Ionic Equilibrium MCQ Quiz - Objective Question with Answer for Ionic Equilibrium - Download Free PDF

CONCEPT:

Solubility Product (K_sp) and Solubility (S)

• The solubility product constant (K_sp) is the equilibrium constant for a solid substance dissolving in an aqueous solution.
• For a salt dissolving into its constituent ions, the relation between solubility (S) and K_sp depends on the stoichiometry of the dissociation.
• The general method is to:
  • Write the dissociation equation
  • Express ion concentrations in terms of solubility S
  • Substitute into the K_sp expression and solve for S

EXPLANATION:

• A - II: AB type (e.g. AgCl)
  • Dissociation: AB ⇌ A⁺ + B⁻
  • K_sp = S × S = S² ⇒ S = √K_sp
• B - I: AB₂ type (e.g. PbI₂)
  • Dissociation: AB₂ ⇌ A²⁺ + 2B⁻
  • K_sp = (2S)² × S = 4S³ ⇒ S = ∛(K_sp/4)
• C - III: AB₃ type (e.g. Al(OH)₃)
  • Dissociation: AB₃ ⇌ A³⁺ + 3B⁻
  • K_sp = S × (3S)³ = 27S⁴ ⇒ S = (K_sp/27)^1/4
• D - IV: A₃B₂ type (e.g. Ca₃(PO₄)₂)
  • Dissociation: A₃B₂ ⇌ 3A²⁺ + 2B³⁻
  • K_sp = (3S)³ × (2S)² = 108S⁵ ⇒ S = ∛(K_sp/108)

Therefore, the correct answer is: Option 1) A - I, B - II, C - III, D - IV

CONCEPT:

• Buffer Solution: A buffer is a solution that resists changes in pH upon the addition of small amounts of acid or base. It typically contains a weak acid and its conjugate base or a weak base and its conjugate acid.
• Henderson-Hasselbalch Equation: Used to calculate the pH of a buffer solution.
  • pH = pKa + log [Salt / Acid]
• pH of Strong Acid-Base Reaction: When a strong acid reacts with a strong base, the pH is determined by the excess amount of H⁺ or OH^- present.
• pOH Concept: pOH = –log[OH^-], and pH + pOH = 14
• Special Equation for Weak Acid + Strong Base: For incomplete neutralization:
  • pH = –log [ (N_AV_A – N_BV_B) / (V_A + V_B) ]

EXPLANATION:

• A -  (r): since OH⁻ is in excess: pOH = –log[OH⁻] ⇒ matches (r)
• B - (p), (r): This is a mixture of strong base (NaOH) and weak acid (CH3COOH). As base is in excess, we apply:
• pH = –log [ (NAVA – NBVB) / (VA + VB) ] ⇒ matches (p)
• • Also, OH⁻ present in solution makes pOH relevant ⇒ matches (r)
• C - (q),(r): A buffer is also formed here, with CH₃COOH and its salt. Use:
  • pH = pKa + log [Salt / Acid] ⇒ matches (q)
  • since OH− is in excess: pOH = –log[OH−] ⇒ matches (r)
• D - (r), (s): This is a neutralization reaction between strong acid and strong base.
  • If complete neutralization occurs, use pH = 7 + (1/2)pK_a + (1/2)log C ⇒ matches (s)
  • If excess OH⁻ or H⁺, then pOH = –log[OH^-] ⇒ matches (r)

Therefore, the correct answer is Option (a): A-(r); B-(q),(r); C-(q)(r); D-(p),(s).

Correct Answer: B) A–6, B–5, C–3, D–4

Explanation:

Concept:

Let the solubility of

Al(OH)₃ ⇌ Al³⁺ + 3OH^-

s 3s

NaoH ⇌ Na⁺⁺ OH^-

0.2 M 0.2M

Calculation:

[(Al³⁺)] = s and [OH^-] = 3s + 0.2 ≈ 0.2

k_sp = 2.4 × 10^-24 = [Al³⁺] [OH^-]

2.4 × 10^-24 = s(0.2)³

CONCEPT:

Solubility Product Constant (Ksp) and Dilution Effects

• The solubility product constant, Ksp, represents the equilibrium between a solid and its dissociated ions in a saturated solution.
• For the dissociation of Mg(OH)2:

  Mg(OH)2(s) ⇌ Mg2+(aq) + 2OH-(aq)

• From this, Ksp = [Mg2+][OH-]2
• Adding water dilutes concentrations, while adding acids (like HCl) can shift equilibrium by reacting with OH-.

EXPLANATION:

• Step I: Determine [Mg2+] from Ksp
  • Let [Mg2+] = x, then [OH-] = 2x
  • Ksp = 4x3
  • 3.2 × 10-11 = 4x3
  • x = 2 × 10-4 M
• Step II: Dilution with water
  • Initial volume = 0.5 L, final volume = 1 L
  • [Mg2+] = (2 × 10-4 M) × (0.5 / 1) = 2 × 10-4 M
• Step III: Adding to 0.5 L of 0.1 M HCl
  • Volume after mixing = 100 mL + 500 mL = 600 mL
  • [Mg2+] = (2 × 10-4 M × 100) / 600 = 3.33 × 10-5 M
• Step IV: Mixing 25 mL of this with 225 mL of 0.060 M MgCl2
  • Mg2+ from MgCl2 = 0.060 M × 0.225 L = 13.5 × 10-3 mol
  • Total volume = 250 mL = 0.250 L
  • [Mg2+] = 13.5 × 10-3 mol / 0.250 L = 5.4 × 10-2 M

Therefore, the final concentration of Mg2+ in the solution is approximately 5.4 × 10-2 M.

Concept:

pH of acidic buffer - 

• Buffer solution - Buffer solution is a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It is a solution highly known for maintaining its pH on dilution with a small amount of strong acid or strong base by maintaining the H⁺ ion concentration inside it. 
• Two types of buffer solutions are there
• Acidic buffer - Highly specific for pH<7 and is a mixture of a weak acid and its conjugate base.
• Weak buffer - Highly specific for pH>7 and is a mixture of a weak base and its conjugate acid.
• pH of the acidic buffer is given by the formula -

pH = pKa + log ([salt]/[acid])

where pK_a = negative logarithms of the acid dissociation constant.

As acetic acid is a weak acid and sodium acetate is its conjugate salt with a strong base(NaOH), they form an acidic buffer whose pH is calculated by the formula -

pH = pKa + log ([salt]/[acid])

Chemical reaction - CH₃COOH + NaOH \(\rightarrow\) CH₃COONa +H₂O

Calculation -

Given,

• pKa = 4.57 (negative logarithms of the acid dissociation constant of acetic acid)
• [acid] = 0.01 M (concentration of acetic acid)
• [salt] = 0.10 M (concentration of salt)

Put all these values in the formula,

pH = pKa + log ([salt]/[acid])

=4.57 + log(0.10 / 0.01)

=4.57 + log(10)

= 4.57 + 1   -- (∵ log10 = 1)

=5.57

So, the pH of the buffer solution is = 5.57

Hence, the correct answer is option 2.

The correct answer is Kolbe.

Key Points

• Synthesis of Acetic Acid
  • Acetic acid was first made or created from inorganic components in 1845 by German scientist Hermann Kolbe.
  • He created carbon disulfide with chlorine, and the end result was carbon tetrachloride.
  • After that, tetrachloroethylene was produced through thermal decomposition, trichloroacetic acid was created through aqueous chlorination, and acetic acid was finally produced through an electrolytic reduction.
  • He exclusively used inorganic materials made of hydrocarbons.
  • Carbon, hydrogen, and oxygen are inorganic elements that are used to create acetic acid while acetic acid is an organic one.
  • Acetic acid has a chemical formula and is a weak acid.
  • Kolbe's work was groundbreaking since he synthesised organic chemicals from inorganic ones.
  • In addition to bacterial fermentation, acetic acid is also made synthetically.
  • Some fruits naturally contain it.

Additional Information

• Kolbe's work was groundbreaking since he synthesised organic chemicals from inorganic ones. 
• In addition to bacterial fermentation, acetic acid is also made synthetically.
•  some fruits naturally contain it.

The correct answer is Less than 7

Key Points 

• When a salt is formed from the neutralization of a strong acid and a weak base, the resulting solution is acidic. This is because the strong acid completely dissociates in water, providing a high concentration of (H+) ions, while the weak base does not dissociate completely and therefore provides fewer (OH^-) ions to neutralize the (H+). As a result, the (H⁺) concentration in the solution is higher than the (OH-) concentration, leading to an acidic solution.

Therefore, the pH value of a salt made up of a strong acid and a weak base is Less than 7

• The cations of strong acids do not hydrolyze and therefore the solutions of salts formed by strong acids and strong bases are neutral, i.e. their pH is 7, whereas the solutions of salts formed by strong bases and weak acids are alkaline, i.e. their pH>7.
• Salts that are from strong bases and weak acids do hydrolyze, which gives them a pH greater than 7.
• The pH value range of a weak base is 7.1 to 10 whereas a strong base is 10.1 to 14.
• All substances can be classified as neutral (with a pH of about 7), basic (pH greater than 7), or acidic (pH less than 7), and the pH tells us how strong or weak that substance is as well. For example, a substance with pH = 8 is a very weak base, but a substance with pH = 3 is a strong acid.

The correct answer is II Only.

Key Points List of Acid and Natural Resources:

 Concept:

Lewis concept of acids and bases is given as follows:

The interaction between Lewis acid and base- 

• Lewis acid has a vacant unoccupied orbital called LUMO.
• Lewis bases have fulfilled occupied orbital called HOMO.
• Electron density from HOMO is donated to LUMO of Lewis acid.
• A simple HOMO and LUMO interaction is shown below:

This donation of electron density forms a covalent coordinate between the acid and the base,

Explanation:

BCl₃ -

• BCl₃ molecule has an empty p orbital because its octet is not fulfilled.
• It can accept an electron pair inti this orbital

Thus it electron-deficient and a Lewis acid

FeCl3:

• Fe is a transition metal having empty d orbitals.
• It can easily accept a lone pair in the empty 4d orbital and can act as Lewis acid.

​

Hence, BCl3, FeCl3 is a pair of Lewis acids.

Additional Information

• AlCl3: AlCl3 also has empty p orbitals and thus is an electrophile.

• Proton acceptors are Bronsted-Lowry bases, while Proton donors are Bronsted-Lowry acids

Thus, HCl, HNO3 and H₂CO₃ NH4+ are Bronsted acids.

The correct answer is Oxalic acid

Concept:-

Chemical reactions in photography: In photographic film, there's a layer of silver halide crystals. When the film is exposed to light, these crystals react and reduce to metallic silver, forming a 'latent image.' Chemicals such as acetic acid are used to control the timing and extent of these reactions.

Acid-base reactions: Oxalic acid is a weak acid, but it's strong enough to neutralize the alkaline developer used in film processing. This neutralization reaction is an acid-base reaction.

Photographic Bleaching: Oxalic acid participates in the bleaching stage of the toning process. It helps to dissolve the metallic silver in the photo paper. This bleaching provides a 'blank canvas' that can then be redeveloped to produce various tonal effects

Explanation:-

Photographic toning is a method to change the color of black-and-white photographs and works by replacing the metallic silver in the photographic material with a silver compound. For instance, in the process known as "bleach and redevelop," oxalic acid is used to bleach the original print (dissolving the silver), which can then be redeveloped in a bath for a different shade or hue.

Here are the explanations for the other acids:

• Formic Acid (Option 1): This type of acid is not typically used in the photography industry. It serves other functions in the agricultural sector and in the production of leather.
• Oxalic Acid (Option 2): Oxalic acid is a weak acid, but it's strong enough to neutralize the alkaline developer used in film processing. This neutralization reaction is an acid-base reaction. Oxalic acid is mainly used as a reducing element in the development of photographic film. This acid is also used in wastewater treatment plants to effectively remove lime from water.
• Citric Acid (Option 3): Citric acid isn’t conventionally adopted in photographic processes but it can work as an acid stop-bath alternative due to its property to neutralize the developer effectively.
• Acetic Acid (Option 4): Acetic acid does not find use in photography.

Oxalic acid is a dicarboxylic acid with a chemical formula C₂H₂O₄. It is also known as Ethanedioic acid or Oxidic acid. This organic compound is found in many vegetables and plants. It is the simplest dicarboxylic acid with condensed formula HOOC-COOH and has an acidic strength greater than acetic acid.

Conclusion:-

So the acid used in photography is Oxalic acid

Concept:

pH of a solution:

• The pH level is a measure of the number of Hydrogen ions in a solution.
• The lower the solution or compound on the pH scale, the higher will be the concentration of hydrogen ions.
• The pH is used to measure the acidity or alkalinity of a solution.
• The range of pH scale 0 to 14.
  • If pH < 7 then solution is acidic.
  • If pH > 7 then solution is basic.
  • If pH = 7 then solution is neutral.

• The pH is given by

\(pH=-log[H^+]\)

\(pH+pOH=14\)

\(pOH=-log[OH^-]\)

Calculation:

Given:

• pH of a tomato juice is 4.
• We know,

\(pH=-log[H^+]\)

Substituting pH = 4, we get:

\(4=-log[H^+]\)

\([H ^+ ] = 10 ^{ - 4} = .0001\)

Hence, the concentration of hydronium ions in tomato juice is .0001.

The correct answer is Oxalic acid.

Key Points

• Oxalic acid is a crystalline substance that dissolves in water to create a colorless solution. Food items such as spinach and cabbage, broccoli, parsley, and tomatoes contain it.
• Oxalic acid is extensively used as an acid rinse in laundries because it is good for removing rust and ink stains.
•  It is the most basic dicarboxylic acid. It is a white crystalline substance that converts most insoluble iron compounds into soluble complex ions in water.

Additional Information

• Tartaric acid is a white, crystalline organic acid found naturally in many fruits, including grapes, bananas, tamarinds, and citrus.
• Lactic acid is generated primarily by muscle cells and red blood cells. It is found primarily in dairy products.
• Citrus fruits, particularly lemons and limes, contain naturally occurring citric acid. Citric acid in its synthetic form is extensively used as an additive in food, cleaning products, and nutritional supplements.

The correct answer is Hydrogen.

Key Points

• Acids react with metals to release hydrogen gas.
• Salts and hydrogen gas are produced when acids react with metals.
• Metal + Acid → Salt + Hydrogen

Additional Information 

• No matter what metal or acid is used, the reaction always produces hydrogen gas along with the salt.
• However, the reaction rate depends on the metal used and the height of the reactivity series.
• Ex:- Zn(s) + 2HCl (aq) → ZnCl2 (aq) + H2 (g)

Concept:

• The solubility product of sparingly soluble salt in a saturated solution can be defined as the product of the equilibrium molar concentration of its constituent ions raised to the power of their stoichiometric coefficient.
• What happens is that in a sparingly soluble salt, such as BaSO₄, the salts are not completely ionised and there exists an equilibrium between the ions and undissociated insoluble salt. At equilibrium, the equilibrium constant is known as the solubility product constant or simply solubility product.

Let us take a general salt A_xB_y. In the equilibrium, the dissociation may be represented as:

A_xB_y = xA^y+ + yB^x-, where x and y are stoichiometric coefficients.

• The generalised solubility product 'K_sp' is: 

K_sp = [Ay+]^x[Bx-]^y

• The K_sp of a slightly soluble salt is constant for a given temperature, irrespective of the source of ion in the K_sp expression.
• Solubility is defined as the number of moles of solute present in a litre of a saturated solution at a given temperature. It is denoted by 'S'.
• The solubility of a substance at a given temperature is not constant and depends on the presence of other ions.
• The salt AxBy dissociates as xAy+ + yBx-, if the solubility of The salt is 'S', the 'xS' amount of ion A^y+ is produced and 'yS' amount of ion B^x- is produced. 
• In solubility product expression, the concentration terms are thus the solubility values of the ions.

Ksp = [xS]x[yS]y

Calculation:

Given:

• The solubility of a salt A2B3 is 1 × 10-3.
• The salt will dissociate as follows:

 A2B3 = 2A³⁺ + 3B^2-

• The K_sp value will be given by: [A3+]²[B2-]³
• The solubility 'S' of the ions is =  1 × 10-3.

Hence, K_sp value =

Ksp = [xS]x[yS]y

Ksp = [2s]²[3s]³ = 108 [s]⁵ = 108 × [1 × 10-3]⁵

So, Ksp = 108 × 1 × 10-15 = 1.08 × 10-13

Hence,  solubility product is 1.08 × 10-13.