Experiment 4

Background of Gas Preparation

• Purpose of Experiment: Prepare three gases and investigate their properties: Hydrogen (H2), Oxygen (O2), and Carbon Dioxide (CO2).

Properties of Gases to Examine

• Colour and Odour: Note any visible characteristics and smells of the gases.
• Density: Compare the gas densities to that of air (mass of nitrogen N2 = 28g).
• Hydrogen (H2): Lighter than air.
• Carbon Dioxide (CO2): Denser than air.
• Solubility: Observe whether gases dissolve in water.
• Ignition: Determine if gases support combustion.
• Identification Test Examples:
• Hydrogen: “pop” test.
• Oxygen: glowing splint test.
• Carbon Dioxide: limewater test.

Techniques for Collecting Gases

1. Downward Displacement of Air: Used for gases less dense than air (e.g., H2).
2. Upward Displacement of Air: Used for gases denser than air (e.g., CO2).
3. Displacement of Water: Suitable for gases that are not water-soluble (e.g., O2).

Keywords

• Displacement, density, solubility, pop test, limewater test, glowing splint test.

Learning Outcomes

• Understand laboratory safety, including:
• Safe handling of chemicals.
• Use of personal protective equipment.
• Develop observational skills and report observations:
• Change in temperature, observation of gases, color changes, etc.
• Preparation, identification, and physical properties of common gases (O2, H2, CO2).
• Convert observations into chemical equations and practice balancing them.

Safety Notes

• Handle glass tubing carefully; avoid forcing glass into plastic or rubber stoppers.
• Be cautious with manganese(IV) oxide (MnO2); do not inhale dust.
• Handle hydrogen peroxide (H2O2) carefully; wear gloves. In case of skin contact, wash with water.

Experimental Procedure

Part 1: Preparing Hydrogen Gas

1. Setup: Use downward displacement of air (use Figure 1).
2. Reaction Setup: In a test tube, combine:

• 2-3 small pieces of magnesium (Mg).
• 2 mol L-1 hydrochloric acid (HCl) to about 2 cm depth.

1. Gas Collection: After placing the delivery tube into the reaction tube, collect hydrogen in an inverted test tube (1-2 minutes).
2. Testing: Use a lit stick to test for ignition; record observations.

Part 2: Preparing Oxygen Gas

1. Setup: Use downward displacement of water (use Figure 3).
2. Water Setup: Fill an inverted test tube with water; place in the bucket.
3. Reaction Setup: In a reaction tube, mix:

• Small quantity (match-head size) of MnO2.
• 5 mL of 6% H2O2.

1. Gas Collection: Direct the plastic tubing into the water-filled test tube and collect O2 gas.
2. Testing: Place a glowing splint in the oxygen test tube, record observations.

Part 3: Preparing Carbon Dioxide Gas

1. Setup: Use upward displacement of air (use Figure 2).
2. Reaction Setup: Place marble chips (CaCO3) in a large test tube and add HCl (2 mol L-1).
3. Gas Collection: Collect CO2, stopper test tube, and place aside.
4. Testing: Use a lit splint in the test tube to test for ignition.
5. Indicator Test: Add Universal Indicator to another test tube of water; bubble CO2 through and record color changes. Repeat with limewater.

Post-Laboratory Questions

Hydrogen Gas

1. Balanced equation for producing hydrogen gas.
2. Characteristics:

• Density: Less dense than air.
• Ignition: Supports combustion.
• Identification: “Pop” test.

1. Balanced equation for the reaction of hydrogen with oxygen.

Oxygen Gas

1. Balanced equation for producing oxygen gas.
2. Role of manganese(IV) oxide in preparation.
3. Characteristics:

• Density: More dense than air.
• Ignition: Supports combustion.
• Identification: Glowing splint test.

1. Can it be collected by upward or downward displacement?

Carbon Dioxide Gas

1. Balanced equation for producing CO2.
2. Properties:

• Density: More dense than air.
• Acidic, basic, or neutral? (Acidic).
• Ignition: Does not support combustion.
• Identification: Limewater test.

1. CO2's solubility and reaction with water; write the dissolving equation.
2. Balanced equations for reactions with limewater when CO2 is bubbled through.