Updates

1
Updates

• Midterm 2 is THIS Thurs., March 15 and will cover
  Chapters 16 17
• Huggins 10, 7-8pm
• For conflicts ELL 221, 6-7pm

2

• explain why as the polarity of H-X bonding
  increases, the acid strength increases?
  especially the section involving oxoacids

3
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

4
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

5

• 16.41) Calculate the concentrations of all the
  species (HCN, H, CN- and OH-) in a 0.15 M HCN
  solution.

If H is 8.6 x 10-6, then OH-
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
6

• 16.97) Henrys 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 Henrys law describes the effect of
pressure on the solubility of gases. The
solubility of CO2 can be calculated from Henrys
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.
7

• 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 Cl- present
initially, and then use the equilibrium
expression to solve for the solubility. 10.0 g
CaCl2 x 2 mol Cl- x 1 0.180
M Cl- 110.99 g mol-1 1 mol CaCl2
1.00 L
Ksp AgCl- 1.6 x 10-10 (s)(0.180 M)
s 8.89 x 10-10 M
8

• 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 0.00555
mol acid 2 mol protons
9

• 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.

10

• Give several examples of conjugate acid-base
  pairs using Arrhenius and Bronsted-Lowry acids
  and bases.

11

• 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?

12

• The pH scale is a logarithmic scale. If we
  change the pH by 2 units, by what factor does the
  H change?

13

• How do you find the pH of a solution
  containing a weak acid? What information do you
  need?

14

• How do you find the pH of a solution
  containing a weak base? What information do you
  need?

15

• What is the relationship between pH and pOH?
  What is the relationship between H and -OH?

16

• How would you make a buffer solution at a
  certain pH?

17

• 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?

18

• 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.