Experiment #7: Conductivity and Colligative Properties of Solutions

Electrolytes

Compounds where solutions in water or whose molten states are capable of conducting electricity

Strong electrolytes

Electrolytes in solution that are almost or completely dissociated into ions are called ______

Poor electrolytes

Solutions that contain mostly covalent molecules are poor conductors of electricity and are called ______

Non-electrolytes

Compounds whose solution does not conduct electricity are called

Colligative properties

Properties of a solution that depend upon the number of solute particles in solution.

• Lowering vapor pressure

• Lowering freezing point

• Elevation of boiling point

• Increase in osmotic pressure

Enumerate the 4 Coliigative properties

1. Prep the ff.:

   • 1M NaCl solution

   • 1M Glycerol solution

   • 1M H2SO4 solution

   • 1M acetic acid solution

   • 1M NaOH solution

   • Sugar solution

   • 3M NH4OH

   • Benzene

   • Detergent solutions

   • NaCl crystals

   • Sugar(s)

2. Fill the beaker about 2/3 of reagents listed above.

3. Immerse wires of the conductivity apparatus into the solutions.

Caution: Electrodes whould be well dried when testing solid samples

Procedures involved in A. Conductivity

1. Place 100 ml Distilled water in a 250 ml round bottom flask fitted with 2-hole stopper. Insert a thermometer thru one hole.

2. Heat over a wire gauze. Adjust the flame to boil water gently. When themometer reading remains constant, record as BP.

3. Repeat with 50 ml of 20% sucrose solution and 20% NaCl solution. Determine BP and compare with distilled H2O.

Procedures involved in B. Colligative Properties - Boiling Point Elevation

1. Place a pack of crushed ice in a large test tube. Record FP.

2. Add NaCl. Determine the temperature of ice-salt mixture. Compare with the FP of pure water.

3. Repeat with sucrose.

4. tabulate results.

Procedures involved in B. Colligative Properties - Freezing Point Depression

Tap water, NaCl crystals, glycerol, benzene and sugar(s) - NEUTRAL

Data & Results: Conductivity

Which substances give off no light?

NaCl solution, H2SO4 solution, NaOH solution, Detergent solution - Strong bases, acids, and ionic substances are strong electrolytes

Data & Results: Conductivity

Which substances give off bright light?

Acetic Acid solution - Weak bases and weak acids are also weak electrolytes

Data & Results: Conductivity

Which substances give off dim light?

The freezing points of solutions are all lower than that of the pure solvent.

What does Freezing Point Depression mean?

The vapor pressure of a solvent in a solution is always lower than the vapor pressure of the pure solvent.

What does Vapor Pressure Lowering mean?

The boiling points of solutions are higher than that of the pure solvent.

What does Boiling Point Elevation mean?

Increasing the temperature and molarity of solution also increases the osmotic pressure causing influx of the solvent.

What does increasse in Osmotic Pressure mean?

Boiling syrup produces a more severe burn than boiling water because it has a higher boiling point and it is more viscous than water and has a higher heat capacity, meaning it can retain heat for longer

Why does boiling syrup produce a more severe burn than boiling water?

Normally, pure water has a freezing point of 0℃. When salt is added to the ice, it effectively lowers the freezing point of the mixture and also enhances the cooling effect by facilitating the absorption of heat, thereby creating a colder environment compared to pure water alone.

Explain the difference between the freezing point of pure water and an ice-salt mixture.