Salts: Formation, Types, and Properties

Definition

Salts are ionic compounds formed from the neutralization reaction of an acid and a base. They consist of positively charged ions (cations) and negatively charged ions (anions) held together by ionic bonds. Essentially, they are the products formed (along with water) when an acid reacts with a base.

Explanation

The formation of a salt is a fundamental concept in chemistry. When an acid (which donates H+ ions) reacts with a base (which accepts H+ ions or provides OH- ions), the H+ ions from the acid combine with the OH- ions from the base to form water ($H_2O$). The remaining ions from the acid and base then combine to form the salt. The type of salt formed depends on the specific acid and base involved in the reaction.

For example:

• Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water ($H_2O$)
• Sulfuric acid ($H_2SO_4$) + Sodium hydroxide (NaOH) → Sodium sulfate ($Na_2SO_4$) + Water ($H_2O$)

Core Principles and Formulae

Formation of Salts: The key reaction is the neutralization reaction: Acid + Base → Salt + Water.

Types of Salts: Salts are categorized based on the acid and base from which they are formed, and the way the salt formed.

• Normal Salts: Formed by the complete replacement of hydrogen ions in an acid by a metal. Example: NaCl.
• Acidic Salts: Formed by the partial replacement of hydrogen ions in a polyprotic acid (an acid with more than one replaceable hydrogen atom) by a metal. Example: $NaHCO_3$.
• Basic Salts: Formed by the incomplete neutralization of a strong base by a weak acid. These salts contain hydroxide ($OH^−$) ions or other basic anions.
• Double Salts: These salts contain two different cations or two different anions. Example: Ammonium iron(II) sulfate (Mohr’s salt) [$(NH_4)_2Fe(SO_4)_2 \cdot 6H_2O$]
• Complex Salts: These salts contain a complex ion. Example: Potassium hexacyanoferrate(II) ($K_4[Fe(CN)_6]$)

pH of Salt Solutions: The pH of a salt solution depends on the strength of the acid and base from which the salt is derived.

• Salt of strong acid and strong base: pH = 7 (neutral)
• Salt of strong acid and weak base: pH < 7 (acidic)
• Salt of weak acid and strong base: pH > 7 (basic)
• Salt of weak acid and weak base: pH depends on the relative strengths of the acid and base.

Examples

Common Salts:

• Sodium Chloride (NaCl): Table salt, formed from the reaction of hydrochloric acid (HCl) and sodium hydroxide (NaOH). Used in food preservation, as a de-icer, and in the production of other chemicals.
• Sodium Hydroxide (NaOH): Caustic soda or lye. A strong base used in the manufacture of soap, detergents, and paper.
• Sodium Bicarbonate ($NaHCO_3$): Baking soda. A weak base used in baking, as an antacid, and in fire extinguishers.
• Bleaching Powder (Calcium hypochlorite, $CaOCl_2$): Used as a disinfectant and bleaching agent. Formed by the reaction of chlorine gas ($Cl_2$) with calcium hydroxide ($Ca(OH)_2$).
• Washing Soda (Sodium carbonate decahydrate, $Na_2CO_3 \cdot 10H_2O$): Used in laundry detergents, glass manufacturing, and water softening.
• Plaster of Paris ($CaSO_4 \cdot \frac{1}{2}H_2O$): Used in construction, for making casts, and in sculptures. Formed by heating gypsum ($CaSO_4 \cdot 2H_2O$).

Common Misconceptions

Misconception 1: All salts are harmful or poisonous.

Reality: Many salts are essential for life, such as sodium chloride (table salt) and various mineral salts. The toxicity of a salt depends on its chemical composition and concentration.

Misconception 2: All salts have a neutral pH.

Reality: The pH of a salt solution depends on the strength of the acid and base used to form it. Salts can be acidic, basic, or neutral.

Importance in Real Life

Salts play a crucial role in various aspects of life and industry:

• In Biology: Electrolytes (salts) are essential for maintaining fluid balance, nerve function, and muscle contraction in living organisms.
• In Food: Sodium chloride is used as a seasoning and preservative. Other salts are used as flavor enhancers and preservatives.
• In Industry: Salts are used in the production of various chemicals (e.g., chlorine, sodium hydroxide, sulfuric acid), in manufacturing processes (e.g., glassmaking, soap production), and in construction (e.g., plaster of Paris).
• In Agriculture: Fertilizers often contain salts of nitrogen, phosphorus, and potassium.

Fun Fact

The Dead Sea, known for its high salt concentration, is so buoyant that people can easily float on its surface. This is due to the high concentration of dissolved salts, which increases the water’s density.

History or Discovery

The concept of salts has been known for centuries. The use of salt (sodium chloride) dates back to ancient times for food preservation and other purposes. The understanding of the chemical nature of salts and their formation through acid-base reactions developed over time with the advancements in chemistry, starting with the work of Antoine Lavoisier.

FAQs

1. What is the difference between an acid, a base, and a salt?

An acid donates hydrogen ions ($H^+$), a base accepts hydrogen ions or donates hydroxide ions ($OH^−$), and a salt is formed when an acid and a base react, usually with the formation of water ($H_2O$).

2. How does the pH of a salt solution depend on the strength of the acid and base?

The pH of a salt solution depends on the strength of the acid and base. Salts from strong acid + strong base = neutral (pH 7). Salts from strong acid + weak base = acidic (pH < 7). Salts from weak acid + strong base = basic (pH > 7).

3. Why is salt added to food?

Salt is added to food for flavor enhancement and preservation. It inhibits the growth of microorganisms that cause food spoilage.

Recommended YouTube Videos for Deeper Understanding

Q.1 When 10 g of calcium carbonate ($CaCO_3$) is heated strongly, it decomposes to form 5.6 g of calcium oxide ($CaO$) and carbon dioxide ($CO_2$). What mass of $CO_2$ is produced?

Check Solution

Ans: B

According to the Law of Conservation of Mass, the total mass of reactants equals the total mass of products. Therefore, mass of $CO_2$ = mass of $CaCO_3$ – mass of $CaO$ = 10 g – 5.6 g = 4.4 g

Q.2 In a chemical reaction, 2 g of hydrogen gas reacts completely with 16 g of oxygen gas to produce water ($H_2O$). What is the ratio of the masses of hydrogen and oxygen in water?

Check Solution

Ans: B

The mass ratio of hydrogen to oxygen is 2 g : 16 g = 1:8

Q.3 A sample of pure water, regardless of its source, is found to contain 11.1% hydrogen and 88.9% oxygen by mass. This observation supports which law?

Check Solution

Ans: C

The Law of Constant Proportions states that a chemical compound always contains the same elements in the same proportions by mass.

Q.4 If 6 g of carbon reacts completely with 16 g of oxygen to form carbon dioxide ($CO_2$), what mass of oxygen is required to react completely with 3 g of carbon?

Check Solution

Ans: B

According to the Law of Constant Proportions, the ratio of masses of C and O in $CO_2$ is constant. If 6 g C reacts with 16 g O, then 3 g C reacts with (16 g / 6 g) * 3 g = 8 g O.

Q.5 The decomposition of 100 g of mercuric oxide ($HgO$) produces 92.6 g of mercury ($Hg$) and oxygen gas ($O_2$). What mass of oxygen gas is produced?

Check Solution

Ans: A

According to the Law of Conservation of Mass, the total mass of reactants equals the total mass of products. Therefore, mass of $O_2$ = mass of $HgO$ – mass of $Hg$ = 100 g – 92.6 g = 7.4 g

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