Even a novice to the world of chemistry will tell you that sodium chloride is the table salt that we use in our daily food items. But do you know what type of chemical compound sodium chloride actually is, what is it composed of and how is it used? All these aspects will be discussed in this article with a microscopic lens. Chemistry governs the synthesis, structure and properties of all the substances, essential to our daily life. All the chemical compounds are made up by the combination of atoms of some specific elements in a set proportion under suitable conditions of temperature and pressure. Sodium chloride is no exception in that regard.
What is sodium chloride?
Sodium chloride is an ionic compound made up of sodium and chloride ions. A sodium (Na) atom from Group 1 (Alkali Metals) of the periodic table lose one mole of electron to change to a sodium (Na+) ion. Chlorine (Cl) from Group 7 (Halogens) gain this one mole of electron to change to a chloride (Cl–) ion. Electrostatic forces of attraction develop between these oppositely charged ions to form a unit cell of an ionic compound called sodium chloride.
Sodium chloride formula is
Chemical reaction of sodium metal with chlorine gas
Na (s) + ½ Cl2 (g) NaCl(s) ………………………………….equation 1
The giant ionic lattice of sodium chloride
A large number of alternating Na+ and Cl– ions arrange together in a giant, three-dimensional cubic lattice to form the crystalline structure of sodium chloride. In this giant ionic lattice; each sodium ion is surrounded by six oppositely charged chloride ions and vice versa. Chloride ions being negatively charged anions are larger in size than the positively charged sodium cations. In result of it, the latter fit into the spaces between the former to form a compactly packed structure. The ratio of ionic radii in this crystal is 0.53 and it forms an octahedral, face-centered, cubic arrangement.
The lattice energy of sodium chloride crystal (energy used to break 1 mole of NaCl into its constituent ions) is 786 kJ. It is this symmetrical, compact crystalline packing that controls the distinct properties of hardness, brittleness, high melting and boiling point of sodium chloride.
The ions present in an NaCl crystal are held together by the strongest forces of attraction i.e., ionic bonds therefore sodium chloride does not conduct electricity in the solid state. NaCl however conducts electricity in the molten state when heat energy breaks free the oppositely charged ions to conduct the flow of electric charges.
Aqueous sodium chloride is also a good conductor of electricity, as water molecules interact and interfere in the bonding chemistry of each NaCl molecule. Six water molecules surround a Na+ ion through their partial negatively charged oxygen ends, while six water molecules surround a Cl– ion through their partial positively charged hydrogen ends. This, breaks free the oppositely charged ions. The process is called solvation and can be further read on in our article on molarity.
|Physical properties of Sodium Chloride
|State and appearance (r.t.p)
|White, crystalline solid
Is sodium chloride salt?
In terms of chemistry, a salt is defined as any chemical substance built up of positive and negative charges, which can be produced by the reaction of an acid with a base. Therefore, in accordance with this definition, sodium chloride is a salt. It can be prepared at laboratory and at the industrial scale by a chemical reaction of sodium hydroxide (a base) with hydrochloric acid (an acid) as shown in equation 2.
NaOH(aq) + HCl(aq) NaCl(s) + H2O(aq) …………………equation 2
The ionizable hydrogen (H+) gets replaced by a positively charged sodium (Na+) ion in this reaction. As the hydrogen ion is replaced completely by the metallic ion in this case so NaCl falls under the ‘normal salt’ category of inorganic salts. It is neutral, has a pH of 7 and does not exhibit any acidic or basic characteristics in aqueous solution. You can read more about the classification of salts here.
Table salt and/or rock salt and sodium chloride are often used interchangeably as different names for the same thing. But there might be a slight difference between the two. Although the table salt that we use as a food flavouring is 97-99% NaCl, but it may have traces of other impurities present as well. Likewise, we should always keep in mind that sodium chloride is a salt but not all salts are sodium chloride. Magnesium chloride (MgCl2), potassium chloride (KCl), zinc chloride (ZnCl2) and sodium sulfate (Na2SO4) are other examples of ‘salts’’.
What is sodium chloride used for?
- Food Flavouring: In the food industry, sodium chloride finds numerous applications as part of table salt, for food preservation, seasoning and flavouring. It is also used for dyeing and bleaching purposes.
- Pharmaceutical Sector: Sodium chloride makes an important constituent of pharmaceutical formulations. NaCl mixed with water creates a ‘saline’ solution. This solution is particularly useful for medicinal purposes: intravenous injections to treat dehydration, for wound cleaning and to treat specific ENT conditions such as for sinus clearance.
- Industrial Sector: Sodium chloride acts as a raw material for the synthesis of other chemicals such as sodium carbonate, specifically useful in glass making industry. Sodium hydroxide (caustic soda) is prepared from a molten solution of NaCl called brine in Nelson cell. Caustic soda is useful for domestic and industrial cleaning.
- Extracellular fluid: Sodium chloride plays an essential role in maintaining many life functions in the human body. Just as water is the universal solvent for regulating all the chemical reactions in the outside world, water make ups 60% of the human body composition as well. Water thus is the survival medium for all the cellular reactions. Sodium ions (Na+) from NaCl acts as an electrolyte to maintain this amount of water in our bodies.
Sodium ions carry electric impulses just as it conducts the flow of electric current in an aqueous medium throughout the body. These electrical nerve impulses aids in muscle contraction which consequently helps us in performing our daily life activities effectively. Maintaining the electrolytic balance of bodily fluids is also important for the digestion, absorption and transport of valuable nutrients inside the body.
Sodium chloride side effects
- Excessive NaCl consumption in salt form can lead to high blood pressure, hypertension which may additionally become a cause of various cardiac ailments. The daily sodium intake requirement of a healthy adult is about 3400 mg. On the contrary, doctors advise heart patients to restrict their sodium intake below 2000 mg/day which is just 1 teaspoon of salt a day.
- A rapid influx of Na+ ions into the kidneys can lead to excessive pressure on the excretory organs, exposing them to the risk of getting collapsed.
- A high chloride concentration inside the body cells may lead to end-osmosis which may ultimately lead to an increased water retention in the body thus swelling occurs.
The importance of sodium chloride as a chemical compound inevitable in food industry, medicinal sector and for maintaining good health cannot be negated. Both excess and dearth of sodium chloride and its constituent ions however can adversely affect the human body. Deficiency of sodium and chloride ions in the body can lead to ‘low salt syndrome’, disturbing the electrolytic and fluid balance of the cells. The side effects associated with sodium chloride deficiency can be read in further detail on this article called 6-little known dangers of restricting sodium.
|Q.1) Why is sodium chloride called a 1:1 ionic compound?
|A sodium chloride (NaCl) unit cell is made up of one Na+ ion and one Cl– ion thus Na: Cl=1:1 and NaCl forms a 1:1 ionic compound
Q.2) Why sodium chloride has high melting and boiling points?
|The three-dimensional compact, crystalline packing of sodium chloride holds oppositely charged ions by strong forces of attraction thus high energy required to break free these ions so high melting and boiling points.
|Q.3) Why sodium chloride a good conductor of electricity in aqueous state and a non-conductor in solid state?
|The ions are held strongly together in solid state but are free to move and conduct electricity in aqueous state by the process of solvation.
Q.4) Calculate the molar mass of sodium chloride from its molecular formula.
|Atomic mass of Na= 22.99Atomic mass of Cl=35.45Molecular formula of sodium chloride=NaClMolar mass of sodium chloride= 22.99+35.45 = 58.44 g/mol
Q.5) How is sodium chloride used? Give three examples
|1. Food seasoning and flavour enhancer2. Preparation of medicines and intravenous injections3. Maintenance of electrolytic balance, digestion and nutrient absorption in the human body