ACIDS, BASES AND SALTS.

 ACIDS, BASES AND SALTS.

Acids

Acids are substances that, when dissolved in water, donate protons or hydrogen ions (H⁺). This donation or acceptance of protons characterizes their acidic properties. Acids generally have a sour taste, turn blue litmus paper red, and have a pH less than 7. Examples

• Hydrochloric acid (HCl)
• Sulfuric acid (H₂SO₄)
• Nitric acid (HNO₃)
• Acetic acid (CH₃COOH)
• Citric acid (found in citrus fruits like lemons and oranges)
• Lactic acid (found in sour milk and yogurt)
• Tartaric acid (found in grapes and tamarinds)
• Malic acid (found in apples and sour cherries)

Types Based on Source

Inorganic Acids

Inorganic acids are derived from inorganic compounds that are mixed in the laboratories in some specific ways and proportions. Examples Hydrochloric acid (HCl), Sulfuric acid (H₂SO₄) and Nitric acid (HNO₃).

 

Organic Acids

Organic acids are derived from organic compounds obtained from plants and animal sources. Examples include;

• Acetic acid      (CH₃COOH)   Found in vinegar.
• Citric acid       (C₆H₈O₇)         Found in citrus fruits.
• Lactic acid      (C₃H₆O₃)         Formed during fermentation in dairy products.
• Tartaric acid    (C₄H₆O₆)         Found in grapes and tamarinds.
• Malic acid       (C₄H₆O₅)         Found in apples and sour cherries.
• Formic acid     (HCOOH)       Found in ant venom and some plants.
• Butyric acid    (C₄H₈O₂)         Found in butter and Parmesan cheese.
• Benzoic acid   (C₇H₆O₂)         Found naturally in many fruits.

 

Bases

Bases are substances that, when dissolved in water, either donate hydroxide ions (OH⁻) or accept protons. Bases are characterized by their bitter taste, slippery feel, and ability to turn red litmus paper blue. They typically have a pH greater than 7. Examples:

• Sodium hydroxide (NaOH)
• Potassium hydroxide (KOH)
• Ammonia (NH₃)
• Calcium hydroxide (Ca(OH)₂)
• Magnesium hydroxide (Mg(OH)₂)
• Aluminum hydroxide (Al(OH)₃)
• Sodium bicarbonate (NaHCO₃)
• Barium hydroxide (Ba(OH)₂)

Types based on Source

Inorganic Bases

Inorganic acids are derived from the combination of measured amounts of inorganic compounds in some specific ways.

• Sodium hydroxide (NaOH)
• Potassium hydroxide (KOH)
• Calcium hydroxide (Ca(OH)₂)

 

Organic Bases

Organic bases are derived from organic compounds obtained from plants and animals.

• Ammonia (NH₃)
• Sodium bicarbonate (NaHCO₃)
• Trimethylamine (CH₃)₃N
• Aniline (C₆H₅NH₂)
• Guanidine (C(NH₂)₃)
• Morphine (C₁₇H₁₉NO₃) - Weak organic base found in opium.
• Caffeine (C₈H₁₀N₄O₂) - Weak organic base found in coffee and tea.
• Nicotine (C₁₀H₁₄N₂) - Weak organic base found in tobacco.

 

Salts

Salts are ionic compounds formed by the reaction between an acid and a base. They are composed of positively charged ions (cations) and negatively charged ions (anions). Salts can be neutral or normal, acidic, basic, or double salts, depending on their composition and formation process.

Examples:

• Sodium chloride (NaCl)
• Calcium carbonate (CaCO₃)
• Potassium nitrate (KNO₃)
• Magnesium sulfate (MgSO₄)
• Ammonium chloride (NH₄Cl)
• Sodium acetate (CH₃COONa)
• Calcium sulfate (CaSO₄)
• Potassium sulfate (K₂SO₄)

 

Types of Salts:

Normal Salts: Normal salts are formed by the complete neutralization of an acid with a base. Normal salts are formed when all the replaceable hydrogen in an acid is replaced by a metal or ammonium ion (NH₄⁺). Examples are Sodium chloride (NaCl) and Potassium nitrate (KNO₃).

Acid Salts

Formed when a part of the hydrogen in the acid remains unreacted or when only part of the replaceable hydrogen in an acid is replaced by a metal or ammonium ion. Examples are Sodium dihydrogen phosphate (NaH₂PO₄) and Ammonium sulfate ((NH₄)₂SO₄).

 

Basic Salts: Formed when a part of the hydroxide in the base remains unreacted, or when there is insufficient acid available to neutralize all the base in a reaction. Examples are

• Sodium Acetate                     CH₃COONa
• Potassium Carbonate           K₂CO₃
• Ammonium Carbonate        (NH₄)₂CO₃
• Calcium Acetate                    Ca(CH₃COO)₂
• Magnesium Carbonate         (MgCO₃)₂

 

Double Salts: Formed when two different salts are crystallized together.

1. Mohr's Salt or Ammonium Iron(II) Sulfate Hexahydrate -  (NH₄)₂Fe(SO₄)₂·6H₂O
2. Carnallite or Potassium Magnesium Chloride Hexahydrate - KCl·MgCl₂·6H₂O
3. Alum or Potassium Aluminum Sulfate Dodecahydrate - KAl(SO₄)₂·12H₂O
4. Tutton's Salt or Potassium Sodium Tartrate Tetrahydrate - KNaC₄H₄O₆·4H₂O
5. Green Vitriol or Iron(II) Ammonium Sulfate Hexahydrate - (NH₄)₂Fe(SO₄)₂·6H₂O

 

Properties and Uses of Acids:

1. Sour Taste: Example: Lemon juice.
2. Corrosive: Example: Sulfuric acid can corrode metals.
3. Conductivity: Acids conduct electricity when dissolved in water. Example: Hydrochloric acid solution.
4. Reactivity: Acids react with bases to form salts and water. Example: Neutralization reaction: HCl + NaOH → NaCl + H₂O.
5. pH: Acids have a pH less than 7. Example: pH of hydrochloric acid is around 1.
6. Turn Litmus Paper Red: Example: Hydrochloric acid turns blue litmus paper red.
7. Preservation: Acids are used as preservatives in food. Example: Citric acid in fruits.
8. Cleaning: Acids are used in cleaning agents. Example: Vinegar (acetic acid) for cleaning surfaces.

 

Properties of Bases:

1. Bitter Taste: Example: Baking soda (sodium bicarbonate).
2. Slippery Feel: Example: Soap.
3. Corrosive: Strong bases can corrode organic matter. Example: Sodium hydroxide.
4. Conductivity: Bases conduct electricity when dissolved in water. Example: Sodium hydroxide solution.
5. pH: Bases have a pH greater than 7. Example: pH of sodium hydroxide is around 13.
6. Turn Litmus Paper Blue: Example: Sodium hydroxide turns red litmus paper blue.
7. Neutralization: Bases neutralize acids to form salts and water. Example: NaOH + HCl → NaCl + H₂O.
8. Medicinal Uses: Bases are used in antacids to neutralize excess stomach acid. Example: Magnesium hydroxide (in milk of magnesia).

 

Properties of Salts:

1. Ionic Nature: Salts are composed of ions held together by ionic bonds. Example: Sodium chloride.
2. Solubility: Some salts are soluble in water, while others are insoluble. Example: Sodium chloride is soluble, while silver chloride is insoluble.
3. Conductivity: Salts conduct electricity when dissolved in water. Example: Sodium chloride solution.
4. pH: Depending on the salt, its solution can be acidic, basic, or neutral. Example: Sodium acetate solution is slightly basic.
5. Formation of Crystals: Salts often form crystals when they precipitate from a solution. Example: Epsom salt (magnesium sulfate) crystals.
6. Melting and Boiling Points: Salts generally have high melting and boiling points due to strong ionic bonds. Example: Sodium chloride has a melting point of 801°C.
7. Hygroscopic Nature: Some salts absorb moisture from the air. Example: Calcium chloride.
8. Food Preservation: Salts are used in food preservation to inhibit microbial growth. Example: Sodium nitrate in cured meats.

 

pH Indicators

pH indicators are substances that undergo characteristic color changes at different pH levels, making them useful tools in determining the acidity or basicity of a solution. They are commonly used in laboratories, industries, and even at home for various applications like titrations, quality control, and educational demonstrations.

1.      Litmus and Litmus Papers

a. Litmus:

1. Original Color: Litmus is a naturally occurring dye extracted from lichens. It is purple in its neutral form.
2. Behavior in Acids: Turns red in acidic solutions due to the formation of the lactone form of litmus.
3. Behavior in Bases: Turns blue in basic solutions due to the formation of the alkaline form of litmus.
4. Application: Litmus is used as a simple pH indicator in various forms, including litmus paper strips, to test the pH of solutions qualitatively.

 

b. Litmus Papers:

Composition

Litmus papers are typically made by impregnating paper with litmus solution or by soaking paper in litmus dye. There three types and these are Red litmus paper, Blue litmus paper and Universal litmus paper.

 

Usage

Litmus papers are convenient and inexpensive tools for quick pH tests. They are available in red and blue varieties, with the former used to test for acidity and the latter for basicity.

 

2.      Methyl Orange:

• Original Color: Methyl orange is an azo dye that is red in its acidic form.
• Behavior in Acids: Remains red in acidic solutions.
• Behavior in Bases: Turns yellow in basic solutions.
• Application: Methyl orange is commonly used in titrations, particularly those involving strong acids and bases, due to its sharp color change at the equivalence point.

 

3. Phenolphthalein:

• Original Color: Phenolphthalein is colorless.
• Behavior in Acids: Remains colorless.
• Behavior in Bases: Turns pink in basic solutions due to the formation of the ionized form of phenolphthalein.
• Application: Phenolphthalein is widely used in acid-base titrations, especially those involving weak acids and strong bases, where its color change at the endpoint indicates the completion of the reaction.

 

4. Methyl Blue

• Original Color: Methyl blue is blue in its neutral form.
• Behavior in Acids: Turns yellow in acidic solutions due to protonation.
• Behavior in Bases: Returns to its blue color in basic solutions.
• Application: Methyl blue is used as an indicator in various chemical reactions, including redox titrations, where it undergoes reversible color changes depending on the pH of the solution.

pH, pH Meter, pH Value, and pH Scale:

1. pH (Potential of Hydrogen)

pH is a measure of the acidity or alkalinity of a solution. It quantifies the concentration of hydrogen ions ([H⁺]) in a solution. The pH scale ranges from 0 to 14, where:

• pH < 7 indicates acidity (higher [H⁺] concentration).
• pH = 7 indicates neutrality (equal [H⁺] and [OH-] concentrations in pure water at 25°C).
• pH > 7 indicates alkalinity (lower [H⁺] concentration).

Mathematically, pH is defined as the negative logarithm of the hydrogen ion concentration: pH = -log[H⁺].

 

2. pH Meter

A pH meter is a scientific instrument used to measure the pH of a solution accurately. It consists of:

• pH electrode: A glass electrode sensitive to hydrogen ion concentration.
• Reference electrode: Often a silver-silver chloride electrode immersed in a solution with a fixed [H⁺].
• pH meter device: It measures the potential difference between the pH electrode and the reference electrode.

Different types of pH meters

Operation

The pH meter measures the electromotive force (EMF) between the two electrodes and converts it into a pH value. Calibration using standard buffer solutions is necessary to ensure accurate measurements.

 

3. pH Value

pH value represents the acidity or alkalinity level of a solution on the pH scale. It is a logarithmic scale, meaning each unit change represents a tenfold change in [H⁺]. For example, a solution with pH 3 is ten times more acidic than a solution with pH 4.

pH values provide essential information about chemical reactions, biological processes, and environmental conditions.

 

4. pH Scale

The pH scale is a logarithmic scale ranging from 0 to 14 that represents the acidity or alkalinity of a solution. Each unit change on the pH scale represents a tenfold change in [H⁺]. pH scale is widely used in various fields including chemistry, biology, environmental science, and industry to describe and quantify the acidity or alkalinity of solutions.

pH Scale

Description: This diagram illustrates the pH scale ranging from 0 to 14, with labels indicating acidic, neutral, and alkaline pH levels.

USES OF ACIDS BASES AND SALTS

Acids and Their Uses

1. Hydrochloric Acid (HCl)
• Used in digestion as gastric acid in the stomach
• Helps in metal cleaning and pickling (removes rust)
• Used in the production of PVC (polyvinyl chloride)
• Helps regulate pH in swimming pools
• Used in household cleaners and toilet cleaners
2. Sulfuric Acid (H₂SO₄)
• Used in car batteries (lead-acid batteries)
• Essential in making fertilizers (phosphates, ammonium sulfate)
• Used in petroleum refining
• Helps in textile and dye production
• Used in making detergents and soaps
3. Nitric Acid (HNO₃)
• Used in manufacturing fertilizers (ammonium nitrate)
• Helps in making explosives (TNT, nitroglycerin)
• Used in refining metals like gold and silver
• Important for etching and engraving metals
• Used in the production of plastics
4. Acetic Acid (CH₃COOH)
• Used in vinegar for cooking and food preservation
• Helps in the production of synthetic fibers (like acetate)
• Used in making adhesives and glues
• Helps in rubber and plastic processing
• Used as a food additive and flavoring agent
5. Citric Acid (C₆H₈O₇)
• Used as a preservative in soft drinks and food
• Helps in cleaning agents for removing limescale
• Used in cosmetics and skincare products
• Essential in pharmaceutical products (vitamin C supplements)
• Acts as a pH regulator in food and drinks

 

Bases and Their Uses

6. Sodium Hydroxide (NaOH)
• Used in soap and detergent production
• Helps in unclogging drains (drain cleaner)
• Used in paper manufacturing
• Essential in textile processing
• Used in refining petroleum products
7. Calcium Hydroxide (Ca(OH)₂) – Slaked Lime
• Used in making cement and mortar
• Helps in neutralizing acidic soil in agriculture
• Used in water purification and treatment
• Helps in the sugar refining process
• Used in making whitewash for walls
8. Ammonium Hydroxide (NH₄OH)
• Used in household cleaners
• Helps in making fertilizers (ammonium salts)
• Used in rubber and plastic manufacturing
• Helps in textile processing
• Used in photographic development
9. Magnesium Hydroxide (Mg(OH)₂) – Milk of Magnesia
• Used as an antacid for indigestion relief
• Helps in wastewater treatment
• Used as a laxative
• Helps in flame retardants
• Used in deodorants and cosmetics
10. Potassium Hydroxide (KOH)

• Used in making liquid soaps
• Helps in alkaline batteries
• Used in biodiesel production
• Helps in food processing (chocolate, soft drinks)
• Used in fertilizers for potassium supply

 

Salts and Their Uses

11. Sodium Chloride (NaCl) – Table Salt

• Used for cooking and seasoning food
• Helps in food preservation
• Used in de-icing roads in winter
• Helps in manufacturing chlorine and sodium hydroxide
• Used in saline solutions for medical treatments

12. Baking Soda (Sodium Bicarbonate - NaHCO₃)

• Used as a baking ingredient (leavening agent)
• Helps in treating acid indigestion (antacid)
• Used in cleaning and deodorizing
• Used in fire extinguishers
• Helps in personal care (toothpaste, skin care)

13. Calcium Carbonate (CaCO₃)

• Used in making chalk and blackboard writing materials
• Helps in cement and concrete production
• Used in antacids for treating acidity
• Used in water treatment to reduce acidity
• Helps in making glass and ceramics

14. Epsom Salt (Magnesium Sulfate - MgSO₄)

• Used in bath salts for relaxation
• Helps in relieving muscle pain
• Used as a fertilizer to boost plant growth
• Helps in treating magnesium deficiency in the body
• Used in skin and beauty care products

15. Potassium Nitrate (KNO₃) – Saltpeter

• Used in fertilizers for plant growth
• Helps in making gunpowder and fireworks
• Used as a food preservative
• Helps in making toothpaste for sensitive teeth
• Used in the glass and ceramics industry