Lecture 15 Flashcards
When is the ratio to observe colour change 1/10 and when is it 10/1
Acid to basic (low pH to high pH) –> [In-]/[HIn] = 1/10
Basic to acid (high to low) –> ratio = 10/1
–> flips
Which formula is used to express when the colour change will be observed when TITRATING AN ACIDIC SOLN containing an indicator using a BASE
pH = pKa - 1 (soln shows colour change at this pH)
pH = pKa + log (1/10)
Which formula is used to express when the colour change will be observed when TITRATING A BASIC SOLN containing an indicator using an ACID
pH = pKa + 1 (soln shows colour change at this pH)
pH = pKa + log(10/1)
Why is it important to choose the right indicator for strong acid-base titrations
For different indicators, the volumes will be VERY similar
–> pH shoots up but volume barely changes
Why is it important to choose the right indicator for weak acid or base titrations
For different indicators, there will be VERY different volumes
–> may be a colour change before the actual eq pt
What is the solubility product eq
Ksp = [P]^n
What does the solubility represent in the ICE table
The change (x)
What is solubility
An equilibrium position
–> will change if common ion is present
What is the solubility product
constant at any one temp
When can you compare the Ksp of salts
When they produce the same number of ions
–> highest Ksp = most soluble
EX:
AgI
CuI
CaSO4
1:1:1
What do you do when you can’t compare Ksp
Must calculate “x” for each (to find solubility)
What would happen to the solubility if there were no common ion
Solubility would be higher (would go completely to the right)
BUT common ion effect decreases solubility
–> doesn’t go as far to the right
How do you know if solubility increases or decreases in acidic soln
- Must contain the conjugate of weak acid for possibility to recombine, thus lowering it (soln must then go to the right) sooo solubility increases if it must be more dissolved
TRAP: if contains a conjugate of strong acid, WONT INCREASE OR DECREASE
What is the ion product (and eq)
Q (uses initial concentration)
Q = [P]^n (initial)
How are Q and Ksp related and how do you know if a precipitate forms
Q > Ksp –> precipitate forms
(not enough ions to form precipitate, stay in soln)
Q < Ksp –> NO precipitate forms
(too many ions, saturated)
How to do precipitation problems
IMPORTANT DIFFERENCE: MUST ADD VOLUMES OF BOTH IN BF WHEN CONVERTING TO MOLES AND BACK TO [ ]!!
- Find Q and compare to Ksp to see if precipitate forms
- FIGHT TO THE DEATH (between 2 atoms that must [ ] must be found)
–> in mol!!
–> BR
AR
Final [ ]
–> LR goes to 0 and excess remains (wins fight) - ICE table (with winner of fight starting at final [ ] found and loser starting at 0)
–> find x (solubility)
What is selective precipitation (for questions asking what precipitates first)
When something precipitates first (lower [ ])
- Find [ ] of ion added when mixed with both ions in solution
–> The one with the lower concentration of ion added will precipitate first cuz less is require for a solid to form
At which position on graph is there the best buffer
When pH = pKa (1/2 eq pt)
