Class 10 Chemistry Chapter 2 Acids Bases and Salts Notes

Chapter Acids, Bases and Salts Notes

Class 10th Chemistry Notes

Acids bases and salts

Background:

Before we fully grasp the idea of acids and bases, we begin by brainstorming that the items, foods, and beverages that we use regularly are acids.

The Acids and Bases We Consume and Use Every day:

In daily life, we employ;

  • Our food contains lemon, tomato, vinegar, apple, and fizzy drinks.
  • Toilet cleanser to eradicate toilet bacteria.

All of these include acids, and the kinds of acids they do so are listed below:

  1. Lemon (Citric Acid)
  2. Tomato (Malic and Citric Acid)
  3. Vinegar (Acetic Acid)
  4. Apple (Malic Acid)
  5. Fizzy beverages (Phosphoric Acid)
  6. Tissue box cleaner (Hydrochloric Acid)

Acid Produces by Our Body:

Our body creates hydrochloric acid through the gastric glands in our stomach, which aids in the digestion of meals. Our stomachs can become acidic on occasion when the content of HCl within rises faster than usual.

Treatment:

We reduce our stomach’s acidity or raise it to the level that our stomach requires by taking antacids, which are basic in nature.

Acid Rain:

Acid rain is defined as rain with a pH value in the acidic medium range (4.0).

Gases like SO2 and NOx that are released into the atmosphere generate acid rain.

  • When SO2 and water (H2O) react, H2SO4 (sulfuric acid) is the result.
  • When NOx (nitrogen oxides) and water (H2O) react, HNO3 (nitric acid) is the result.

The effects of Acid Rain:

The following are damaged as a result of acid rain:

  • Acid rain leads to damage to forests
  • Washing can reduce the amount of Al ions in the soil (Al ions go to rivers and lakes and)
  • Neglect aquatic life (Al is toxic in nature)
  • Destroy statues and buildings (the Taj Mahal and Statue of Liberty are the present examples)

Bases that we utilize every day:

In daily life, we employ;

  • Antacids to relieve stomach acidity
  • Baking soda for use in baking cakes, etc.
  • Washing soda for cleaning clothing

Below are listed all of them along with the kind of bases they each include.

  1. Antacids (Magnesium hydroxide and Aluminum hydroxide)
  2. Baking soda (Sodium bicarbonate)
  3. Washing soda (Sodium carbonate)

Characteristics enable us to determine if a substance is acidic or basic:

S.No

Property

Acid

Base

1

Taste

Acid has a sour flavour.

Base tastes bitter.

2

Color change of litmus paper

Acid turns blue litmus paper red

Base leaves blue litmus paper unchanged

3

Color change of litmus paper

Acids leave red litmus paper unchanged

Base changes the color of red litmus paper to blue

4

Which type of damage caused to skin

Skin can be corroded by acid

Skin can be corroded by base

5

Current / Electricity

In an acidic aqueous solution, current can flow.

In a basic aqueous solution, current can flow.

These, therefore, are the traits and qualities of acids and bases.

Some Common Acids:

Below is a table of several common acids’ names, chemical formulas, and applications.

Name of Acid

Formula of Acid

Uses of Acid

Hydrochloric Acid

HCl

HCl is frequently employed in the cleaning, electroplating, tanning, pickling, and refining of metals.

Sulphuric Acid

H2SO4

Sulfuric acid is used as a raw material for the production of fertilizers, explosives, and many chemicals, including HCl, HNO3, dyes, medicines, and paints.

Nitric Acid

HNO3

Use of nitric acid as a doping agent in electrochemistry, the production of fertilizers, explosives like TNT, colours, and plastic.

Phosphoric Acid

H3PO4

About 80% of the phosphoric acid is used in the production of fertilizers. Additionally utilized as a food additive, a reducing agent in chemical analysis, and an acid in carbonated beverages.

Some Common Bases:

Below is a table that lists some common bases’ names, formulas, and applications.

Name of Base

Formula of Base

Uses of Base

Sodium Hydroxide

NaOH

Detergents like soap are made using sodium hydroxide. Used to clean stoves and drains, as well as while making paper and medications. Used to disinfect. Detergents like soap are made using sodium hydroxide. Used to clean stoves and drains, as well as while making paper and medications. Used to disinfect.

Magnesium Hydroxide

Mg(OH)2

Antacids are made with magnesium hydroxide to reduce stomach acidity. utilized as a laxative to treat sporadic constipation

Calcium Hydroxide

Ca(OH)2

Plasters, paper, sewage treatment, and the production of mortar and cement all utilize calcium hydroxide.

Potassium Hydroxide

KOH

Potassium hydroxide is a chemical that is used to make paper, face wipes, fungicides, and herbicides.

Theories concerning acids and bases

(Acids and Bases Concepts):

The acids and bases are the subjects of various well-known theories. Below are the theories.

  1. Arrhenius Theory
  2. Bronsted-Lowery Theory
  3. Lewis Theory

1. The Arrhenius Theory

  • This theory, first put forth by a Swedish chemist named Svante Arrhenius in 1887,
  • Described the relationship between acids and bases.

As stated by Arrhenius:

Acid:

Acid is a chemical that, upon ionization, creates H+ ions in a water solvent.

Example:

Below is an example to illustrate this concept:

We can observe from the aforementioned reaction that when hydrochloric acid ionizes in water, H+ and Cl ions are produced. However, the Arrhenius hypothesis stipulates that acid must create H+ ions in water upon ionization, and the aforementioned reaction demonstrates that this is indeed the case. Thus, HCl is acid according to the Arrhenius concept.

Base:

A material is said to as a base if it ionizes to form OH ions in a water solvent.

Example:

Below is an example to illustrate this concept:

In the aforementioned reaction, Na+ and OH ions are produced when sodium hydroxide is ionized in water. However, the Arrhenius hypothesis stipulates that a base must produce OH ions in water upon ionization. As we can see from the preceding process, NaOH did indeed form an OH ion upon ionization in water. So NaOH is a base in the Arrhenius concept.

Now that the Arrhenius idea of acids and bases has been dispelled, it is simple to determine if an observed reaction is coming from acid or a base by looking at it.

Examples:

The following reactions are listed, and we must determine which reaction is an acid reaction and which is a base reaction.

(1)

Explanation:

In this reaction, HNO3 ionization into water results in the production of H+ and NO3-1 ions. The Arrhenius theory, however, stipulates that an acid’s ionization in water must result in the production of H+ ions. We can see from this reaction that HNO3 has indeed formed an H+ ion upon ionization in water. HNO3 is therefore an acid by Arrhenius’ theory.

(2)

Explanation:

We can observe in this reaction that the ionization of H2SO4 into water results in the production of 2H+ and SO4-2 ions. The Arrhenius theory, however, stipulates that an acid’s ionization in water must result in the production of H+ ions. We can see from this reaction that H2SO4 did indeed form 2H+ ions upon ionization in water. H2SO4 is therefore an acid under Arrhenius’ theory.

(3)

Explanation:

In this reaction, we can observe the formation of K+ and OH ions from the ionization of potassium hydroxide (KOH) into water. The Arrhenius hypothesis stipulates that a base must generate OHions in water upon ionization, and the foregoing reaction demonstrates that KOH did indeed generate an OH ion upon ionization in water. KOH is, therefore a base according to Arrhenius’ theory.

(4)

Explanation:

In this reaction, we can observe that ammonium hydroxide (NH4OH) creates NH4+ and OH ions when it is ionized with water. A base must, however, produce OH ions in water upon ionization for the Arrhenius theory to hold true, and the above reaction demonstrates that this is the case. So NH4OH is a base according to the Arrhenius concept.

Defects in the Arrhenius Theory:

This theory states that upon ionization in water, the acid must provide (H+) and the base must yield (OH). But not all acids and bases were treated according to this theory. This idea has some flaws, some of which are listed below:

  • Why are CO2 and SO2 acids and NH3 basic, respectively, if acid gives (H+) and base gives (OH) on ionization in water?
  • We are aware that neither CO2 nor SO2 contain any hydrogen. So, how will they deliver (H+) upon ionization in water?
  • NH3 contains no (OH). So, how will it produce (OH) upon ionization in water?
  • It only applies to solutions that use water as a solvent (aqueous solution).

Watch-> Arrhenius Concept of Acids and Bases

2): Bronsted-Lowery Theory:

To address the shortcomings of the Arrhenius theory, Bronsted and Lowery produced the Bronsted-Lowery theory, a different theory for acids and bases.

In line with Bronsted-Lowery

If two species exist. Then,

Acid:

An acid is a species that can donate a proton (H+) to another species, while

Base:

A species that accepts the proton (H+) is referred to as a base. This specie was mentioned above as another specie in the definition of an acid.

For example:

Explanation:

We can observe from this process that when ammonia (NH3) and water (H2O) were combined, the water provided protons (H+) and the NH3 absorbed them. So, in this approach, NH3 functions as a base and water as an acid.

Important aspects of the Bronsted-Lowery Theory include:

  • Both the Arrhenius and the Bronsted-Lowery theories have the same idea of acid.
  • The bases of the Arrhenius and Bronsted-Lowery theories differ from one another.
  • According to the Bronsted-Lowery theory, all acids are also acids according to the Arrhenius theory.
  • All bases in accordance with the Arrhenius theory and the Bronsted-Lowery theory give (OH) ions upon ionization in water, respectively.
  • However, the bases in the Bronsted-Lowery theory that accepts H+ are not bases in accordance with the Arrhenius theory.

Let’s look at another illustration:

Explanation:

In this example, we can see that when HCl reacts with water (H2O), the proton (H+) that HCl donates to the water (H2O) is accepted by the water (H2O) in the reaction’s mechanism. Therefore, water (H2O) is a base because it receives (H+), whereas HCl is an acid since it contributes (H+) according to the Bronsted-Lowery theory.

Point To be noted:

It should be noticed that in the first reaction in the above two reactions, water is donating (H+) or acting like an acid. According to the Bronsted-Lowery theory, water is acting as a base in the second reaction when it accepts (H+). So, keep in mind that an organism is said to be an amphoteric species or an amphoteric substance if it has the capacity to function both as an acid and a base depending on the needs of a reaction.

Watch –> Bronsted Lowery Concept of Acid and Base

Problems with the Bronsted-Lowery Theory

This idea states that acid must give (H+) while base must accept (H+). However, unlike the Arrhenius hypothesis, this idea was not applied to all acids and bases. As a result, this theory also has some flaws, some of which are listed below:

  • Why CO2, SO2, and BF3 are acids and CaO a base if acid contributes (H+) and base accepts (H+) respectively?
  • We are aware that CO2, SO2, and BF3 are incapable of transferring protons (H+).
  • We are also aware that CaO is incapable of absorbing protons (H+).

Therefore, Lewis proposed a third hypothesis regarding the nature of acids and bases known as the Lewis theory after discovering these flaws in both the Arrhenius and Bronsted-Lowery theories.

Lewis Theory:

  • This theory was put forth by G.N. Lewis in 1923.
  • It is based on giving and accepting lone pairs of electrons.
  • It corrects all flaws in the Arrhenius and Bronsted-Lowery theories.
  • Between an acid and a base, a coordinate covalent connection will develop, symbolized by a single-headed arrow.
  • An acid’s core must be electron-deficient for it to take an electron pair.
  • At least one lone pair of electrons must be present in a base.

Claims Regarding Acids and Bases:

Acid:

A species that can accept a lone pair of electrons is referred to as an acid.

Base:

A species that can give away a lone pair of electrons is referred to as a base.

By way of illustration, let’s better comprehend what Lewis acid and base are:

Example:

Explanation:

In this reaction, ammonia (NH3) is giving a single pair of electrons to the electron-poor core of BF3. Therefore, in accordance with the Lewis concept, the species NH3 donates a single pair whereas the species BF3 accepts an electron. Additionally, NH3 and BF3 form a coordinate covalent connection, which is symbolized by a single-headed arrow. This link is created by sharing a full lone pair of electrons with an electron-deficient specie.

Watch –> Lewis Acids and Bases

Watch –> Is H+ ion acts as a Lewis acid

Water’s Self-Ionization(Self ionization of H2O):

Introduction

Proton donation and acceptance are both possible for water molecules (H+). We have already covered the Bronsted-Lowery theory, which states that water has an amphoteric character and can act both as an acid and a base. However, when only water molecules are present in a container, the water molecules can self-ionize by one water molecule giving a proton (H+) and turning it into OH, while another water molecule accepts this proton (H+) and transforms it into H3O+.

For instance, we are aware of

Water that has self-ionized can be visualized as:

Mechanism of Reaction of autoionization (self ionization ) of water:

Explanation:

The aforementioned reaction mechanism illustrates how water can ionize itself by giving a proton (H+) to another water molecule, which accepts the proton and produces H3O+. This process is known as water self-ionization. By giving a proton, one water molecule acts as an acid, and by absorbing a proton, another water molecule acts as a base.

Watch –> Self ionization of water

Point to Recall:

Water is a weak electrolyte, therefore self-ionization only occurs in a very limited amount of it. Its ionization power is thus low.

(H+) and (OH-) concentration at 25 oC:

It has been established through experimentation that the concentration of H+ and OH in pure water at 25 oC is equivalent to 1 X 10-7 M.

Equation-wise, this can be expressed as:

[H+] = [OH] = 1 X 10-7 M

The formula for Kc for self-ionization of water is:

Water is a weak electrolyte, as we all know. Water’s concentration won’t alter as a result.

Kc [HsO] = [H+] [OH]

Kw = [H+] [OH-]

Kw = (1 x 10-7) (1 x 10-7) = 1 x 10-14 at 25 oC

Water’s ionization constant, Kw, is used here.

Power of Hydrogen Ion (pH)

  • Danish biochemist Soren Sorenson proposed pH in 1909. He defines pH as the following:
  • Negative logarithm of the molar concentration of H+ ions in a solution in which water serves as the solvent, for example.

[H+] = -log pH

  • Pure water’s pH at 25 oC is 7 (neutral), for instance.

pH = (1 x 10-7) -log(pH) = 7

  • Acids have a pH between 1 and 6, bases have a pH between 8 and 14, and all neutral solutions including water have a pH of 7.
  • When a solution’s pH is between 1 and 6, it indicates that (H+) ion concentration will be higher than (OH) ion concentration.
  • When a solution’s pH is between 8 and 14, it indicates that its (OH) ion concentration will be higher than its (H+) ion concentration.
  • When a solution’s pH is 7, it indicates that the concentration of (H+) ions and (OH) ions are equal.

Significance of Kw:

Kw is significant since it directly relates to temperature. So, the temperature has a complete impact on its worth. Because of this, at 25 oC, the Kw will be equal to 1 x 10-14 of any solution. The formula Kw = [H+] [OH] = 1 x 10-14 can also be used.

The pH Scale:

Chemists use a scale known as the pH scale, which includes the numbers 0 to 14 as well as colours.

Watch –> concept of pH scale

The pH Paper:

You may purchase pH papers from stores. It’s similar to a tiny packet that includes a colourful pH scale with digits 0 to 14 and a bundle of papers called pH papers.

Method to use pH scale and pH paper:

If someone gives us a solution and said that find out that, the solution is basic, neutral, or acidic. Then for this purpose, we will do some steps:

  • Take a small piece of pH paper
  • Dip it in a solution
  • Then, note the color of the pH paper
  • Match the color of pH paper with the pH scale
  • If its color matches any number from 0-6 then the solution is acidic
  • If the color matches with 7 then the solution is neutral

If the color matches any number from 8-14 then the solution is basic.

Watch –> pH Paper Test for Acid and Base

Simple pH Scale:

[H3O]+

pH

100

0

10-1

1

10-2

2

10-3

3

10-4

4

10-5

5

10-6

6

10-7

7

10-8

8

10-9

9

10-10

10

10-11

11

10-12

12

10-13

13

10-14

14

Table: pH scale and pH values of daily used substances

pH

Examples of solutions

0

Battery acid, strong hydrochloric acid

1

Hydrochloric acid secreted by the stomach lining

2

Lemon juice, gastric acid, vinegar

3

Grapefruit juice, orange juice, soda

4

Tomato juice, acid rain

5

Soft drinking water, black coffee

6

Urine, saliva

7

Pure water

8

Sea water

9

Baking soda

10

Great salt lake, milk of magnesia

11

Ammonia solution

12

Soapy water

13

Bleach, oven cleaner

14

Liquid drain cleaner

Litmus paper:

Second widely used technique for determining the type of solution:

Most often, litmus sheets are used in laboratories by students to determine the type of solution. There are two types of Litmus papers:

  • Red litmus paper
  • Blue litmus paper
  • A solution is considered basic when red litmus paper immersed in it turns blue.
  • Acidic solutions are indicated by blue litmus paper that turns red when immersed in a solution.
  • Watch –> Litmus papers Experiment

pH Indicator (pH paper):

The third method for determining the kind and pH of a solution is the use of pH indicators, which are organic molecules that are coloured.

Utilization of pH Indicator:

  • Add a few drops of indicator to a solution whose pH is unknown.
  • Watch for colour changes. Compare the colour to the pH colour chart for universal indicators.
  • Acids’ colour shifts from green to red, and bases’ colour shifts from green to purple.
  • If a universal indication pH colour chart’s 0–6 colour range matches the colour, the solution is acidic.
  • The solution is neutral if the colour matches the colour that is represented by the number 7 on a universal indicator pH colour chart.
  • The solution is basic if the colour matches the hues from 8 to 14 on a universal indicator pH colour chart.
  • Watch -> pH Indicator test

Examples of pH acid and base indicators:

The pH Level at Which Some Common Indicators Change Color:

The pH range at which an indicator changes colour is listed below:

• At pH 5.5, the colour of the indicator (methyl orange) turns yellow.

• At pH 7, the indicator’s (bromothymol blue) colour shifts from yellow to blue.

• At pH 9, the colour of the indicator (phenolphthalein) turns pink from colourless.

Watch –> Indicators Definition, Types, Examples and Facts

Salts:

Introduction:

We are well aware that the H atom must be included in the formula for an acid. Therefore, an acid will change from being acid to salt when the H atom of the acid is replaced by a metal atom.

How this substitution will be made:

Acid and base interaction causes this substitution. As a result, salt will be the final product.

Salt is the material created when a metal atom is substituted for the hydrogen atom in an acid. Or

The material is created when acid and base react.

For instance:

Explanation:

The aforementioned process demonstrates that

  • Sodium metal is substituted for the hydrogen in the acid (HCl), which results in the formation of salt (NaCl).
  • The partial positive charge will carry by the sodium metal atom in NaOH and the partial negative charge will be carried out by OH
  • In NaCl, the sodium metal atom has a partial positive charge, whereas the atom of chlorine has a partial negative charge.
  • Since the reaction of HCl and NaOH results in the synthesis of salt and water, both of which have a pH of 7, we can see that water is also created by this process.
  • This reaction is known as a neutralization reaction.

The properties of salts may be summed up as follows:

  • They are ionic in nature
  • They are composed of metal and non-metal atoms linked together by an ionic bond
  • Metal part carry a positive charge and non-metal carry a negative charge
  • The name of the metal atom can be written first and then the name of the non-metal atom

List of acids from which various salts can be made by swapping out their H atoms for various metal atoms:

  • If a hydrogen atom in HCl is swapped out for a metal atom from either Na, K, or Ca, HCl will result in the creation of the salts NaCl, KCl, and CaCl2, respectively.
  • If a hydrogen atom in HNO3 is swapped out for a metal atom from Na, K, or Ca, HNO3 will result in the creation of the salts NaNO3, KNO3, and Ca(NO3)2, respectively.
  • The production of salts such as Na2SO4, K2SO4, and CaSO4 will occur if a hydrogen atom in H2SO4 is substituted with either a Na, K, or Ca metal atom.
  • When a hydrogen atom in H3PO4 is swapped out for a metal atom from Na, K, or Ca, H3PO4 will result in the creation of the salts Na3PO4, K3PO4, and Ca3(PO4)3, respectively.

Watch –> Salt Definition, Formation, Examples, Properties and Uses

Salt Synthesis Methods:

There are five different ways to create salt. The following five techniques are listed in order:

  • In the first approach, salt and water are created when an acid and a base react, for example.
  • In the second process, salt and water are created when metal oxide and acid react, for example.
  • Thirdly, the reaction between an acid and a metal atom produces salt and hydrogen gas, for example.
  • In the fourth process, salt, carbon dioxide, and water are produced as a result of the reaction between an acid and metal carbonate. e.g.
  • The fifth approach, for example, causes the creation of salts via the reaction of salts and salt.

Watch –>Methods for making Salts

Salt uses:

The following list includes some of the more typical salt uses:

  • Food is preserved for a longer time with salts. Preservation techniques include:
  1. Fruits and vegetables are dried
  2. Salting them, second
  3. Cooking them.
  4. Boxes for storage
  • Salts are employed in bleaching powders and as a flavouring for food, such as NaCl (table salt).
  • Salts are employed in the creation of soap and pottery, respectively.
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Chapter Acids Bases and salts important terms

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