Class 10 Chemistry Chapter 2 Acids Bases and Salts Important Questions

Chapter Acids Bases and Salts Important Questions:

10th Class Chemistry notes

Acids bases and salts

–>Respond to the following inquiries:

1) Create the water’s self-ionization equation.

When just 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:

Self-Ionization of water can be represented as:

Mechanism of Reaction:

Explanation:

The aforementioned chemical mechanism demonstrates the self-ionization of water. It can be seen that,

  • One water molecule donates a proton (H+) to another, which accepts the proton (H+) and produces H3O+.
  • This process is known as water self-ionization.
  • One water molecule acts as an acid by giving a proton
  • Whereas another acts as a base by taking a proton.

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.

Watch –> Self ionization of water

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2) Describe Arrhenius acids and provide examples.

Arrhenius Theory is the response.

  • This hypothesis introduced the idea of bases and acids.
  • Svante Arrhenius, a Swedish scientist, proposed it in 1887.

As stated by Arrhenius:

Acid:

Acids are substances that, upon ionization, create H+ ions in the water solvent.

Example 1:

Below is an example to illustrate this concept:

However, the Arrhenius principle stipulates that,

  • An acid must produce H+ ions in water on ionization.
  • As can be seen in the preceding process, hydrochloric acid produces H+ and Cl ions.
  • According to the Arrhenius idea, HCl is an acid since it created an H+ ion upon ionization in water, as seen in the reaction above.

Example 2:

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.
  • This reaction demonstrates that HNO3 did indeed form an H+ ion when it was ionized in water.
  • Thus, HNO3 is acid in accordance with the Arrhenius theory.

Example 3:

Explanation:

We can observe from this reaction that,

  • 2H+ and SO4-2 ions are produced when H2SO4 is ionized with water.
  • 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.
  • Thus, H2SO4 is acid in accordance with the Arrhenius principle.

Watch –> Arrhenius Concept of acid and base

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3): Why does the H+ ion function as a Lewis acid?

Response: Lewis Theory

Acid:

Lewis defined an acid as a species with the capacity to accept a single pair of electrons.

Since H+ has an electron-deficient core, we know from the definition that it can accept a lone pair of electrons (The duplet of Hydrogen is empty).

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

Watch –> Lewis Concept of Acid and base

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4): Why does NH3 serve as the Bronsted-Lowery base?

Referring to the Bronsted-Lowery Theory

In line with this hypothesis:

Base:

The term “base” refers to a species that can receive protons (H+).

For instance:

Explanation:

This process demonstrates that,

  • When ammonia (NH3) and water (H2O) are combined, the water donates a proton (H+), and the NH3 accepts the proton (H+).
  • So, in this approach, NH3 functions as a base and water as an acid.

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5): Why does BF3 function as a Lewis acid?

Answer: Lewis Theory

Base:

Lewis states that a base is a species that can give a lone pair of electrons.

Example:

Explanation:

The reaction can be summarized as;

  • The electron-deficient core of BF3 is receiving a lone pair of electrons from ammonia (NH3) in this reaction.
  • Thus, lone pair-donating species (NH3) behave like a base whereas electron-accepting species (BF3) behave like acid in accordance with the Lewis concept.
  • BF3‘s electron deficient core allows it to take lone pairs of electrons. Boron’s octet is lacking one element.
  • Therefore, Boron will receive a lone pair of electrons to complete its octet.
  • In addition, NH3 and BF3 form a coordinate covalent bond, which is symbolized by a single-headed arrow. This bond is created by sharing a full lone pair of electrons with an electron-deficient specie.

Watch –> Trick to Find Lewis Acid and Base

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6) Nitric acid and ammonium hydroxide combine to form ammonium nitrate and water. For the following neutralizing reactions, create a balanced chemical equation.

  1. Sulphuric acid + Magnesium hydroxide πŸ‘ͺ magnesium sulphate + water
  2. Sulphuric acid + calcium hydroxide πŸ‘ͺ Sodium sulphate + water
  3. Hydrochloric acid + calcium hydroxide πŸ‘ͺ calcium chloride + water

Answer:

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7) Recognize the Bronsted-Lowery bases or acids in the subsequent reactions.

Answer: In line with the Bronsted-Lowery Theory:

Acid:

A species is referred to as an acid if it can donate a proton (H+) to another species.

Base:

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

Reaction I demonstrates that,

  • HNO3 behaves like an acid by donating proton while H2O behaves like a base by accepting a proton.
  • As a result, water becomes H3O+ by accepting proton while acid becomes NO3-.

As can be seen in reaction (ii),

  • HNO3 is giving off protons while NH3 is accepting them.
  • As a result, HNO3 is acting as an acid by giving off protons while NH3 is acting as a base by accepting a proton.

Watch –> Bronsted Lowery Concept of Acid and Base

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8) In the subsequent processes, distinguish between the Lewis acids and bases.

Answer: According to Lewis Theory:

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 single pair of electrons is referred to as a base.

Reaction I demonstrates that:

  • The incomplete octet of boron in BF3 makes it an electron-deficient centre
  • In contrast, F only has one pair of electrons.
  • Therefore, F behaves as a base by donating a lone pair of electrons.
  • While BF3 behaves like an acid by absorbing a lone pair of electrons

In reaction (ii), we can observe that:

  • H+ is an electron-deficient centre
  • NH3 has a lone pair of electrons
  • NH3 behaves as a base by donating lone pairs of electrons
  • H+ behaves as an acid by receiving lone pairs of electrons.

We may observe from reaction (iii) that:

  • AlCl3 possesses an electron-deficient core because Al has an incomplete octet
  • Since NH3 has a lone pair of electrons, it acts as a base by giving those electrons to other molecules.
  • While AlCl3 behaves as an acid by absorbing a line pair of electrons

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9) Label the following mixtures as neutral, basic, or acidic.

  1. A solution that has a hydrogen ion concentration 1.0 x 10-3 M
  2. A solution that has a hydrogen ion concentration 1.0 x 10-10 M
  3. A solution that has a hydroxyl ion concentration 1.0 x 10-3 M
  4. A solution that has a hydroxyl ion concentration 1.0 x 10-10 M

Answer:

(i)

If a solution has hydrogen ion concentration 1.0 x 10-3 M. Then the solution is acidic because

The exponent of 10 is (-3) , pH = – log [1.0 x 10-3] = – log (10-3) – log 1 = – (-3) – log 1 = 3 – 0 = 3

pH = 3

And we know that pH of acids ranging from 0-6

(ii)

If a solution has hydrogen ion concentration 1.0 x 10-10 M. Then the solution is basic because

The exponent of 10 is (-10) so, pH = – log [1.0 x 10-10] = – log (10-10) – log 1 = – (-10) – log 1 = 10 – 0 = 10

pH = + 10

And we know that pH of bass ranging from 8-14

(iii)

If a solution has hydroxyl ion concentration 1.0 x 10-3 M. Then the solution is basic because

The exponent of 10 is (-3) so, pOH = – log [1.0 x 10-3] = – log (10-3) – log 1 = – (-3) – log 1 = 3 – 0 = 3

pOH = = +3

We know that, pH + pOH = 14

pH = 14-pOH

pH = 14-3 = 11

And we know that pH of bases ranging from 8-14

(iv)

If a solution has hydroxyl ion concentration 1.0 x 10-10 M. Then the solution is acidic because

The exponent of 10 is (-10) so, pOH = – log [1.0 x 10-10] = – log (10-10) – log 1 = – (-10) – log 1 = 10 – 0 = 10

pOH = + 10

We know that, pH + pOH = 14

pH = 14-pOH

pH = 14-10 = 4

And we know that pH of acids ranges from 0-6

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10) Group the following compounds into the Lewis acid and base categories.

BF3, NH3, F, H2O,

Answer:

NH3:

Ammonia is known as a Lewis base because it has a single pair of electrons that it can give to species lacking in electrons. Lewis further claims that a lone pair donating species is known as an acid.

F:

Because it has a lone pair of electrons, F is known as a Lewis base. Which it can easily donate to species lacking in electrons. Lewis further claims that a lone pair donating species is known as an acid.

H2O:

Because it has a lone pair of electrons, water is known as a Lewis base. Which it can easily donate to species lacking in electrons. Lewis further claims that a single electron pair donating species is known as an acid.

BF3:

Because boron possesses an electron-deficient centre in BF3 due to an incomplete octet, the compound is known as a Lewis acid. Its octet needs a single pair of electrons to complete it.

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11. State the acid’s Bronsted-Lowery definition. Describe the definition with an equation.

Answer: According to Bronsted-Lowery:

Acid:

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

For instance:

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.

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12. Recognize the Bronsted-Lowery bases and acids in the subsequent reactions.

Answer:

(i)

In this reaction, we can see that,

  • The acetic acid, CH3COOH, is giving a proton to the water
  • This means that, in accordance with the Bronsted-Lowery theory, the acetic acid is acting like an acid since it is giving a proton to the water.
  • Additionally, water behaves as a base by absorbing proton

(ii)

In this reaction, we can observe that,

  • HCO3donates a proton and water accepts a proton.
  • Therefore, according to the Bronsted-Lowery hypothesis, HCO3 behaves as an acid when it donates a proton
  • And water as a base when it accepts a proton

(iii)

This response demonstrates that.

  • According to the Bronsted-Lowery theory, because water (H2O) is providing protons
  • Whereas ammonia (NH3) is receiving them,
  • So, water behaves as an acid because it is donating protons.
  • And ammonia act as a base by taking on the proton NH3.

(iv)

In this reaction, we can observe that,

  • HCO3 is receiving proton while HCl is providing proton
  • Therefore, according to the Bronsted-Lowery hypothesis, HCl is acting as an acid by accepting a proton
  • While HCO3 is acting as a base by donating a proton.

(v)

In this reaction, it can be seen that,

  • HS is donating proton and H2O is accepting a proton.
  • Therefore, the Bronsted-Lowery theory states that HS- is acting as an acid by donating a proton
  • And H2O is acting as a base by accepting a proton.

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13. Recognize the Lewis bases and acids in the subsequent reactions.

Answer:

(i)

This reaction demonstrates that,

  • By taking a lone pair of electrons, the electron-deficient centre H+ will behave as an acid
  • And by donating a lone pair of electrons, the electron-rich centre CN will behave as a base.

(ii)

This reaction demonstrates that,

  • B(OH)3 has an electron deficient core because the boron octet is incomplete.
  • According to Lewis theory, OH possesses a lone pair of electrons.
  • As a result, by absorbing a lone pair of electrons, B(OH)3 acts as an acid, and by donating a lone pair of electrons, OH acts as a base.

(iii)

This reaction demonstrates that,

  • Because NH3 possesses a lone pair of electrons and Cu+2 is an electron-deficient centre
  • In this reaction, Cu+2 behaves as an acid by accepting the lone pair of electrons.
  • In addition, NH3 acts as a base by giving a lone pair of electrons.

(iv)

We may see from this reaction that:

  • In Al(OH)3 (Al) has an electron-deficient core because of an incomplete octet
  • According to Lewis theory, Al(OH)3 behaves as an acid by accepting the lone pair of electrons that OH has.
  • Additionally, OH acts as a base by contributing a lone pair of electrons.

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14) From the list below, pick out the Lewis bases and acids.

AlCl3, Ag+, CH3-OH, CH3-NH2, FeCl3

Answer:

AlCl3:

  • Due to the incomplete Al octet, AlCl3 possesses an electron-deficient center.
  • Lewis refers to an electron-deficient specie as an acid.
  • AlCl3 is a Lewis acid, then.

Ag+:

  • Ag+ is an electron-deficient centre,
  • And according to Lewis, an acid is an electron-deficient species.
  • Ag+ is a Lewis acid, then.

CH3-OH:

  • Lewis defined lone pair donating specie as a base.
  • CH3-OH has a lone pair of electrons (on the oxygen atom).
  • CH3-OH is a Lewis base, then.

CH3-NH2:

  • Lewis defined lone pair donating specie as a base.
  • CH3-NH2 has a lone pair of electrons (on the nitrogen atom).
  • CH3-NH2 is a Lewis base, then.

FeCl3:

  • Due to the incomplete octet of the Fe atom, FeCl3 possesses an electron-deficient centre
  • According to Lewis, an electron-deficient species is referred to as an acid.
  • FeCl3 is a Lewis acid, then.

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15) Identify whether water is a proton acceptor or donor.

Answer:

A special word (amphoteric) is used for water. It is because

  • Water can act as an acid by donating proton e.g.

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.

  • Water can act as a base by accepting proton e.g.

Explanation:

In this example, we can see that when HCl is given to 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.

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16) Create equations that depict the following Arrhenius acids being ionized.

  1. HI
  2. HNO2

Answer:

Ionization equation for HI:

Ionization equation for HNO2:

17) Create equations demonstrating how the following Bronsted-Lowery acids ionize.

Answer:

Ionization Equation for HNO2:

Ionization equation for HCN:

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18) What is the difference between the relative amounts of hydrogen and hydroxide ions in each type of solution?

  1. Acidic
  2. Basic
  3. Neutral

Answer:

Acidic:

In acidic solution [H+] > [OH]

Basic:

In basic solution [H+] < [OH]

Neutral:

In neutral solution [H+] = [OH]

19) Codeine, chemical formula C18H21NO3, is a frequent analgesic. The following reaction causes it to dissolve in water.

As a Bronsted-Lowery acid or base, distinguish between codeine and water.

Answer:

According to the Bronsted-Lowery theory,

  • Because water is donating proton in the aforementioned reaction
  • And codeine is accepting a proton
  • Water behaves as an acid because it is donating a proton.
  • In addition, codeine acts as a base by accepting a proton

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20) Consider a few methods for figuring out whether a specific water solution contains an acid or a base.

Answer:

We can predict the nature of any solution in three ways:

pH paper:

Utilization of pH Paper:

If someone gave us a solution and instructed us to determine whether it was basic, neutral, or acidic, we would do so. Then, for this, we’ll take the following actions:

  • 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

Litmus paper

Litmus paper is of two types:

  1. Red litmus paper
  2. Blue litmus paper

Utilization of Litmus Paper:

  • Individual test tubes should be used to collect samples of unknown solutions.
  • The test tubes should be labelled.
  • Red and blue litmus paper should be dipped into each solution.
  • Note the colour shift
  • If the red litmus paper turns blue, the solution is basic
  • If the blue litmus paper turns red, the solution is acidic

Watch –> Litmus Paper test

pH indicator

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 at 7 on a universal indicator pH colour chart.
  • If the colour matches the colours between 8 and 14 on the same colour chart, the solution is basic.

Watch –> pH Scale

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21) The table below displays two indicators’ colours in alkaline and acidic liquids.

Indicator

Colour in Acidic Solution

Colour in Basic Solution

A

Red

Blue

B

Colourless

Red

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  1. What colour will indication A be?
  2. In a solution of pH 3
  3. In a solution of pH 10
  4. What colour will indicator B be in a pH 5 solution?
  5. A solution X immediately turns red when a few drops of indicator B are added to it. Evaluate the answer X’s characteristics?

Answer:

(i) Color of indicator A at pH 3:

When a solution has a pH of 3, indicator A turns colour. The solution will then be red in color, indicating that it is acidic.

  1. Color of indicator A at pH is 10:

If a solution’s pH is 10, indicator A will be colourless. If so, it denotes that the solution is basic, and its colour will be blue.

b): When pH is 5, indicator B’s color is:

If a solution has a pH of 5. The solution is then described as acidic and colorless.

c): If a few drops of the pH-5 indicator B are poured into a solution and it turns red, the solution is basic, and its characteristics will be;

  • Bitter taste
  • Inability to change the color of blue litmus paper
  • Ability to turn the color of red litmus paper to blue
  • Ability to cause skin corrosion
  • Ability to conduct electricity

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22) The bacteria in our mouth convert food debris attached to our teeth into acid as they feed. A toothpaste with a pH of 10 can assist in protecting our teeth from acid damage. Justify the assertion.

Answer:

The basic composition of toothpaste with a pH of 10 helps to neutralize the acids that cause tooth decay.

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23) Is it possible for a substance to be both a Lewis acid and a Bronsted-Lowery acid? Argue.

Answer: Yes because;

  • According to Lewis theory, lone pair of electron-accepting specie with an electron-deficient center is referred to as an acid.
  • According to Bronsted-Lowery theory, the proton-donating specie is referred to as an acid.
  • Consequently, both theories’ conceptions of acid are distinct.
  • While Lewis concept is about accepting a lone pair of electrons,
  • Bronsted-Lowery only discusses the H+ ion. We may therefore claim that all Bronsted-Lowery acids are Lewis acids.
  • But all Lewis acids are not acids according to Bronsted-Lowery theory

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24) Explain acid rain.

Answer: Acid Rain:

Acid rain is defined as rain with a pH of 4 and contains H2SO4 and HNO3. To prevent acid rain

  • The release of SO2 into the air caused by the burning of fossil fuels and cigarette smoke
  • The emission of NOx (nitrogen oxides) into the air caused by the burning of fossil fuels and cigarette smoke
  • When SO2 reacts with oxygen and water vapour in the air, H2SO4 is created, which combines with raindrops to make acid rain. The response is provided below.
  • Acid rain forms when nitrogen oxides in the air combine with oxygen and water vapour to generate HNO3, which then falls as rain. The response is provided below.

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25) The reason why swimming pools have a pH between 7.2 and 7.6. Cite a cause.

Answer: The pH of a swimming pool varies between 7.2 and 7.6. Because human tears also have a pH that fluctuates from 7.2 to 7.6. Our eyes begin to itch when the pH falls or rises outside of this range.

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26) The reasons smoking contributes to acid rain. Cite a cause.

Answer:

Smoke from cigarettes contains:

  • SO2 and NOx (nitrogen oxides).
  • When these gases are inhaled, they combine with oxygen and water vapour to produce H2SO4 and NHO3.
  • H2SO4 and HNO3 enter in raindrops and release acid rain, for example.

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27) List a few typical applications for H2SO4.

Answer: Applications of H2SO4:

Following are some typical applications for sulfuric acid:

Sulfuric acid is used as a raw material to make

  • Fertilizer
  • Explosives
  • Chemicals including HCl and HNO3
  • Dyes
  • Medicines
  • Paints

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28) List a few typical applications for KOH.

Answer: Applications of KOH:

Following are some typical uses for potassium hydroxide:

In addition to being used in the production of

  • Face washes
  • Shaving creams
  • Paper
  • Fungicides
  • Herbicides

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29) How well do you understand stomach acidity?

Answer: Acidity of Stomach:

  • Gastric glands in the stomach create hydrochloric acid.
  • When the stomach produces too much acid, this condition is known as stomach acidity
  • Medicines (Antacids) are used to treat stomach acidity
  • Because Antacids are bases and neutralize the stomach’s acid.
  • This hydrochloric acid aids in the following processes:
  1. Digestion of food by destroying chemical bonds in it
  2. The killing of bacteria present in food

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30) What do preservers do? Which function do they serve? List the traditional and modern techniques for food preservation.

Answer: Preservatives:

They act as physical and chemical process inhibitors, preventing the deterioration of food.

Purpose of Use:

They are used to keep food fresher for a longer amount of time.

Dated technique for food preservation

The steps involved in this process are as follows:

Fruits and vegetables should be;

  • Dried
  • Salted
  • Boiled
  • And packaged

New Food Preservation Technique:

Preservatives are now added to food to extend its shelf life. The preservatives are made to prevent the growth of microorganisms that are present in food.

Negative Effects of Preservative Use

  • Make breathing challenging
  • Weaken cardiac tissues
  • Can lead to cancer and allergy concerns

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31) Explain the differences between acidic, basic, and regular salt.

Answer: Acid Salt:

Acid salts, such as NaHCO3, are made by partially neutralizing acid or containing replaceable hydrogen atoms.

Basic Salt:

Basic salt is a salt created when a polyhydroxy base is partially neutralized. Simple salts have interchangeable hydroxyl groups, for example. Zn(OH)Cl

Normal Salt:

Normal salt, such as Na2CO3, is a salt that is created when acid is completely neutralized.

Watch –> Salt definition,formation and Facts

Watch –> Methods for making Salts

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Numerical Issues:

Exercise for Self-Evaluation 10.1

Q) Which of the following reactions contains Bronsted bases and acids?

Solution:

(1)

Explanation:

We can observe from this reaction that,

  • H3O+ and HSO4 ions are produced when H2SO4 is ionized with water.
  • The Arrhenius theory, however, stipulates that an acid’s ionization in water must result in the production of H+ ions.
  • This reaction demonstrates that H2SO4 has indeed created H+ ions upon ionization in water.
  • And water accepts this proton and behaves as a base
  • H2SO4 is an acid, then, using the Arrhenius idea

(2)

Explanation:

In this reaction, we can see that,

  • Acetic acid CH3COOH is donating a proton
  • Water is accepting a proton
  • So, according to Bronsted-Lowery theory, by donating proton acetic acid behaves as an acid
  • And by accepting proton water behaves as a base

(3)

Explanation:

In this example, we can see that,

  • When H2S is donating a proton
  • Ammonia (NH3) is accepting (H+)
  • So, according to Bronsted-Lowery theory, by donating proton H2S behaves as an acid
  • And by accepting proton NH3 behave as a base.

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Exercise for Self-Evaluation 10.2

Q) In the cases below, identify the Lewis acid and Lewis base.

Solution:

Answer: (I)

From this reaction, we can demonstrate that,

  • Due to the incomplete octet of the Al atom, AlCl3 has an electron-deficient center.
  • Cl has a lone pair of electrons.
  • Cl is donating a lone pair of electrons to the AlCl3‘s electron-deficient centre.
  • According to Lewis theory, this causes Cl to behave as a Lewis base,
  • While AlCl3 acts as a Lewis acid.

(II)

In this reaction, it can be seen that,

  • The H+ is an electron-deficient core, OH has a lone pair of electrons, and OH is donating a lone pair of electrons to the H+.
  • Therefore, OH behaves as a Lewis base in accordance with Lewis theory by donating a lone pair of electrons.
  • H+ behaves as a Lewis acid by accepting a lone pair of electrons.

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Exercise for Self-Evaluation 10.3

Q) The [H+] content of a soft drink is 3 x 10-3 M. Is the beverage basic, neutral, or acidic?

Answer: Solution:

If [H+] = 3 x 10-3 M

Then, we know that if power of 10 is (-3). So, pH = – log [H+]

pH = – log [3 x 10-3]

pH = – log (10-3) – log 3

pH = -(-3) – log 3

pH = 3 – log 3

pH = 3 – log 3 (Hence, log 3 = 0.47)

pH = 3 – 0.47

pH = 2.53

Means solution is acidic.

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The average vinegar contains about 1M CH3COOH. It has an H+ concentration of 4.2 x 10-3 M. Is vinegar neutral, basic, or acidic?

Answer: Solution:

If [H+] = 4.2 x 10-3 M

Then, we know that if power of 10 is (-3). So, pH = – log [H+]

pH = – log [4. 2 x 10-3]

pH = – log (10-3) – log 4. 2

pH = -(-3) – log 4. 2

pH = 3 – log 4. 2

pH = 3 – log 4. 2 (Hence, log 4.2 = 0.623)

pH = 3 – 0.623

pH = 2.37

Means solution is acidic.

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Q) The [OH] of milk of magnesia, a suspension of solid magnesium hydroxide in its saturated solution, is measured by a student who comes up with a value of 4.2 x 10-3 M. Is the solution neutral, acidic, or basic?

Answer: Solution:

If [OH] = 4.2 x 10-3 M

Then, we know that if power of 10 is (-3). So, pOH = – log [OH]

pOH = – log [4. 2 x 10-3]

pOH = – log (10-3) – log 4. 2

pOH = -(-3) – log 4. 2

pOH = 3 – log 4. 2

pOH = 3 – log 4. 2 (Hence, log 4.2 = 0.623)

pOH = 3 – 0.623

pOH = 2.37

We know that,

pH + pOH = 14

pH = 14 – pOH

pH = 14 – 2.37

pH = 11.63

Means solution is basic.

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Exercise for Self-Evaluation 10.4

Q) List the three acid-base indicators by their names.

Answer: Names of three acid-base indicators:

  1. Thymol blue
  2. Methyl orange
  3. Phenol red

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Question: What shade does methyl red in solution have?

(i) pH = 4 (ii) pH = 9

Answer: (i) Red (ii) Yellow

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Q) What is the pH of the solution that becomes blue when bromothymol blue is added? pH = 5 or 9

Answer: The pH of this solution will be 9 when bromothymol blue is added and gives it a blue tint.

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Exercise for Self-Evaluation 10.5

Q) Milk of Magnesia, a hydroxide of magnesium, is used as an antacid. It reduces excessive stomach acid (HCl). For this neutralizing reaction, can you construct a comprehensive and rational chemical equation?

Answer:

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Q) Potassium hydroxide (KOH) and hydrochloric acid (HCl) react to form potassium chloride. For this neutralizing reaction, can you construct a comprehensive and rational chemical equation?

Answer:

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Q) Balance the following neutralization reactions:

Answer:

(i)

(ii)

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Exercise for Self-Evaluation 10.6

Q) Classify the following salts as normal or as acid salts.

(a) NaHSO4

(b) Na2SO4

(c) KHCO3

(d) K2CO3

Answer:

  1. NaHSO4 is an acidic salt
  2. Na2SO4 is normal salt
  3. KHCO3 is Acidic salt
  4. K2CO3 is a basic salt

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Activity 10.1

For testing the pH of solutions, use litmus paper, pH paper, and other indicators.

The recommended remedies are:

  • Lemon juice
  • Vinegar
  • Soap solution
  • HCl solution
  • And NaOH solution

Use the following steps to use a litmus paper:

  • Place each solution in a separate beaker,
  • Labeling each beaker with the name of the solution
  • Place about 2-3 cm3 of each solution in a separate test tube,
  • Dipping the red and blue litmus paper in each test tube;
  • Record the color change in each case.

Result:

  • If the blue litmus paper makes the red litmus paper blue, the answer is straightforward.
  • If the color of the red litmus paper remains unchanged, the solution is acidic.
  • Acidic solutions result in the blue litmus paper turning red.
  • If the blue litmus paper’s color does not change, the solution is straightforward.

Method to use a pH paper:

Utilize the following steps to use a pH paper:

  • Collect samples of each solution listed above in separate test tubes
  • Label each test tube
  • Submerge a piece of pH paper in each solution
  • Watch the pH paper’s color
  • Next, fill out the table below

Substance

pH

Lemon juice

2

Vinegar

2

Soap solution

12

HCl solution

3

NaOH solution

13

Method to use pH indicators:

Use a pH indicator as follows:

  • Take a sample of each of the aforementioned solutions in separate test tubes
  • Label each test tube
  • Put a drop or two of an indicator in each test tube.
  • Fill out the table below, taking note of how the solution’s color changes.

Substance

Color of methyl orange

pH

Lemon juice

Red

2

Vinegar

Red

2

Soap solution

Yellow

12

HCl solution

Red

3

NaOH solution

Yellow

13

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Activity 10.2

To uniformize the supplied hydrochloric acid solution

You will require:

  • Beakers
  • A conical flask
  • A pipette
  • A burette stand
  • And a glass rod
  • A standard solution of 0.1 M NaOH and phenolphthalein
  • Chemical equation:
  • n1 = 1 mole , n2 = 1 mole

Make the following decisions:

  • With the aid of a pipette, transfer 10 cm3 of NaOH solution into a conical flask.
  • Add a few drops of phenolphthalein to the conical flask as an indicator.
  • Note the initial reading on the burette.
  • Add the acid solution to the conical flask drop by drop while vigorously shaking the flask.
  • Fit a clean burette into the burette stand vertically.
  • Fill the burette with HCl solution up to the zero mark. Continue adding the acid solution until the pink tint is completely gone.
  • Keep a record of the burette’s final reading.
  • The difference between the final and initial readings indicates how much acid was used to neutralize 10.0 cm3 of NaOH solution.
  • Get three consistent readings by repeating the experiment.
  • Calculate the typical amount of HCl solution used.

Calculations and observations

Used HCl solution volume is V1 = 10 cm3.

HCl solution molarity = M1 =?

Used NaOH solution volume equals V2 = 10 cm3.

NaOH solution has a molarity of M2 = 0.1 M.

Number of moles of HCl = n1 = 1

Number of moles of NaOH = n2 = 1

M1 = 0.1 M


Continue Reading

Chapter Acids bases and salts important mcqs

Chapter Chemical Equilibrium Important mcqs

Chapter Chemical Equilibrium important questions

Chapter Chemical Equilibrium notes

-> Click to Watch Chemistry Class 10 Chapter Chemical Equilibrium Tutorials

-> Click to Watch Chemistry Class 10 Chapter Acids Bases and Salts Tutorials

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