STRENGTH OF SOLUTIONS

STRENGTH OF SOLUTIONS

Q1. Rewrite the following statements by selecting the correct options.

1. H₂SO₄ is a ________________________ acid.

a.       Monobasic

b.      Dibasic

c.       Tribasic

d.      Weak

2. Relation between normality and molarity for NaOH is _________________

a.      Normality = Molarity

b.      Normality = 2(Molarity)

c.       Normality = Basicity

d.      Normality = Acidity

3. The solution of common salt in water is ____________________

a.      Homogeneous

b.      Heterogeneous

c.       Acidic

d.      Basic

4. Basicity of acid depends on ______________________

a.      Number of H⁺ ions it produces.

b.      Number of OH^- ions it produces.

c.       Both, H⁺ and OH^- it produces.

d.      Its solubility in water.

5. Brass is an example of _____________________ type of solution.

a.       solid in liquid

b.      gas in liquid

c.       gas in gas

d.      solid in solid

Q2. Rewrite the columns II and III so as to match column I

No.	Column I	Column II	Column III
	Solution	Solute	Solvent
i	Copper in mercury	Copper	Mercury
ii	Sea water	Different salts	Water
iii	NaOH solution	NaOH	Water
iv	Copper in gold	Copper	Gold
v	Soda water	CO2  gas	Water

Q3. Distinguish between the following pairs.

i.      Acid and Base

Acid	Base
1.      The substance which gives hydrogen ions (H+) when dissolved in water is called an acid. 2.      Number of replaceable hydrogen present in acid is called basicity of acid. 3.      The relation between Normality and Molarity of an acid is given by the formula Normality = Basicity x molarity	1.      The substance which gives hydroxyl ions (OH)- when dissolved in water is called a base. 2.      Number of replaceable hydroxyl group present in based is called acidity of base. 3.      The relation between Normality and Molarity of a base is given by the formula Normality = Acidity x Molarity

ii. Normality and Molarity

Normality	Molarity
1.      Normality of a solution is based on the equivalent weight of the solute. 2.      The Normality of the solution is the number of gram equivalent weight of solute present per litre of its solution.	1.      Molarity of a solution is based on the molecular weight of the solute. 2.      The Molarity of a solution is the number of moles of solute dissolved per litre of solution.

Q4. Solve the following numerical.

Problems on equivalent weight of an acid.

1. Calculate equivalent weight of

1. Hydrochloric acid
2. Sulphuric acid
3. Acetic acid
4. Nitric acid

Problems of equivalent weight of a base

2.  Calculate equivalent weight of

1. Sodium hydroxide
2. Calcium hydroxide
3. Ammonium hydroxide
4. Potassium hydroxide

Problems on Normality

3. Find the Normality of HCl, HNO₃, H₂SO₄, KOH and NaOH.

4. 100 grams of NaOH are present in 4 litres of its solution. Find the normality of the solution.

5. If 2gm of KOH is dissolved in 500 ml water. Find the normality of the solution.

6. Sulphuric acid solution contains 4.9gm of sulphuric acid per litre. Find its normality.

Problems on Gram/ Litre

7. Find Grams/Litre of the 0.1N NaOH solution.

8. Find gram/litres of 0.25N NaOH.

9. Find the gms per litre of 0.15N HCl.

Problem on Normality equation i.e.

10. An acid is 0.01 N.9 ml of this acid required 10 ml of basic solution for complete neutralisation. Find the normality of base and weight of base dissolved in 1000 ml of solution.

(Equivalent weight of base = 56) (N=0.009N.0.504g)

Q5. Define the following:

Textual questions

i.                    Molarity: - The molarity of a solution is the number of moles of solute dissolved per litre of solution.

ii.                  Equivalent weight: - Equivalent weight is that weight of a substance which combines with or displaces 1.008 parts by weight of hydrogen or 8 parts by weight of oxygen or 35.5 parts by weight of chlorine.

iii.                Basicity: - Number of replaceable hydrogen present in acid is called basicity of acid. For example:          NaOH, KOH  are called Mono acidic base

H₂SO₄ is called Dibasic acid.

H₃PO₄ is called Tribasic acid.

iv.                Acid: - The substance which gives hydrogen ions (H⁺) when dissolved in water is called an acid for example.

v.                  Normality: - The normality of the solution is the number of gram equivalent weight of the solute present per litre of the solution.

Non – textual questions

1.      Solution: - A solution is a homogeneous mixture of two or more non – reacting substances.

2.      Aqueous solution: - A solution in which water is used as a solvent is called aqueous solution.

3.      Non – Aqueous solution: - A solution in which solvent other than water is used is called non – aqueous solution.

4.      Gram mole: - The quantity of the substance expressed in grams numerically equal to the molecular mass is termed as ‘gram mole’.

5.      Molecular mass (molecular weight): - Molecular mass is the relative mass of a molecule with reference to ¹²C which is assigned mass of 12u.

6.      Equivalent weight of an acid: - The weight of an acid which contains one part by weight of replaceable hydrogen is called its equivalent weight.

7.      Equivalent weight of a base: - The weight of a base which contains one part by weight of replaceable hydroxyl group is called its equivalent weight.

8.      Acidity: - Number of replaceable hydroxyl groups present in base is called acidity of base. For example:    NaOH, KOH are Mono acidic base.

Ca(OH)₂ Diacidic base

Al(OH)₃ Triacidic base

9.      Standard solution: - The solution whose concentration is accurately known is called standard solution.

10.  Base: - The substance which gives hydroxyl ions (OH)^- when dissolved in water is called base. For example

Q6. Explain neutralisation reaction

Answer. Neutralisation reaction: - Acids and bases in their aqueous solutions react with each other and produce salt and water. The resulting solution is neither acidic nor basic but is neutral. This reaction is known as neutralisation reaction. For example

Q7. State the types of solutions and give one example of each.

Answer. There are give types of solutions, they are as follows.

a. Solid in liquid: - In this type, solute is solid and solvent is liquid. Solution exists in liquid state.

Example: Salt of sugar in water, Copper in mercury, sea water etc.

b. Gas in Liquid: - In this type, solute is gas and solvent is liquid, solution exists in liquid state.

Example: Carbon dioxide gas dissolved in water i.e. soda water.

c. Gas in Gas: - In this type, the solute and solvent both are gases. Solution exists in gaseous state.

Example: Air.

d. Liquid in Liquid: - In this type, the solute and solvent both are liquids. Solution exists in liquid state. Example: Alcohol and water.

e. Solid in Solid:- In this type, the solute and solvent both are solids. Solution exists in solid state. Example Alloy of copper, iron etc.

Q8. Give scientific reasons

Non – textual questions

1. Formation of solution is a physical change.

Answer.

1.      A solution is a homogeneous mixture of two or more non – reacting substances.

2.      The substance which is present in larger proportion is called ‘solvent’ and that which is present in lesser proportion is called ‘solute’.

3.      Solute and solvent do not chemically react with each other, so no new substance is formed chemically.

4.      Sometimes original substances i.e. solute and solvent can be recovered by easy means.

5.      Hence, formation of solution is a physical change.

2. The nature of aqueous solution may be acidic or basic.

Answer.

1.      Substances when dissolved in water undergo dissociation.

2.      According to Arrhenious theory, a substance which gives hydrogen ions(H⁺) when dissolved in water is called an acid and a substance which gives hydroxyl ions (OH)^- when dissolved in water is called as base.

3.      Thus due to the formation of hydrogen ions (H⁺) or hydroxyl ion (OH)^-, the nature of aqueous solution may be acidic or basic.

3. CH₃COOH is a weak acid.

Answer.

1.      The acids which dissociate to lesser extent and give less number of hydrogen ions in solution are called weak acids.

2.      CH₃COOH, when dissolved in water dissociates as

3.      It dissociates to lesser extent in water and gives less number of hydrogen ions.

4.      Hence, CH₃COOH is a weak acid.

4. HCl and H₂SO₄ are called strong acids.

Answer.

1.      The acids which dissociate to a large extent in water and give large number of hydrogen ions in solution are called strong acids.

2.      HCl and H₂SO₄ when dissolved in water dissociates as follows

3.      They dissociates to a large extend in water and gives large number of hydrogen ions.

4.      Hence, HCl and H₂SO₄ are called strong acids.

5. NaOH and KOH are called strong bases.

Answer.

1.      The bases which dissociate to large extent in water and give large number of hydroxyl ions in solution are called strong bases.

2.      NaOH and KOH, when dissolved in water dissociates as follows.

3.      They dissociate to a large extent in water and gives large number of hydroxyl ions.

4.      Hence, NaOH and KOH are called strong bases.

6. NH₄OH is a weak base.

Answer.

1.      The bases which dissociate to lesser extent and give less number of hydroxyl ions in solution are called weak base.

2.      NH₄ OH, when dissolved in water dissociates as

3.      It dissociates to lesser extent in water and gives less number of hydroxyl ions.

4.      Hence, NH₄OH is a weak base.

Q9. Answer the following

1. State the Arrhenious theory of acid and base

Answer. Arrhenious theory of acid and base are

1. In 1887, Arrhenious proposed the theory of acids and bases.
2. Substances when dissolved in water undergo dissociation and the nature of he aqueous solution may be acidic or basic.

Arrhenious defined acids and bases as follows:

Acid: - The substance which gives hydrogen ions (H⁺) when dissolved in water is called an acid for example.

                        

Base: - The substance which gives hydroxyl ions (OH)^- when dissolved in water is called base. For example

                         

2. What are strong acids? Give examples.

Answer. The acids which dissociate to a large extent in water and give large number of hydrogen ions (H⁺) in solution are called strong acids.

Example:         Hydrochloric acid (HCl)

                        Nitric acid (HNO₃)

                        Sulphuric acid (H₂SO₄)

3. What are weak acids? Give examples.

Answer. The acids which dissociate to lesser extent and give less number of hydrogen ions(H⁺) in solution are called weak acids.

Example:         Acetic Acid (CH₃COOH)

4. What are strong bases? Give examples.

Answer. The bases which dissociate to a large extent in water give large number of hydroxyl ions (OH)^- in solution are called strong bases.

Examples: -     Sodium hydroxide (NaOH)

                        Potassium Hydroxide (KOH)

5. What are weak bases? Give examples

Answer. The bases which dissociate to lesser extent and give less number of hydroxyl ions (OH)^- in solution are called weak bases.

Example: - Ammonium hydroxide [NH₄OH].

6. How is normality and molarity related?

Answer.

For Acids: The relation between normality and molarity of an acid depends upon the basicity of that acid.

Normality = Basicity x Molarity

For monobasic acids such as HCl, HNO₃

Normality = 1 x Molarity

i.e. Normality = Molarity.

For dibasic acids such as H₂SO₄

Normality = 2 x Molarity

For Tribasic acids such as H₃PO₄

Normality = 3 x Molarity.

For bases: The relation between normality and molarity of a base depends upon the acidity of that base.

Normality = Acidity x Molarity.

For monoacidic base such as NaOH, KOH

Normality = 1 x Molarity

i.e. Normality = Molarity

For diacidic base such as Ca (OH) ₂

Normality = 2 x Molarity

For triacidic base such as Al (OH) ₃

Normality = 3 x Molarity.