Lets walk through them all together StrongStrong Titration Calculations If 100 mL of a MgOH 2 solution is titrated with 250mL of 200 M HCl What is the pH at the equivalence point ID: 191588
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Slide1
Atkins and Jones
Lets walk through them all together:Slide2
Strong/Strong Titration CalculationsIf 100. mL of a Mg(OH)2 solution is titrated with 25.0mL of 2.00 M
HCl…..What is the pH at the equivalence point?How many moles of Mg(OH)2 were initially present?What was the concentration of Mg(OH)2?Slide3
Strong/Strong Titration CalculationsA student weighs 1.823 g of an unknown strong acid into a beaker with 10mL of water. It is titrated to equivalence with 50.0mL of 1.0M NaOH. What was the molecular mass of the acid. Slide4
Conjugate Acid/Base pairsAcids lose a proton to become the conjugate base.
Bases gain a proton to become it’s conjugate acidAll acid/base reactions have both an acid and a base in them? So what is the base and conjugate acid in the first reaction? What is the acid and conjugate base in the second reaction?
AcidConjugate Base
BaseConjugate Acid
Acid
Conjugate
BaseSlide5
Relations between [H+], [OH-], Kw, pH and pOH
Important Relations
Can you just memorize this without understanding it?
What happens if the temperature changes?
H
2
O
K
]=1x10
-14
@25
o
C
pH=7 @25
o
C
Taking the log of both sides:
]=1x10
-7
@25
o
C
Slide6
Kw Example ProblemIf water is heated and placed under pressure it has a pH of 6.8. Find the Kw of water under these conditions.
Is it acidic, basic or neutral?
]
K
]
k
w
=[
10
-6.8
] [10
-6.8
]=2.5x10
-14
Slide7
Weak and Strong Acid and Bases: Compare and ContrastFor strong acids and bases, we assume they completely
ionize.
Equilibrium lies far to the right
Equilibrium lies far to the
left
Weak acids and bases ionize to a very
limited
extent.
Very Large
Ka
Very small
Ka
How do I know which is strong and weak?
Memorize the strong, the rest are weakSlide8
What happens to Ka as the strength of the acid increases?
The
larger
the Ka the stronger the acid.
vs
https://todaysmeet.com/1CBrindleySlide9
What happens to Kb as the strength of the base increases?If a base is stronger, which way does the equilibrium shift?It shifts to the right, so what happens to the amount of each product?
So for a stronger base, Kb is higher!!!
https://todaysmeet.com/1CBrindleySlide10
Ranking: Rank the following solutions in order of increasing acidity. Assume the concentration for each is the same, and that all are within solubility limits.
HClNaOH
Ca(OH)2NH(CH3)2
NH2(CH3)2+
CH
3
COOH
Strong
Base
Weak
Base
Weak
acid
Strong
acidSlide11
Ranking:
Rank the following solutions in order of increasing acidity. Assume the concentration for each is the same, and that all are within solubility limits. HCl
NaOHCa(OH)2
NH(CH3)2
NH2(CH3)
2
+
CH
3
COOH
Strong
Base
Weak
Base
Weak acid
Strong
acid
Ka
=1.8x10
-5
Slide12
Acid/Base Conceptual Understanding Questions:In what range must the pH of a 0.17M solution of a weak acid fall? pH<7
pH>-log(0.1) pH= 0.77-7What must be true about the [H+] of a weak acid solution @25oC?Neutral gives [H+]=[OH-]=10-7
Acidic has more [H+] so: >10-7What must be true about the [OH-] of a weak acid solution? Neutral gives [H+]=[OH-
]=10-7Acidic has less [OH-] so: <10-7Slide13
Percent Ionization: Pictorial Representation
Original Acid: 14
Dissociated Acid: 3% ionization= 3/14*100%= 21.4%Slide14
Example: The percent dissociation of a 0.800 M aqueous monoprotic
weak acid is 0.10%. What is the Ka value for the acid?
HA
I
C
E
0.8 M
0M
0M
0.8-8x10
-4
M
8x10
-4
M
8x10
-4
M
= 8.00x
Slide15
Polyprotic acids:Poly=many protic=protons
polyprotic=many proton atoms
K
a1
K
a2
K=Kw/K
a1
K=Kw/K
a2
What is the Kb of CO
3
2-
?Slide16
Molecular Structure and Strength of AcidsHX, where X designates a halide (F, Cl, Br, I)
Two competing forces: Enthalpy and PolarityEnthalpy of HI is much lower than HF, says HI is strongestBond polarity would make it seem as if HF should be the strongestSo which wins?Bond enthalpy
weak
strong
Hydrohalic
AcidsSlide17
Generalization of Acid Strengths Other AcidsThe more you stabilize the anion, the stronger the acid
REMEMBER
Different Central Atoms, Same oxidation number (aka same number of attached groups)
Strength increases with increasing electronegativity of central atom.
Example: HClO
3
>HBrO
3
Same central atom, different number of attached groups
Increases as oxidation number of central atom increases
Example:
HClO
4
>HClO
3
>HClO
2
>
HClO
<
+7
+5
+3
+1
Oxidation number
Strength of acidSlide18
BuffersAcid and its conjugate base, or a base and its conjugate acidOr some combination of components which create this.
(next slide)It works by converting a strong acid into a weak acid, or a strong base into a weak base. A strong base can’t exist in solution with a weak acid it must reactA strong acid can’t exist in solution with a weak
base it must reactSlide19
Can you make a buffer with?NH3 and HCl
?Yes!How: when NH3 and HCl react, they form NH4
+NH3 + H+ → NH4
+ ICF
0.20M
0.10M
0M
-
0.10M
-
0.10M
+
0.10M
0.10M
0.10M
0M
Gives us a
conjugate
acid base pairSlide20
Buffer Calculation Example
A 100 mL buffer solution is 0.100M Nitrous acid and 0.100M Sodium nitrite. Calculate the pH if 0.005 moles of
NaOH is added to the solution
calculate the pH of 0.002 moles of HCl
is added to the solution.
calculate the pH of 0.0150
mols
of
NaOH
is added to the solution. Assume no change in volume.