends on [H ], which depends on C. The Henderson-Hasselbalch Equation for Buffers: [HA]

[A - ] [A ] pH pK a log [HA] a) We can use this simple equation instead of doing the longer equilibrium problem approach for most buffer problems b) Any concentration of buffer with the same [A-]/[HA] ratio will have the same pH c) The Henderson-Hasselbalch Equation assumes that [A-] and [HA] are the same as [A-]0 and [HA]0. If we keep the buffer concentration high, this is a valid approximation. IV. Procedure and Calculations for Buffers A. Make 50ml of a buffer with pH = 5.00 from 1.00 M Acetic Acid and 5.00 g of Sodium Acetate 1) Example calculation for pH = 5.20 2) Ka = 1.8 x 10-5 so pKa = 4.74 [A ] [A ] 5.20 4.74 log pH pK a log [HA] [HA] [A ] [A ]

0.46 10 2.88 0.46 log [HA] [HA] 1mol 0.061mol 0.061mol NaC2 H 3O 2 (5.00g) 1.22M 0.050L 82.034g [A ] 1.22M 2.88 [HA] 0.424M [HA] [HA] M V (0.424M)(50ml) V1 2 2 21.2ml M1 1.00M 3) To make buffer: Add 5.00g Sodium Acetate and 21.2ml 1.00M Acetic Acid to a 50ml Volumetric Flask and dilute with water to the mark. B. Test the pH of your buffer with the pH meter, and calculate %Error %Error C. D.

Initial After H+ Experimental - Assigned x 100% Assigned Add 10ml of your buffer to a 100ml Volumetric and dilute to the line. Find pH 1) Original buffer: [HA] = 0.424M [A-] = 1.22M 2) Diluted buffer: [HA] = 0.0424M [A-] = 0.122M What is the pH when we add 5.00ml of 0.10M HCl to our diluted buffer? 1) 100ml + 5ml = 105ml = new volume (0.122mol/L)(0.100L) = 0.0122mol A(0.0424mol/L)(0.100L) = 0.00424 mol HA 2) HCl will completely dissociate to H+ (0.10mol/L)(0.005L) = 0.0005mol H+ 3) C2H3O2+ H+ HC2H3O2 0.0122mol 0.0117mol 0.0005mol 0 0.00424mol 0.00474mol [A ] 0.0117mol/0.105L 4.74 log pH pK a log 5.13 0.00474mol/0.105L [HA] E.

What is the pH when we add 5.00ml of 0.10M NaOH to our diluted buffer? 1) 100ml + 5ml = 105ml = new volume (0.122mol/L)(0.100L) = 0.0122mol A(0.0424mol/L)(0.100L) = 0.00424 mol HA 2) NaOH will completely dissociate to OH- (0.10mol/L)(0.005L) = 0.0005mol OH3) HC2H3O2 + OHC2H3O2- Initial After OH- 0.00424mol 0.00374mol 0.0005mol 0 0.0122mol 0.0127mol [A ] 0.0127mol/0.105L pH pK a log 4.74 log 5.27 0.00374mol/0.105L [HA]

Recently Viewed Presentations

• SLAiP standards and PEFs felt to have improved mentoring and mentor training but there are still issues. ... (2015) and expected New NMC Standards. Need for a practitioner that is fit for practice - to ensure that Practice is high...
• Episodes 400 The episode in Which Twilight Sparkle is Crowned as a princess Q: What is "Magical Mystery Cure"? DAILY DOUBLE! Episodes 400 Q:Who is Zecora? In "Bridle Gossip" Apple Blossom is the only one who isn't scared of this...
• Eos Energy StorageCREA Energy Innovations Summit | Denver, COPhilippe Bouchard, VP of Business Development . Eos' mission is to develop energy storage solutions that are less expensive than incumbent solutions used to provide the same service todayâ€”namely gas turbines for...
• Just-In-Time is a Japanese manufacturing management method that was developed in the 1970's. It was first adopted by Toyota manufacturing plants by Taiichi Ohno. The main concern at that time was to meet consumer demands along with providing good quality....
• Part 2 * Ye say, "Wherefore?" (Why is God displeased with us?) Malachi 2:10-16 The Lord's Answer: Ye divorced your wives and "married the daughter of a foreign god."
• using RobotC. Key tasks. Find the edge of the table. Follow the edge of the table. Find a putting green. Find the golf ball. Aim for the hole. ... This empty loop with allow the robot to spin until an...
• Product life cycle. Introduction. Growth. Maturity. Decline. ProductExtension. Sales. Time. Embracing the product life cycle where you realize that you need to have new products to replace old (or certainly need to reinvigorate old to make them new) is a...
• Flexible Learning: the role of Libraries Leonie Pope and Susannah Ball 2003 Learnscope project Purpose Participants Box Hill - library staff, interns, support & teaching staff Chisholm - library staff Swinburne - library staff Process Session 1 Explored possibilities Session...