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Freundlich Isotherm

Environmental Engineering · FE Reference Handbook section

Environmental Engineering
6 formulas
10 exam-style examples
~57 min
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Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
Freundlich Isotherm — solve for adsorption capacity (x/m) — Freundlich Isotherm

Freundlich isotherm for activated carbon adsorption of an organic compound Given Freundlich capacity coefficient (K_f) = 92.5000; equilibrium concentration (C_e) = 10.2000 mg/L; Freundlich intensity constant (n) = 4.3500, determine the adsorption capacity (x/m) (x_m) in mg/g.

Given

  • Freundlichcapacitycoefficient(Kf)=92.5000Freundlich capacity coefficient (K_f) = 92.5000
  • equilibriumconcentration(Ce)=10.2000mg/Lequilibrium concentration (C_e) = 10.2000 mg/L
  • Freundlichintensityconstant(n)=4.3500Freundlich intensity constant (n) = 4.3500

Find

adsorption capacity (x/m) (x_m), in mg/g

Start with the thinking

  • The governing relation printed in this handbook section is Freundlich Isotherm.
  • Everything except x_m is given, so isolate x_m symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Freundlich isotherm relates adsorption capacity to equilibrium concentration for activated carbon adsorption in a linearized form.
log Celog (x/m)Freundlich isotherm linearized form

Figure 1 — schematic for Freundlich Isotherm — solve for adsorption capacity (x/m) — Freundlich Isotherm

Step-by-step solution

  1. Step 1 — State the governing relation:

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}
  2. Step 2 — Rearrange symbolically for x_m:

    xm=KfCe1/nx_{m} = K_f C_e^{1/n}
  3. Step 3 — List the givens: Freundlich capacity coefficient (K_f) = 92.5000, equilibrium concentration (C_e) = 10.2000 mg/L, Freundlich intensity constant (n) = 4.3500.

  4. Step 4 — Substitute the given values:

    xm=KfCe1/4.3500x_{m} = K_f C_e^{1/4.3500}
  5. Step 5 — Evaluate:

    xm=157.8 mg/gx_{m} = 157.8\ \text{mg/g}
  6. Step 6 — Check: returning x_m = 157.8 mg/g to

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}

    reproduces the given quantities, and both sides carry the same units.

Answer:
xm=157.8 mg/gx_{m} = 157.8\ \text{mg/g}

Why the other options are there

  • 315.5 — kept a factor of two that cancels in the correct rearrangement.
  • 78.8813 — dropped that same factor in the other direction.
  • 173.5 — rounded an intermediate value before the final step.

Reference: FE Handbook — Freundlich Isotherm

Example 2
Freundlich Isotherm — solve for Freundlich capacity coefficient — Freundlich Isotherm (2)

Freundlich isotherm linearized form fit to laboratory adsorption data Given equilibrium concentration (C_e) = 21.2000 mg/L; Freundlich intensity constant (n) = 2.1500; adsorption capacity (x/m) (x_m) = 72.6000 mg/g, determine the Freundlich capacity coefficient (K_f).

Given

  • equilibriumconcentration(Ce)=21.2000mg/Lequilibrium concentration (C_e) = 21.2000 mg/L
  • Freundlichintensityconstant(n)=2.1500Freundlich intensity constant (n) = 2.1500
  • adsorptioncapacity(x/m)(xm)=72.6000mg/gadsorption capacity (x/m) (x_m) = 72.6000 mg/g

Find

Freundlich capacity coefficient (K_f)

Start with the thinking

  • The governing relation printed in this handbook section is Freundlich Isotherm.
  • Everything except K_f is given, so isolate K_f symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Freundlich isotherm relates adsorption capacity to equilibrium concentration for activated carbon adsorption in a linearized form.
log Celog (x/m)Freundlich isotherm linearized form

Figure 2 — schematic for Freundlich Isotherm — solve for Freundlich capacity coefficient — Freundlich Isotherm (2)

Step-by-step solution

  1. Step 1 — State the governing relation:

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}
  2. Step 2 — Rearrange symbolically for K_f:

    Kf=x/mCe1/nK_{f} = \dfrac{x/m}{C_e^{1/n}}
  3. Step 3 — List the givens: equilibrium concentration (C_e) = 21.2000 mg/L, Freundlich intensity constant (n) = 2.1500, adsorption capacity (x/m) (x_m) = 72.6000 mg/g.

  4. Step 4 — Substitute the given values:

    Kf=x/mCe1/2.1500K_{f} = \dfrac{x/m}{C_e^{1/2.1500}}
  5. Step 5 — Evaluate:

    Kf=17.5403K_{f} = 17.5403
  6. Step 6 — Check: returning K_f = 17.5403 to

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Kf=17.5403K_{f} = 17.5403

Why the other options are there

  • 35.0805 — kept a factor of two that cancels in the correct rearrangement.
  • 8.7701 — dropped that same factor in the other direction.
  • 19.2943 — rounded an intermediate value before the final step.

Reference: FE Handbook — Freundlich Isotherm

Example 3
Freundlich Isotherm — solve for equilibrium concentration — Freundlich Isotherm (3)

Freundlich isotherm used to design a granular activated carbon column Given Freundlich capacity coefficient (K_f) = 14.0000; Freundlich intensity constant (n) = 4.8500; adsorption capacity (x/m) (x_m) = 24.1000 mg/g, determine the equilibrium concentration (C_e) in mg/L.

Given

  • Freundlichcapacitycoefficient(Kf)=14.0000Freundlich capacity coefficient (K_f) = 14.0000
  • Freundlichintensityconstant(n)=4.8500Freundlich intensity constant (n) = 4.8500
  • adsorptioncapacity(x/m)(xm)=24.1000mg/gadsorption capacity (x/m) (x_m) = 24.1000 mg/g

Find

equilibrium concentration (C_e), in mg/L

Start with the thinking

  • The governing relation printed in this handbook section is Freundlich Isotherm.
  • Everything except C_e is given, so isolate C_e symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Freundlich isotherm relates adsorption capacity to equilibrium concentration for activated carbon adsorption in a linearized form.
log Celog (x/m)Freundlich isotherm linearized form

Figure 3 — schematic for Freundlich Isotherm — solve for equilibrium concentration — Freundlich Isotherm (3)

Step-by-step solution

  1. Step 1 — State the governing relation:

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}
  2. Step 2 — Rearrange symbolically for C_e:

    Ce=(x/mKf)nC_{e} = \left(\dfrac{x/m}{K_f}\right)^{n}
  3. Step 3 — List the givens: Freundlich capacity coefficient (K_f) = 14.0000, Freundlich intensity constant (n) = 4.8500, adsorption capacity (x/m) (x_m) = 24.1000 mg/g.

  4. Step 4 — Substitute the given values:

    Ce=(x/mKf)4.8500C_{e} = \left(\dfrac{x/m}{K_f}\right)^{4.8500}
  5. Step 5 — Evaluate:

    Ce=13.9335 mg/LC_{e} = 13.9335\ \text{mg/L}
  6. Step 6 — Check: returning C_e = 13.9335 mg/L to

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Ce=13.9335 mg/LC_{e} = 13.9335\ \text{mg/L}

Why the other options are there

  • 27.8671 — kept a factor of two that cancels in the correct rearrangement.
  • 6.9668 — dropped that same factor in the other direction.
  • 15.3269 — rounded an intermediate value before the final step.

Reference: FE Handbook — Freundlich Isotherm

Example 4
Freundlich Isotherm — solve for adsorption capacity (x/m) (case 2) — Freundlich Isotherm (4)

Freundlich isotherm for activated carbon adsorption of an organic compound Given Freundlich capacity coefficient (K_f) = 9.0000; equilibrium concentration (C_e) = 29.5000 mg/L; Freundlich intensity constant (n) = 2.9500, determine the adsorption capacity (x/m) (x_m) in mg/g.

Given

  • Freundlichcapacitycoefficient(Kf)=9.0000Freundlich capacity coefficient (K_f) = 9.0000
  • equilibriumconcentration(Ce)=29.5000mg/Lequilibrium concentration (C_e) = 29.5000 mg/L
  • Freundlichintensityconstant(n)=2.9500Freundlich intensity constant (n) = 2.9500

Find

adsorption capacity (x/m) (x_m), in mg/g

Start with the thinking

  • The governing relation printed in this handbook section is Freundlich Isotherm.
  • Everything except x_m is given, so isolate x_m symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Freundlich isotherm relates adsorption capacity to equilibrium concentration for activated carbon adsorption in a linearized form.
log Celog (x/m)Freundlich isotherm linearized form

Figure 4 — schematic for Freundlich Isotherm — solve for adsorption capacity (x/m) (case 2) — Freundlich Isotherm (4)

Step-by-step solution

  1. Step 1 — State the governing relation:

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}
  2. Step 2 — Rearrange symbolically for x_m:

    xm=KfCe1/nx_{m} = K_f C_e^{1/n}
  3. Step 3 — List the givens: Freundlich capacity coefficient (K_f) = 9.0000, equilibrium concentration (C_e) = 29.5000 mg/L, Freundlich intensity constant (n) = 2.9500.

  4. Step 4 — Substitute the given values:

    xm=KfCe1/2.9500x_{m} = K_f C_e^{1/2.9500}
  5. Step 5 — Evaluate:

    xm=28.3457 mg/gx_{m} = 28.3457\ \text{mg/g}
  6. Step 6 — Check: returning x_m = 28.3457 mg/g to

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}

    reproduces the given quantities, and both sides carry the same units.

Answer:
xm=28.3457 mg/gx_{m} = 28.3457\ \text{mg/g}

Why the other options are there

  • 56.6914 — kept a factor of two that cancels in the correct rearrangement.
  • 14.1729 — dropped that same factor in the other direction.
  • 31.1803 — rounded an intermediate value before the final step.

Reference: FE Handbook — Freundlich Isotherm

Example 5
Freundlich Isotherm — solve for Freundlich capacity coefficient (case 2) — Freundlich Isotherm (5)

Freundlich isotherm linearized form fit to laboratory adsorption data Given equilibrium concentration (C_e) = 32.5000 mg/L; Freundlich intensity constant (n) = 1.2000; adsorption capacity (x/m) (x_m) = 40.9000 mg/g, determine the Freundlich capacity coefficient (K_f).

Given

  • equilibriumconcentration(Ce)=32.5000mg/Lequilibrium concentration (C_e) = 32.5000 mg/L
  • Freundlichintensityconstant(n)=1.2000Freundlich intensity constant (n) = 1.2000
  • adsorptioncapacity(x/m)(xm)=40.9000mg/gadsorption capacity (x/m) (x_m) = 40.9000 mg/g

Find

Freundlich capacity coefficient (K_f)

Start with the thinking

  • The governing relation printed in this handbook section is Freundlich Isotherm.
  • Everything except K_f is given, so isolate K_f symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Freundlich isotherm relates adsorption capacity to equilibrium concentration for activated carbon adsorption in a linearized form.
log Celog (x/m)Freundlich isotherm linearized form

Figure 5 — schematic for Freundlich Isotherm — solve for Freundlich capacity coefficient (case 2) — Freundlich Isotherm (5)

Step-by-step solution

  1. Step 1 — State the governing relation:

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}
  2. Step 2 — Rearrange symbolically for K_f:

    Kf=x/mCe1/nK_{f} = \dfrac{x/m}{C_e^{1/n}}
  3. Step 3 — List the givens: equilibrium concentration (C_e) = 32.5000 mg/L, Freundlich intensity constant (n) = 1.2000, adsorption capacity (x/m) (x_m) = 40.9000 mg/g.

  4. Step 4 — Substitute the given values:

    Kf=x/mCe1/1.2000K_{f} = \dfrac{x/m}{C_e^{1/1.2000}}
  5. Step 5 — Evaluate:

    Kf=2.2481K_{f} = 2.2481
  6. Step 6 — Check: returning K_f = 2.2481 to

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Kf=2.2481K_{f} = 2.2481

Why the other options are there

  • 4.4963 — kept a factor of two that cancels in the correct rearrangement.
  • 1.1241 — dropped that same factor in the other direction.
  • 2.4729 — rounded an intermediate value before the final step.

Reference: FE Handbook — Freundlich Isotherm

Example 6
Freundlich Isotherm — solve for equilibrium concentration (case 2) — Freundlich Isotherm (6)

Freundlich isotherm used to design a granular activated carbon column Given Freundlich capacity coefficient (K_f) = 73.0000; Freundlich intensity constant (n) = 1.2000; adsorption capacity (x/m) (x_m) = 62.9000 mg/g, determine the equilibrium concentration (C_e) in mg/L.

Given

  • Freundlichcapacitycoefficient(Kf)=73.0000Freundlich capacity coefficient (K_f) = 73.0000
  • Freundlichintensityconstant(n)=1.2000Freundlich intensity constant (n) = 1.2000
  • adsorptioncapacity(x/m)(xm)=62.9000mg/gadsorption capacity (x/m) (x_m) = 62.9000 mg/g

Find

equilibrium concentration (C_e), in mg/L

Start with the thinking

  • The governing relation printed in this handbook section is Freundlich Isotherm.
  • Everything except C_e is given, so isolate C_e symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Freundlich isotherm relates adsorption capacity to equilibrium concentration for activated carbon adsorption in a linearized form.
log Celog (x/m)Freundlich isotherm linearized form

Figure 6 — schematic for Freundlich Isotherm — solve for equilibrium concentration (case 2) — Freundlich Isotherm (6)

Step-by-step solution

  1. Step 1 — State the governing relation:

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}
  2. Step 2 — Rearrange symbolically for C_e:

    Ce=(x/mKf)nC_{e} = \left(\dfrac{x/m}{K_f}\right)^{n}
  3. Step 3 — List the givens: Freundlich capacity coefficient (K_f) = 73.0000, Freundlich intensity constant (n) = 1.2000, adsorption capacity (x/m) (x_m) = 62.9000 mg/g.

  4. Step 4 — Substitute the given values:

    Ce=(x/mKf)1.2000C_{e} = \left(\dfrac{x/m}{K_f}\right)^{1.2000}
  5. Step 5 — Evaluate:

    Ce=0.8364 mg/LC_{e} = 0.8364\ \text{mg/L}
  6. Step 6 — Check: returning C_e = 0.8364 mg/L to

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Ce=0.8364 mg/LC_{e} = 0.8364\ \text{mg/L}

Why the other options are there

  • 1.6727 — kept a factor of two that cancels in the correct rearrangement.
  • 0.4182 — dropped that same factor in the other direction.
  • 0.9200 — rounded an intermediate value before the final step.

Reference: FE Handbook — Freundlich Isotherm

Example 7
Freundlich Isotherm — solve for adsorption capacity (x/m) (case 3) — Freundlich Isotherm (7)

Freundlich isotherm for activated carbon adsorption of an organic compound Given Freundlich capacity coefficient (K_f) = 96.0000; equilibrium concentration (C_e) = 19.9000 mg/L; Freundlich intensity constant (n) = 3.9500, determine the adsorption capacity (x/m) (x_m) in mg/g.

Given

  • Freundlichcapacitycoefficient(Kf)=96.0000Freundlich capacity coefficient (K_f) = 96.0000
  • equilibriumconcentration(Ce)=19.9000mg/Lequilibrium concentration (C_e) = 19.9000 mg/L
  • Freundlichintensityconstant(n)=3.9500Freundlich intensity constant (n) = 3.9500

Find

adsorption capacity (x/m) (x_m), in mg/g

Start with the thinking

  • The governing relation printed in this handbook section is Freundlich Isotherm.
  • Everything except x_m is given, so isolate x_m symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Freundlich isotherm relates adsorption capacity to equilibrium concentration for activated carbon adsorption in a linearized form.
log Celog (x/m)Freundlich isotherm linearized form

Figure 7 — schematic for Freundlich Isotherm — solve for adsorption capacity (x/m) (case 3) — Freundlich Isotherm (7)

Step-by-step solution

  1. Step 1 — State the governing relation:

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}
  2. Step 2 — Rearrange symbolically for x_m:

    xm=KfCe1/nx_{m} = K_f C_e^{1/n}
  3. Step 3 — List the givens: Freundlich capacity coefficient (K_f) = 96.0000, equilibrium concentration (C_e) = 19.9000 mg/L, Freundlich intensity constant (n) = 3.9500.

  4. Step 4 — Substitute the given values:

    xm=KfCe1/3.9500x_{m} = K_f C_e^{1/3.9500}
  5. Step 5 — Evaluate:

    xm=204.7 mg/gx_{m} = 204.7\ \text{mg/g}
  6. Step 6 — Check: returning x_m = 204.7 mg/g to

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}

    reproduces the given quantities, and both sides carry the same units.

Answer:
xm=204.7 mg/gx_{m} = 204.7\ \text{mg/g}

Why the other options are there

  • 409.4 — kept a factor of two that cancels in the correct rearrangement.
  • 102.3 — dropped that same factor in the other direction.
  • 225.2 — rounded an intermediate value before the final step.

Reference: FE Handbook — Freundlich Isotherm

Example 8
Freundlich Isotherm — solve for Freundlich capacity coefficient (case 3) — Freundlich Isotherm (8)

Freundlich isotherm linearized form fit to laboratory adsorption data Given equilibrium concentration (C_e) = 21.4000 mg/L; Freundlich intensity constant (n) = 4.0500; adsorption capacity (x/m) (x_m) = 159.0 mg/g, determine the Freundlich capacity coefficient (K_f).

Given

  • equilibriumconcentration(Ce)=21.4000mg/Lequilibrium concentration (C_e) = 21.4000 mg/L
  • Freundlichintensityconstant(n)=4.0500Freundlich intensity constant (n) = 4.0500
  • adsorptioncapacity(x/m)(xm)=159.0mg/gadsorption capacity (x/m) (x_m) = 159.0 mg/g

Find

Freundlich capacity coefficient (K_f)

Start with the thinking

  • The governing relation printed in this handbook section is Freundlich Isotherm.
  • Everything except K_f is given, so isolate K_f symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Freundlich isotherm relates adsorption capacity to equilibrium concentration for activated carbon adsorption in a linearized form.
log Celog (x/m)Freundlich isotherm linearized form

Figure 8 — schematic for Freundlich Isotherm — solve for Freundlich capacity coefficient (case 3) — Freundlich Isotherm (8)

Step-by-step solution

  1. Step 1 — State the governing relation:

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}
  2. Step 2 — Rearrange symbolically for K_f:

    Kf=x/mCe1/nK_{f} = \dfrac{x/m}{C_e^{1/n}}
  3. Step 3 — List the givens: equilibrium concentration (C_e) = 21.4000 mg/L, Freundlich intensity constant (n) = 4.0500, adsorption capacity (x/m) (x_m) = 159.0 mg/g.

  4. Step 4 — Substitute the given values:

    Kf=x/mCe1/4.0500K_{f} = \dfrac{x/m}{C_e^{1/4.0500}}
  5. Step 5 — Evaluate:

    Kf=74.6277K_{f} = 74.6277
  6. Step 6 — Check: returning K_f = 74.6277 to

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Kf=74.6277K_{f} = 74.6277

Why the other options are there

  • 149.3 — kept a factor of two that cancels in the correct rearrangement.
  • 37.3138 — dropped that same factor in the other direction.
  • 82.0904 — rounded an intermediate value before the final step.

Reference: FE Handbook — Freundlich Isotherm

Example 9
Freundlich Isotherm — solve for equilibrium concentration (case 3) — Freundlich Isotherm (9)

Freundlich isotherm used to design a granular activated carbon column Given Freundlich capacity coefficient (K_f) = 58.5000; Freundlich intensity constant (n) = 4.7000; adsorption capacity (x/m) (x_m) = 153.1 mg/g, determine the equilibrium concentration (C_e) in mg/L.

Given

  • Freundlichcapacitycoefficient(Kf)=58.5000Freundlich capacity coefficient (K_f) = 58.5000
  • Freundlichintensityconstant(n)=4.7000Freundlich intensity constant (n) = 4.7000
  • adsorptioncapacity(x/m)(xm)=153.1mg/gadsorption capacity (x/m) (x_m) = 153.1 mg/g

Find

equilibrium concentration (C_e), in mg/L

Start with the thinking

  • The governing relation printed in this handbook section is Freundlich Isotherm.
  • Everything except C_e is given, so isolate C_e symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Freundlich isotherm relates adsorption capacity to equilibrium concentration for activated carbon adsorption in a linearized form.
log Celog (x/m)Freundlich isotherm linearized form

Figure 9 — schematic for Freundlich Isotherm — solve for equilibrium concentration (case 3) — Freundlich Isotherm (9)

Step-by-step solution

  1. Step 1 — State the governing relation:

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}
  2. Step 2 — Rearrange symbolically for C_e:

    Ce=(x/mKf)nC_{e} = \left(\dfrac{x/m}{K_f}\right)^{n}
  3. Step 3 — List the givens: Freundlich capacity coefficient (K_f) = 58.5000, Freundlich intensity constant (n) = 4.7000, adsorption capacity (x/m) (x_m) = 153.1 mg/g.

  4. Step 4 — Substitute the given values:

    Ce=(x/mKf)4.7000C_{e} = \left(\dfrac{x/m}{K_f}\right)^{4.7000}
  5. Step 5 — Evaluate:

    Ce=91.9922 mg/LC_{e} = 91.9922\ \text{mg/L}
  6. Step 6 — Check: returning C_e = 91.9922 mg/L to

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Ce=91.9922 mg/LC_{e} = 91.9922\ \text{mg/L}

Why the other options are there

  • 184.0 — kept a factor of two that cancels in the correct rearrangement.
  • 45.9961 — dropped that same factor in the other direction.
  • 101.2 — rounded an intermediate value before the final step.

Reference: FE Handbook — Freundlich Isotherm

Example 10
Freundlich Isotherm — solve for adsorption capacity (x/m) (case 4) — Freundlich Isotherm (10)

Freundlich isotherm for activated carbon adsorption of an organic compound Given Freundlich capacity coefficient (K_f) = 61.5000; equilibrium concentration (C_e) = 8.4000 mg/L; Freundlich intensity constant (n) = 4.3000, determine the adsorption capacity (x/m) (x_m) in mg/g.

Given

  • Freundlichcapacitycoefficient(Kf)=61.5000Freundlich capacity coefficient (K_f) = 61.5000
  • equilibriumconcentration(Ce)=8.4000mg/Lequilibrium concentration (C_e) = 8.4000 mg/L
  • Freundlichintensityconstant(n)=4.3000Freundlich intensity constant (n) = 4.3000

Find

adsorption capacity (x/m) (x_m), in mg/g

Start with the thinking

  • The governing relation printed in this handbook section is Freundlich Isotherm.
  • Everything except x_m is given, so isolate x_m symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • The Freundlich isotherm relates adsorption capacity to equilibrium concentration for activated carbon adsorption in a linearized form.
log Celog (x/m)Freundlich isotherm linearized form

Figure 10 — schematic for Freundlich Isotherm — solve for adsorption capacity (x/m) (case 4) — Freundlich Isotherm (10)

Step-by-step solution

  1. Step 1 — State the governing relation:

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}
  2. Step 2 — Rearrange symbolically for x_m:

    xm=KfCe1/nx_{m} = K_f C_e^{1/n}
  3. Step 3 — List the givens: Freundlich capacity coefficient (K_f) = 61.5000, equilibrium concentration (C_e) = 8.4000 mg/L, Freundlich intensity constant (n) = 4.3000.

  4. Step 4 — Substitute the given values:

    xm=KfCe1/4.3000x_{m} = K_f C_e^{1/4.3000}
  5. Step 5 — Evaluate:

    xm=100.9 mg/gx_{m} = 100.9\ \text{mg/g}
  6. Step 6 — Check: returning x_m = 100.9 mg/g to

    xm=KfCe1/n\dfrac{x}{m} = K_f C_e^{1/n}

    reproduces the given quantities, and both sides carry the same units.

Answer:
xm=100.9 mg/gx_{m} = 100.9\ \text{mg/g}

Why the other options are there

  • 201.8 — kept a factor of two that cancels in the correct rearrangement.
  • 50.4422 — dropped that same factor in the other direction.
  • 111.0 — rounded an intermediate value before the final step.

Reference: FE Handbook — Freundlich Isotherm

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