Question

Describe the manufracture of sodium hydroxide

Answer 1

Answer:

Industrial Production

What do paper, soap, and (some) clothing have in common? We need to use sodium hydroxide (NaOH) to make them! As of 2004, we produce 60 million metric tons per year worldwide! As you can guess, industrial processes for sodium hydroxide have therefore become very efficient.

Let's take a look at the first method used to create it, look at the corresponding equations, and explore some of the newer methods as well.

Castner-Kellner Cell

In the mid 1800's the foundation for the Castner-Kellner process was developed. This cell had a positive electrode and a negative electrode inside a tank. The reactions proceeded as follows:

A sodium chloride brine (salt water) is put into the tank.

The positive electrode (the anode) attracts the chloride away from the sodium.

The chloride builds up and combines to form chlorine gas (an excellent disinfectant). But we now have free sodium ions roaming around.

The water is broken apart with the negative electrode (the cathode) into hydrogen ions (which form into hydrogen gas, which also has many practical applications) and hydroxide (OH) ions.

Then hydroxide and sodium are combined, forming sodium hydroxide.

At first this method wasn't very effective because sodium (formed at the cathode) kept reacting with chlorine at the anode or with other constituents. But by the late 1800's this problem was fixed by using mercury as the cathode, which amalgamated with sodium.

Castner-Kellner cell. The right and left sections have a sodium chloride solution, with a graphite anode (A), and a mercury cathode (M). The middle section has a sodium hydroxide solution, the same mercury anode (M), and an iron cathode (D).

Castner-Kellner Cell