Principles of Water Chemistry - Environmental Chemistry - Environmental Science & Engineering Previous Year Questions

1

2024 · Environmental Science & Engineering · Environmental Chemistry · Principles of Water Chemistry

Environmental Science & Engineering (ES) 2024

A saturated CaCO₃ stock solution is existing at 25°C. In one experiment (i) 25 g Na₂CO₃ is added to the stock solution. In another experiment (ii) 25 g Na₂SO₄ is added to the stock solution. Select the correct statement from the following.

A

Addition of (i) increases the concentration of Ca²⁺ and addition of (ii) decreases the concentration of Ca²⁺

B

Addition of (i) decreases the concentration of Ca²⁺ and addition of (ii) increases the concentration of Ca²⁺

C

Addition of (i) and (ii) increase the concentration of Ca²⁺

D

Addition of (i) and (ii) decrease the concentration of Ca²⁺

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2

2024 · Environmental Science & Engineering · Environmental Chemistry · Principles of Water Chemistry

Environmental Science & Engineering (ES) 2024

The pH of a solution containing 0.1M of acetic acid and 0.05 M of sodium acetate is __________ (rounded off to 2 decimal places).
The pKa value of ionization of acetic acid is 4.76.

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3

2024 · Environmental Science & Engineering · Environmental Chemistry · Principles of Water Chemistry

Environmental Science & Engineering (ES) 2024

An industry discharges 2 million liters per day (MLD) of wastewater with a temperature of 45°C and a pH of 2, whereas the neighboring industry produces 3 MLD of wastewater with a temperature of 30°C and pH of 8. If both the wastewaters are mixed and carried through a pipeline, then the resultant pH of mixed wastewater is __________ (rounded off to 2 decimal places).
Neglect buffering capacity of the system and the temperature effect on pH.

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4

2025 · Environmental Science & Engineering · Environmental Chemistry · Principles of Water Chemistry

Environmental Science & Engineering (ES) 2025

A researcher added certain amount of HgCl₂ to water at pH 10. He calculated the expected concentration of mercury in the water. He asked his student to measure the concentration. His student used an instrument that can measure only the free metal, Hg²⁺. The student observed that the concentration measured by him was significantly less than the concentration calculated by the researcher. How can he explain the paradox to the researcher? Explanation 1: Significant fraction of the mercury would have changed phase from aqueous to gaseous phase, thus leaving less mercury in the water Explanation 2: Fraction of the mercury added to water would have formed aqueous complexes Explanation 3: Fraction of the mercury added to water could have precipitated Choose the correct option from the following

A

only Explanation 1 is correct

B

Explanations 1 and 2 are correct

C

Explanations 1 and 3 are correct

D

Explanations 2 and 3 are correct

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5

2025 · Environmental Science & Engineering · Environmental Chemistry · Principles of Water Chemistry

Environmental Science & Engineering (ES) 2025

Correctly label the speciation diagram below:

A

I=PO₄³⁻, II=HPO₄²⁻, III=H₂PO₄⁻, IV=H₃PO₄

B

I=H₃PO₄, II=HPO₄²⁻, III=H₂PO₄⁻, IV=PO₄³⁻

C

I=H₃PO₄, II=H₂PO₄⁻, III=HPO₄²⁻, IV=PO₄³⁻

D

I=PO₄³⁻, II=H₂PO₄⁻, III=H₃PO₄, IV=HPO₄²⁻

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6

2021 · Environmental Science & Engineering · Environmental Chemistry · Principles of Water Chemistry

Environmental Science & Engineering (ES) 2021

What is the pH of a water sample having H⁺ concentration of 10 mg/L? The atomic weight of H is 1 g/mol.

A

2

B

4

C

6

D

8

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7

2021 · Environmental Science & Engineering · Environmental Chemistry · Principles of Water Chemistry

Environmental Science & Engineering (ES) 2021

The molar concentrations (M, i.e. mol/L) of some ionic species in a water sample were estimated as follows:
Na⁺ = 0.25 M; Ca²⁺ = 0.12 M; Cl⁻ = 0.32 M; HCO₃⁻ = 0.05 M.
The ionic strength of this water sample is ______________ M (correct up to two decimal places).

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8

2021 · Environmental Science & Engineering · Environmental Chemistry · Principles of Water Chemistry

Environmental Science & Engineering (ES) 2021

Excess amount of solid calcium sulphate (CaSO₄) was added to a pure water sample (pH = 7) so that some solids remain undissolved at the equilibrium. The solubility product of CaSO₄ is 2×10⁻⁵ mol²/L². The molar concentration of SO₄²⁻ in this water sample at equilibrium will be ______________ mol/L (rounded off to three decimal places).

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9

2022 · Environmental Science & Engineering · Environmental Chemistry · Principles of Water Chemistry

Environmental Science & Engineering (ES) 2022

A solution has 0.001 mole/L zinc ions having pH of 6. Solubility product of zinc hydroxide is given as \(8 \times 10^{-18}\) (mole/L)\(^3\). Ignoring activity corrections, the ratio (rounded off to two decimal places) of reaction coefficient to solubility product would be __________

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10

2022 · Environmental Science & Engineering · Environmental Chemistry · Principles of Water Chemistry

Environmental Science & Engineering (ES) 2022

The Henry’s law constant of CO\(_2\) is \(3.4\times 10^{-2}\) M per atm in neutral water at 25°C. The dissolved CO\(_2\) (i.e., CO\(_2\cdot\)H\(_2\)O) at equilibrium undergoes the following reactions.

CO\(_2\cdot\)H\(_2\)O \(\rightleftharpoons\) H\(^+\) + HCO\(_3^-\) (Equilibrium constant = \(4.3 \times 10^{-7}\) M)
HCO\(_3^-\) \(\rightleftharpoons\) H\(^+\) + CO\(_3^{2-}\) (Equilibrium constant = \(4.7 \times 10^{-11}\) M)

If ambient CO\(_2\) concentration is 300 ppm, the total dissolved CO\(_2\) (in μM, rounded off to one decimal place) is __________.

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11

2023 · Environmental Science & Engineering · Environmental Chemistry · Principles of Water Chemistry

Environmental Science & Engineering (ES) 2023

The solubility of gas A is 16 mg/L in water and its vapor pressure is 0.042 atm. at 25 °C. In a closed system, the gas phase concentration of A is \(10^{-3}\) mol/L. Assuming Ideal gas constant (R) value as 0.0821 L-atm/mol-K, the concentration of gas A in water at 25 °C is ______________ (in mg/L, rounded off to two decimal places).

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12

2026 · Environmental Science & Engineering · Environmental Chemistry · Principles of Water Chemistry

Environmental Science & Engineering (ES) 2026

The following two reactions describe the chemistry of S(IV) in an aquatic system.
Under ideal conditions, the equilibrium constants for reactions (i) and (ii) are 1.3 × 10⁻² M (Kₛ₁) and 6.6 × 10⁻⁸ M (Kₛ₂), respectively.
If the pH of the system is 4.0 and the equilibrium concentration of SO₂(aq) is 1.0 M, the equilibrium concentration of SO₃²⁻ is ______ mM (rounded off to one decimal place).
\[ SO_2(aq) ightleftharpoons H^+ + HSO_3^- \quad (i) \]
\[ HSO_3^- ightleftharpoons H^+ + SO_3^{2-} \quad (ii) \]

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13

2026 · Environmental Science & Engineering · Environmental Chemistry · Principles of Water Chemistry

Environmental Science & Engineering (ES) 2026

The calibration graph between absorbance and the concentration of chromate (CrO₄²⁻) in a water sample is shown in the figure.
For an absorbance of 0.35 in a water sample, the estimated Cr(VI) concentration is ______ mg/L (rounded off to two decimal places).
Use the atomic weight (g/mol) of Cr and O as 52 and 16, respectively.

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