Supplies: Hoffman electrolyzer, DC power supply (or lead-acid battery), wires, test tubes, alcohol lamps, gas pipes, induction coils, electric keys, iron stands, iron clamps, gas bottles, and glass sinks.
Dilute sulfuric acid, hydrogen, oxygen, wood strips.
principle
Water can be decomposed into hydrogen and oxygen under the action of direct current. When an electric spark passes through a mixture of hydrogen and oxygen, they combine to form water. Both experiments show that water is composed of two elements, hydrogen and oxygen. From the experimental results, we can also know that their volume ratio is 2:1.
 

Prepare
1. Assembling the Hoffmann electrolyzer The Hoffmann electrolyzer is composed of two graduated glass tubes of 50 ml each. Each has a piston at the upper end and is connected to a tee tube at the lower end. The bottom of the scale tube is plugged tightly with a rubber stopper embedded with a platinum electrode, and a spherical funnel tube is connected to the middle glass tube of the tee tube.
If you do not have a Hoffmann electrolyzer, you can use two acid burettes. At the lower end of the buret, install a rubber stopper with an electrode and a right-angled glass tube. Electrodes can be made of nickel-chromium wire, copper sheets or stainless steel sheets. Two right-angle glass tubes are connected with a T-shaped tube, and a funnel tube is connected for injecting electrolyte. A simple device can use only two burettes, stand them upside down in the water tank, and insert an electrode into each tube mouth. But when you want to test the hydrogen and oxygen generated by electrolyzing water, you must take the burette out of the water tank and check it upside down.

If you don't even have a buret, you can assemble it with two glass tubes about 40 cm long and 1 cm in inner diameter. A single-hole plug equipped with a glass tube is installed on the upper end, and a short glass tube is connected to a sharp-nosed tube about 4 cm long as an exhaust tube, and a spring clamp is used to control the air flow. A rubber stopper with an electrode and a right-angled glass tube is installed at the lower end. The right-angled glass tube is then connected to the T-shaped tube and funnel tube. The volume of gas obtained in the glass tube can be measured using a scale plate. First, hold one end of the glass tube with the pointed nose downward and vertically, remove the rubber stopper with the electrode, pour 3 ml of water, make the liquid higher than the opening of the glass tube on the rubber stopper, and draw a line along the liquid surface. Add another 20 ml of water and draw a line along the liquid surface. Pour out the water, place the glass tube horizontally on a piece of white paper, and draw the distance between the two lines marked on the glass tube into 20 equal parts. Each equal part represents 1 ml and mark it with a number. Assemble the required parts and fix them on the wooden board together with the marking paper to become a water electrolyzer.

In order to facilitate the detection of hydrogen and oxygen obtained after electrolyzing water, a rubber tube is often connected to the upper end of the glass tube containing the cathode with a curved pointed glass tube to allow the hydrogen to flow out slowly. Use a rubber tube to connect an empty calcium chloride drying tube to the glass tube containing the anode, so that the outflowing oxygen can accumulate in it.

2. Assemble the water synthesizer. Water synthesis is often carried out in a gas measuring tube. It is a thick-walled glass tube with a length of about 45 cm and an inner diameter of about 1.3 cm. One end is closed and the other is open. Insert two platinum wires into the closed end, with the wire ends about 2 to 3 mm apart. There is a scale on the tube, and there are two types: 25 ml and 50 ml. If you don't have such a trachea tube, you can assemble it yourself. Take a thick-walled glass tube about 40 to 45 cm long and 1.2 to 1.5 cm in inner diameter, and install a rubber stopper with two copper wire electrodes inserted into the upper end. Leave the copper wire in the plug about 3 cm long, bend 1 cm upward into a hook, connect it with a tungsten wire taken from a waste light bulb (you can also use a thin electric heating wire instead), clamp it tightly, and fix it on the between two copper wires. The copper wire outside the rubber plug is also about 3 cm long and rolled into a circle to connect to the wire.

In the hydration synthesizer assembled in this way, the rubber plug at the glass tube mouth must be tightly plugged, otherwise the plug will be ejected from the tube mouth by the expanding gas when hydrogen and oxygen explode. The volume of gas in the glass tube can be measured with the scale plate made by the above method, but it can be simpler, as long as it is divided into 4 equal parts. Turn the glass tube together with the stopper upside down, add water into it four times, 3 ml each time, put a rubber band on the outside of the tube along the horizontal surface and make four marks.