Updates
• Midterm 2 is THIS Thurs., March 15 and will
cover Chapters 16 & 17
– Huggins 10, 7-8pm
– For conflicts: ELL 221, 6-7pm
…explain why “as the polarity of H-X
bonding increases, the acid strength
increases”? …especially the section
involving oxoacids
Binary acids (HX, H2X, H3X, H4X)
•
Bond strength determines acidity within the same group (column), size
•
Bond polarity determines acidity within the same period (row), electronegativity
Oxyacids
Central atoms derived from same group (same oxidation state)
•
More electronegative central atom polarizes the OH bond more,
facilitating ionization (effect is weakening the O-H bond)
•
More electronegative central atom better able to stablize resulting
negative charge following ionization, making a happier (more stable)
conjugate base
16.41) Calculate the concentrations of all
the species (HCN, H+, CN- and OH-) in
a 0.15 M HCN solution.
2
[H  ][CN  ]
x
Ka 
 4.9 x1010 
HCN
0.15
x  8.6 x106 M  [H  ]  [CN  ]
If [H+] is 8.6 x 10-6, then [OH-]:
1x1014
9

1
.
2
x
10
M
6
8.6 x10
If [H+] = [CN-] = 8.6 x 10-6, then we have lost this amount
of HCN, so:
[HCN] = 0.15 – (8.6 x 10-6) = 0.15 M
16.97) Henry’s law constant for CO2 at 38oC is
2.28 x 10-3 mol/L.atm. Calculate the pH of a
solution of CO2 at 38oC in equilibrium with the
gas at a partial pressure of 3.20 atm.
Remember that Henry’s law describes the effect of pressure
on the solubility of gases. The solubility of CO2 can be
calculated from Henry’s law:
2.28 x 10-3 mol/L.atm x 3.20 atm = 7.30 x 10-3 mol/L.
Remember that CO2 dissolves in water to form H2CO3.
Therefore, the pH will depend on the extent of ionization of
H2CO3, which can be found from Ka (4.2 x 10-7):
4.2 x 10-7 = x2/(7.30 x 10-3 M), x = 5.54 x 10-5 M;
pH = -log x = -log(5.54 x 10-5), pH = 4.26.
17.47) Calculate the molar solubility of AgCl in a
solution made by dissolving 10.0 g of CaCl2 in
1.00 L of solution.
This is a problem that asks you to calculate the solubility of
AgCl when you have a large quantity of Cl- already present as
CaCl2. We must first calculate the concentration of Clpresent initially, and then use the equilibrium expression to
solve for the solubility.
10.0 g CaCl2 x
2 mol Cl110.99 g mol-1
1 mol CaCl2
x
1
= 0.180 M Cl1.00 L
Ksp = [Ag+][Cl-] = 1.6 x 10-10 = (s)(0.180 M)
s = 8.89 x 10-10 M
17.18) A 5.00-g quantity of a diprotic acid is
dissolved in water and made up to exactly 250 mL.
Calculate the molar mass of the acid if 25.0 mL of
this solution required 11.1 mL of 1.00 M KOH for
neutralization. Assume that both protons of the
acid are titrated.
0.0111 L x 1.00 M KOH = 0.0111 mol KOH
0.0111 mol protons x 1 mol acid
2 mol protons
0.00555 mol acid =
x
25 mL
250 mL
5.00 g acid
0.0555 mol acid
= 90.1 g/mol
=
0.00555 mol acid
, x = 0.0555 mol acid
Define and give examples of an Arrhenius
acid, a Bronsted-Lowry acid, and a Lewis
acid.
Define and give examples of an Arrhenius
base, a Bronsted-Lowry base, and a Lewis
base.
Give several examples of conjugate acid-base
pairs using Arrhenius and Bronsted-Lowry
acids and bases.
Give an example of a strong acid. How do
you determine the pH of a solution containing
a strong acid?
Give an example of a strong base. How do
you determine the pH of a solution containing
a strong base?
The pH scale is a logarithmic scale. If we
change the pH by 2 units, by what factor does
the [H+] change?
How do you find the pH of a solution
containing a weak acid? What information do
you need?
How do you find the pH of a solution
containing a weak base? What information
do you need?
What is the relationship between pH and
pOH? What is the relationship between [H+]
and [-OH]?
How would you make a buffer solution at a
certain pH?
What is the pH at the equivalence point of a
titration of a strong base with a strong acid?
Weak base with strong acid?
Weak acid with strong base?
Give an example of a salt that would dissolve
to yield a basic solution.
Give an example of a salt that would dissolve
to yield an acidic solution.