To determine if a water sample is completely free from hydrogen and oxygen gases after electrolysis, you can perform a simple test called the gas test or the flame test. Here's how you can do it:
Collect a small amount of the water sample after the electrolysis process is complete.
Take a test tube or a glass container and fill it with the collected water sample.
Carefully invert the test tube or container over the water source while ensuring no air bubbles are trapped inside.
Use a long, thin glass tube or a delivery tube to displace the water inside the container with air. Connect one end of the tube to a gas source (such as a gas cylinder or an inverted gas syringe) and the other end into the container below the inverted water source.
Allow the air to displace the water completely. The gases present in the container will rise and occupy the upper part of the container.
Carefully remove the delivery tube while keeping the container inverted to prevent any gas escape.
Ignite a wooden splint or a matchstick to produce a flame.
Bring the flame close to the mouth of the container without touching it. Be cautious and avoid getting burned.
Observe the flame carefully. If there are no further combustion reactions or flame bursts, it indicates that the gases (hydrogen and oxygen) are not present in the container.
It's important to exercise caution while performing this experiment and handle flammable gases with care. Also, ensure proper ventilation and conduct the experiment in a safe environment.