1. Exp 4A: Conductivity Of Aqueous Solutions
Purpose
Study conductivity of a series of solutions to determine the difference between strong electrolytes, weak electrolytes and nonelectrolytes
Use conductivity to distinguish between strong and weak acids and strong and weak bases
Use conductivity to study the effects of ion concentration

2. Conductivity of Solutions Conductivity units
The conductivity (or specific conductance) of an electrolyte solution is a measure of its ability to conduct or allow the passage of electricity.
Conductivity units
The SI unit of conductivity is siemens per meter (S/m)
Conductivity vs Conductance
Consider a piece of wire.
Electrical conductivity is a property of the material of the wire, and its value changes only with temperature (it decreases linearly with temperature).
On the other hand conductance is the measure of the ease with which current can flow in the wire. It depends on the physical parameters of the wire (length,area of cross section) as well as the conductivity of the material of the wire conductance=conductivity x area of cross section / length

3. APPLICATIONS and CONCEPT CONNECTIONS
Conductivity measurements are used routinely in many industrial and environmental applications as a fast, inexpensive and reliable way of measuring the ionic content in a solution. For example, the measurement of product conductivity is a typical way to monitor and continuously trend the performance of water purification systems.
For water quality- Conductivity is linked directly to the total dissolved solids (T.D.S.).
High quality deionized water has a conductivity of about 5.5 μS/m,
Typical drinking water in the range of 5-50 mS/m
Sea water about 5 S/m (one million times higher than deionized water).
Conductivity is traditionally determined by measuring the AC (alternating currect) resistance of the solution between two electrodes.
Dilute solutions follow Kohlrausch's Laws of concentration dependence and additivity of ionic contributions. Onsager gave a theoretical explanation of Kohlrausch's law by extending the Debye–Hückel theory.

4. Exp 4A: Conductivity Of Aqueous Solutions
Electrolytes
Aqueous solutions of ionic compounds
Ionic compounds dissolve and dissociate in water
NaCl(s)  Na+(aq) + Cl-(aq)
Formation of positive and negative ions in solution
Solution conducts electricity
Strong electrolytes conduct electricity easily
Strong electrolytes are completely dissociated (100%)
Weak electrolytes conduct electricity poorly
Weak electrolytes are only partially dissociates (<100%)
Mostly undissociated = molecular form
CH3COOH(l) H+(aq) + CH3COO-(aq)
Nonelectrolytes
Compounds that do not conduct electricity in solution
Compounds that do not form ions in aqueous solution

5. Exp 4A: Conductivity Of Aqueous Solutions
NaCl(s) + H2O(l)  Na+(aq) + Cl-(aq)
1 positive charge + 1 negative charge
2 ionic charges
MgCl2(s) + H2O(l)  Mg2+(aq) + 2 Cl-(aq)
1 ion with +2 charge, 2 ions with –1 charge
4 ionic charges
Fe(NO3)3+ H2O(l)  Fe3+(aq) + 3 NO3-(aq)
1 ion with +3 charge, 3 ions with –1 charge
6 ionic charges
Conductivity depends on
Concentration of ions
Charge of ions
(Size of ions (mobility in solution: large ions move more slowly))

6. Exp 4A: Conductivity Of Aqueous Solutions
Electrolytes conduct electricity

7. Exp 4A: Conductivity Of Aqueous Solutions
Strong electrolytes
Conduct electricity easily
Electrolyte (almost) completely dissociated in solution
NaCl(s) + H2O(l)  Na+(aq) + Cl-(aq)
Weak electrolytes
Poorly conducting solutions
Electrolytes mostly in molecular form with few ions
NaH2PO4(s) + H2O(l) Na+(aq) + H2PO4-(aq)
Magnitude of conductance of a solution
proportional to the number and type of ions in solution
More ions (higher ion concentration): more conductivity
More ionic charges: more conductivity

8. Exp 4A: Conductivity Of Aqueous Solutions
Strong Acids
HCl(g) + H2O(l)  H+(aq) + Cl-(aq)
HNO3(l) + H2O(l)  H+(aq) + NO3-(aq)
Strong Bases
KOH(s) + H2O(l)  K+(aq) + OH-(aq)
Weak Acids
CH3COOH(l) + H2O(l) H+(aq) + CH3COO-(aq)
Weak Bases
NH3(g) + H2O(l) NH4+(aq) + OH-(aq)

9. Exp 4A: Conductivity Of Aqueous Solutions
Strong and Weak electrolytes
Strong Electrolyte
Weak Electrolyte

10. Exp 4A: Conductivity Of Aqueous Solutions
Mixtures of electrolytes
Conductance shows additive effect if electrolytes do not react with each other
more ions, more charges, more conductivity
If a chemical reaction occurs between the electrolytes, the properties of the new substance(s) determine conductivity
typically reaction between a weak acid and a base or a weak base and an acid
NH3(aq) + HCl(aq)  NH4+(aq) + Cl-(aq)

12. Exp 4A: Conductivity Of Aqueous Solutions
Dilution
A certain amount of a solution added to an amount of solvent to lower the concentration
Add 10 mL of 1.0 M NaCl to 90 mL of H2O
Final volume = 10 mL + 90 mL = 100 mL
Dilution = 1:10
Concentration = (10 mL x 1.0 M NaCl)/ 100 mL = 0.10 M NaCl
The concentration changes. Does the total amount of NaCl particles change?
Dilution formula:
initial molarity (mol/L) x initial volume (L) =
final molarity (mol/L) x final volume (L) =
Mi x Vi = Mf x Vf =
mol/L x L = mol

13. Exp 4A: Conductivity Of Aqueous Solutions
Prelab Question 4a
How will you prepare 10 mL of M HCl from 0.10 M HCl?
Answer
Use dilution formula V1 x M1 = V2 x M2
M1 = 0.10 M
M2 = M
V2 = 10 mL
V1 = V2 x M2/M1 = 10 mL x M/0.10M = 5.0 mL of 0.10 M HCl
Take 5.0 mL of 0.10 M hydrochloric acid in a 10.0-mL graduated cylinder and dilute to 10 mL with dH2O

14. Exp 4A: Conductivity Of Aqueous Solutions
Prelab Question 5a
How will you prepare 80 mL of 0.10 M CH3COOH from 6.0 M acetic acid?
Answer
Use dilution formula V1 x M1 = V2 x M2
M1 = 6.0 M
M2 = 0.10 M
V2 = 80 mL
V1 = V2 x M2/M1 = 80 mL x 0.10 M/6.0M = 1.3 mL of 6.0 M acetic acid
Take 1.3 mL of 6.0 M acetic acid in a 5.0-mL graduated cylinder or use a 5.0 mL pipet. Add ~ 50 mL dH2O to a 100-mL graduated cylinder, then add the 1.3 mL of acetic acid. If you use a 5.0 mL cylinder for the acetic acid, rinse it out with dH2O and add it to the 100-mL cylinder. Repeat this process 2 more times. Add dH2O to a total volume of 80 mL.
Prelab Question 5b
Same as 5a

15. Exp 4A: Conductivity Of Aqueous Solutions
Part 1: Compare conductance of
20 mL dH2O, 20 mL tap water, 20 mL ethanol in 50 mL beaker
Why is there a difference in conductance, if any, between distilled water and tap water?
Part 2: Measure conductance of hydrochloric acid solutions
20 mL 0.10 M HCl
0.050 M HCl: dilute 10 mL 0.10 M HCl + 10 mL dH2O
0.020 M HCl: dilute 10 mL M HCl + 15 mL dH2O
How do you make dilutions?
 See prelab assignment 4!

17. Exp 4A: Conductivity Of Aqueous Solutions
Next Lab Period:
1. Turn in the following, stapled in this order
Data and Calculations sheets for Exp 4A: Conductivity Of Aqueous Solutions
Answers to post-lab questions on the lab manual sheets
2. Prelab Assignment for Exp 4B: Ionic Reactions in Aqueous Solutions
Avoid getting definitions from Google or Wikipedia. Use a textbook or lab manual or a science dictionary
Read Prelab preparations and Procedure
Answer Prelab questions 1a-d, 2a-h, 3, 4

18. Exp 4A: Conductivity Of Aqueous Solutions
Part 3: Measure conductivity in different solutions
Solution
Concentration
Conductance 1
10 mL 0.10 M HNO mL dH2O 2
10 mL 0.10 M KOH + 10 mL dH2O 3
10 mL 0.10 M KCl + 10 mL dH2O 4
10 mL 0.10 M KNO mL dH2O 5
10 mL 0.10 M Ca(NO3) mL dH2O 6
10 mL 0.10 M NH mL dH2O 7
10 mL 0.10 M HC2H3O mL dH2O 8
10 mL 0.10 M HCl + 10 mL 0.10 M KNO3
Calculate new concentrations 9
10 mL 0.10 M HNO mL 0.10 M KCl 10
10 mL 0.10 M HCl + 10 mL 0.10 M KOH 11
10 mL 0.10 M NH mL 0.10 M HC2H3O2

19. Exp 4A: Conductivity Of Aqueous Solutions
Measure conductivity in different solutions
Solution
Concentration
Conductance 1
10 mL 0.10 M HNO mL dH2O
0.05 2
10 mL 0.10 M KOH + 10 mL dH2O 3
10 mL 0.10 M KCl + 10 mL dH2O 4
10 mL 0.10 M KNO mL dH2O 5
10 mL 0.10 M Ca(NO3) mL dH2O 6
10 mL 0.10 M NH mL dH2O 7
10 mL 0.10 M HC2H3O mL dH2O 8
10 mL 0.10 M HCl + 10 mL 0.10 M KNO3 9
10 mL 0.10 M HNO mL 0.10 M KCl 10
10 mL 0.10 M HCl + 10 mL 0.10 M KOH 11
10 mL 0.10 M NH mL 0.10 M HC2H3O2