Lecture 14 Flashcards
What is another way to say that the equivalence point was reached
That the strong acid/base was neutralized
At what point in the graph would we have the best buffer
At the halfway pt
NOTE: on graph, buffer is the slight curve before or after equivalence pt (where you add V but pH barely changes)
How to do titration problems (WEAK ACIDS WITH STRONG BASE)
Remember! Weak acid will react to completion with added strong base
DIFFERENCE! P will have a final [ ] during fight!!
- Find initial pH (before strong base added)
- Add strong base and identify species in soln
- FIGHT TO THE DEATH
–> between weak acid and strong base added
–> in moles!!
BR
AF
Final [ ] (VOLUME GOES UP) - ICE table to find [H+] and then pH
What happens once you reach the equivalence pt in weak acid-strong base problems
No more weak acid –> so we have a weak base and so, must be treated as a weak base problem now
When can you NOT use the Henderson-H eq
When it is a base problem
– CAN ONLY USE FOR ACID PROBLEMS
Which concentration must you use once you’ve past the eq pt (weak acid-strong base)
[ ] of excess OH- (cuz because a base problem)
Where is the equivalence point for weak acid-strong base problems
NOT AT pH = 7
How to do titration problems (WEAK BASE-STRONG ACID)
Same as for weak acid-strong base BUT
AT eq pt, problem becomes a weak acid problem
–> CAN use H-H equation
PAST eq pt, use excess H to determine pH
How can you find the eq pt (2)
- pH meter and plot pH vs volume titrant added
- Use acid-base indicator (weak acid - so doesn’t change pH)
–> changes colour at end point
What is the indicator formula
Ka = [In-][[H+]/[HIn]
Ka/[H+] = [In-]/[HIn] –> ratio of deprotonated over protonated
When do we perceive a colour change (ratio)
[In-]/[HIn] = 1/10
