Isoterm Adsorption

  1. A.  PURPOSE

Determining adsorption isoterms according to Freundlich adsorption process of hydrochloric acid on charcoal.

 

  1. B.  BASIC THEORY

Adsorption is the phenomenon of collecting the molecules of a subtance on the surface adsorben as a result of unbalanced forces on the surface. For the adsorption in solution, the amount of adsorbed substance depends on several factors:

  1. The type of adsorben.
  2. The type of adsorbate or substance that adsorbed.
  3. The surface area of adsorbent.
  4. Concentration of solute.
  5. Temperatur.

For a particular adsorption system, the relationship between the amount of substance adsorbed per unit area or per unit weight of adsorbent, with the concentration of solute, at a certain temperature, called adsorption isoterm. By Freundlich, the adsorption isoterm is expressed as:

                        ………………………………………………………………….(1)

Where:

x = the amount of substance adsorbed

m = the amount of adsorben, in grams

C= the concentration of solute at equilibrium

k = constant

n= constant

Equation (1) rearranged become:

log= log k + n log C ………………………………………(2)

This equation reverals that if a prosess of adsorption obeyed the Freundlich isoterm, the plot log x/m againts log C is a straight line. From the graph can be evaluated the constants k and n (Wahyuni, 2011).

The amount adsorbed at the surface of the adsorbent is equilibrium process, because the rate of adsorption is accompanied by the occurrence of events desorption. At the beginning of the reaction, the incident is more dominant than the adsorption desorption event, so the adsorption is rapid. At any given time tends to slow adsorption events, and vice versa desorption rate tends to increase. The time when the rate of adsorption is equal to the rate of desorption is often referred to as the equilibrium state. In a state of equilibrium is not observed macroscopic changes. The time to achieve a state of equilibrium in the adsorption process is different, It is influenced by the type of interaction that occurs between the adsorbent with adsorbate. In general, the time to achieve equilibrium through the mechanism of physical adsorption (fisisorpsi) faster than through chemical mechanisms or chemisorpsi (Castellans 1982).

According M.T. Sembiring et al, 2003 that activated carbon is good to have the requirements as listed on the SII No.0258 -79. The nature of the activated carbon is the most important absorption. There are several factors that affect the absorption of adsorption, namely:

  1. Absorption properties

Many compounds can be adsorbed by activated carbon, but its ability to adsorb different for each compound. Adsorption will increase with increasing molecular size the same uptake of its structure, as in the homologous series. Adsorption is also influenced by the functional groups, the position of the functional group, double bond, the chain structure of compound uptake.

  1. Temperature

In the use of activated carbon are encouraged to investigate the temperature during the process. Since there is no general rule can be given about the temperature used in the adsorption. Factors affecting the temperature of the adsorption is the viscosity and thermal stability of compound uptake. If heating does not affect the absorption properties of compounds, such as color changes like decomposition, the treatment performed at the boiling point. For volatile compounds, adsorption carried out at room temperature or, if possible at lower temperatures.

  1. pH (degree of acidity).

For organic acids, the adsorption increases when pH is lowered, with the addition of mineral acids. This is because the ability of a mineral acid to reduce the ionization of organic acids. Conversely, if the pH of organic acid increased by adding alkali, adsorption will be reduced as a result of salt formation.

  1. Mention Time

When activated carbon is added to a liquid, it takes time to reach equilibrium. The time required is inversely proportional to the amount of charcoal used. The difference is determined by the activated carbon dosing, mixing also affects a tangent. Stirring is intended to allow the activated carbon particles to intersect with the absorption of compounds. For solutions that have a high viscosity, it takes a longer tangent.

 

  1. C.  THE EQUIPMENT AND CHEMICAL SUBSTANCE USED
  2. Equipment:
  • A porcelain cup 1 pc
  • Tripod and screen 1 set
  • Burner 1 set
  • Erlenmeyer flask with cover 250 ml 9 pc
  • Erlenmeyer flask 150 ml 6 pc
  • Pipette 5 mL 1 pc
  • Pipette 10 mL 1 pc
  • Pipette 25 mL 1 pc
  • Burette 50 mL 1 pc
  • Mounthpiece 6 units
  • Funnel 1 pc
  • Filter paper 6 pc
  1. Chemical substance:
  • Hydrochloric acid solution 0.5 N, 0.25 N, 0.125 N, 0.0625 N, 0.0313 N, and 0.0156 N (each 125 mL)
  • Charcoal adsorben
  • Standard solution NaOH 0.1 N
  • Methyl orange indicator

 

  1. D.  PROCEDURE

Prepare hydrochloric acid: 0.5 N,0.25 N,0.125 N,0.0625 N,0.0313 N, 0.0156 N each 125 ml

 

Activate the charcoral

 

                                                                 

 
   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  1. E.  OBSERVATION DATA
  2. The result of 25 mL HCl was titrated with NaOH 0.1 N

No.

[HCl] (N)

V HCl (mL)

[NaOH] (N)

V titrate NaOH (mL)

V1

V2

Vaverage

1.

0.5

10

0.1

56.8

55.1

55.95

2.

0.25

10

0.1

26.9

26.6

26.75

3.

0.125

10

0.1

14.5

13.7

14.1

4.

0.0625

10

0.1

7.2

7.3

7.25

5.

0.0313

10

0.1

3.5

2.9

3.2

6.

0.0156

10

0.1

1.3

1.5

1.4

 

  1. The result of filtrate solution which was titrated with NaOH 0.1 N

No.

[HCl] (N)

V HCl (mL)

[NaOH] (N)

V titrate NaOH (mL)

V1

V2

Vaverage

1.

0.5

10

0.1

53.3

51.5

52.4

2.

0.25

20

0.1

49.5

48.7

49.1

3.

0.125

25

0.1

36.1

36

35.55

4.

0.0625

35

0.1

23

23.3

23.15

5.

0.0313

40

0.1

13

13.5

13.25

6.

0.0156

50

0.1

5.5

6.1

5.8

 

  1. The result of calculation to find k (constant) and n (constant).

No.

Mass of charcoal (gram)

[HCl] (N)

X (gram)

x/m

Log x/m

Log C

Initial

Final

1.

1.0039

0.559

0.524

0.12775

0.127

-0.895

-1.455

2.

1.0060

0.267

0.245

0.0803

0.079

-1.097

-1.657

3.

1.0114

0.041

0.142

-0.36865

-0.364

4.

1.0056

0.072

0.066

0.0219

0.022

-1.661

-2.221

5.

1.0059

0.032

0.033

-0.00365

-0.003

6.

1.0091

0.014

0.011

0.01095

0.011

-1.964

-2.522

 

  1. F.  DISCUSSION

            In these experiments, aimed at understanding the properties of the solute adsorption from a solution to the adsorbent surface. Adsorption is an example of a method typically used to clear up a solution, for example in everyday life is in the process of water purification.

            The experiment was carried out quantitatively, by calculating the volume of a solution of hydrochloric acid early before plus activated carbon compared to the volume of hydrochloric acid solution after the addition of activated carbon, as noted in the results of the experiment and represented in the form of curves.

            The experiments in this chapter , activated charcoal adsorption isoterm is to use organic solvent is hydrochloricc acid with 6 variation of concentration. The adsorbent used is charcoal that has been activated before. The activation of charcoal can be done in several ways.

            In this experiment the activation of charcoal is done by heating using a high temperature, this is done because the trial adsorbs organic solution (hydrochloric acid) so that the activation is done by high temperature and not get burned. This treatment is not intended to be charcoal to ash.

            Activated charcoal was used to adsorb hydrochloric acid concentration variation are, 0.5 N; 0.25 N; 0.125 N; 0.0625 N; 0.0313 N; 0.0156 N obtained from the titration with NaOH 0.1 N, hydrochloric acid is titrated from the rest of the acid used in the experiment. Period of activated charcoal used in any concentration is 1 gram. The volume of hydrochloric acid used in the adsorption is 100 mL.

            In this experiment the price will be determined constants Freundlich adsorption isoterms for the adsorption process HCl against charcoal. The variables measured in the experiment is the volume of 0.1 N NaOH used to titrate HCl. After the initial and final concentration is known, the concentration of adsorbed HCl can be determined by the reduction of the initial concentration of the final concentration. Further weight can be searched adsorbed HCl.

From the observation data and analyze data results, the concentration of hydrochloric acid before adsorption is higher than after adsorption. This is because the hydrochloric acid was adsorbed by activated charcoal. From the data also made a graph in which the x / m is plotted as ordinate and C as abscissa.

 

 

 

 

 

 

 

 

 

 

 

 

 

Graph1. Graph Isoterm Adsorption of Freundlinc

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Graph 2. Graph Isoterm Adsorption of Langmuir

 

From the experimental results shown in the table the experimental results, it can be seen that the greater the solute concentration, the greater the solute that can be adsorbed. Adsorbed solute is the result of the reduction of hydrochloric acid solution at first and hydrochloric acid solution after the addition of the adsorbent. It can be seen from the weight calculation of adsorbed. From the experimental results are then represented in graphical form. The graph is a graph made Freundlich isoterm and Langmuir isoterm charts. Graph Freundlich isoterm describes a logarithmic relationship between the weight of the adsorbate in the adsorbent to the concentration of hydrochloric acid solution after the adsorption. From  the graph that has been drawn, it is known that the curve shows a linear model with a value of linearity (R2) = 0.996. This is consistent with the theory proposed by Freundlich on the value of k which indicates the capacity of absorption. The larger the surface area of ​​the adsorbent, the greater the price intercept k.

The second graph is a graph that illustrates the relationship Langmuir isoterm concentration on adsorption. From the graph that has been drawn, it is known that the curve shows a linear model with a value of linearity (R)2 = 0.996, n =  0.644, and the value of k= 1.009. This is consistent with the theory put forward the theory of Langmuir adsorption isoterm illustrating that the adsorbent surface there are a number of active sites is proportional to the surface area of ​​the adsorbent. That is, the greater the surface of adsorbed, the greater the adsorption power.

Carbon adsorption create hydrochloric acid concentration decreased. In each experiment data above the absorption occurs dissimilarity between data 1 to 6 can be seen from the x grams (amount of substance adsorbed) less stable. This happens due to the adsorption there are several factors that can affect the results of adsorption.

 

G. CONCLUSION AND SUGGESTION

  1. Conclusion
    1. Isoterm that occurs in this experiment is the Freundlich adsorption isoterm, where the adsorbent adsorbs organic solvent which is great with sites like hoterogen Freundlich site.
    2. From this calculation was obtained value of n = 0.644 and k = 1.009.
  2. Suggestion
    1. We must use the same solution of NaOH to titrate the hydrochloric acid and filtrate.
    2. We must heat charcoral precisely to activeted charcoral.

 

  1. H.  REFERENCE

Castellan. 1983. Physical Chemistry. Edisi ketiga. Addison-Wesley Publishing Company.

Sembiring, dkk. 2003. Isoterm Adsorpsi Ion Cr3+ Oleh Abu Sekam Padi Varietas IR 64. Skripsi. Jurusan Pendidikan Kimia FMIPA Undiksha.

Wahyuni, Sri, and Team Lecturer of Physical Chemistry. 2011. Practicum Guide of Physical Chemistry. Semarang: UNNES.

 

                                                                                                                                                                     Semarang, 29 Oktober 2012

            knowing,

            Practicum Lecture                                                                                                                                 Practitioner

 

 

 

           Ir. Sri Wahyuni, M.Si                                                                                                                               Falasifah Aulia

           NIP.                                                                                                                                                                NIM. 4301410044

 

ANSWER THE QUESTION

 

  1. Is this adsorption process is physical adsorption or chemical adsorption?

Answer: In this experiment, the adsorption process occurs is physical adsorption which is characterized by  molecules bound to the adsorbent by Van Der Walls force, has a reaction enthalpy.

  1. What is the difference between these two types of adsorption? Give some examples of both types of adsorption?

Answer: Physical adsorption, namely related to the Van der Waals force, and is a reversible process of an affinity between the solute and adsorbent greater affinity between the solute with the solvent, it will dissolve the substance adsorbed on the adsorbent surface, and does not involve the activation energy . Chemical adsorption, which is a reaction that occurs between solids and solutes adsorbed, occurs termination and formation of chemical bonds, the heat adsorption is high, and involves the activation energy. Example: SDBS adsorption. Physical Adsorption: liquid nitrogen at 1900C will adsorpted into iron metal. Chemical adsorption: at a temperature of 5000C rapid nitrogen adsorbed on metal surfaces.

  1. What is the difference that occurs in the activation of charcoal by heating?

Answer: Activated carbon by heating it will expand its surface area, so that 1 gram of charcoal will have a surface area of 500 m2.

  1. How Freundlich adsorption isoterm when applied to gas adsorption on solid surface? What restrictions?

Answer: Freundlich isotherms for adsorption of gases on the surface of the solid is not good or satisfactory. This happens because the Freundlich adsorption active sites on the adsorbent surface is heterogeneous. Gas is a homogeneous mixture that is less suitable when used in the Freundlich isotherm. Restriction: Freundlich adsorption active sites on the adsorbent surface is heterogeneous.

  1. Why Freundlich adsorption isoterm for gas adsorption on solid surface is less satisfactory than the Langmuir adsorption isoterm? What is the shape of Langmuir adsorption isotherm? 

Answer: Since the Freundlich adsorption active sites on the adsorbent surface is heterogeneous, whereas the Langmuir adsorption homogeneous. When his form adsorbed gases homogeneous mixture, the Freundlich adsorption less suitable. From the experiments that have been carried out, this form of adsorption is Langmuir adsorption.

Isotherm adsorption curve:

 

 

 

 

 

 

 

APPENDIXS

 

  1. To Find the [HCl] initial and [HCl] final.

[HCl] initial (N)

[HCl] final (N)

[HCl]  =   V NaOH x[NaOH]

                          V HCl

          =   55.95 x 0.1

                       10

          =  0.559

[HCl]  =   V NaOH x[NaOH]

                          V HCl

          =   52.4 x 0.1

                      10

          =  0.524

[HCl]  =   V NaOH x[NaOH]

                          V HCl

          =   26.75 x 0.1

                       10

          =  0.267

[HCl]  =   V NaOH x[NaOH]

                          V HCl

          =   49.1 x 0.1

                      20

          =  0.245

[HCl]  =   V NaOH x[NaOH]

                          V HCl

          =   14.1 x 0.1

                      10

          =  0.041

[HCl]  =   V NaOH x[NaOH]

                          V HCl

          =   35.55 x 0.1

                       25

          =  0.142

[HCl]  =   V NaOH x[NaOH]

                          V HCl

          =   7.25 x 0.1

                      10

          =  0.072

[HCl]  =   V NaOH x[NaOH]

                          V HCl

          =   23.15 x 0.1

                       35

          =  0.066

[HCl]  =   V NaOH x[NaOH]

                          V HCl

          =   3.2 x 0.1

                    10

          =  0.032

[HCl]  =   V NaOH x[NaOH]

                          V HCl

          =   13.25 x 0.1

                       40

          =  0.033

[HCl]  =   V NaOH x[NaOH]

                          V HCl

          =   1.4 x 0.1

                       10

          =  0.014

[HCl]  =   V NaOH x[NaOH]

                          V HCl

          =   5.3 x 0.1

                    50

          =  0.011

 

  1. To find the value of x.

X1 = ( Cin – Cfin ) x Mr x

 

                = (0.559 – 0,524) x 36.5 x =0.12775

 

X2= ( Cin – Cfin ) x Mr x

 

                = (0.267 – 0.245) x 36.5 x = 0.0803

X3= ( Cin – Cfin ) x Mr x

 

                = (0.041 – 0.142) x 36.5 x = -0.36865

 

X4= ( Cin – Cfin ) x Mr x

 

                = (0.072 – 0.066) x 36.5 x = 0.0219

 

X5= ( Cin – Cfin ) x Mr x

 

                = (0.032 – 0.033) x 36.5 x = -0.00365

 

X6= ( Cin – Cfin ) x Mr x

 

                = (0.014 – 0.011) x 36.5 x = 0.01095

 

 

 

 

 

 

 

 

 

 

Figure 1. Graph of x/m against C

 

 

 

 

 

 

No.

Mass of charcoal (gram)

[HCl] (N)

X (gram)

x/m

Log x/m

Log C

Initial

Final

1.

1.0039

0.559

0.524

0.12775

0.127

-0.895

-1.455

2.

1.0060

0.267

0.245

0.0803

0.079

-1.097

-1.657

3.

1.0114

0.041

0.142

-0.36865

-0.364

 

 

 

                                    Figure 2. Graph of log x/m against log C

 

ü  Find the value of n and k

Log x/m           =          log k    + n.log c

 

y                      =          c          + m.x

y                      =          0.004   + 0.644 x

n = m = 0.644

c  = log k = 0.004

             k = 1.009

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