SI

Titrations

100

A 50.0 mL sample of 0.200 M NaOH is titrated with 0.200 M HNO₃. What is the pH at equivalence point?

pH = 7 (strong acid, strong base!)

200

A 1.0 L sample of 0.40 M lactic acid (HC3H5O3) is titrated with 0.30 M NaOH. Determine the pH of the solution after the addition of 40.0 mL of NaOH. The Ka of lactic acid is 1.4 × 10⁻⁴.

pH = 2.3

300

What type of titration does this graph show?

*savannah show picture

Strong acid with a strong base

400

Consider the titration of 50.0 mL of 0.200 M acetic acid (CH₃COOH) with 0.150 M NaOH.

Given:

• Ka=1.8×10^-5

Calculate the pH:

1. Before the addition of NaOH

2. After the addition of 50.0 mL of NaOH

1. pH = 2.72

2. pH = 5.22

500

A 40.0 mL sample of a 0.300 M diprotic acid (H₂B) solution is titrated with 0.150 M NaOH.

At what added volume of base (in milliliters) does the following occur:

1. First equivalence point

2. Second equivalence point

1. 80.0 mL

2. 160 mL

Buffers

100

What is a buffer?

A solution that resists changes in pH when limited amounts of acid or base are added to it.

200

Calculate the pH for a buffer solution composed of 0.754 M HCN and 0.998 M NaCN. Ka for HCN = 4.9 x 10^-10.

pH = 9.43

300

A 1.0 L buffer solution contains 0.300 mol of NH₃ and 0.300 mol of NH₄Cl. The pKa of NH₄Cl is 9.25.
a. Calculate the initial pH of the buffer.           

b. Calculate the pH after adding 0.025 mol of NaOH.

c. Calculate the pH after adding 0.020 mol of HCl.

a. pH = 9.25

b. pH = 9.32

c. pH = 9.19

400

Calculate the pH of a buffer solution that is formed by mixing 367 mL of 0.26 mol NH4Cl with 200 mL of 0.67 mol NH3. The Kb for NH3 is 1.8 x 10^-5.

pH = 9.67

500

A 500.0 mL solution contains 15.6 g of NH₃ (ammonia) and 18.4 g of NH₄Cl (ammonium chloride). The Kb of NH₃ = 1.8×10^-5. Calculate the pH.

pH = 9.69

Molecular Shapes

100

What is the main principle of VSEPR?

To minimize electron repulsion.

200

Determine the molecular geometry at the 2 labeled atoms.

*show picture

C1 = trigonal planar, C2 = tetrahedral

300

How many of the following molecules are nonpolar?

XeF₄, CCl₄, NF₄, SO₃

3 (XeF₄, CCl₄, SO₃)

400

For the molecule CCl₃F, determine the following:

1. Determine the number of valence electrons for the entire molecule.

2. Determine the electron pair geometry.

3. Determine the molecular geometry.

4. Determine the bond angles.

1. 32 valence electrons

2. tetrahedral

3. tetrahedral

4. 109.5

500

For the molecule SF₄, determine the following:

1. Determine the number of valence electrons for the entire molecule.

2. Determine the electron pair geometry.

3. Determine the molecular geometry.

4. Determine the bond angles.

5. Determine whether the S-F bond is polar or nonpolar. (S = 2.5, F = 4.0)
6. Determine whether the molecule is polar or nonpolar

1. 34 valence electrons

2. trigonal bipyramidal

3. see saw

4. bond angles between equatorial positions is <120, bond angles between axial and equatorial positions is <90

5. S-F bond is polar.

6. Molecule is polar.