Question

Can you think of a physical means of separating hydrogen from oxygen in a sample of pure water, \(\mathrm{H}_{2} \mathrm{O}\) ?

Short answer

One effective physical method to separate hydrogen and oxygen from a sample of pure water (H₂O) is through electrolysis. This involves using a direct current power source, electrodes, a container, and water with a dissolved electrolyte to increase conductivity. The positive and negative terminals of the power source are connected to the electrodes, which are placed in the water solution. Upon turning on the power source, gas bubbles are produced at both electrodes: hydrogen gas at the cathode and oxygen gas at the anode. The reaction taking place is \(2 H_{2}O (l) \rightarrow 2 H_{2} (g) + O_{2} (g)\).

Step-by-step solution

Understand the process of electrolysis

Electrolysis is a method that uses electrical energy to break or decompose a compound into its constituent elements. In the case of water, the electrolysis process will break the H₂O molecules into hydrogen and oxygen gases.

Prepare the setup for electrolysis

You will need the following items to perform electrolysis of water: 1. A power source: A direct current (DC) power supply or a battery (at least 9 V) to supply the electrical energy required. 2. Electrodes: Two conductive electrodes, typically made of inert metals like platinum or graphite, which are inserted into the water to allow electrical current to pass through the water. 3. A container: A container to hold the water sample. 4. Water: Pure water (preferably distilled water) to perform the electrolysis.

Dissolve an electrolyte in the water

Pure water is not a good conductor of electricity. Adding a small amount of an electrolyte, such as sodium sulfate or table salt (sodium chloride), helps increase the conductivity of the water and allows the electrolysis to occur.

Set up the electrodes

Place the two conductive electrodes in the water container with electrolyte solution, ensuring that they do not come into contact with each other. Connect the positive terminal of the power source to one electrode (anode) and the negative terminal to the other electrode (cathode).

Turn on the power source

Turn on the power source to supply electrical energy to the setup. This will initiate the flow of electricity through the electrodes and the water solution.

Observe the production of gases

As the electrical current passes through the water, the electrolysis process begins, and you will observe the production of gas bubbles at both electrodes. At the anode, oxygen gas is produced, while at the cathode, hydrogen gas is produced. You can collect these gases by inverting small tubes or containers over each electrode. The electrolysis process can be represented by the following reaction: \(2 H_{2}O (l) \rightarrow 2 H_{2} (g) + O_{2} (g)\) This method effectively separates the hydrogen and oxygen in water by using electrical energy to split the H₂O molecules into their individual elements.

Key concepts

Electrolysis of Water

Electrolysis of water is a fascinating chemical process where electrical energy is used to split water, \( H_2O \), into its basic elements, hydrogen and oxygen. When you immerse two electrodes in water and pass a direct current through them, the water undergoes a transformation. At the negative electrode, or cathode, you will see bubbles of hydrogen gas forming due to the reduction reaction where hydrogen ions gain electrons. Conversely, at the positive electrode, or anode, oxygen gas bubbles appear as a result of the oxidation reaction where water molecules lose electrons. It's like magic in a beaker, but clearly grounded in the principles of chemistry!

It is crucial to note that pure water doesn't conduct electricity well, which is why we add an electrolyte to aid the flow of current. The addition of an electrolyte, a substance that contains free ions, makes the solution conductive and facilitates the electrolysis. The beauty of electrolysis lies in its efficiency to cleanly and precisely break the chemical bonds, making it an essential method in chemistry to obtain pure elements from their compounds.

Electrical Energy in Chemical Decomposition

Transforming electrical energy into chemical changes is a keystone of modern chemistry. During the electrolysis of water, electrical energy is the vital force that drives the decomposition of water molecules. The power source you use in your setup, such as a battery, supplies this energy. Once the circuit is complete and the current flows, this energy disrupts the stable water molecule, causing it to separate into hydrogen and oxygen through a series of reactions at the electrodes.

The amount of electrical energy used correlates directly with the quantity of water decomposed, which is described by Faraday's laws of electrolysis. These laws provide the link between electrical charge and the amount of substance that undergoes chemical change during electrolysis. It's a conversion of energy from one form to another—electrical energy to chemical potential energy stored in the bonds of hydrogen and oxygen gases.

Conductivity and Electrolytes

Conductivity is the capability of a substance to allow the passage of an electric current, and in the case of electrolysis, we rely on this to make the process work. But here's the catch—pure water is a poor conductor of electricity. This is where electrolytes come to the rescue. Electrolytes are compounds that, when dissolved in water, release ions that carry an electric charge.

Common electrolytes used for water electrolysis include sodium sulfate \( Na_2SO_4 \) and table salt \( NaCl \). By dissolving these electrolytes in water, we're effectively creating a path that allows current to flow from one electrode to another, completing the electrical circuit necessary for electrolysis. The ions in solution are the workhorses, moving to the respective electrodes where they either gain or lose electrons, leading to the production of gases.

Chemical Reactions and Equations

Understanding chemical reactions is crucial when studying electrolysis. The entire process is a chemical reaction, where reactants (water and electrical energy) are transformed into products (hydrogen and oxygen gases). Writing down this transformation requires a chemical equation which looks like this: \[ 2 H_2O (l) \rightarrow 2 H_2 (g) + O_2 (g) \]. Each symbol and formula represents a different substance involved in the reaction, and the arrow indicates the direction of change.

The balanced equation tells you the proportions in which molecules react and are formed. For every two water molecules, two molecules of hydrogen and one molecule of oxygen are produced. This tells us that hydrogen and oxygen are formed in a 2:1 ratio, which is observed as a larger volume of hydrogen forming at the cathode compared to oxygen at the anode. Chemical equations are the language of chemists, allowing them to describe and predict the outcomes of reactions with clarity and precision.