Question

4. In the covalent compaound HCL, H-Cl, or H:Cl, which element has the greater electronegativity? __________ The shared electrons should be closer to ________.

3. Of the following pH values, which indicates a weak basic solution?

a.) 2.7         b.) 8.3         c.) 4.2       d.) 10.8        e.) 14.0

A. Dissociation of Water Molecules

H2O + H2O -----------------> H3O^+ + OH^-

                  <----------------

B. Acids and Bases

At equilibrium in pur water at 25 degrees Celsius, the number of H+ ions = number of OH- ions.

[H^+] = [OH^-]; M = 10^-7

[H+] = [OH^-] neutral.                       [H^+]>[OH^-] acidic.                      [H^+]<[OH^-] basic.

1. HCl ionizes completely in water. What is the [H^+[ of a 0.01 M solution? What is the pH?

2. Is the hydrogen ion concentration of pH 3 solution high or lower than that of solution with a pH of 6?

3. If one solution has 100 times as many hydrogen ions as another solution, what is the difference, in pH units, between the two solutions?

4. If solution A contains 1 X 10^-6 M H^+ ions and solution B contains 1 X 10^-8 M H^+ ions, which solution contains more H^+ ions?

5. Make a statement relating hydrogen ion concentration to the acidity and basicity of solutions.

6. HA is an acid that ionizes 10% in solution. What is the [H^+] of a 0.01 M solution of HA? What is its pH?

7. What is the [H^+] of a solution whose pH is 8? What is the [OH^-]?

8. Complete the following tables

[H+]                          |                   [OH-]                |                   pH

blank                        |              1 X 10^-6                |                blank

blank                        |             blank                  |                    4

1 X 10^-3                  |                 blank                  |                blank

BUFFERS

         A buffer solution maintains a constant pH upon the addition of small amounts of either acid or base. A buffer consists of a weak acid and a weak base. A buffer solution can 'sponge up" excess H^+ if added to a solution, or it can release H^+ if the H^+ concentration drops.

1. When a strong acid is added to water, the pH of the solution should go ____________ up/down.

2. When a strong base is added to water, the pH of the solution should go _____________up/down.

SOLUTIONS

       A solution consists of a solute dissolved in a solvent. A method of expressing solution concentration is in the term of molarity, or moles of solute per liter of solution. A mole of a compound is the number of grams of that compound equal to its molecular mass.

       The atomic mass (weight) of hydrogen is 1 and that of oxygen, 16. The molecular mass (weight) of water, H2O, which consists of 2H and 1O, is (2 X 1) + ( 1 X 16), or 18. Therefore, one mole of water has a mass of 18 g.

       A 1-molar (1M) glucose solution contains 1 mole (180 g) of glucose dissolved in enough water to make 1 liter of solution. To calculate the amount of solute required to make a liter of M solution, simply multiply the gram molecular weight by the molarity.

Use the following atomic masses in making calculations:

H          1                            O          16                      N        14

Mg       24                           S          32                      P        31

Na       23                           Cl          35.5                   C        12.

1. a. When oxygen dissolves in water, oxygen is the _____.

    b. When alcohol is dissolved in water, alcohol is the _____.

   c. When salt is dissolved in water, water is the ________.

2. Compute the molecular mass of ATP (C11H18O13N5P3);

Element                  Number of Atoms       x             Atomic Mass             =              Molecular Mass

______                   _______________      x            _____________           =              ______________

______                   _______________      x            _____________           =              ______________

______                   _______________      x            _____________           =              ______________

______                   _______________      x            _____________           =              ______________

______                   _______________      x            _____________           =              ______________

                                                                              Total                        =               _____________

3. To prepare a 1 M MgSO4 solution, take ______ mole(s) of MgSO4 and dissolve in enough water to prepare _______ (how much?) solution.

4. To prepare a 1 M MgSO4 solution, take ______ g of MsSO4 and dissolve in enought water to make 1 liter of solution.

5. To prepare a 0.1 M NaCl solution, take ______ mole(s) of NaCl and dissolve in enought water to make 1 liter of solution.

6. To prepare a 0.1 M NaCl solution, take ______ g of NaCl and dissolve in enought water to make 1 liter of solution.

7. A 0.2 M solution of NaCl contains ________ g of NaCl in 1 L of ___________.

           Grams of solute = molecular weight (in grams) X volume (in liters) X molarity

8. How would you prepare 500 ml of a 0.4 M solution of NaCl?

9. How would you prepare 250 ml of a 2 M solution of NaCl?

Answer 1

B. Acids and Bases

1. When HCl ionizes completely [H⁺] = 0.01 M

pH = -log ( 0.01) = 2

2. [H⁺] concentration of pH 3 solution is higher than pH 6 solution.

3. [H⁺]_a = 100[H⁺]_b

pHb - pHa = -log ([H⁺]b) - ( - log ([H⁺]a))

= log (100[H⁺]b) - log ([H⁺]b) = log (100[H⁺]b/[H⁺]b) = log(100) = 2

4. As 10^-6 > 10^-8 , Solution A contains more H⁺ ions

5. If pH < 7 or solution is acidic. If pH > 7 solution is basic. And if pH = 7 solution is neutral.

pH = -log ([H⁺]).

6. [HA] = 0.01 M

[H⁺] = (10% of [HA]) = 10 /100 * 0.01 = 0.001 M

7. - log ([H⁺]) = 8

[H⁺] = 10^-8 ; [OH-] = 10^-14/[H⁺] = 10^-6 M

8.

[H⁺] | [OH^-] | pH

10^-8 | 10^-6 | 8

10^-4 | 10^-10 | 4

10^-3 | 10-¹¹ | 3

BUFFERS

1. When a strong acid is added to water, the pH of the solution should go down.

2. When a strong base is added to water, the pH of the solution should go up.

SOLUTIONS

1. a. When oxygen dissolves in water, oxygen is the solute.

    b. When alcohol is dissolved in water, alcohol is the solute.

c. When salt is dissolved in water, water is the solvent.

2. Molecular mass of ATP (C11H18O13N5P3):

3. To prepare a 1 M MgSO4 solution, take 1 mole of MgSO4 and dissolve in enough water to prepare 1 liter solution.

4. To prepare a 1 M MgSO4 solution, take 120 g of MgSO4 and dissolve in enough water to make 1 liter of solution.

5. To prepare a 0.1 M NaCl solution, take 0.1 mole of NaCl and dissolve in enough water to make 1 liter of solution.

6. To prepare a 0.1 M NaCl solution, take 5.85 g of NaCl and dissolve in enough water to make 1 liter of solution.

7. A 0.2 M solution of NaCl contains 11.7 g of NaCl in 1 L of solution.

8. To prepare a 0.4 M NaCl solution, take 0.2 mole (11.7 g) of NaCl and dissolve in enough water to make 500 ml of solution.

9. To prepare a 2 M NaCl solution, take 8 mole (468 g) of NaCl and dissolve in enough water to make 250 ml of solution.