41. Conductivity measurement, determination of weak acid dissociation

Question 1

What is Electrical conduction?

Answer 1

the ordered movement of charged particles in an electric field

Question 2

Which method that measure conductivity of an electrolyte solution?

Answer 2

by the conductometric method.

Question 3

What is conductivity?

Answer 3

the reciprocal of resistance (I/U), the unit of measurement is siemens (S).

Question 4

2 things that conductivity depend on

Answer 4

(1) The intrinsic nature of the anions and cations they contain, i.e. their mobility and charge
(2) concentrations of anions and cations

Question 5

can degree of dissociation be measured from conductivity measurement?

Answer 5

YES

Question 6

can degree of dissociation be measured from conductivity measurement?

Answer 6

YES

Question 7

The actual concentrations of the ions, in turn, are dictated by the extent to which the electrolyte ______

Answer 7

dissociates

Question 8

e meas- urement of conductivity is suitable for determining the degree of ___.

Answer 8

dissociates

Question 9

Summary of conductometry

Answer 9

1. Immersing 2 metal plates with same size into an electrolyte solution
2. Applying a voltage
3. Measuring the current generated

Question 10

Conductometry

What does current generated depend on? (chemical factors and geometric factors)

Answer 10

1. Chemical nature and amount of ions
2. Surface and distance of metal plates (geometric factors)
   
   1. By convention, metal plates with surface areas of 1cm2 are fixed at a distance of 1cm from each other => 1 cm3 solution is tested

Question 11

Conductometry

What does current generated depend on? (chemical factors and geometric factors)

Answer 11

1. Chemical nature and amount of ions
2. Surface and distance of metal plates (geometric factors)
   
   1. By convention, metal plates with surface areas of 1cm2 are fixed at a distance of 1cm from each other => 1 cm3 solution is tested

Question 12

Conductometry

Unit of the specific conductivity of the solution

Answer 12

κ (kappa), in S/cm.

Question 13

Conductometry

When solutions of different concentrations and electrolytes are prepared and tested, the measured specific conductivity of the more dilute solution is always ((1)___(Lower/higher), and that of the more concentrated solution is always (2)___(Lower/higher

Answer 13

1. Lower
2. Higher

Question 14

Conductometry

When solutions of different concentrations and electrolytes are prepared and tested, the measured specific conductivity of the more concentrated solution is always higher.

Question: Why?

Answer 14

1. Lower
2. Higher

Question 15

Does the amount of ions depend on degree of dissociation?

Answer 15

YES

Question 16

Explain the concept of equivalent conductivity?

Answer 16

The extent in the difference of conductivities between the particular concentrations is distinct for each substance

→ It is due to the difference in the initial concentrations can be eliminated

Question 17

What is the symbol and unit for quivalent conductivity

Answer 17

Symbol - A (capital lambda)

Unit: Scm2/mol.

Question 18

For substances that dissociate into monovalent ions, what is the equivalent conductivity?

Answer 18

the equivalent conductivity is the total conductivity of a portion of the solution that contains exactly 1 mole of solute

Question 19

Describe dissociation of strong electrolytes

Answer 19

Strong electrolytes always dissociate completely regardless of the concentration

Question 20

Describe dissociation in infinitely dilute solutions

Answer 20

The dissociarion is always complete, regardless of the strength of electrolyre

Question 21

What is the equivalent conductivity of infinitely dilute solutions?

Answer 21

The equivalent conductivity of such a solution (Λ∞) is a constant

Question 22

Is there solute in the infinitely dilute solution,? What is the consequence?

Answer 22

In fact, there is no solute in the infinitely dilute solution, so the conductivity of such a solution cannot be determined directly in practice.

Question 23

How to calculate the conductivity of multicomponent electrolyte solution?

Answer 23

the sum of the conductivity values of the individual ions

Question 24

The conductivity of a solution containing a reasonable amount of a __ (strong/weak) electrolyte is measurable

Answer 24

strong

Question 25

For weak electrolytes, how to calculate the equivalent conductivity?

Answer 25

the equivalent conductivity is directly proportional to the degree of dissociation, which in turn increases with dilution

→ the degree of dissociation of the electrolyte solution can be calculated from the equivalent conductivity of a given concentration c (Λc) and the infinitely dilute solution (Λ∞)

Question 26

in concentrated solutions, the equivalent conductivity of strong electrolytes is ___(higher/lower) than in dilute solutions.

Answer 26

lower

Question 27

in concentrated solutions, the equivalent conductivity of strong electrolytes is lower than in dilute solutions.

WHY IS THAT?

Answer 27

because of the congestion

→ the distance between the oppositely charged ions decreases

→ an attractive electrostatic interaction develops between them

→ arrange in pairs and are less willing to separate and move in opposite directions → their mobility decreases.

Question 28

Describe the measuring equipment

Answer 28

1. A Jenway 3540 conductivity (and pH) meter, to which a bell-shaped conductivity cell is connected
2. The conductivity cell consists of a glass bell hiding two platinum plates in the standardized arrengement.
3. The plates form the conductivity cell with the electrolyte solution to be measured between them

Question 29

What are the materials and equipments for the conductometry (except Jenway)

Answer 29

− 0.01 M CH3COOH solution

− 0.05 M CH3COOH solution

− 0.1 M CH3COOH solution

− 4 beakers

Question 30

8 steps of conductometry with CH3COOH solutions

Answer 30

1. Fill separate beakers with three CH3COOH solutions of different concentrations.
2. Immerse the bell electrode in the first beaker (0.01 M acetic acid) so that the solution covers the top hole of the glass bell.
3. Read the specific conductivity () of the solution measured from the conductometer.
4. Rinse the bell electrode by sinking-lifting it a couple of times into-from a beaker filled with distilled water before placing it in a new solution.
5. Similarly measure the conductivity of the other two solutions.
6. Determine how the specific and equivalent conductivity and the degree of dissociation changed with dilution. (For acetic acid  = 344 Scm2/mol).
7. Calculate the dissociation constant of the acetic acid using the