Production of Hydrogen - Experiment 8

The procedure will allow the student to generate hydrogen gas and examine some of its properties.

Materials Substitutions
mossy zinc galvanized nail
3 M hydrochloric acid muriatic acid, diluted to 3 M
125 mL Erlenmeyer flask small jar
stopper lid
wood splint toothpick
beral pipets droppers
candle and matches

Procedure

  1. Place a small amount of mossy zinc or a galvanized nail in the flask.
  2. Add one dropper full of HCl (aq) or muriatic acid to the zinc. This will produce gas bubbles. Stopper the flask loosely.
  3. After 20 seconds, light the wood splint with the candle and prepare to test for the gas.
  4. After 20 seconds, light the candle and prepare to test for the gas.
  5. CAREFULLY, place the burning splint at the mouth of the flask. Be prepared for the reaction! Replace the lid and wait for more gas to collect.
  6. Re-light a splint and test the gas again.

Questions

  1. Write the equation for the production of the gas in the above experiment.
  2. Describe the reaction between the gas and the burning splint.
  3. Why must the container be stoppered for the gas to be collected?
  4. What property of hydrogen made it less than desirable as the fill-gas for the large dirigibles of the 1920’s and 1930’s?

Teacher’s Notes
During the sixteenth century, Paracelsus, a Swiss-German physician, noted that a flammable gas was formed when iron reacted with sulfuric acid. However, he did not realize that the gas was a pure substance. In 1766, Cavendish determined that the flammable material was a distinct substance when he was able to produce the gas by causing a variety of acids and several metals to react. It was Lavoisier, however, who named the gas “hydrogen,” which means “water producer”.

An active metal replaces hydrogen in hydrochloric acid and produces hydrogen gas. This reaction is called a single-replacement reaction.

Zn (s) + 2HCl (aq) —> ZnCl2 (aq) + H2 (g)

Hydrogen has a density that is less than that of air so we must use a stopper or lid to keep it from escaping.

For large commercial ventures, hydrogen is generally produced by the electrolysis of water. Hydrogen is liberated at the cathode when a direct current passes through water that contains a small amount of an electrolyte.

Solution Preparation
Commercial muriatic acid is a strong acid and, therefore, must be used with care! Gloves should be worn when working with this chemical. To prepare a 3M solution, slowly add 100 mL of concentrated muriatic acid to 300 mL of water (preferably distilled). The mixture will get HOT.

Safety Precautions

  1. Proper eye protection should be used at all times.
  2. Hydrochloric acid is corrosive. Proper care should be used to protect skin and clothing.
  3. If you are using glass bottles or jars, the containers should be wrapped with tape to avoid glass fragments if the container breaks.
  4. Hydrogen gas is very reactive! Do not allow open flames or sparks near gas production or storage area. Pressure will build up quickly inside the flask or jar so the container should never be tightly sealed. Explosions could occur from increased pressure.

Disposal
All solids may be placed in the trash can. Acid solutions should be poured down the sink and followed with water to clear the plumbing.