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Acids, Bases and Salts

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  • Last Updated : 27 Sep, 2021

We have a good understanding of acids and bases in modern chemistry (also called alkalis). Acids and bases are utilized as laboratory reagents, industrial catalysts, culinary additives, and cleaning products, and they pervade our life from the laboratory to the kitchen. However, it took centuries for chemists to completely comprehend these chemicals over the course of history. 

What are Acids?

An acid is a molecule that can contribute an H+ ion while also remaining energetically favourable after losing that ion. e.g. Sulfuric acid (H2SO4), Acetic Acid (CH3COOH), Nitric Acid (HNO3) etc.

Following are some physical properties of acids:

  1. Acids have a sour flavour to them.
  2. Blue litmus turns red.
  3. Electricity can be conducted through an acidic solution.
  4. In an aqueous solution, release H+ ions.

Following are some chemical properties of acids: 

  • The reaction of acids with metal: When an acid reacts with a metal, it produces hydrogen gas and the corresponding salt. 

Metal + Acid → Salt + Hydrogen

e.g. When hydrochloride acid combines with zinc metal, it produces hydrogen gas and zinc chloride.

Zn + 2HCl  → ZnCl2 + H2 

  • The reaction of acids with metal carbonate: When acids react with metal carbonates, they produce carbon dioxide gas and salts as well as water.

Metal carbonate + Acid → Salt + Carbon dioxide + Water

e.g. When hydrochloric acid combines with sodium carbonate, it produces carbon dioxide gas, sodium chloride, and water.

 Na2CO3 + 2HCl → 2NaCl + H2O + CO2

  • The reaction of an acid with hydrogen carbonates (bicarbonates): When acids react with metal hydrogen carbonate, they produce carbon dioxide gas, salt, and water.

Acid + Metal hydrogen carbonate → Salt + Carbon dioxide + Water

e.g. Sulfuric acid gives sodium sulfate, Carbon dioxide gas and water when it reacts with sodium bicarbonate.

2NaHCO3 + H2SO4 → NaCl + CO2 + H2O

Types of Acids

Acids are classified on different bases like:

  • On the basis of their occurrence, they are subdivided into two Natural and Mineral Acids.
    1. Natural Acid: Natural acids, often known as organic acids, are acids derived from natural sources. For example Methanoic acid (HCOOH), Acetic acid (CH3COOH), Oxalic acid (C2H2O4) etc.
    2. Mineral Acids: Mineral acids are acids that are created from minerals. Inorganic acids, man-made acids, and synthetic acids are all examples of Mineral Acids. For example Hydrochloric acid (HCl), Sulphuric acid (H2SO4), Nitric acid (HNO3), Carbonic acid (H2CO3), Phosphoric acid (H3PO4) etc.
  • On the basis of concentration, acids are categorized as Strong and Weak acids.
    1. Strong Acids: Strong Acid is an acid that is totally ionized in water and produces (H+). For example Hydrochloric acid (HCl), Sulphuric acid (H2SO4), Nitric acid (HNO3) etc.
    2. Weak Acids: A weak acid is one that is partially ionized in water and hence creates a tiny amount of hydrogen ions (H+). For example Acetic acid (CH3COOH), Carbonic acid (H2CO3) etc. 

Applications of Acids:

  1. Vinegar is a diluted solution of acetic acid that has a variety of uses in the home. It’s mostly utilized in the food industry as a preservative.
  2. Orange and lemon juice contain a significant amount of citric acid. It can also be used for food preservation.
  3. In batteries, sulfuric acid is commonly utilized. This acid is typically found in the batteries used to start vehicle motors.
  4. Sulfuric and nitric acid is used in the industrial production of dyes, explosives, paints, and fertilizers.
  5. Many soft drinks contain phosphoric acid as the main ingredient.

What are Bases?

The term “alkali” refers to a base that can be dissolved in water. When these compounds react chemically with acids, they produce salts and hydroxide ions (OH) in water. For example Potassium hydroxide (caustic potash or KOH), Calcium hydroxide (Ca(OH)2), Sodium hydroxide (caustic soda or NaOH) etc.

Following are some physical properties of bases:

  1. It has a bitter taste to it.
  2. To the touch, it feels soapy.
  3. Changes the colour of red litmus to blue.
  4. In solution, it conducts electricity.
  5. In an aqueous solution, release OH ions

Following are some chemical properties of bases:

  • The reaction of Base with Metals: When alkali (base) reacts with metal, salt and hydrogen gas is produced.

Alkali + Metal → Salt + Hydrogen

For Example: When sodium hydroxide interacts with aluminium metal, sodium aluminate and hydrogen gas are generated.

2NaOH + 2Al + 2H2O → 2NaAlO2 + 2H2

  • The reaction of Non-Metallic Oxides with Base: Salt and water are formed when non-metallic oxides react with a base.

Non-metallic oxide + Base → Salt + Water

For Example:

Ca(OH)2 + CO2 → CaCO3 + H2O

  • The action of Alkalis/Base with Ammonium Salts: Ammonia is produced when alkalis react with ammonium salts.

Alkali + Ammonium salt   →   Salt   +  Water  +  Ammonia

For Example:

When calcium hydroxide reacts with ammonium chloride, calcium chloride, water, and ammonia are produced.

Ca(OH)2 + NH4Cl  →  CaCl2 + H2O + NH3

Types of Bases

Acidity, concentration, and degree of ionization are three variables that can be used to classify bases.

  • Types of Bases Based on Acidity: Acidity in bases is determined by the number of hydroxyl ions present. Based on acidity, bases are classified into three categories:
    1. Monoacidic: Mono acidic bases are those that contain only one hydroxyl ion and interact with only one hydrogen ion. Mono acidic bases include NaOH, KOH, and others.
    2. Diacidic: Di acidic base is a base with two hydroxyl ions that interact with two hydrogen ions. Ca(OH)2, Mg(OH)2, and other di acidic bases are examples.
    3. Triacidic: Triacidic base is a type of base that comprises three hydroxyl ions and three hydrogen ions. Triacidic bases include Al(OH)3, Fe(OH)2, and others.
  • Types of Bases Based on their Concentration in Aqueous Solution: Based on their concentration in an aqueous solution, bases are divided into two categories:
    1. Concentrated: The concentration of base in these types of bases is higher in the solution. Concentrated NaOH solution, for example.
    2. Diluted: These types of bases have a lower concentration of base in their aqueous solution. For instance, dilute NaOH, dilute KOH, and so on.
  • Types of Bases Based on Their Degree of Ionization: The degree of ionization of bases in solution can be used to classify them. It’s also known as foundation strength. When dissolved in water, it produces a certain quantity of hydroxyl ions. The degree of ionization distinguishes two types of bases.
    1. Strong: A strong base is one that dissociates entirely or to a large extent in water. For instance, NaOH, KOH, and so forth.
    2. Weak: A weak base is one that does not dissolve entirely or only dissociates to a very little level. For instance, NH4OH, and so on.

Applications of Bases:

  1. Sodium hydroxide is used in the making of paper and soap. The sodium hydroxide (NaOH) is also utilized in the production of rayon.
  2. Bleaching powder is made from Ca(OH)2, commonly known as calcium hydroxide or slaked lime.
  3. Calcium hydroxide is used to create dry mixtures for painting and decorating.
  4. Magnesium hydroxide, popularly known as milk of magnesia, is a laxative that is extensively used. It is also used as an antacid since it decreases excess acidity in the human stomach.
  5. In laboratories, ammonium hydroxide is a critical reagent.
  6. Slaked lime can be used to neutralize any excess acidity in soils.

What are Salts?

When an acid and a base react to neutralise one another, they generate sales, which are ionic substances. Salts do not have an electrical charge. Salts come in a variety of forms, the most common of which being sodium chloride. Table salt or common salt are both terms for sodium chloride. Sodium chloride is used to make dishes taste better.

Following are some physical properties of Salts:

  1. In nature, the bulk of the salts are crystalline.
  2. Salts that are transparent or opaque are available.
  3. The bulk of salts are soluble in water.
  4. Salt solutions, in their molten state, also transmit electricity.
  5. The flavour of salt can be salty, sour, sweet, bitter, or umami (savoury).
  6. There is no odour to neutral salts.
  7. Salts that are colourless or coloured are available.
  8. Because it contains ions, saltwater is an excellent conductor of electricity.
  9. Electrostatic attraction holds the ions together, and a chemical bond is established between them..

Types of Salts

  1. Acidic salt- A partial neutralisation of a diprotic or polyprotic acid produces an acidic salt. These salts contain both an icon and a cation that can be ionised. The ionizable H+ makes up the majority of the anion. Certain acid salts are used in baking. e.g. NaHSO4­, KH2PO4 etc.
  2. Basic or Alkali Salt- A basic salt is formed when a strong base reacts with a weak acid to partially neutralise it. When they are hydrolyzed, they decompose into a basic solution. This is because when a basic salt is hydrolyzed, it produces the conjugate base of a weak acid in the solution. e.g. White lead (2PbCO3·Pb(OH)2) etc.
  3. Double salt- Salts with more than one cation or anion are known as double salts. They’re created by mixing two different salts that crystallised in the same ionic lattice. e.g. Potassium sodium tartrate (KNaC4H4O6.4H2O) also known as Rochelle salt.
  4. Mixed Salts- A preset mixing of two salts, which generally share a common cation or anion, is called mixed salt. e..g. CaOCl2.

Neutral, Acidic and Basic Salts

Neutral Salts: Salts generated by the reaction of a strong acid with a strong base are neutral in nature. The pH of these salts is 7, which is considered neutral. Potassium chloride, sodium chloride, and sodium sulphate

For example:

  • Sodium chloride (NaCl):  When hydrochloric acid (a strong acid) mixes with sodium hydroxide, it produces it (a strong base).

NaOH + HCl → NaCl + H2O

  • Sodium Sulphate (Na2SO4): It’s made when sulphuric acid combines with sodium hydroxide (a strong basic) ( a strong acid).

2NaOH + H2SO4 → Na2SO4 + 2H2O

Acidic Salts: Acidic salts are the salts formed when a strong acid reacts with a weak base. The pH of acidic salt is less than 7. Examples include ammonium sulphate, ammonium chloride, and various ammonium compounds.

For example:

  • Ammonium chloride: Ammonium chloride is formed when hydrochloric acid (a strong acid) interacts with ammonium hydroxide (a weak base).

NH4OH + HCl → NH4Cl + H2O

  • Ammonium sulphate: Ammonium sulphate is formed when ammonium hydroxide (a weak basic) reacts with sulphuric acid (a strong acid).

2NH4OH + H2SO4 → (NH4)2SO4 + 2H2O

Basic Salts: The salts formed when a weak acid reacts with a strong base are known as basic salts. Examples include sodium carbonate, sodium acetate, and other salts.

For example:

  • Sodium carbonate: Sodium carbonate is formed when sodium hydroxide (a strong base) reacts with carbonic acid (a weak acid)

H2CO3 + 2NaOH → Na2CO3 + H2O

  • Sodium acetate: Sodium acetate is formed when a strongly basic, sodium hydroxide (a strong base), reacts with acetic acid (a weak acid)

CH3COOH + NaOH → CH3COONa + H2O

What is the cause of the formation of acidic, basic and neutral salts?

  • When a strong acid reacts with a weak base, the base is unable to completely neutralise the acid. As a result, a salt that is acidic forms.
  • When a strong base is combined with a weak acid, the acid is unable to completely neutralise it. As a result, you get a simple salt.
  • When an equal-strength acid and base react, they totally neutralise each other. A neutral salt is formed as a result of this process.

Sample Questions

Question 1: When HCl combines with salt, what happens?

Answer:

The acid is dilute hydrochloric acid, and the metal is iron in this example. To make iron (II) chloride and hydrogen, dilute hydrochloric acid is poured to the iron filings. Iron substitutes hydrogen from hydrochloric acid in this process, resulting in iron chloride and hydrogen. This is a basic displacement reaction for gas.

Question 2: What is the most important distinction between an acid and a base?

Answer:

Acids and bases are two types of corrosive chemicals. Acidic materials have a pH value between 0 and 7, while bases have a pH value between 7 and 14. Acids are ionic chemicals that break down in water to create the hydrogen ion (H+).

Question 3: What are the physical properties of bases?

Answer:

  • They have a bitter taste to them.
  • Their aqueous solutions have a soapy quality to them.
  • They change the colour of litmus paper from red to blue.
  • Their aqueous solutions are electrically conductive.
  • With the release of hydrogen gas, bases react with metals to generate salt.

Question 4: When the pH of the mouth falls below 5.5, why does tooth decay begin?

Answer:

When the pH of our mouth falls below 5.5, tooth decay begins. This is because below this pH value, the mouth’s medium becomes more acidic, causing tooth enamel to deteriorate more quickly.

Question 5: Write the physical properties of acids.

Answer:

The properties of the acids are:

  • Acids have a sour flavour to them.
  • Blue litmus turns red.
  • Electricity can be conducted through an acidic solution.
  • In an aqueous solution, release H+ ions.

Question 6: What will happen when sodium hydroxide interacts with aluminium metal?

Answer:

When sodium hydroxide interacts with aluminium metal, sodium aluminate and hydrogen gas are generated

                                    2NaOH + 2Al + 2H2O → 2NaAlO2 + 2H2

Question 7: What will happen when hydrochloric acid combines with sodium carbonate?

Answer:

When hydrochloric acid combines with sodium carbonate, it produces carbon dioxide gas, sodium chloride, and water.

                                             Na2CO3 + 2HCl → 2NaCl + H2O + CO2


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