Electrolysis of Water

Summary

In this demonstration of electrolysis of water using a Hoffman apparatus, the process begins by filling two test tubes with a sodium hydroxide solution, followed by running a current through them. As gases are generated, their volumes are measured, showing a two-to-one ratio of hydrogen to oxygen. The gases are tested with a flaming splint: hydrogen produces a popping sound, while oxygen reignites the splint. After confirming the presence of both gases, the experiment concludes with further tests, solidifying the relationship between gas volumes and the electrolysis process.

Takeaways

• 😀 The setup involves an electrolysis of water using a mini Hoffman apparatus.
• 😀 The test tubes are filled with a three molar sodium hydroxide solution to allow gas collection.
• 😀 The experiment uses a battery with a red lead connected to the negative terminal and a black lead to the positive terminal.
• 😀 Bubbles begin forming in the test tubes when the electrolysis process starts, with gas collecting on both sides.
• 😀 A measurement is taken after the reaction slows down, revealing about 3.8 ml of gas on one side and 7.6 ml on the other.
• 😀 The gas volume suggests a two-to-one ratio, with twice as much gas on the side with the larger reading.
• 😀 A splint test is conducted on the gas to identify it. The larger volume contains hydrogen gas, as indicated by a popping sound.
• 😀 A separate splint test confirms that the gas in the smaller tube is oxygen, with the splint reigniting.
• 😀 The total volume of collected gases was 328 milliliters of oxygen and 7.6 milliliters of hydrogen.
• 😀 The successful tests confirm the production of hydrogen and oxygen gases in a two-to-one ratio during water electrolysis.

Q & A

What is the purpose of the mini Hoffman apparatus in the electrolysis setup?

The mini Hoffman apparatus is used to perform the electrolysis of water, allowing the collection of gases, specifically hydrogen and oxygen, to demonstrate the process.

Why is sodium hydroxide used in this electrolysis experiment?

Sodium hydroxide (NaOH) is used as an electrolyte because it enhances the conductivity of water, making the electrolysis process more efficient.

What does the negative terminal of the battery do in this setup?

The negative terminal of the battery is connected to the lead that will cause hydrogen gas to form at the cathode during the electrolysis process.

What happens when the splint is inserted into the gas collected from the left test tube?

When the flaming splint is inserted into the gas from the left test tube, the popping sound indicates the presence of hydrogen gas, which is highly flammable.

What does the splint test reveal about the gas in the right test tube?

The splint test reveals that the gas in the right test tube is oxygen because the splint reignites, a characteristic reaction with oxygen.

How much gas was collected in the left test tube compared to the right test tube?

The left test tube collected about 7.6 milliliters of gas, while the right test tube collected about 3.8 milliliters of gas, showing a roughly 2:1 ratio of hydrogen to oxygen.

What is the significance of the two-to-one ratio of hydrogen to oxygen in this experiment?

The two-to-one ratio of hydrogen to oxygen is a direct result of the electrolysis of water, which produces twice as much hydrogen gas as oxygen gas based on the chemical reaction (2H2O → 2H2 + O2).

Why was the electrolysis reaction slowed down by unclipping the test tube?

Unclipping the test tube slows down the electrolysis reaction to allow more accurate gas collection and measurement.

What happens when the test tube with hydrogen gas is filled completely during the experiment?

When the test tube with hydrogen gas is filled completely, the electrolyte no longer contacts the electrodes, and electrolysis stops, limiting further gas production.

What is the purpose of the parallax correction when measuring the gas volume?

The parallax correction ensures accurate reading of the gas volume by aligning the observer's eye with the measurement scale to avoid visual errors caused by angle discrepancies.