We are all familiar with salt, particularly sodium chloride, or table salt. We regularly use it to season and preserve our food. However, not everyone is familiar with other types of salts and their uses, for example, in manufacturing products like fertilisers, dyes, and polyester fabrics.
But salts also have a biological function. In biological organisms such as humans, salt serves as an electrolyte that enables neural signals to be transmitted by the brain to the muscles and organs, and vice-versa. Neural signals control the voluntary and involuntary movements of muscles. They also transmit information from sense organs like the eyes and tongue, and regulate the release of hormones from the endocrine system.
What is Meant by a Salt in Chemistry?
In chemistry, salt is defined as either an inorganic or organic compound that has ionic bonds. When dissolved in water, the ions dissociate into positively charged cations and anions which are negatively charged. These make ionic solutions ideal electrolytes that can easily conduct electricity.
Salts are often the product of neutralisation reactions between acids and bases. For example, sodium chloride can be produced through the neutralisation reaction between hydrochloric acid and sodium hydroxide, as shown in the balanced chemical equation below.
HCl + NaOH → NaCl + H2O
As you can see, the acidic hydrochloric acid is neutralised by the basic sodium hydroxide, forming table salt and water. The reaction can also be classified as a double replacement reaction, wherein the anions and cations exchange partners.
Salts can also be produced through combination reactions. For example, sodium chloride can be made through the combination reaction between metallic sodium and gaseous chlorine, as this balanced chemical equation shows.
2Na + Cl2 → 2NaCl
As this equation demonstrates, it requires two molecules of sodium and one diatomic molecule of chloride to produce two molecules of sodium chloride. This type of reaction between an alkali metal and a halogen is extremely exothermic.
What are the Different Types of Salt in Chemistry?
- Simple salts – Simple salts are formed via neutralisation reactions between acids and bases. They can be further subclassified into acidic, basic, and neutral salts.
- Acidic salts – Acidic salts are produced when a strong acid reacts with a weak base. The pH of this type of salt is below 7 because of the incomplete neutralisation reaction.
- Basic salts – The opposite of acidic salts, basic salts are formed through the reaction between a weak acid and a strong base. The pH level is above 7.2.
- Neutral salts – Neutral salts neither contain replaceable hydrogen ions nor hydroxyl ions, resulting in a neutral pH level.
- Double salts – Produced via the reactions between simple salts, double salts contain more than one anion or cation per molecule.
- Complex salts – These are a combination of molecular compounds and ions, which means they both have charged ions and neutral molecules. A central metal is surrounded by the ions and neutral molecules, thereby forming a complex.
- Mixed salts – Mixed salts are composed of two anions that share a cation, or vice versa. They’re produced through the reaction of more than one acid or base.
Examples of Salts in Chemistry
Here are some examples of each category or type of salt:
- Simple salts – sodium chloride (NaCl)
- Acidic salts – sodium carbonate (NaHCO3) and ammonium chloride (NH4Cl)
- Basic salts – sodium acetate (NAOOCCH3), potassium cyanide (KCN), and zinc chloride hydroxide (Zn(OH)Cl)
- Neutral salts – potassium chlorate (KClO3), calcium phosphate (Ca3(PO4)2), and sodium nitrate (NaNO3)
- Double salts – potassium cerium fluoride (KCeF4) and Mohr’s salt ((NH4)2Fe(SO4)2.6H2O)
- Complex salts – tetra amino cupric sulfate ([Cu(NH3)4]SO4) and hexamine chromium (III) chloride [CR(NH3)6]Cl3]
- Mixed salts – bleaching powder (Ca(ClO)2) and sodium potassium sulphate (NaKSO4)
What are the Properties of Salt in Chemistry?
Salts have different properties when it comes to taste, colour, smell, solubility, conductivity, and melting point. These characteristics are determined by the salt’s composition and crystalline structure.
Aside from their crystalline lattice structure and ionic bonds, here are some other properties of salt:
Although many salts have a characteristic “salty” taste, others have a very different flavour. Lead diacetate, for example, can be sweet-tasting but poisonous. Magnesium sulphate, on the other hand, has a bitter taste, while potassium bitartrate is sour. Monosodium glutamate has a savoury flavour, which highlights the tastes of other food ingredients.
Many salts are transparent or translucent, but some are opaque. The opacity, transparency, and colour of salts is largely dictated by the arrangement or structure of the monocrystals. Salts come in a wide range of colours, which are dependent on the ionic composition. For example, cobalt nitrate is red due to the presence of hydrated cobalt (II), while copper sulphate is blue as a result of copper (II) chromophore.
Salts that are produced from the neutralisation reactions between strong acids and strong bases do not have odours. However, those that are formed either from a weak acid and a strong base, or vice versa, tend to have an odour. The most common are cyanide salts, which are formed from hydrogen cyanide. They have a distinct almond-like smell.
Since salts are ionic compounds, most of them are highly soluble in water as well as other types of solvents. Some exceptions include ammonium hexachloroplatinate, potassium cobaltinitrite, and most metal carbonates.
Molten salts and solutions of salts conduct electricity because of their ionic and polar properties.
Salts tend to have high melting points due to their strong ionic bonds. For example, the common table salt has a melting point of 801°C.
How is Salt Formed in Chemistry?
There are various ways to produce salt, but the most common is via the neutralisation reaction (or double replacement reaction) that occurs between acids and bases.
Salts can also be formed through the reaction between alkali metals and halogens, which is classified as a combination reaction.
Salts are important because they have several applications. Here are some examples:
- Sodium chloride – also known as table salt, sodium chloride is the most common type of salt used in seasoning and preserving food.
- Monosodium glutamate – this type of salt is used to make food more savoury and enhance its flavour.
- Sodium nitrate – commonly used in the manufacturing of explosives and fertilisers.
- Potassium permanganate – used in treating some skin conditions like fungal infections. It is also used in synthesising organic compounds like ascorbic acid.
- Tetra amino cupric sulphate – this type of salt is used in manufacturing artificial fabrics, particularly cuprammonium rayon.
- Zinc chloride hydroxide monohydrate – a common feed additive and nutritional supplement for domesticated animals. It is also an antifungal component for treating plants.
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