All About Sodium Hydroxides

Many kinds of hydroxides substances can be found in our daily life. One of them is sodium hydroxide. This alkali metal hydroxides have many important roles and many uses that make us have to learn about them.

So this article will give you information about the general properties, preparation and uses of sodium hydroxide in many parts of life.

General Properties of Sodium Hydroxide
Sodium hydroxides have a solid state in room temperature and the color is white. But, the solid sodium hydroxide is differing from other solid substance. It is because they can absorb moisture (H2O molecules in gas state) from the air until they dissolve in the excess of water. This process is known as deliquescence. Many other alkali metal hydroxides also shown this properties.

Solid sodium hydroxides is very hazardous substance. The reason is because of the hydroxide ion (OH-) that contain in the substance can react with skin protein to destroy the skin surface. It will be more dangerous if a large amount of hydroxides ion touches the skin surface. So, to work with this substance, we have to be very careful.

Besides adsorb the moisture from the air, solid and solution of sodium hydroxides also absorb carbon dioxide from the atmosphere to produce sodium carbonate.

2NaOH (aq) + CO2(g) (from atmosphere) → Na2CO3(aq) + H2O(l)

Sodium hydroxide is the most commonly used as the source of hydroxide ion. It is because of the sodium is the cheapest metal in all alkali metal. So because of that, sodium hydroxides became the sixth most important inorganic chemical based on the quantity of production.

Preparation Of Sodium Hydroxides
Sodium hydroxide is prepare by electrolysis of sodium chloride solutions (brine). There are three types of commonly electrolytic cell that used to produce sodium hydroxide, that is :

1. Diaphragm cell
2. Membrane cell
3. Mercury cathode cell

This cell used very large amount of electricity to run the electrolysis process. Diaphragm and membrane cell running between 30.000 – 150.000 A and the mercury cathode cell is running up to 400.000 A.

Let see what the different process that happened in the three cell.

Diaphragm Cell
In this cells:
1. Water is reduced to hydrogen gas and hydroxides ion in the cathode.
2. Chloride ion is oxidized to chlorine gas in anode

Cathode : 2H2O(l) + 2e → H2(g) + 2OH-(aq)
Anode : 2Cl-(aq) → Cl2 + 2e

The important feature of this cell is the diaphragm or separator. This separator have function to prevents the hydroxide ion that produced in the cathode mixed with chlorine gas that produced in anode.

This separator has pores which is big enough to allow the brine molecule pass through of them. This separator usually made from asbestos or Teflon mesh.

During the electrolysis process, the solutions that produced in cathode, wich is contain of 11 percent of sodium hydroxide and 16 percent of sodium chloride is removed continuously.

This solution and then evaporated, which is make the sodium chloride molecule crystallize and can be separate from sodium hydroxides. This process will produce final product which is contain of 50 percent sodium hydroxide and 1 percent of sodium chloride as impure.

Membrane Cell
This cell have a similar function like diaphragm cell. But the separator that use in this cells is made from micro pore polymer membrane. This membrane only permeable (can pass through) to the cations product that is sodium ion.

It is mean that the chloride ions from the brine cannot enter the cathode compartment but the hydroxide ions that produce in the cathode can escape in the top of opposite direction.

This process will produce sodium hydroxide that contained not more that 50 ppm of chloride ion the solutions. The product have a better result than diaphragm cell.

But, there is a problem using this cell to produce sodium hydroxide that is the membrane is very expensive and it can clogged by trace impurities of calcium ion, which is form insoluble calcium hydroxide on the membrane surface.

If it happened, the membrane can not be used anymore so we must replace with the new one.

Mercury Cathode Cell
This cell is using liquid mercury as a cathode. At the anode chlorine gas is produce but in the cathode, sodium ions is reduced to sodium metal.

Na+(aq) + e → Na(s)

Why the reduction of sodium happened in the cathode? It is because the mercury electrode surface inhibits any half - reaction that produce gas.

The sodium metal that produce in the cathode and then is pumped to a separate chamber. In this chamber, the sodium metal will react with water to produce sodium hydroxide. This reaction is happened in the graphite surface.

2 Na(s) + 2H2O(l) → 2 NaOH(aq) + H2(g)

The sodium hydroxide that produce from this cell is pure and concentrated.

But unfortunately, there is a loss of mercury metals to the environment when we use this cell to produce sodium hydroxides. We know that mercury is a heavy metal that very hazard to humans and can cause a very dangerous diseases.

Sow, which one of the cell that you think is a better choice to produce sodium hydroxides?

Uses Of Sodium Hydroxides
About 30 percent of sodium hydroxide that produces every years is used as a reagent in organic chemistry.

1. About 20 percent is used for synthesis of other inorganic cemicalls.
2. About another 20 percent is consumed in the pulp and paper industry.
3. And the 30 percent remaining is used in hundred of other ways.
4. Sodium hydroxide is very important bases in the chemistry laboratory.
5. Sodium hydroxide is also have many household uses.
6. Sodium hydroxide is also used in food industry, mainly to provide hydroxide ion for breaking proteins. For example, potatoes are spray by sodium hydroxide solution (with a certain concentration) to soften and remove the skin before processing. An of course it wash thoroughly before the next processing.
7. Olives have to be soaked in sodium hydroxides solution to make them soft and flesh enough to make them edible.
8. Sodium hydroxide is uses to make a hard soap.

And many other uses of the sodium hydroxide that you can found by yourself. Just search in google.

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