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.

][][.

..

]][[

CNHMxx

xx

HCN

CNHKa

6

210

1068

1501094

If [H+] is 8.6 x 10-6, then [OH-]:

Mxx

x 96

14

10211068

101

..

If [H+] = [CN-] = 8.6 x 10-6, then we have lost this amountof 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 pressureon 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 ofH2CO3, 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 ofAgCl when you have a large quantity of Cl- already present asCaCl2. 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 = [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 = 0.00555 mol acid 2 mol protons

5.00 g acid = 90.1 g/mol0.0555 mol acid

0.00555 mol acid = x , x = 0.0555 mol acid25 mL 250 mL

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.