Sodium Hydroxide Preparation and Uses
Salt hydroxide is sometimes called caustic soda or lye. It is a common ingredient in cleaners and soaps.
At room temperature level, sodium hydroxide is a white, odor-free solid. Liquid sodium hydroxide is colorless and has no odor. It can react violently with strong acids and with water. Sodium hydroxide is corrosive. NaOH can react with moisture from the air and might generate heat as it dissolves. This heat can be enough to cause a fire if it is near flammable materials.
Sodium hydroxide is useful for its ability to alter fats. It is used to make soap and as the main ingredient in home products such as liquid drain cleaners. Sodium hydroxide is typically sold in pure form as white pellets or as a solution in water.
Commercial Preparation of Sodium Hydroxide by the Diaphragm Cell
Salt hydroxide is produced on a large scale by the electrolysis of an aqueous solution of common salt in a diaphragm cell. The cell is made from a steel tank.
An oblong perforated steel vessel lined inside with asbestos diaphragm acts as a cathode. It is supplied with a continuous level device to keep the vessel filled to the specified level with brine. A graphite anode is held within the U-shaped diaphragm and it projects into the salt solution. The steam is blown during the procedure which keeps the electrolyte warm and assists to keep the perforations clear.
The chlorine released at the anode increases into the dome at the top while hydrogen emitted at the cathode escapes through a pipe. The sodium hydroxide solution slowly percolates into a catch basin.
When the electrolysis takes place, chlorine is given off at the anode according to the following reaction.
2Cl – (aq) à Cl 2 (g) + 2 e–
At the cathode, hydrogen is discharged by the reduction of water.
2H 2O + 2e–à2 OH– (aq) + H 2 (g) At Cathode
The general outcome of the above reactions is that the brine loses its chloride ions and the solution turns progressively alkaline in the cathode compartment.
Problems during reaction
We can deal with 2 significant issues during the working of the cell.
- Chlorine produced can react with hydroxide ions in cold providing hypochlorite ions.
Cl 2 (g) + 2OH- (aq) à OCl– (aq) +Cl- (aq) + H2O
The first problem is solved by using the asbestos diaphragm. This keeps the two solutions separate while allowing sodium ions to move towards the cathode. This motion of ions keeps the current following through the external current.
2.Hydroxide ions might be attracted towards the anode, where they can be released emitting oxygen gas. This oxygen gas might pollute the chlorine and renders it impure.
The second issue is fixed keeping the level of saltwater in the anode compartment a little greater, this keeps the direction of flow of liquid toward the cathode and hence preventing the possibility of hydroxide ions to reach the anode.
The solution that drains the cathode compartment contains 11% NaOH and 16% NaCl. Evaporation of this solution crystalizes the less soluble NaCl which is filtered off, the liquid left contains about 50% NaOH and just 1% NaCl as an impurity. For industrial purposes, this small impurity is not important.
Uses of Sodium Hydroxide
Sodium Hydroxide in Cleaning and Disinfectant Products
- Sodium hydroxide is used to manufacture soaps and a range of cleaning agents used in homes and commercial applications.
Sodium Hydroxide in Pharmaceuticals and Medicine
- Sodium hydroxide is used to help produce a range of medicines and pharmaceutical products, from common painkillers like aspirin to anticoagulants that can assist to prevent blood clots, to cholesterol-reducing medications.
Sodium Hydroxide in Water Treatment
- Municipal water treatment facilities use sodium hydroxide to control water acidity and to help get rid of heavy metals from water.
Sodium Hydroxide in Food Production
- Sodium hydroxide is used in a number of food processing applications, such as treating foods like olives and eliminating skins from tomatoes, potatoes, and other fruits and vegetables for canning.
- Sodium hydroxide is also used to refine raw materials for wood items such as cabinets and furniture and in wood bleaching and cleaning.
Frequently Asked Questions
Q1: What is sodium hydroxide?
Ans: Sodium hydroxide or NaOH, is a soft, waxy white corrosive solid commonly known as lye or caustic soda.
Q2: What is the principle of the diaphragm cell?
Ans: Sodium hydroxide is prepared on large scale by the electrolysis of an aqueous solution of common salt in a diaphragm cell.
Q3: How much NaOH obtained at the end of the process?
Ans: In the end, 50 % NaOH is obtained with only 1 % of NaCl as an impurity which for a commercial purposes is a very small impurity and is not important.