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Preparation of Hydrogen (1 Favorite)

DEMONSTRATION in Observations, Density, Chemical Change, Balancing Equations, Classification of Reactions, Chemical Change. Last updated October 14, 2019.


Summary

In this demo, students witness a single displacement reaction between zinc and sulfuric acid that produces hydrogen gas. The gas is collected via water displacement and ignited.

Grade Level

High school

Objectives

By the end of this lesson, students should be able to

  • Recognize a single displacement reaction has taken place.
  • Know that hydrogen is produced because of the splint test.

Chemistry Topics

This lesson supports students’ understanding of

  • Classification of reactions
  • Chemical change

Time

Teacher Preparation: 20 minutes

Lesson: 40 minutes

Materials

For each group:

  • Ring stand
  • Clamp
  • Erlenmeyer flask (250 mL)
  • Thistle tube
  • Rubber stopper, 2 hole (for flask)
  • Glass tubing
  • Delivery tube, rubber or plastic
  • Gas collecting bottles (3)
  • Trough
  • Glass squares (2)
  • Safety glasses
  • Zinc, mossy
  • 18-M sulfuric acid
  • Wooden splints

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • When working with acids and bases, if any solution gets on your skin immediately rinse the area with water.
  • When diluting acids, always add acid to water.
  • When lighting the match and wooden splint, be cautious with the flame.

Teacher Notes

Because of the use of 18-M sulfuric acid, this is best done as a demonstration.

For the Student

Lesson

Background

Hydrogen is unique among the elements because it does not definitely belong to a group on the periodic table. In fact, in some versions of the table hydrogen is separated from the body of the table.

Although hydrogen is classified as a nonmetal, it combines with almost all elements. The hydrogen atom consists of one proton and one electron, which is very close to the nucleus. Hydrogen forms covalent compounds with other nonmetals by sharing its electrons. In such compounds, the oxidation state of hydrogen is +1. Hydrogen also combines with some Group 1A and 2A metals to form ionic compounds called metal hydrides, and in those instances it has an oxidation state of -1.

In this experiment, you will prepare hydrogen gas by reacting an active metal with an acid. The gas will be collected by water displacement, and several properties of hydrogen will be investigated.

Purpose

Generate hydrogen and investigate some of its properties.

Materials

  • Ring stand
  • Clamp
  • Erlenmeyer flask (250 mL)
  • Thistle tube
  • Rubber stopper, 2 hole
  • Glass tubing
  • Delivery tube, rubber or plastic
  • Gas collecting bottles (3)
  • Trough
  • Glass squares (2)
  • Safety glasses
  • Zinc, mossy
  • 18-M sulfuric acid
  • Wooden splints

Safety

The use and handling of 18-M sulfuric acid needs caution. Handle this acid carefully. It will cause painful burns if it comes in contact with skin.

Procedure

  1. Place four or five pieces of mossy zinc in a 250-mL Erlenmeyer flask. Add sufficient water to the flask to just cover the zinc. Clamp the flask to a ring stand as shown in the diagram.
  1. Place the stopper, fitted with a thistle tube and curved piece of glass tubing, securely in the flask, making sure that the end of the thistle tube extends below the surface of the water in the flask. Attach the delivery tubing to the trough.
  2. Fill the trough with water. Fill the gas-collecting bottles with water and leave them upside down in the trough.
  3. Slowly and carefully add 3.0 mL of 18-M sulfuric acid through the thistle tube. CAUTION: HANDLE ACID CAREFULLY!
  4. Allow the bubbles to escape into the trough for about 30 seconds. Then, place a gas-collecting bottle (filled with water) mouth-down over the end of the delivery tube. Allow the bottle to fill with hydrogen gas.
  5. When the bottle is filled, lift the bottle slightly, and slide a glass square over the mouth of the bottle under water. Holding the glass square in place, lift the bottle out of the water and place it mouth-down on the lab bench with the glass square still in place.
  6. In the same manner, collect another bottle of hydrogen gas.
  7. Disconnect the rubber stopper and remove the tube from the trough. Unclamp the flask and carefully fill the flask with cold tap water. Decant (to pour a liquid off of a solid) the mixture and pour all liquid down sink. Add more tap water to the zinc and swirl. Decant all liquid down sink. Discard zinc into paper towel and throw it in the garbage can.
  8. Keeping the bottle mouth-down, lift one of the bottles of hydrogen gas and insert a burning splint into the bottle. Record your observations.
  9. Keeping the glass square in place over the mouth of the bottle, turn the second bottle of hydrogen gas over. Place and inverted “empty” gas-collecting bottle on the glass square so that the two bottles are mouth to mouth. Slide the glass square away, leaving the two bottle mouths resting against each other. After about 30 seconds, test both bottles of hydrogen with a burning splint. Record your observations.

Observations

Step 9 observations:

Step 10 observations:

Analysis

  1. Why is it important to have the end of the thistle tube extend below the surface of the liquid in the flask?
  2. Why is the generator allowed to operate for 30 seconds before you collect hydrogen gas?
  3. Write a balanced equation for the reaction used to produce hydrogen gas in this experiment.
  4. What product results from the burning of hydrogen? Write a balanced equation for this reaction.
  5. On the basis on observations from this experiment, describe the solubility of hydrogen gas in water and describe its relative density.