GATE ES Principles of water chemistry PYQs & Answers

Questions 1–10 of 22. Imported answers require independent review unless marked reviewed.

The analysis of a water sample is shown in the table. The hardness of the water sample is ______ mg/L as CaCO

Atomic weight (g/mol): Ca = 40; Mg = 24; Na = 23; Cl = 35.5; S = 32; O = 16; N = 14

Species	Concentration (mg/L)
Na	30
Ca	10
Mg	15
Cl	30
SO	60
NO	5

Your answerChoose one option.

87.5

62.5

25.5

47.5

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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).

SO₂(aq) ⇌ H⁺ + HSO₃⁻ (i)

HSO₃⁻ ⇌ H⁺ + SO₃²⁻ (ii)

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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.

Diagram for Environmental Science and Engineering question 52

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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

Your answerChoose one option.

only Explanation 1 is correct

Explanations 1 and 2 are correct

Explanations 1 and 3 are correct

Explanations 2 and 3 are correct

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Correctly label the speciation diagram below:

Diagram for Environmental Science and Engineering question 37

Your answerChoose one option.

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

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

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

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

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Choose the correct option(s) from the following regarding the solubility in water

Your answerSelect all correct options. You can choose more than one.

Water is a polar molecule because of the asymmetric distribution of charge between the oxygen and hydrogen atoms of the water molecule.

In a water molecule, the electrons shared between oxygen and hydrogen are attracted more towards the hydrogen atom.

Non-polar compounds are highly soluble in water because of their strong interaction with water molecules.

Aromaticity and charge of molecules influence their solubility in water.

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Hardness in water is NOT caused by _________.

Your answerChoose one option.

Ca²⁺

Si²⁺

Mg²⁺

CO₃²⁻

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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.

Your answerChoose one option.

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

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

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

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

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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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The ionic strength of a solution containing 0.01M of CaCl₂ and 0.001M of Na₂SO₄ is ______ M (rounded off to 3 decimal places).

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GATE ES Principles of water chemistry PYQs

How to practice Principles of water chemistry

Question 41

Question 51

Question 52

Question 36

Question 37

Question 43

Question 12

Question 38

Question 50

Question 51