Jumat, 29 Maret 2013

contoh laporan buffer


BUFFER SOLUTION
Basic Theory
Buffer solution
            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 pKa = 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 = pKa ± 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 4th 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.