Chapter 2: Acid base and Salts notes

The chemical compounds around us can easily be categorised as Acids, Bases and Salts. Acids, Bases and Salts are compounds which occur naturally and can also be created artificially. They are found in various substances including our food. Vinegar or acetic acid is used as a food preservative. Citrus fruits have citric acid and etc.

Other than food they also have a wide variety of uses such as in various industries, manufacturing plants, processing plants, laboratories and others. In this article, we will learn about Acids, Bases, and Salts, their properties, types, uses and others in detail. The image given below shows acid and base which when reacting form salt.

Acid, Base and Salts

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. The image given below shows an acid in its aqueous medium.


Physical Properties of Acid

Acids have specific physical properties and they can easily be distinguished by their physical properties. Some physical properties of acids are:

Chemical Properties of Acid

Acid has various chemical properties few of the following chemical properties of acids include, 

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

Metal + Acid → Salt + Hydrogen

Example: When hydrochloride acid combines with zinc metal, it produces hydrogen gas and zinc chloride.

Zn + 2HCl  → ZnCl2 + H2 

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

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

 Na2CO3 + 2HCl → 2NaCl + H2O + CO2

Reaction of acid with hydrogen carbonates (bicarbonates): When acids react with metal hydrogen carbonates, they produce carbon dioxide gas, salt, and water.

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

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

2NaHCO3 + H2SO4 → NaCl + CO+ H2O

Types of Acids

Acids are classified into different categories, the classification of acids is discussed below in the article.

On the basis of their Occurrence 

On the basis of their Occurrence  acid are subdivided into two categories

  • Natural Acid
  • Mineral Acids

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.

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

On the basis of Concentration, acids are categorized into two categories

  • Strong Acid
  • Weak Acid

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.

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. 

Uses of Acids

Acids have various uses some of the important uses of acid are,

  • 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.
  • Orange and lemon juice contain a significant amount of citric acid. It can also be used for food preservation.
  • In batteries, sulfuric acid is commonly utilized. This acid is typically found in the batteries used to start vehicle motors.
  • Sulfuric and nitric acid is used in the industrial production of dyes, explosives, paints, and fertilizers.
  • Many soft drinks contain phosphoric acid as the main ingredient.

What are Bases?

Bases are chemical compounds that 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. The image given below shows a base in its aqueous medium.


Physical Properties of Base

Bases have specific physical properties and they can easily be distinguished by their physical properties. Some physical properties of bases are:

  • Base has a bitter taste
  • Bases are soapy to touch
  • Base change red litmus to blue
  • Aquaus solution of base conducts electricity

Chemical Properties of Base

Bases have various chemical properties few of the following chemical properties of bases are,

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

Alkali + Metal → Salt + Hydrogen

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

2NaOH + 2Al + 2H2O → 2NaAlO2 + 2H2

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

Example: When calcium hydroxide reacts with carbon dioxide calcium carbonate is formed along with water.

Ca(OH)2 + CO→ CaCO3 + H2O

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

Alkali + Ammonium salt   →   Salt   +  Water  +  Ammonia

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

Ca(OH)2 + NH4Cl  →  CaCl+ H2O + NH3

Acid + Metal  ⇢  Ionic compound + Hydrogen (⇡)

For example,

Zn + 2HCl  ⇢  ZnCl2 + H2 (⇡)

  • They combine with an acid to create salt and water.

Acid + Base  ⇢  Salt + Water

For example,

HCl + NaOH  ⇢  NaCl + H2

Formation of Dilute Acids: How Diluted acids are prepared?

The process of dilution takes place by adding concentrated acid in water with continuous stirring. The process is highly exothermic in nature because of which it cannot be performed in a reverse way. We don’t add water to the concentrated acid as a large amount of heat will evolve and explosions are possible. But when acid is added to water the amount of heat evolved is gradually absorbed by a large amount of water.

Therefore, by adding water to acid, water molecules assist to decrease the concentration of ions in the solution. The pH gradually rises towards 7. As a result, the acid loses its acidity.

While conducting the operation, diluting acids might be quite dangerous. As a result, safety precautions such as lab coats, gloves, and so on should be taken when conducting it. The acid should be introduced to the water after the concentrations of acid and water have been accurately measured. When water is introduced to acid, a large quantity of energy is released, which can produce caustic vapours and droplets to spray on you. Because this heat must be absorbed, it is preferable to add acid to water.

Handling and Storage of Diluted Acids

Acid dilution should be done with adequate safety measures. To avoid injury, we should use suitable PPE such as chemical-resistant aprons, chemical-resistant gloves, and chemical splash goggles when handling them. Breathing should be avoided since certain acids might be harmful if breathed. The dilution should ideally take place in a fume hood.

Small quantities of dilute acids should be stored after carefully marking them with the concentration and pH. Acid chloride and fuming acids should be kept in well-ventilated locations. Flammable liquids should be kept separate and labelled with a warning sign.

Uses of Diluted acid

  • Diluted hydrochloric acid is used for cleaning surfaces, medical treatments, production of batteries, etc.
  • Acetic acid is used as a daily food item and as a cleaning agent.
  • Other acids like sulphuric acid, nitric acid, etc are used in their diluted form in laboratories for educational purposes.

Sample Questions

Question 1: Why are metallic containers made of brass has a coating of tin?


Metals are reactive to acid and form corresponding ionic compounds. But tin is nonreactive to acids which prevent the poisoning of food.

Question 2: Why it is recommended to add acid in water during dilution of acid?


It is recommended to add acid to water during the process because the process is highly exothermic in nature. While adding acid gradually in to the water the amount of heat produced is absorbed by the large amount of water.

Question 3: Why food items like curd and other dairy products should not be stored in copper vessels?


The dairy products like curd contains lactic acid. When we store acidic food in brass or copper vessels they react with the given metal and form corresponding compounds which causes food poisoning.

Question 4: What will happen if water is added to concentrated acid?


If water is added to any concentrated acid a large amount of heat will evolve which will change some of the water into vapor and acid will splash all over.

Question 5: What happens to the pH value of a diluted acid?


The pH value of a substance depends on the concentration of hydrogen ions (H+) in it. The pH value of acid is directly proportional to its level of dilution. Hence, diluted acid has a higher pH value than concentrated acid.

Question 6: How to store diluted acid?


Diluted acids should be stored in small quantities with proper labeling mentioning about its concentration level and pH value. Also, a warning should be written on the container if the liquid is flammable or a fuming acid. Fuming acids should be packed in ventilated areas. And flammable acids should also be kept separately in checked temperature. 

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.
Strong Base
Weak Base
Strong Base: A strong base is one that dissociates entirely or to a large extent in water. For example, NaOH, KOH, and strong bases.
Weak Base: A weak base is one that does not dissolve entirely or only dissociates to a very little level. For example, NH4OH, and others are weak bases.
Uses of Bases
Base has various uses some of the important uses of the base are,
Sodium hydroxide is used in the making of paper and soap. Sodium hydroxide (NaOH) is also utilized in the production of rayon.
Bleaching powder is made from Ca(OH)2, commonly known as calcium hydroxide or slaked lime.
Calcium hydroxide is used to create dry mixtures for painting and decorating.
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.
In laboratories, ammonium hydroxide is a critical reagent.
Slaked lime can be used to neutralize any excess acidity in soils.
Bases which are easily dissolved in water are called Alkali, in other words, water-soluble bases are called Alkali. For example, NaOH is an alkali as it dissolves in water forming Naand OH ions.
Difference between Alkali and Base
The difference between Alkali and Base can easily be understood with the help of the table given below,
Water soluble bases are called alkali
Bases do not dissolve in water
All alkalis are bases
Not all bases are alkali
Alkali releases OH ions on dissolving in water, they also are proton acceptors.
Bases neutralise the acid in an acid-base neutralization reaction.
Example: Potassium Hydroxide (KOH), Sodium Hydroxide(NaOH)
Example: Zinc hydroxide(ZnOH), Copper Oxide(CuO)

pH Scale

pH scale is used to measure the basicity and acidity of a solution. It gives the strength of any solution. pH is determined by the amount of hydrogen ion concentration in the solution.

It is calculated using the formula,

pH = -log[H+]

For an acid, pH ranges from 0 to 7 whereas for a base it ranges between 7 and 14. The lower the pH higher is the strength of the acid and the higher the pH higher the strength of the base.

Note: pH ranges of acids and bases.

  • 0 < Acid < 7
  • 7 < Base< 14


Indicators are chemical compounds which help to indicate the presence of acid or base in a chemical reaction. They possess different colours in acidic solutions and different colours in basic solutions. Indicators are made naturally by plants and animals or artificially by humans. The image shows a litmus test of acids and bases.

Litmus test of acid and base

An indicator indicating the pH

  • The range of 0 to 7 indicates an acidic solution. 
  • The range of 7 to 14 indicates the basic solution.
  • 7 is a neutral solution.

Types of Indicators

There are various types of indicators used for various purposes some of which are,

  • Natural Indicators: Indicators derived from plants, animals or any living organism are natural indicators. Examples, Red Cabbage, Litmus paper and others.
  • Synthetic Indicators:  Indicators made artificially in laboratories and factories are synthetic indicators. Examples, are Phenopthelien, Methyl orange, and others.
  • Olfactory Indicators: Substances that have different smells in acidic or basic mediums are called Olfactory Indicators. Example onions, olives and others.

Olfactory Indicators: 

An olfactory indicator is a chemical that changes its scent depending on whether it’s combined with an acidic or basic solution. In the laboratory, olfactory indicators can be used to determine whether a solution is a basic or an acid, a technique known as olfactory titration. Simply defined, olfactory markers are compounds in acid and basic solutions that have distinct odours. For example, vanilla extract, onion and clove oil, and so on have distinct aromas. Olfactory indicators are very helpful to identify acids or bases for visually impaired students.

Some of the olfactory indicators are as follows:

  • Onion Extract: Onion Extract can be obtained by boiling the water and adding chopped onion into it. When the water cools down, the onion extract is ready. Onion extract shows the change in smell in acid and bases. When it is added to an acid, it retains its pungent smell but in bases, it becomes completely odourless.
  • Vanilla Extract: Vanilla extract works just like onion extract. It retains its pleasant smell in an acidic solution but loses its smell in a basic medium.

Following are the list of the indicators and their colours in acids and bases respectively:

IndicatorColour in AcidColour in Base
Methyl orange RedYellow
Phenolphthalein ColourlessPink
Litmus RedBlue
Turmeric No changeReddish Brown
Red cabbage extract RedBluish Green
Onion extract No colour changeRetains its smellNo colour changeBecomes odourless 
Vanilla Extract No colour change Retains its pleasant smell No colour change Loses its smell 

Importance of Indicators

The nature of a material is significant in biology, chemistry, civil engineering, water purification, agriculture, forestry, food science, environmental science, water treatment, oceanography, medicine, nutrition, and agronomy, among other fields.

Lichens are even used to make litmus. It’s a colour combination that dissolves in water. It is then absorbed into filter paper to create one of the first types of pH indicator, which is used to determine the acidity or basicity of things.

Sample Questions

Question 1: What do you mean by an indicator?


An indicator is generally a weak acid or weak base that dissociates in a solution to form ions. Indicators are used to test whether a medium is acidic or basic in nature.

Question 2: An indicator turned red in HCl and blue in NaOH solution. Identify the indicator.


We know that HCl is acidic in nature and NaOH is basic in nature. As the indicator turned red in acid and blue in base, it is surely litmus.

Question 3: What do you mean by olfactory indicators? Give examples.


Those indicators that change their smell depending upon the acidic or basic nature of the medium are termed as olfactory indicators. Example: Onion extract, Vanilla Extract

Question 4: Red cabbage turned red in a solution while red litmus showed no change in colour. Identify the nature of the solution.


As red cabbage turned red and red litmus did not change its color in the solution, the solution must be acidic in nature.

Question 5: HCl vapours were passed onto a blue litmus paper but it did not show any colour change. Explain.


As we know that indicators show color change when the acid or base dissociates into hydrogen or hydroxide ions. Here HCl was converted to vapors and did not dissociate to ions, thus litmus paper did not show any color change.

Question 6: A stain of turmeric was washed with soap and later lemon was rubbed onto it. Identify the colour changes.


When turmeric stain was rubbed with soap it turned reddish brown in color but it again changes to its original yellow color when lemon is rubbed onto it.

Importance Of pH in Everyday Life

Digestive System 

In the human body, all the physiological reactions take place at the pH of 7 – 7.8. Hydrochloric acid is secreted as food enters the stomach(turns the pH of the stomach between 1 and 3) because of overeating or various reasons excess of HCl (hydrochloric acid) is released. The excess of HCl in the stomach causes indigestion which produces pain and irritation (pH level of the stomach decreases). To cure indigestion, we can take bases called antacids (anti-acid). Antacids are a group of mild bases. Being basic in nature, they react with excess acid in the stomach and neutralise it. (which have no toxic effects on our body)

Common antacids used for curing indigestion due to acidity are:-

  • Milk of Magnesia (Magnesium hydroxide)

Mg(OH)2(s) + 2HCl(aq) → 2H2O(l) + MgCl2(aq)

  • Baking Soda (Sodium hydrogen carbonate)

NaHCO₃ + HCl ➝ NaCl + CO₂ + H₂O

Tooth Decay

When we eat food, the bacteria present in our mouths break down the sugar to form acids. The acid lowers the pH in the mouth making it acidic. When the pH of the mouth falls below 5.5, our tooth starts decaying. Tooth Decay happens because the acid becomes strong enough to attack the enamel (of our teeth) and corrode it. The best way to prevent tooth decay is to clean the mouth thoroughly after eating food. Many kinds of toothpaste contain bases to neutralise mouth acid (The pH of toothpaste being about 8.0). So using toothpaste for cleaning the teeth can neutralise the excess acid in the mouth. 

Plants and Animals are Sensitive to pH changes 

Most of the plants grow best when the pH of the soil is close to 7. If the soil is too acidic (low pH), then it is treated with:-

  • Quicklime (Calcium Oxide)
  • Slaked lime (Calcium Hydroxide)
  • Chalk (Calcium Carbonate).

If the soil is too alkaline then it can be reduced by adding Manure or Compost (decaying organic matter) which contains acidic materials. The pH also plays an important role in the survival of animals, including human beings. The aquatic animals can survive in water bodies within a narrow range of pH change. The high acidity of water bodies can kill aquatic animals. Calcium Carbonate is often added to acidic lake water to neutralise the acid that comes from acid rain.

Self Defence by Animals and Plants through Chemical Warfare

When a honey bee stings a person, it injects Formic Acid into the skin. By rubbing a mild baking soda neutralises the acidic liquid injected by a bee sting. When a wasp stings, it injects an alkaline liquid (Methanoic Acid(HCOOH)) into the skin causing burning pain. By rubbing mild acid vinegar on the stung area gives relief. When a person touches the leaves of a nettle plant, the stinging hair of nettle leaves injects Methanoic Acid into the skin. It can be neutralized by rubbing Baking Soda or Dock Plant which grows beside the nettle plant and is basic in nature.


Lemon juice to clean copper vessels

A dull green coloured film forms on a copper vessel when it is exposed to damp air over an extended period of time. Copper hydroxide (Cu(OH)2) and copper carbonate (CuCO3) are combined to form this greenish layer.

The reaction is,

2Cu + H2O + CO+ O2 ⟶ Cu(OH)2 + CuCO3

Because these goods are basic in nature, acidic substances such as lemon or tamarind juice are required to clean them. These sour compounds are chosen for cleaning since they are good at cleaning copper vessels.

Sample Problems

Question 1: What does the pH value of any solution indicate?


The pH value of any solution indicates whether it is acidic, neutral, or basic. Also, it is used to determine the strength of acid and base.( As we go from 7 to 1 the acidity of the solution increases i.e a solution with pH value of 2 is more acidic than a solution with pH value of 3. The alkalinity of a solution increases from 7 to 14 (opposite to the acidity)  i.e a solution with pH value of 11 is more alkaline than a solution with pH value of 9.)

Question 2: Group the following solutions according to their nature (acidic, basic or neutral) and arrange them in order of their concentration and state which is more acidic and basic (pH values of the solution are given in the bracket):-

Solution 1(8), Solution 2(3), Solution 3(10), Solution 4(7),  Solution 5(13), Solution 6(1)


  • Acidic – Solution 6(1), Solution 2(3)

Solution 6 is the most acidic solution as it has the least pH value.

  • Basic – Solution 5(13), Solution 3(10), Solution 1(8)

Solution 5 is the most basic solution as it has the highest pH value.

  • Neutral – Solution 4(7)

Question 3: What is the normal pH level inside a Human stomach? Why does the pH level decrease while digestion?


In the human body, all the physiological reactions take place at the pH of 7 – 7.8. A decrease in the pH level is observed while digestion because HCl is released inside the stomach to break down the food into simple compounds so it can be absorbed by the body.

Question 4: Name the common antacids used for curing indigestion due to acidity.


Common antacids used for curing indigestion due to acidity are:-

  • Milk of Magnesia (Magnesium hydroxide)

          Mg(OH)(s) + 2HCl (aq) → 2H2O (l) + MgCl(aq)

  • Baking Soda (Sodium hydrogen carbonate)

          NaHCO₃ + HCl ➝ NaCl + CO₂ + H₂O

Question 5: How can you neutralise the effect of Bee stings on a human body? 


When a honey bee stings a person, it injects Formic Acid into the skin. By rubbing a mild baking soda neutralises the acidic liquid injected by a bee sting.


Question 6: What can be added to soil to reduce its acidity and make it suitable for crops to grow?


Following substances can be added to the soil to neutralise its acidity:-

  • Quicklime (Calcium Oxide)
  • Slaked lime (Calcium Hydroxide)
  • Chalk (Calcium Carbonate)

Question 7: You are been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each tube?

Answer :

Put the red litmus paper in all the test tubes turn by turn. The solution which turns red litmus to blue will be a basic solution. The blue litmus paper formed can now be used to test the acidic solution. The solution which turns blue litmus paper to red will be the acidic solution. And the solution which has no effect on any litmus paper will be neutral(i.e distilled water).  

Some Common Salts

Salts are chemical compounds which are formed as a result of a neutralization reaction between acids and bases. When we hear salt we only think about common salt which is Sodium chloride that we eat in our daily life but there are several other salts also which are widely useful. Here in this article, we will learn about some common salt which is widely used.

  • Baking Soda or Sodium Bicarbonate
  • Washing Soda or Sodium Carbonate
  • Bleaching Powder or Calcium Hypochlorite

Baking Soda

Baking soda also called Sodium Hydrogen Carbonate, is a chemical compound whose chemical formula is NaHCO3. Baking soda has a sodium cation (Na+) and a bicarbonate anion (HCO3). Sodium bicarbonate is a white, crystalline powder and as the name suggests is used for baking.

Chemical Name: Sodium hydrogen carbonate

Chemical Formula: NaHCO3


Baking soda can be prepared with the help of the reaction given below.

NaCl(aq) + NH3(g) + CO2(g) + H2O(l) → NaHCO3(aq) + NH4Cl(aq)


A few of the uses of Baking Soda are,

  • It is used as an antacid in case of acidity.
  • It is used for baking purposes.
  • It is used as a water softener.

Washing Soda

Washing soda also called Sodium Carbonate, is a chemical compound whose chemical formula is Na2CO3. Washing soda has two sodium cations (Na+) and a carbonate anion (CO32-). Sodium carbonate is a white, crystalline powder and as the name suggests is used for washing purposes.

Chemical Name: Sodium Carbonate

Chemical Formula: Na2CO3


A few of the uses of Washing Soda are,

  • It is used in the glass, soap and paper industries.
  • It is used as washing powder.

Bleaching Powder

Bleaching Powder also called Calcium Hypochlorite, is a chemical compound whose chemical formula is CaOCl2. Bleaching Powder is used for bleaching purposes. In its aqueous solution bleaching powder releases chlorine which is responsible for the bleaching action.

Chemical Name: Calcium Hypochlorite

Chemical Formula: CaOCl2


Bleaching Powder can be prepared with the help of the reaction given below.

Ca(OH)2(aq) + Cl2(g) → CaOCl2(aq) + H2O(l)


A few of the uses of Bleaching Powder are,

  • It is used for bleaching the laundry.
  • It is used as an oxidizer in many industries.
  • It is used as a disinfectant to clean water

Crystals of Salts

Some salts combining with water form crystals and these water molecules which are required to form crystals are called water of crystallisation. Some examples of crystal salts are Table salt (sodium chloride crystals), Sugar (sucrose crystals).

Plaster of Paris

Plaster of Paris is a widely used chemical compound is used for various purposes such as sculpting materials, gauze bandages, building and furnishing houses and others. Plaster of Paris is hydrated calcium sulphate obtained by calcining gypsum. It is a white powdery chemical compound.

Chemical Name: Calcium Sulphate Hemi Hydrate.

Chemical Formula: CaSO4. ½ H2O

Preparation of Plaster of Paris

Plaster of Paris can easily be prepared with the help of the equation given below,

CaSO4.2H2O (s) (heating at 100°C ) —> CaSO4. ½ H2O + 3/2 H2O

Also, Check

FAQs on Acids, Bases and Salts

Question 1: What are salts in acids, bases and, salts?


The neutralization reaction of acids and bases results in a substance called salt. Salts are made of cations and anions. Some examples of salt are NaCl, Na2SO4

Question 2: What are the two types of acids?


Acids can easily be categorised as,

  • Inorganic Acids: Examples, Sulphuric Acid (H2SO4), Nitric acid (HNO3), and others.
  • Organic Acids: Examples, Acetic acid Citric acid, and others.

Question 3: What is the difference between an acid and a base?


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

Question 3: What are the physical properties of bases?


The physical properties of bases are,

  • 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.
  • In an aqueous solution, they release OH ions.

Question 4: What are the physical properties of acids?


The physcial 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, they release H+ ions.

Question 5: What happens when hydrochloric acid reacts with sodium carbonate?


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

                                             Na2CO3 + 2HCl → 2NaCl + H2O + CO2

Question 6: Are salt basic or acidic?


A salt can either be basic ar be acidic depending on the types of acid and base that react to form a salt.

Question 7: Is NH4Cl a basic salt?


No, Ammonium chloride (NH4Cl) is an acidic salt because it is a salt of a strong acid (hydrochloric acid) and a weak base (ammonium hydroxide).

Question 8: What happens when metal reacts with HCl?


Metal reacting with acid produces salt and hydrogen.

Acid + Metal → Salt + Hydrogen

Question 1: What is the Chemical Formula of Baking Soda?


The chemical formula of baking soda is NaHCO3. It is also called as sodium bicarbonate.

Question 2: What is Baking Soda also known as?


The chemical name of baking soda is Sodium bicarbonate.

Question 3: List Uses of Baking Soda.


Various uses of Baking Soda are,

  • Reduces stomach acidity and acts as an antacid to relieve stomach discomfort and indigestion.
  • It is used as a water softener in the washing process.

Question 4: What is the Chemical Formula of the Plaster of Paris?


The chemical formula of Plaster of Paris is CaSO4.1/2H2O

Question 5: What is Plaster of Paris also known as?


The chemical name of Plaster of Paris is Calcium Sulphate hemihydrate.

Question 6: List uses of Plaster of Paris.


Various uses of Plaster of Paris are,

  • Plaster of Paris is used in coating walls and ceilings. 
  • Plaster of Paris is used by doctors as a plaster for setting fractured bones.

Question 7: What is Washing Soda also known as?


The chemical name of washing soda is Sodium carbonate.

Question 8: What is the Chemical Formula of Washing Soda?


The chemical formula of washing soda is Na2CO3.

Question 9: List Uses of Washing Soda.


Various uses of Washing soda are,

  • In industry and the home, it is used as a cleaning agent.
  • It’s used in the paper, textile, soap, and detergent sectors, among others.
Question 1: What is Bleaching Powder?
Bleaching powder is a chemical compound with a pale yellow colour which has a strong smell of chlorine. It is a strong oxidising agent and is used for bleaching purposes.
Question 2: What are the uses of Bleaching Powder?
Bleaching Powder is used for various purposes, and some of its important uses are,
It is used as an oxidizer in industries because of its strong oxidizing property.
It is used as a disinfectant for cleaning purposes.
Question 3: What is the chemical name for Bleaching Powder?
The chemical name for Bleaching Powder is Calcium Oxychloride.
Question 4: What is the formula for bleaching powder?
The formula for Bleaching Powder is CaOCl2
Question 5: Is Bleaching Powder Acidic or Basic?
Bleaching Powder reacts with acids to release chlorine gas, so it can be considered a base.
Question 4: What is the pH value of bleaching powder? 
Bleaching powder is considered to be basic in nature with a pH of  nearly 11.
Question 5: Why does bleaching powder act as an oxidising agent? 
The bleaching powder reacts in the presence of a very small amount of dilute acid to release nascent oxygen. The release of the nascent oxygen causes the bleaching powder to act as both an oxidising and a bleaching agent.
Question 6: What are some harmful effects of bleaching powder? 
Some harmful effects of bleaching powder are:
Fumes of bleaching powder are really strong in nature which on inhalation may cause various health problems.
It is highly irritating and corrosive to the skin.
It may even result in the formation of lumps on the eyes.
It may burn human tissue both internally and externally.

Water of Crystallization Examples

Water of Crystallization Examples
  • Copper Sulphate Pentahydrate (CuSO4.5H2O) is the pentahydrate of Copper (2+) sulfate and it is a bright blue crystalline solid. 
  • Washing Soda (Na2CO3.10H2O) is an inorganic hydrate of sodium carbonate and has a white or colorless crystalline salt-like appearance.
  • Gypsum (CaSO4.2H2O) is a soft sulfate mineral consisting of Calcium Sulfate Dihydrate. It has a dark color solid rock-like appearance. 
  • Tin (II) Chloride Dihydrate (SnCl2.2H2O) is a white crystalline solid.

Hydrated Salts 

A hydrated salt is a crystalline salt molecule that is loosely connected to a small number of water molecules. When the anion of an acid and the cation of a base are joined to form an acid-base molecule, salt is formed. An anhydrate is a salt molecule that is not bound to any water molecules, while a hydrated salt is one that is bound to water molecules. 

The water molecules in a hydrated salt are incorporated into the crystalline structure of the salt. A hydrated salt is one in which the ions in its crystalline structure are coupled with a number of water molecules. These water molecules are referred to as crystallisation fluids or hydration waters. Hydrated salts are salts that contain water during crystallisation. Every hydrated salt has a fixed number of crystallisation water molecules in its single ‘formula unit.’ 

The following are some examples of hydrated salts.

  • CuSO4.5H2O copper sulphate crystals, which include 5 molecules of crystallisation water in one formula unit.  Copper sulphate pentahydrate is the chemical name for it.
  • Calcium sulphate crystals, often known as gypsum crystals, are written as CaSO4.2H2O because they contain two molecules of water of crystallisation in one formula unit.  Calcium sulphate dihydrate is another name for it.
  • Sodium carbonate crystals, also known as washing soda crystals, are written as Na2CO3.10H2O because each formula unit contains 10 molecules of water of crystallisation. It’s known as sodium carbonate decahydrate

Copper sulphate, Calcium sulphate, and Sodium carbonate are some of the hydrated salts based on the above-mentioned examples. Hydrated salts can be found in a variety of conditions, including freshwater. Salt has a flexible crystalline structure that allows it to easily bond to water molecules and becomes hydrated. Sodium chloride or salt absorbs water vapour in the air or comes into touch with liquid water. Free-flowing chemicals, for example, generate salt molecules when the compounds in a particular area’s soil or rock dissolve and mix with the groundwater, eventually becoming hydrated with the water molecules.

Uses of Hydrated Salt

  • Epsom salts are the most well-known application of hydrated salts in daily life. Many of the compounds found in salts are required by the human body. Those compounds, however, may be difficult to absorb or receive only through diet. People have traditionally taken healing baths in regions where hydrated salts naturally occur, believing them to have curative effects. Epsom salts are an example of this. Even though its medicinal properties haven’t been proven, Epsom salt has commercial potential as a home remedy. Another important application of hydrated salt is in industry.
  • Salt, including hydrated salts, has a wide range of industrial applications. Many industries depend on hydrated salt. In the chemical industry, salt is the primary constituent in more than half of the products. Glass, paper, rubber, and textile industries also employ hydrated salt.
  • Salt is also employed as water-softening salt in both industrial and home water-softening systems. Furthermore, hydrated salt is employed extensively in the alternative energy sector because of its capacity to maintain a constant temperature for an extended period of time.

Anhydrous salts

Anhydrous refers to a substance that is completely devoid of water. Anhydrous salts are salts that have lost their water of crystallisation. As a result, anhydrous salts lack crystallisation water. An anhydrous salt becomes hydrated when water is introduced to it. 

Calcium chloride, in its anhydrous state, has a variety of applications. It can also detect humidity in the air and vapour. Calcium chloride is used in several industrial safe checks to measure road erosion or cracks.

In experiments, removing moisture is important because it typically controls side reactions or other unexpected consequences in the chemicals being studied. Organic compounds can be dried with drying agents like Na2SO4 and MgSO4. When these anhydrous materials come into touch with water, however, the water is absorbed rather than merely evaporated. As a result, such drying solutions are incomplete, traces of water may be left behind, and compounds may be regarded as polluted as a result.

Action of Heat on Hydrated Salts

When hydrated salts are heated to high temperatures, they lose their crystallisation water. The hydrated salts lose their regular shape and colour when the water of crystallisation is lost, and they become colourless powdery particles. Since there is no water of crystallisation in anhydrous salts, so when water is added to an anhydrous salt, it hydrates and returns to its original colour. The following example will help to clarify this.

The copper sulphate crystals are blue in colour. When copper sulphate crystals are heated to a high temperature, they lose all of their water and become anhydrous copper sulphate, which is white.

CuSO4.5H2O                   →                CuSO4                     +             5H2O
(Hydrated copper sulphate)               (Anhydrous copper sulphate)            (Water)

As a result of the loss of water during crystallisation, blue copper sulphate crystals turn white when heated vigorously. Copper sulphate crystal dehydration is a reversible process. As a result, adding water to anhydrous copper sulphate causes it to become hydrated and turn blue, resulting in the production of hydrated copper sulphate.

CuSO4                       +           5H2O                            CuSO4.5H2O
(Anhydrous copper sulphate)               (Water)                     (Hydrated copper sulphate)

When you add water to anhydrous copper sulphate, it turns blue. This property of anhydrous copper sulphate is utilised to detect the presence of moisture or water in a liquid. To white anhydrous copper sulphate powder, a few drops of the liquid to be tested are added. The presence of moisture or water in anhydrous copper sulphate is indicated by the appearance of blue colour.

FAQs on Water of Crystallization 

Question 1: Which of the following salts has no Water of Crystallization? Blue vitriol, Baking soda, Washing soda, and Gypsum.


Out of the four given salts, only baking soda does not contain water of crystallization as its chemical formula is NaHCO3.

Question 2: Name a salt which does not contain Water of Crystallization.


There is a huge number of salts that does not contain water of crystallization, that are Sodium Nitrate (NaNO3), Potassium Chloride (KCl), Potassium Nitrate (KNO3), etc. 

Question 3: Give any three compounds comprising water of crystallization.


Here is the list of Salts that comprising of water of crystallization:

  • Copper (II) Sulfate Pentahydrate (CuSO4.5H2O), 
  • Cobalt (II) Chloride Hexahydrate (CoCl2.6H2O), 
  • Tin (II) (or Stannous) Chloride Dihydrate (SnCl2.2H2O), etc. 

Question 4: Why do salts containing water of crystallization appear to be perfectly dry?


The water of crystallization is a part of the crystal structure of water. Since the water of crystallization is not free water, so it does not wet the salt. Thus, the salts containing water of crystallization appear to be perfectly dry.

Question 5: How is the water of crystallization useful for the crystals of salts?


The water of crystallization gives the crystals of salts their shape and in some cases imparts their colour. For example, the presence of the water of crystallization in iron sulphate crystals imparts them a green colour.

Question 6: Write the name and formula of a salt that has five molecules of crystallisation water in it.


Copper sulphate crystals include five molecules of water of crystallisation in one formula unit. Its formula is CuSO4.5H2O.

Question 7: What is the colour of FeSO4.7H2O crystals? What happens to the colour when it’s heated? 


FeSO4.7H2O  crystals are green in colour. It loses the water of crystallisation when heated, resulting in anhydrous ferrous sulphate. It has a reddish-brown colour to it.

Question 8: Is water present in anhydrous sodium chloride crystals? 


Since there are no water molecules in an anhydrous material, so there is no water present in anhydrous sodium chloride crystals. These anhydrous crystals were created by carefully eliminating the water of crystallisation from hydrated salts.

Question 9: Why do copper sulphate crystals change colour when heated?


The blue colour of the copper sulphate crystals turns white on heating because of the loss of water during crystallisation.

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