Salt is an ionic compound comprising a metal (cation) and non-metal (anion). The compound is made by a chemical reaction between an acid and a base/ alkali/ carbonate/ metal. When an acid reacts with any of the aforementioned elements, it neutralizes or ceases to exist. During the process, the acid’s hydrogen ion gets replaced by the reactant’s positive ion, resulting in an ionic compound called salt. Salt has a neutral charge (neither positive nor negative), which means it has equal proportions of both ions. These ions are bonded together courtesy an ionic bond.
There are different kinds of salts. Generally, salts are categorized based on their non-metal component or the negative ions they comprise. Carbonate or bicarbonate, cyanide, chlorate, chloride, phosphate, nitrate, sulfate, silicate, etc. are non-metals that help make salt. Table salt or the salt most widely used by regular people comprises chloride.
Salts can be soluble and insoluble. Soluble salts are water-dissolvable and denoted by the symbol “aq” in chemical equations, which stands for aqueous. Generally, the salt preparation and purification method determines whether the salt is water-soluble or not. All potassium, nitrate (silver nitrate), and ammonium salts, and the majority of sulfate and chloride (sodium chloride) salts are soluble. Insoluble salts are calcium sulfate, barium sulfate, silver chloride, and most carbonates.
With various kinds of reactants interacting with acids to form different types of salts, let’s get to know them in some detail.
Acid + Base → Salt + Water
A metal oxide (copper oxide) or metal hydroxide (magnesium hydroxide) is a base. When a metal oxide or base reacts with acid, the result is salt and water. For example, when sulfuric acid reacts with copper oxide, the resulting product is copper sulfate (salt) and water. Metal oxides/hydroxides don’t dissolve in water; therefore, the salt created from this reaction is generally insoluble.
Acid + Alkali → Salt + Water
Alkali is water-soluble metal hydroxide or a dissolvable base, meaning it contains both a metal and hydroxide. Sodium hydroxide, for instance, is an alkali that’s a soluble metal hydroxide. When hydrochloric acid reacts with sodium hydroxide (alkali), the result is sodium chloride (salt) and water.
Acid + Metal → Salt + Hydrogen
When hydrochloric acid (acid) reacts with zinc (metal), the result is zinc chloride (salt) and hydrogen gas. Similarly, when copper (metal) is added to sulfuric acid (acid), the chemical reaction gives out copper sulfate (salt) and hydrogen. Likewise, nitric acid and silver react to churn out silver nitrate and hydrogen. To separate the salt or extract salt crystals from water, the salt is evaporated or moderately heated. There is no filtration process.
Not all metals react the same; some tend to be very reactive or can explode when added to acid – for instance, potassium. Gold, on the other hand, reacts ever so slowly, making it almost impractical to make a salt with it. Also, chemical salts made with acid and metal generally have the metal part first in their names. By the way, hydrochloric acid always makes salts that comprise the chloride ion, with their names ending as chloride.
Acid + Carbonate → Salt + Water + Carbon Dioxide
When carbonates (calcium carbonate) and acids react, the result is salt, carbon dioxide and water. For example, when hydrochloric acid reacts with sodium carbonate, the output is sodium chloride, carbon dioxide and water. Similarly, sulfuric acid and copper carbonate react to make copper sulfate, carbon dioxide and water. Nitric acid and magnesium carbonate make magnesium nitrate, and acetic acid and sodium hydrogen carbonate make sodium acetate, in addition to carbon dioxide and water.