Calculate the ionic strength of the following solutions containing 50 mM NaCl, 1 mM AIC13, 1 mM A12 (SO4) 3.

50 mM NaCl I = 0.05 M

1 mM AICl₃ I = 6 * 10⁻³ M

1 mM Al₂ (SO₄) ₃ I = 0.02 M

Explanation:

Ionic strength (I) is a measure of the concentration of ions in solution and can be calculated with the following expression:

I = 1/2 ∑Ci * Zi²

where,

Ci is the molarity of each ion (molarity of the salt * number of each ion in the salt)

Zi is the charge of each ion

50 mM NaCl

NaCl → Na⁺ + Cl⁻

I = 1/2 [C (Na⁺) * Z (Na⁺) ² + C (Cl⁻) * Z (Cl⁻) ² ]

I = 1/2 [50 * 10⁻³ M * (+1) ² + 50 * 10⁻³ M * (-1) ² ]

I = 0.05 M

1 mM AICl₃

AICl₃ → Al⁺³ + 3 Cl⁻

I = 1/2 [C (Al⁺³) * Z (Al⁺³) ² + C (Cl⁻) * Z (Cl⁻) ² ]

I = 1/2 [1 * 10⁻³ M * (+3) ² + 3 * 10⁻³ M * (-1) ² ]

I = 6 * 10⁻³ M

1 mM Al₂ (SO₄) ₃

Al₂ (SO₄) ₃ → 2 Al⁺³ + 3 SO₄²⁻

I = 1/2 [C (Al⁺³) * Z (Al⁺³) ² + C (SO₄²⁻) * Z (SO₄²⁻) ² ]

I = 1/2 [2 * 10⁻³ M * (+3) ² + 3 * 10⁻³ M * (2-) ² ]

I = 0.02 M