Materials Included In Kit

Additional Materials Required

Safety Precautions

Zinc dust may be flammable. Hydrochloric acid is toxic by ingestion and inhalation and is severely corrosive to skin and eyes. Hydrogen gas is flammable. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Hydrochloric acid may be disposed of according to Flinn Suggested Disposal Method #24b. Zinc may be reused or disposed of according to Flinn Suggested Disposal Method #26a. The resulting zinc chloride solution can be neutralized, then disposed of according to Flinn Suggested Disposal Method #26b.

Teacher Tips

• The pipet bulb used for collecting gases is made by cutting off most of the stem from a graduated Beral pipet (see Figure 4). Note: using a sharp razor blade or scissors for this operation will ensure excellent, uniform results. The remaining portion of the stem from the graduated pipet can be further used to make a gas delivery stopper. Simply cut off a portion of the tip of the graduated stem (see Figure 4) and insert it into a 1-hole rubber stopper.
  {12563_Tips_Figure_4}
• The gas-generator unit can be replenished with fresh acid without much loss of time. Remember, when filling the test tube with the acid, fill it only about 4⁄5 full. This will leave a small area of air between the acid and the stopper which cuts down on the time for flushing out the air.
• The pipet bulb can be removed any time. Due to the surface tension of water, the pipet bulb can be held upside-down and any water in the bulb will remain there. This bulb can be placed, upside-down, into one of the wells of a 96-well reaction plate. To save time, many pipet bulbs of gas can be collected and placed into the wells of the reaction plate if a small amount of water is left at the neck of the pipet bulb. The water will serve as a seal between the gas and the atmosphere.

Answers to Questions

1. Complete the following chemical equation

   Zn(s) + 2HCl(aq) → H₂(g) + ZnCl₂(aq)

2. What were your observations when pure hydrogen was tested?

   When tested, the hydrogen gas gave off a very soft pop ping sound.

3. What were your observations when the mixture of air and hydrogen was tested?

   When tested, the mixture of air and hydrogen gases gave off a much louder popping sound than that of pure hydrogen gas.

4. Is hydrogen lighter than air? What is the reason for this conclusion?

   Since the soap bubbles filled with hydrogen gas rose in the air, hydrogen gas must be lighter than air.

5. Indicate whether the following statements are True or False
   1. Hydrogen gas is colorless. T
   2. Hydrogen does not diffuse in air. F
   3. Hydrogen is very soluble in water. F
   4. Hydrogen has a greater density than air. F
   5. Hydrogen is flammable. T
   6. Hydrogen supports combustion. F
   7. Hydrogen and air will explode when ignited. T
   8. Zinc and sulfuric acid will form a gas. T

Introduction

In this experiment, hydrogen (H₂) is prepared in the laboratory and some of its characteristic properties examined.

Concepts

• Preparation of hydrogen
• Properties of hydrogen

Background

Hydrogen gas was first discovered by Henry Cavendish in 1766; however, it was Lavoisier who named this gas “hydrogen” from the Greek word meaning “water-former.” Very little hydrogen is found in its free state here on Earth, partly because of its ability to escape and partly because it is easily oxidized. Although hydrogen stands next to oxygen in its abundance, hydrogen is found in more com pounds than any other known element. Most hydrogen is found in water and petroleum-based materials.

Materials

Safety Precautions

Zinc dust may be flammable. Hydrochloric acid is toxic by ingestion and inhalation and is severely corrosive to skin and eyes. Hydrogen gas is flammable. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Preparation of the Gas Generator

1. Place about 0.5 grams of granular zinc into a small test tube and insert the gas-delivery stopper (see Figure 1).
   {12563_Procedure_Figure_1}
2. Obtain some 3 M hydrochloric acid and set it aside.
3. Fill a pipet bulb with water so that the hydrogen gas can be collected by the displacement of water.

4. Set up the gas generator as shown in Figure 2. To generate the hydrogen gas, remove the gas-delivery stop per, fill the test tube about ¾ full of acid, and replace the stopper. There should be only a small air space between the acid and the bottom of the stopper. This will keep the flushing time of the air in the gas generator to about 5 seconds.
   {12563_Procedure_Figure_2}
5. The reaction between the acid and zinc produces hydrogen gas which can be collected by the process of water displacement if a pipet bulb full of water is placed on top of the gas-delivery stop per as shown in Figure 2.
6. Collect a pipet bulb full of the gas.

7. To test for pure hydrogen gas, bring a pipet bulb full of the gas to a Bunsen burner, mouth down. Holding the pipet bulb horizontally, place a flaming toothpick near the mouth of the pipet bulb and quickly squeeze the bulb of gas. Record your observations.

8. Fill a pipet bulb only ¼ full of water. Collect enough hydrogen until the water is displaced.
9. To test the mixture, bring the pipet bulb to a Bunsen burner, mouth down. Holding the pipet bulb horizontally, place a flaming toothpick near the mouth of the pipet bulb and quickly squeeze the bulb of gas. Record your observations.

10. Insert a bar straw so that it tele scopes into the gas-delivery stopper of the gas-generator unit (see Figure 3). Now generate some hydrogen. While the gas is being generated, place a film of soap solution (using your finger) at the mouth of the straw so that a bubble of hydrogen gas can be formed. When the bubble is approximately 1 cm in diameter, raise the apparatus just above your head and gently blow up ward at the bubble in order to jar the bubble loose without breaking it. Record your observations.
    {12563_Procedure_Figure_3}
11. See instructor for disposal procedures.

Student Worksheet PDF

12563_Student1.pdf