Week 4. Shane s Updates

Transcription

1 Week 4 Shane s Updates

2 Announcements Lecture/Discussion information: Don t forget to be reading the handouts on the website Next week we will have two discussions (bring laptop)! Quiz Sometime after next Friday (4/25) Up through last lecture (Week 3) and this week s laboratory and assignments Course website

3 Week 4 Objectives By the end of the week, you will be able to: Be able to construct and explain alpha fractions using distribution diagrams / Bjerrum plots, as a function of p values Use indicators to determine the various points in a titration curve Quantify the issues that can arise when performing titrations, due to dilution and/or dissociation

4 Reading for this week during lab (MTB 6- in ph 12 solution): MTB

5 Barium MTB Complexation Equilibrium where K f is the Ba MTB formation constant, and C Ba tot is the total barium concentration

6 Alpha fractions for free and complexed Ba 2+

7 How does one experimentally determine this?

8 How does one experimentally determine this?

9 Distribution Diagram / Bjerrum Plot This shape is called sigmoidal p[mtb free ]

10 Buffers

11 -log[h + free]

12

13 -log[h + free]

14 -log[h + free] It is time for Excel!

15 Flashback to a real experiment at the end point equivalence point ph volume of titrant added

16 Flashback to a real experiment at the end point equivalence point ph 14 poh 14 + log[oh - free] volume of titrant added Volume of NaOH added

17 Flashback to a real experiment at the end point equivalence point ph 14 poh 14 + log[oh - free] volume of titrant added Volume of NaOH added hopefully this is small

18 Adding a strong base to a strong acid Start with 100 ml of 0.1 M HCl mmoles free Gran Plot Volume of NaOH added

19 Adding a strong base to a strong acid Start with 100 ml of 0.1 M HCl mmoles free 200 ml Gran Plot Volume of NaOH added

20 Adding a strong base to a strong acid Start with 100 ml of 0.1 M HCl 300 ml mmoles free 200 ml Gran Plot Volume of NaOH added

21 Adding a strong base to a strong acid Start with 100 ml of 0.1 M HCl 300 ml mmoles free 200 ml Gran Plot [H + free] Volume of NaOH added

22 Adding a strong base to a strong acid Start with 100 ml of 0.1 M HCl 300 ml mmoles free 200 ml Gran Plot -log[h + free] Volume of NaOH added

23 Adding a strong base to a strong acid Start with 100 ml of 0.1 M HCl mmoles free -log[h + free] not symmetric Volume of NaOH added

24 Adding a strong base to a strong acid mmoles free -log[h + free] What is your buffer?

25 Adding a strong base to a strong acid mmoles free -log[h + free] What is your buffer? WATER ITSELF!

26 Adding a strong base to a strong acid mmoles free -log[h + free] OH - H 3 O + What is your buffer? WATER ITSELF!

27 Adding a strong base to a strong acid H 3 O + H 2 O + H + pk a = H 2 O OH - + H + pk a = log[h 3 O + free] OH - H 3 O + What is your buffer? WATER ITSELF!

28 Adding a strong base to a strong acid H 3 O + H 2 O + H + pk a = H 2 O OH - + H + pk a = 15.7 What concentration is your buffer?

29 Adding a strong base to a strong acid H 3 O + H 2 O + H + pk a = H 2 O OH - + H + pk a = 15.7 What concentration is your buffer? 55.3 M

30 Adding a strong base to a strong acid H 3 O + H 2 O + H + pk a = H 2 O OH - + H + pk a = 15.7 What concentration is your buffer? 55.3 M The density of water at room temperature is g/ml The molar mass of water is g/mol Thus, the concentration is mol/ml = 55.3 M (~1/18)

31 Adding a strong base to a strong acid H 3 O + H 2 O + H + pk a = H 2 O OH - + H + pk a = 15.7 What concentration is your buffer? 55.3 M The density of water at room temperature is g/ml The molar mass of water is g/mol Thus, the concentration is mol/ml = 55.3 M (~1/18) Why can we not make an aqueous ph = -2 solution?

32 Adding a strong base to a weak acid Start with 100 ml of 0.1 M HA mmoles free Volume of NaOH added

33 Adding a strong base to a weak acid Start with 100 ml of 0.1 M HA mmoles free Simply diluting the conjugate base the of buffer Volume of NaOH added

34 Adding a strong base to a weak acid Start with 100 ml of 0.1 M HA mmoles free -log[h 3 O + free] not symmetric not symmetric Volume of NaOH added

35 Weak acids will equilibrate

36 Weak acids will equilibrate Overhead time!

37 Weak acids will equilibrate More Excel!

38 Weak acids will equilibrate

39 Weak acids will equilibrate

40 Weak acid salts will equilibrate

41 Weak acid salts will equilibrate

42 Check out the website for these and more Monoprotic Diprotic Monobasic Dibasic Monobuffer Ampholyte start with only acidic form of buffer start with only acidic form of diprotic buffer start with only basic form of buffer start with only basic form of diprotic buffer start with both acidic and basic form of buffer start with only middle form of diprotic buffer

43 Check out the website for these and more Monoprotic Diprotic Monobasic Dibasic Monobuffer Ampholyte start with only acidic form of buffer start with only acidic form of diprotic buffer start with only basic form of buffer start with only basic form of diprotic buffer start with both acidic and basic form of buffer start with only middle form of diprotic buffer Have a great 12 days!

44 Week 4 Objectives By the end of the week, you will be able to: Be able to construct and explain alpha fractions using distribution diagrams / Bjerrum plots, as a function of p values Use indicators to determine the various points in a titration curve Quantify the issues that can arise when performing titrations, due to dilution and/or dissociation