contoh laporan buffer

BUFFER SOLUTION

Basic Theory

Buffer solution

            A buffer is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. Its pH changes very little when a small amount of strong acidor base is added to it and thus it is used to prevent changes in the pH of a solution. Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. Many life forms thrive only in a relatively small pH range so they utilize a buffer solution to maintain a constant pH. One example of a buffer solution found in nature is blood.

            Buffer solutions achieve their resistance to pH change because of the presence of an equilibrium between the acid HA and its conjugate base A^-.

HA  H⁺ + A^-

      When some strong acid is added to an equilibrium mixture of the weak acid and itsconjugate base, the equilibrium is shifted to the left, in accordance with Le Chatelier's principle. Because of this, the hydrogen ion concentration increases by less than the amount expected for the quantity of strong acid added.

      Similarly, if strong alkali is added to the mixture the hydrogen ion concentration decreases by less than the amount expected for the quantity of alkali added. The effect is illustrated by the simulated titration of a weak acid with pK_a = 4.7. The relative concentration of undissociated acid is shown in blue and of its conjugate base in red. The pH changes relatively slowly in the buffer region, pH = pK_a ± 1, centered at pH = 4.7 where [HA] = [A^-]. The hydrogen ion concentration decreases by less than the amount expected because most of the added hydroxide ion is consumed in the reaction

OH^- + HA → H₂O + A^-

and only a little is consumed in the neutralization reaction which results in an increase in pH.

OH^- + H⁺ → H₂O

Once the acid is more than 95% deprotonated the pH rises rapidly because most of the added alkali is consumed in the neutralization reaction.

Worksheet

Judul               : Larutan Penyangga

Tujuan             : mempelajari sifat larutan penyangga dan bukan penyangga pada penambahan sedikit  asam, basa atau pengenceran.

Alat dan bahan:

Ø  Gelas ukur 10 ml

Ø  pH meter

Ø  NaCl 0,1 M

Ø  HCl 0,1 M

Ø  NaOH 0,1 M

Ø  Akuades

Ø  Pipet tetes

Ø  CH₃COOH

Ø  NaCH₃COO

Ø  NH₃

Ø  NH₄Cl

Ø  Pipet sedot

Cara kerja        :

1.      By using universal indicator, measure the pH of a 0.1 M NaCl solution
Prepare 3 100 ml beaker. each with 10 ml of 0.1 M NaCl solution

2.      Measure the pH 3 of the solution.

3.       Combine 25 m CH3COOH 0.1 M solution in a beaker. Measure the pH of the solution.

4.       Mix 25 ml of 0.1 M solution of NH3 and 25 ml of 0.1 M NH4Cl solution in a beaker. Measure the pH of the solution.

 

NH3

NH4Cl

NH4Cl + NH3

NH4Cl + NH3

NH4Cl + NH3

5.     

Data Analisys / Questions

1.      Based on the solution that been tested, which is the buffer? ?

2.      Make a conclution about characteristic of buffer !

Ø  NaCl solution

Early pH of NaCL is 7,2

Num	Solution	Additional Solution	pH value
1.	NaCl 0,1 M	HCL 0,1 M 1ml	2,6
2.	NaCl 0,1 M	NaOH 0,1 M 1 ml	12
3.	NaCl 0,1 M	Akuades 10 ml	6

            Based on the data above we can conclude that NaCl isn’t Buffer, because it can’t hold its pH value.

Ø  CH₃COOH’s pH        : 3,1

Ø  NaCH₃COO’s pH      : 7,3

Num	Solution	Additional Solution	pH value
1	CH3COOH	NaCH3COO	5
2	CH3COOH+ NaCH3COO	HCl	5
3	CH3COOH+ NaCH3COO	NaOH	5
4	CH3COOH+ NaCH3COO	akuades	5,1

Based on the data above, CH₃COOH and NaCH₃COO are buffer because they can hold their pH. Though at the 4^th solution occurred a little change into 5,1. But that change is not too significant.

Ø  NH₃’s  pH                           :9

No	Solution	Additional Solution	pH value
1	NH3	NH4Cl	9
2	NH3 + NH4Cl	HCl	9,1
3	NH3 + NH4Cl	NaOH	9,2
4	NH3 + NH4Cl	akuades	9,1

Based on the data above NH₃ is buffer because it can hold its pH.

Conclution

thus, the buffer solution have characteristic as below :

1.      Buffer can hold its pH.

2.      Buffer are composed of  weak-acid and its conjugate-base ( or its salt), also weak-base and its conjugate-acid (or its salt).

3.      Buffer’s pH won’t change if be diluted.

4.      Buffer’s pH won’t change if you just add a little of acid or base.