ENGG.tv

Learning Objectives:

Describe the structure and components of electrochemical cells, including electrodes, electrolytes, and the cell potential. Differentiate between galvanic (voltaic) and electrolytic cells.

Electrochemistry is a fundamental branch of chemistry that deals with the study of the relationship between electrical energy and chemical reactions.

The potential difference between the two electrodes is called the cell potential (Ecell), which is measured in volts (V). It represents the driving force for the redox reaction and is a key parameter in electrochemical cells.

Tiff592, CC BY-SA 4.0, via Wikimedia Commons

Solved Example: 9114-01

Find out the solubility of $Ni(OH)_2$ in 0.1 M NaOH. Given that the ionic product of $Ni(OH)_2$ is $2 \times 10^{-15}$

A. $2 \times 10^{-13}$ M

B. $2 \times 10^{-8}$ M

C. $1 \times 10^{-13}$ M

D. $2 \times 10^{8}$ M

$Ni(OH)_2{<=>} \underset{(S)}{Ni^{2+}} + \underset{(2S)}{2OH^-}$ where,
S = molar conc. of $Ni(OH)_2$
$NaOH {->} Na^+ +\underset{(0.1\,M)}{OH^-}$ \[\begin{aligned} K_{SP} &= [Ni^{2+}][OH^-]^2 \\ &= (S)(2S + 0.1)^2\\ &=(S)(4S^2 + 0.01 + 0.4S) \\ &= 4S^3 + 0.01S + 0.4 S^2 \\ \end{aligned}\]

Neglecting higher power of $S$, \[\begin{aligned} 2 \times 10^{-15} &= 0.01\ S\\ S &= 2 \times 10^{-13}M \end{aligned}\]

Correct Answer: A

Solved Example: 9458-01

What is the standard electrode potential (E$^0$) for a half-reaction in an electrochemical cell?

A. The potential of the half-reaction when the concentration of all species is 1 M

B. The potential of the half-reaction when the concentration of all species is 0.5 M

C. The potential of the half-reaction when the concentration of all species is 2 M

D. The potential of the half-reaction when the concentration of all species is 0 M

Correct Answer: A

Solved Example: 9458-02

What is Faraday's law of electrolysis?

A. The total current passing through a solution is directly proportional to the time of electrolysis

B. The mass of a substance deposited or liberated at an electrode during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte

C. The voltage of a cell is directly proportional to the concentration of ions in the electrolyte

D. The rate of reaction in an electrochemical cell is directly proportional to the temperature

Correct Answer: B

Solved Example: 9458-03

What is the Nernst equation used for in electrochemistry?

A. To calculate the standard cell potential

B. To calculate the equilibrium constant of a reaction

C. To calculate the concentration of reactants and products at non-standard conditions

D. To determine the rate of an electrochemical reaction

Correct Answer: C

Learning Objectives:

Define and understand the concept of molarity as a fundamental concentration unit used in chemistry.
Perform molarity calculations for various solutions and reactions.
Differentiate between normality and molarity, understanding that normality is based on the number of equivalents of a solute.
Learn how to calculate normality for various solutions, acids, and bases.
Differentiate between molality (m) and molarity (M) and understand the advantages of using molality in certain contexts.
Explain the role of molality in colligative properties, such as boiling point elevation, freezing point depression, and osmotic pressure.

Molarity (M) is the amount of a substance in a certain volume of solution.
Molarity is defined as the moles of a solute per liters of a solution.
Molarity is also known as the molar concentration of a solution.

\[M = \dfrac{\mathrm{No.\ of\ moles\ of\ the\ solute}}{\mathrm{Volume\ of\ the\ solution\ in\ liter}}\] Units of Molarity = Moles/liter.

Silk interest, CC BY-SA 4.0, via Wikimedia Commons

Normality:

The strength of a solution measured in terms of gram equivalent per liter is called normality.It is denoted by 'N'.

A solution having 1 gram equivalent of the dissolved solute in one liter of its solution is called normal solution.

Normality (N) is defined as the number of mole equivalents per liter of solution
normality = number of mole equivalents/1 L of solution.

Normality depends upon two factors:

Dilution
Temperature

Mathematically, \[N = \dfrac{\mathrm{weight\ in\ grams} \times 100}{\mathrm{equivalent\ weight\ expressed\ in\ grams} \times V}\]

Normality Formula:

Suppose N$_1$ and V$_1$ are normality and volume of one solution and N$_2$ and V$_2$ are the normality and volume of another solution, then according to the law of equivalent: \[N_1 V_1 = N_2 V_2\] This is called Normality Formula

Molality:

Molality is a measure of the number of moles of solute in a solution corresponding to 1 kg or 1000 g of solvent.

Molarity vs. Molality:

Molarity (M) is the amount of a substance in a certain volume of solution. Molarity is defined as the moles of a solute per liters of a solution. Molarity is also known as the molar concentration of a solution.

Molality is a measure of the number of moles of solute in a solution corresponding to 1 kg or 1000 g of solvent.

Solved Example: 9115-01

Which of the following terms representing the concentration of a solution does not depend on temperature?

A. Molarity

B. Molality

C. Normality

D. Molar fraction

Correct Answer: B

Solved Example: 9115-02

If you are given a 10% (mass by mass) aqueous solution of sugar, what is the mass of sugar dissolved in 180 g of water?

A. 18 g

B. 1.8 g

C. 10 g

D. 20 g

Correct Answer: D

Solved Example: 9115-03

10 g substance (molar mass = 50) is dissolved in 200 ml water and density of this solution was found to be 1.05 g/ml and approx molality of the solution is:

A. 1.05 mol/kg

B. 1.0 mol/kg

C. 0.1 mol/kg

D. 2.0 mol/kg

Correct Answer: B

Solved Example: 9116-01

The units of normality are:

A. mole. ml$^{-1}$

B. g. equivalent. lit$^{-1}$

C. mole. Kg$^{-1}$

D. mole. lit$^{-1}$

Correct Answer: B

Learning Objectives:

Define and understand the fundamental concepts of acids and bases in chemistry, including the Bronsted-Lowry and Lewis definitions.
Differentiate between acids and bases based on their characteristics, including the presence of hydrogen ions (H+) in acids and hydroxide ions (OH-) in bases.

Acid: A substance that produces Hydrogen ions when dissolved in water. Common examples are: Hydrochloric acid (HCl), Sulphuric acid (H$_2$SO$_4$) and Nitric Acid (HNO$_3$). Acids turn blue litmus paper red and their pH value is less than 7. Acids can be strong acids or weak acids based on how many H+ ions they contribute.

Base: A base is a substance that react with an acid to give salt and water. e.g. Sodium Oxide, Zinc Oxide, Alumnium Hydroxide, etc. Bases can be soluble (alkalis) or insoluble (Metal Oxides or Hydroxides). Alkalis turn red litmus paper blue and their pH values are greater than 7.

Solved Example: 9113-01

Sulphur Dioxide when dissolved in water forms:

A. Sulphur Trioxide

B. Sulphurous acid

C. Sulphuric acid

D. Sulphur

Correct Answer: B

Solved Example: 9113-02

Which of the following contains Citric acid?

A. Tomato

B. Orange

C. Tamarind

D. Sour milk

Correct Answer: B

Solved Example: 9113-03

Which type of medicines are used for treating indigestion?

A. Antibiotic

B. Analgesic

C. Antacid

D. Antiseptic

Correct Answer: C

Solved Example: 9113-04

What is the pH value of acid rain?

A. Less than 5.6

B. More than 5.6

C. Equal to 7.0

D. More than 7.0

Correct Answer: A

Solved Example: 9113-05

Which of the following substances can be used for identifying an acid solution?

A. NaCl

B. KNO$_3$

C. Na$_2$CO$_3$

D. K$_2$SO$_4$

Correct Answer: B

Redox reactions involve two half-reactions: one in which a substance loses electrons (oxidation) and another in which a substance gains electrons (reduction). Oxidation is the process of losing electrons, and reduction is the process of gaining electrons. The two processes are always coupled in a redox reaction. The species being oxidized is called the reducing agent because it causes reduction in another species. The species being reduced is called the oxidizing agent because it causes oxidation in another species.

Types of Redox Reactions: Redox reactions can be categorized into various types, including combination (synthesis), decomposition, displacement, and combustion reactions, among others. Combination reactions involve the formation of a compound from its elements, while decomposition reactions involve the breakdown of a compound into simpler substances. Displacement reactions occur when one element displaces another from a compound, and combustion reactions involve the rapid oxidation of a substance, often accompanied by the release of heat and light.

Solved Example: 9118-01

Which among the following happens in an oxidation reaction?

A. Electrons are gained

B. Electrons are lost

C. Protons are gained

D. Protons are lost

A. D

B. A

C. C

D. B

Correct Answer: D

Solved Example: 9118-02

Which one of the following statements is NOT correct for the given reaction?

\[Fe(S) + CuSO_4(aq) → FeSO_4(aq) + Cu(s)\]

A. Iron is the reducing agent

B. The solution turns green in colour after the reaction

C. Copper is a more reactive metal than iron

D. The reaction is an example of a redox reaction

Correct Answer: C

Learning Objectives:

Understand the concept of valence as it pertains to the combining capacity of an atom.
Recognize the valence electrons in an atom and understand their significance in determining chemical properties.

Valence refers to the combining capacity of an atom, expressed as the number of chemical bonds it can form with other atoms. It is a measure of the number of electrons an atom can gain, lose, or share to achieve a stable electron configuration.

Types of Valence:

Electron Valence: The number of electrons an atom can lose, gain, or share in a chemical reaction.
Covalence: The number of electron pairs shared between atoms in a covalent bond.
Ionic Valence: The charge on an ion formed by gaining or losing electrons.

Solved Example: 9120-01

Valency of an element depends on which of the following?

I. Number of losing electron

II. Number of gaining electron

III. Number of sharing electron

A. Only I and II

B. Only I and III

C. Only II and III

D. All I, II and III

Correct Answer: D

Solved Example: 9120-02

The oxidation state of V in V_2(O^{-4})_7 is:

A. +5

B. -5

C. +4

D. +10

Correct Answer: A

Learning Objectives:

Understand the concept of solubility product as it applies to sparingly soluble salts.
Define the equilibrium expression for solubility product (Ksp).
Calculate the solubility product constant (Ksp) for a given ionic compound using experimental data.

The solubility of a substance is the amount of that substance that will dissolve in a given amount of solvent. Factors that affect solubility:

Temperature: Solubility generally increases with temperature.
Common ion effect: Common ion reduces solubility.
pH of solution: pH affects the solubility of ionic compounds
Formation of complex ion: The formation of complex ion increases solubility.

Solubility product K$_{sp}$, is the mathematical product of its dissolved ion concentrations raised to the power of their stoichiometric coefficients. \[M_yX_z (s) \rightleftharpoons yM^{Z+} (aq) + zX^{Y-} (aq)\] \[K_{sp} = [M^{Z+}]^y[X^{y-}]^z\]

Solved Example: 9119-01

The solubility product for the dissociation of Mg(OH)$_2$ is 8 $\times$ 10$^{-9}$. Determine the concentration of OH$^-$ at equilibrium expressed as milligram per litres of CaCO$_3$.

A. 252 mg/l

B. 50 mg/l

C. 300 mg/l

D. 126 mg/l

Correct Answer: D

Solved Example: 9119-02

A solution in which no more solute can be dissolved at a given temperature is called:

A. Unsaturated solution

B. Universal solvent

C. Volatile solution

D. Saturated solution

Correct Answer: D

Solved Example: 9459-01

If the ion product (Q) is greater than the solubility product constant (Ksp) for a given salt, what is the likely outcome?

A. No reaction will occur.

B. Precipitation will occur until Q equals Ksp.

C. The solution will remain unsaturated.

D. The solution will become supersaturated.

Correct Answer: B

Solved Example: 9459-02

What is the primary application of solubility product principles in qualitative analysis?

A. Predicting the pH of a solution

B. Identifying insoluble salts in a mixture

C. Determining the rate of a chemical reaction

D. Calculating the concentration of ions in a solution

Correct Answer: B

Learning Objectives:

Use the pH scale to describe substances as weak or strong acids or alkalis.
Calculate pH values given strength of an acid or a base solution.

Definition:

pH is a measure of concentration of [H$^+$].

The pH Scale:

Pure water has a pH of 7.
Acidic solutions have pH less than 7.
Base solutions have pH more than 7.

The pOH Scale:

\[pH + pOH = 14\] \[pOH = 14- pH\]

Christinelmiller, CC BY-SA 4.0, via Wikimedia Commons
PH_Scale

OpenStax College, CC BY 3.0, via Wikimedia Commons

Solved Example: 9121-01

The pH value of the solution in which particular amino acid does not migrate under the influence of an electric field is called its:

A. Effusion point

B. Neutralisation point

C. Isoelectric point

D. Eutectic point

Correct Answer: C

Solved Example: 9121-02

The solution which resist the change in pH is called _____ Solution.

A. Acidic

B. Basic

C. Buffer

D. Neutral

Correct Answer: C

Solved Example: 9121-03

Which of the following statements are correct about an aqueous solution of an acid and a base?

Higher the pH, stronger is the acid.
Higher the pH, weaker is the acid.
Lower the pH, stronger is the base.
Lower the pH, weaker is the base.

A. 1 and 3

B. 2 and 3

C. 1 and 4

D. 2 and 4

Correct Answer: D

Solved Example: 9121-04

The pH of water at 25$^\circ C$ is 7. When it is heated to 100$^\circ C$, the pH of water:

A. Increases

B. Decreases

C. Remains same

D. Decreases up to 27$^\circ C$ and then increases

Correct Answer: B

Solved Example: 9121-05

What will happen when a few drops of HCl are added to a solution having a pH of 6.5?

A. The solution will become more acidic and the pH will decrease

B. The solution will become more acidic and the pH will increase

C. The solution will become less acidic and the pH will increase

D. The solution will become more alkaline and the pH value will increase

Correct Answer: A

Learning Objectives:

Understand the relationship between pK and the strength of acids and bases.
Develop the ability to interpret pK values in the context of acid-base equilibria and predict the behavior of chemical species in solution.

The term "pK" is often used to represent the negative logarithm (base 10) of the acid dissociation constant (Ka) or the ionization constant (Ki) for a particular chemical species.

In the context of acids, a lower pK value indicates a stronger acid. Strong acids have a higher tendency to donate protons (H⁺) in solution.

For bases, the pKb (negative logarithm of the base dissociation constant Kb) is used. A lower pKb value indicates a stronger base.

Solved Example: 9122-01

Which of the following indicates that the pK of an acid is numerically equal to the pH of the solution when the molar concentration of the acid and its conjugate base are equal?

A. Michaelis-Menten equation

B. Haldanes equation

C. Henderson-Hasselbalch equation

D. Hardy-Windberg law

Correct Answer: C

Inorganic Chemistry