Acid Base Reactions that lead to...

We know that: acid + base --> salt + water
but what if
- the acid and base are completely neutralized, but the salt is not neutral (see lessons on pH of an acidic/basic salt)
- there is leftover strong acid/base reactant?
- there leftover weak acid/base reactant?

Good questions.

Generally the reactions that are under consideration involve 1:1 mole ratios [insert a nice happy face here]

If the leftover reactant is strong, then
-determine the moles of leftover strong
-calc conc using the total volume
-determine pH

If the leftover is weak, then....it becomes a buffer question because there will be both weak acid/base and salt of the weak present. [A solution of weak acid/base and its conjugate salt = BUFFER!]
-determine moles of leftover weak
-determine moles of salt produced (=moles of reactant all used up - that nice 1:1 mole ratio]
-write llbm reaction for acidic/basic buffer
-determine conc of weak and salt using total volume
-use Ka and/or Kb all the way to pH

If there is no leftover reactant, only product salt - and the salt is acidic and/or basic
-determine moles of salt (nice 1:1 mole ratio)
-determine total volume
-write out llbm equation
-set up ICE chart to track changes
-use Ka and/or Kb all the way to pH
***remember that it is sometimes necessary to use the Ka of a weak acid to determine the Kb of its conjugate basic salt KaKb=Kw

From today complete:
p607(4) and p608(6)
A few points about 4 and 6:
4(a) before the titration begins - pH of a weak acid (check your notes)
4(b) the 10.00mL of NaOH is suppose to represent a stage of the titration in progress
4(c) the titration is now over, more than 10.00mLof NaOH was used, but how much? A salt was also produced, a salt with the conjugate ion of the weak acid - a basic salt - need to determine Kb
6(a) before the titration begins - pH of a weak base (check your notes)
6(b) the titration is over, how much acid was required to completely neutralize the weak base? what is the concentration of the salt of the weak base that was formed? {consider the total volume from the weak base and the acid)

Also, all of the remaining questions on the Buffer/Neutralization/Titration handout are now 'fair game'. The remainder of the handout questions are not necessarily like the questions on page 607 & 608. It is not intended that the remaining questions be completed for Monday. There will be more time next week, but not that much!
As I type this post, the game plan is that I will go home and moodlize some of the solutions. If I load them up using the same technology as some of the most recent moodlized solution postings - you may require a current version of Adobe reader 9. It is now several hours later. things have been moodlized -including the aromatic organic outline. If time permits additional organic stuff and buffer/tritration/neutralization solutions will also be moodlized. BufferTitrationNeutralization solutions up to question number 10ab have been moodlized. I am finished moodlizing for today. The solutions are part way down the A/B llbm, just after the BufferTitrationNeutralization Question Sheet. Each of the PDF file names identifies the questions on that particular image.

Next week:
Monday = more calculator work
Tuesday = 7-Up lab
Wednesday = 7-Up follow-up
Thursday = Rvw
Friday = test
Finishing joke: What colour is a burp? [Burple]

AB - another day and another question

Today was a day to re-visit some previously learned concepts.
 In what way did you re-visit earlier concepts?
The following handouts were completed:

(1) Acid-Base Equilibrium Overview (handout on moodle)
-the instructions are on the handout
-you may need to consult your notes
-consider the type of each substance (weak acid, weak base, acidic salt, etc…) before writing the equation and need for an ICE chart
-actually go full out and carry out the calculation to determine pH for the last three on the page
(2) Strong Acid-Strong Base Titration (handout on moodle)
-well laid out example in your text (page 598)
(3) Aromatic Reactions (Organic)

What about a few questions to get you thinking? In each case there will be some acid or base leftover. Notice the type of substances [strong A/B? weak A/B salt?] leftover after the reaction....take into account the total volume as you move beyond the neutralization reaction.
(1) Determine the pH of  the solution that is formed when 15.00mL of 0.100M HCl is combined with 25.00mL of 0.0800M NaOH.
(2) Determine the pH of the solution that is formed when 20.0mL of 0.100M acetic acid is combined with 10.0mL of 0.150M NaOH.
(Will the worked out solutions to these posed questions be moodlized later today? Hmmmm... Further hmmm...why is one question outlined in blue, while the other is outlined in red?)  It is a few hours later as I type these red sentences. The solutions to the above two questions (and a few more things) have been moodlized. Have a question while you moodling? Try the post a question forum.

A few jokes to close out this entry. Why did the child study in the airplane ? [The child wanted a higher education.]  Why was the broom late? [It over swept.] There is room for one more. Whats red and flies and wobbles at the same time? [A jelly copter.]

Acid Base Titrations that lead to another question...

The lesson was about neutralization via an acid/base titration.

In a titration, all of the acid and base are consumed (at the equivalence point) yielding a salt and water. [Thus the reason for writing A/B equations as acid + base --> salt + water]

An interesting aspect fromt these questions is what kind of salt is produced. Is it neutral, acidic or basic?

If the salt is acidic or basic, then what is the pH of the resulting solution.

If the pH of the resulting solution is known, then what is a suitable indicator to use to find the equivalence point of the neutralization (via titration)?

A few questions were left to complete.
For each of the following, determine
(i) the conc of the acid
(ii) the pH at the equivalence point
(iii) a suitable indicator (name, explain why it was selected, expected colour?)
(a) 13.72mL of acetic acid is completely neutralized by 25.00mL of 0.100M NaOH.
(b) 25.00mL of 0.150M NaOH is titrated with 21.44mL of HCl
(c) 8.68mL of HCl completely neutralizes 10.00mL of 0.0750M NH3

The solutions to these questions will posted on moodle within the next 2 hours.
[provided technical issues do not get in the way.]

The solutions to the pH of titration questions (outlined above and in class) are posted on moodle.
{I still need to work on 'sizing' the document...something for another day I suppose.}

I am testing out a new to me moodle feature - post a question forum...currently it is the last item in A/B llbm unit list

A few 'jokes'(?). Ready or not.... Why are gold fish orange? [The water makes them rusty.]  Who held the baby octopus to ransome? [Squidnappers.]  What part of a fish weighs the most?  [It's scales.]

Acid Base Neutralization

Neutralization of acid + base proceeds to the product side, no llbm

Generally:  acid + base --> salt + water

A few examples:
Strong acid/Strong base
   HNO3(aq)  +  NaOH(aq)  -->  NaNO3(aq)  + H2O

Weak acid/Strong base:
   HC2H3O2(aq)  +  NaOH(aq)  -->  NaC2H3O2(aq)  + H2O

Strong acid/Weak base:
-difficult to see "salt + water" products; write strong acid as H3O+
HNO3 + NH3 becomes H3O+  +  NH3  -->  NH4+  +  H2O

Follow-Up
Buffer/Titration/Neutralization handout (#11)
Stuck on the chemical equations? - check moodle.

And now for something a little amusing. On the first day of school, the Kindergarten teacher said, "If anyone has to go to the bathroom, hold up two fingers." A little voice from the back of the room asked, "How will that help

Upsetting Buffers

Dealing with acidic and/or basic buffers.
The buffer is upset by the addition of a small amount of either strong acid or strong base.

Acidic Buffer:
HA  +  H2O  <=>   H3O+   +  A-
  add strong acid (H3O+), llbm shifts to left (reactant) side
    thus [HA] increases, [A-] decreases
  add strong base (OH-), llbm shifts to the right (product) side
     {Why? OH- joins with H3O+ to create H2O}
    thus decreasing [HA], increasing [A-]

Basic Buffer:
Base + H2O  <=>  BaseH+   +   OH-
    add strong acid (H3O+), llbm shifts to right (product) side
           {Why? OH- joins with H3O+ to create H2O}
       thus [Base] decreases,  [BaseH+] increases
    add strong base (OH-), llbm shifts to the left (reactant) side
    thus increasing [Base], decreasing [BaseH+]

Typical Question:
500.0mL of a 0.10M NH3/0.080M NH4Cl solution has 3.00mL of 3.00M NaOH added. Determine the pH of the resulting solution.

-write the llbm reaction for the weak (in this case weak base NH3)
-determine the concentration change of the strong (base in this example) will undergo as it is added to the buffer solution (c1V1=c2V2)**
-organize and ICE chart to track changes to the two components of the buffer (the weak and its salt)
-calculate [OH-] at llbm, (since it is a basic buffer in this example)
-determine pOH
-finally determine pH

**since a small amount of strong base is being added to a much larger volume, the strong base concentration will be greatly impacted.
However the addition of a few mLs to the much larger buffer volume will have negligible impact on the initial buffer concentrations
-buffer concentrations are impacted by the llbm shift that results from the addition of the strong base (or acid)

Homework: From the Buffer/Neutralization/Titration Handout
5,6,7,8
 (do you appreciate?)

Why is it easy to swindle a sheep?  [Because it is so easy to pull the wool over its eyes.] Did you hear about the bungee jumper who shot up and down for 3 hours before they could bring him under control? [He had a yo-yo in his pocket!] Why did the French farmer only keep the one chicken? [Because in France one egg is un oeuf!]