Ionic Strength Quiz (20 Questions)
CSIR NET / GATE / SLET / IIT JAM Level
1. The ionic strength (I) of a solution containing 0.1 M NaCl and 0.05 M CaCl₂ is:
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Correct Answer: (c) 0.25 M
I = ½ Σ (c_i z_i²)
Na⁺: 0.1 × 1² = 0.1
Cl⁻ from NaCl: 0.1 × 1² = 0.1
Ca²⁺: 0.05 × 2² = 0.2
Cl⁻ from CaCl₂: 0.1 × 1² = 0.1
Total sum = 0.5 → I = ½ × 0.5 = 0.25 M
2. Which of the following 0.1 M solutions has the highest ionic strength?
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Correct Answer: (d) K₄[Fe(CN)₆]
Calculations:
NaCl: I = 0.1 M
MgCl₂: I = 0.3 M
AlCl₃: I = 0.6 M
K₄[Fe(CN)₆]: K⁺ 0.4 × 1 = 0.4, [Fe(CN)₆]⁴⁻ 0.1 × 16 = 1.6, sum = 2.0 → I = 1.0 M (highest)
3. The ionic strength of 0.05 M K₂SO₄ solution is:
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Correct Answer: (b) 0.15 M
K⁺: 0.10 × 1² = 0.10
SO₄²⁻: 0.05 × 2² = 0.20
Sum = 0.30 → I = 0.15 M
4. According to Debye-Hückel limiting law, log γ± is proportional to:
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Correct Answer: (a) √I
Debye-Hückel limiting law: log γ± = –A |z⁺z⁻| √I
5. For a 1:1 electrolyte at 25°C in water, the Debye-Hückel limiting law is:
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Correct Answer: (a) log γ± = –0.51 √I
A ≈ 0.51 for water at 25°C; for 1:1 electrolyte |z⁺z⁻| = 1.
6. The ionic strength of 0.01 M La₂(SO₄)₃ is:
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Correct Answer: (d) 0.15 M
La³⁺: 0.02 × 9 = 0.18
SO₄²⁻: 0.03 × 4 = 0.12
Sum = 0.30 → I = 0.15 M
7. Which salt contributes most to ionic strength for the same molar concentration?
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Correct Answer: (c) Al₂(SO₄)₃
Highest charges on ions (Al³⁺ and SO₄²⁻) give largest Σ c_i z_i².
8. The ionic strength of a solution containing 0.01 M Na₂SO₄ and 0.02 M CaCl₂ is:
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Correct Answer: (b) 0.09 M
Na⁺: 0.02 × 1 = 0.02
SO₄²⁻: 0.01 × 4 = 0.04
Ca²⁺: 0.02 × 4 = 0.08
Cl⁻: 0.04 × 1 = 0.04
Sum = 0.18 → I = 0.09 M
9. The exact value of constant A in Debye-Hückel equation at 25°C in water for 1:1 electrolyte is approximately:
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Correct Answer: (b) 0.509
Often rounded to 0.51, but precise value is 0.509.
10. The approximate ionic strength of human blood plasma is:
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Correct Answer: (a) 0.15 M
Physiological ionic strength is ~0.15 M (mainly from Na⁺, Cl⁻, etc.).
11. The ionic strength of 0.001 M Na₃PO₄ solution is:
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Correct Answer: (a) 0.006 M
Na⁺: 0.003 × 1 = 0.003
PO₄³⁻: 0.001 × 9 = 0.009
Sum = 0.012 → I = 0.006 M
12. According to Debye-Hückel limiting law, the plot of log γ± versus ___ is linear:
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Correct Answer: (b) √I
Slope = –A |z⁺z⁻|.
13. The extended Debye-Hückel equation includes an additional term of the form:
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Correct Answer: (a) +BI
To account for finite ion size at higher concentrations.
14. For a 2:2 electrolyte like MgSO₄, the magnitude of the slope in log γ± vs √I plot is approximately:
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Correct Answer: (b) 2.04
Slope = A × |z⁺z⁻| = 0.51 × 4 ≈ 2.04
For detail explanation Click Here
15. The ionic strength of 0.1 M H₂SO₄ (assuming complete dissociation) is:
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Correct Answer: (b) 0.3 M
H⁺: 0.2 × 1 = 0.2
SO₄²⁻: 0.1 × 4 = 0.4
Sum = 0.6 → I = 0.3 M
16. The ionic strength of 0.005 M FeCl₃ solution is:
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Correct Answer: (b) 0.030 M
Fe³⁺: 0.005 × 9 = 0.045
Cl⁻: 0.015 × 1 = 0.015
Sum = 0.060 → I = 0.030 M
17. Mean ionic activity coefficient (γ±) generally _____ with increasing ionic strength:
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Correct Answer: (a) decreases
Due to stronger inter-ionic interactions.
18. Ionic strength of a mixture containing 0.02 M KCl and 0.01 M BaCl₂ is:
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Correct Answer: (a) 0.05 M
K⁺: 0.02 × 1 = 0.02
Cl⁻ from KCl: 0.02 × 1 = 0.02
Ba²⁺: 0.01 × 4 = 0.04
Cl⁻ from BaCl₂: 0.02 × 1 = 0.02
Sum = 0.10 → I = 0.05 M
19. Ionic strength primarily affects which property in conductometric measurements?
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Correct Answer: (a) Conductance
It influences ion mobility and activity.
20. The ionic strength of 0.1 M Na₃PO₄ solution is:
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Correct Answer: (b) 0.6 M
Na⁺: 0.3 × 1 = 0.3
PO₄³⁻: 0.1 × 9 = 0.9
Sum = 1.2 → I = 0.6 M
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