Buffer Solution

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A. TITLE : Buffer SolutionB. DATE : March, 19th 2013C. PURPOSE : To learn the effect of adding strong acid,

strong base and dilution toward the PH of Buffer Solution

D. BASIC THEORY :

A buffer solution is a solution of a weak acid or a weak base and its salt; both

components must be present. The solution has the ability to resist changes in pH

upon the addition of small amounts of either acid or base. Buffers are very

important to chemical and biological systems. The pH in the human body varies

greatly from one fluid to another; for example, the pH of blood is about 7.4,

whereas the gastric juice in our stomachs has a pH of about 1.5. These pH values,

which are crucial for proper enzyme function and the balance of osmotic pressure,

are maintained by buffers in most cases.

A buffer solution must contain a relatively large concentration of acid to react

with any OH- ions that are added to it, and it must contain a similar concentration

of base to react with any added H+ ions. Furthermore, the acid and the base

components of the buffer must not consume each other in a neutralization

reaction. These requirements are satisfied by an acid-base conjugate pair, for

example, a weak acid and its conjugate base (supplied by a salt) or a weak base

and its conjugate acid (supplied by a salt).

A simple buffer solution can be prepared by adding comparable amounts of

acetic acid (CH3COOH) and its salt sodium acetate (CH3COONa) to water. The

equilibrium concentrations of both the acid and the conjugate base (from

CH3COONa) are assumed to be the same as the starting concentrations. A

solution containing these two substances has the ability to neutralize either added

[ | INTERNATIONAL CHEMISTRY EDUCATION 2012 1

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acid or added base. Sodium acetate, a strong electrolyte, dissociates completely in

water:

CH3COONa(s) CH3COO-(aq) +Na+(aq)

If an acid is added, the H- ions will be consumed by the conjugate base in the

buffer, CH3COO-, according to the equation

CH3COO-(aq) + H+(aq) CH3COOH(aq)

If a base is added to the buffer system, the OH- ions will be neutralized by the

acid in the buffer:

CH3COOH(aq) +OH-(aq) CH3COO-(aq) +H2O(l)

The buffering capacity, that is, the effectiveness of the buffer solution,

depends on the amount of acid and conjugate base from which the buffer is made.

The larger the mount, the greater the buffering capacity. In general, a buffer

system can be represented as salt-acid or conjugate base–acid. Thus the sodium

acetate–acetic acid buffer system discussed above can be written as

CH3COONa/CH3COOH or simply CH3COO-/CH3COOH.

Citric acid is a weak organic acid. It is a natural preservative/conservative and

is also used to add an acidic, or sour, taste to foods and soft drinks and cakes. In

biochemistry, the conjugate base of citric acid, citrate, is important as an

intermediate in the citric acid cycle, and therefore occurs in the metabolism of

virtually all living things. It can also be used as an environmentally benign

cleaning agent. It is very corrosive to the touch of the skin and can burn severely.


http://en.wikipedia.org/wiki/Life

http://en.wikipedia.org/wiki/Metabolism

http://en.wikipedia.org/wiki/Citric_acid_cycle

http://en.wikipedia.org/wiki/Biochemistry

http://en.wikipedia.org/wiki/Soft_drink

http://en.wikipedia.org/wiki/Taste#Sourness

http://en.wikipedia.org/wiki/Preservative

http://en.wikipedia.org/wiki/Organic_acid

http://en.wikipedia.org/wiki/Weak_acid

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Citric acid exists in greater than trace amounts in a variety of fruits and

vegetables, most notably citrus fruits. Lemons and limes have particularly high

concentrations of the acid; it can constitute as much as 8% of the dry weight of

these fruits (about 47 g/L in the juices). The concentrations of citric acid in citrus

fruits range from 0.005 mol/L for oranges and grapefruits to 0.30 mol/L in lemons

and limes. Within species, these values vary depending on the cultivar and the

circumstances in which the fruit was grown.

Application of buffer solution in daily life, Buffer solutions are necessary

to keep the correct pH for enzymes in many organisms to work. Many enzymes

work only under very precise conditions; if the pH moves outside of a narrow

range, the enzymes slow or stop working and can denature, thus permanently

disabling their catalytic activity. A buffer of carbonic acid (H2CO3) and

bicarbonate (HCO3−) is present in blood plasma, to maintain a pH between 7.35

and 7.45.

Industrially, buffer solutions are used in fermentation processes and in

setting the correct conditions for dyes used in colouring fabrics. They are also

used in chemical analysis and calibration of pH meters.

The majority of biological samples that are used in research are made in

buffers, especially phosphate buffered saline (PBS) at pH 7.4.


http://en.wikipedia.org/wiki/Cultivar

http://en.wikipedia.org/wiki/Molarity

http://en.wikipedia.org/wiki/Gram_per_litre

http://en.wikipedia.org/wiki/Lime_(fruit)

http://en.wikipedia.org/wiki/Lemon

http://en.wikipedia.org/wiki/Citrus

http://en.wikipedia.org/wiki/Fruit

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E. DESIGN OF EXPERIMENT :a) Tools and Materials :

Tools :o Test tube : 9 Pieceso Rack : 1 Pieceo Graduate Cylinder : 2 Pieceso Mortar

Materials :o NaOH :0,5 Mo HCl : 0,5 Mo CH3COOH : 0,5 Mo CH3COONa : 0,5 Mo NH4OH : 0,5 Mo NH4Cl : 0,5 Mo NaCl : 0,5 Mo Pineappleo Orangeo Tomatoo Cucumbero Soft drink

b) Experiment Step :a. Determining the Comparison Solution

1. Prepare 9 of clean test tube, pour 5 mL solution to each test tube that the pH, has already know and labeled according to the pH value of the solution.

2. Add 3 drops of universal indicator each solution.3. Write the color of each solution and the pH

value, save it as a comparison.

b. Making a Solution from Juice

1. Prepare fruits that will be made as solutions. 2. Squeezed the fruits about to get the juice.3. Add 20 mL aquades as much as the juice4. Filter the juice that has been diluted and save

the juice in a beaker glass which has been labeled according to the name of the fruit.

c. The effect of adding a strong acid

1. Prepare 10 pieces of clean test tube and pour the solution into each tube as follows :

a. Test tube 1 : 2 mL CH3COOH and 2 mL CH3COONa


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b. Test tube 2 : 2 mL NH4OH and 2 mL NH4Cl

c. Test tube 3 : 2 mL NaCl and 2 mL HCld. Test tube 4 : 2 mL NaCl and 2 mL NaOHe. Test tube 5 : 4 mL pineapple solutionf. Test tube 6 : 4 mL orange solutiong. Test tube 7 : 4 mL tomatoesh. Test tube 8 : 4 ml cucumberi. Test tube 9 : 4 mL soft drinkj. Test tube 10 : 4 mL aquades

2. Add 2 drops of universal indicator to the each test tube, shake and record the color of the solution and its pH value by comparing with the first experiment

3. Add drop of HCl 0.5M into each test tube until the color was changing.

4. Count, the total drops of HCl.

d. The effect of adding a strong bases

1. Prepare 10 pieces of clean test tube and pour the solution into each tube as follows :

a. Test tube 1 : 2 mL CH3COOH and 2 mL CH3COONa

b. Test tube 2 : 2 mL NH4OH and 2 mL NH4Cl

c. Test tube 3 : 2 mL NaCl and 2 mL HCld. Test tube 4 : 2 mL NaCl and 2 mL NaOHe. Test tube 5 : 4 mL pineapple solutionf. Test tube 6 : 4 mL orange solutiong. Test tube 7 : 4 mL tomatoesh. Test tube 8 : 4 ml cucumberi. Test tube 9 : 4 mL soft drinkj. Test tube 10 : 4 mL aquades

2. Add 2 drops of universal indicator to the each test tube, shake and record the color of the solution and its pH value by comparing with the first experiment

3. Add drop of NaOH 0.5M into each test tube until the color was changing.

4. Count, the total drops of NaOH.

c). Procedur :

1. Determining the Comparison Solution


-Write the pH

-Observe and write the result

5 mL solution A

5 mL solution B

5 mL solution C

5 mL solution D

5 mL solution E

5 mL solution F

5 mL solution G

5 mL solution H

5 mL solution I

3 drops of indicator universal

Change Colour

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Fruit

Squeezed to get the extract

Placed the juice into 50 mL beaker glass

Add aquades as much as 10 times of the juice volume

Filtered the juice

Saved in beaker glass that already labeled

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2. Making a Solution from Juice


TUBE 1 :2 ml CH3COOH + 2 ml

CH3COONa

TUBE 2 :2 ml NH4OH + 2 ml NH4Cl

TUBE 3 :2 ml NaCl + 2 ml HCl

TUBE 4 :2 ml NaCl + 2 ml NaOH

TUBE 5 :4 ml pineapple solution

TUBE 6 :4 ml orange solution

TUBE 7 :4 ml tomato solution

TUBE 8 :4 ml cucumber solution

TUBE 9 :4 ml sprite

TUBE 10 :4 ml aquades

Added 2 drops of universal indicatorShake and noted the color of the solution and also pH rangeAdded drops of HCl until there is color changingCounted total drops of HCl to until there is a color changing

RESULT

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3. The Effect of Adding Strong Acid


TUBE 1 :2 ml CH3COOH + 2 ml

CH3COONa

TUBE 2 :2 ml NH4OH + 2 ml NH4Cl

TUBE 3 :2 ml NaCl + 2 ml HCl


TUBE 5 :4 ml pineapple solution

TUBE 6 :4 ml orange solution

TUBE 7 :4 ml tomato solution

TUBE 8 :4 ml cucumber solution

TUBE 9 :4 ml sprite

TUBE 10 :4 ml aquades

Added 3 drops of universal indicatorShake and noted the color of the solution and also pH rangeAdded drops of NaOH until there is color changingCounted total drops of NaOH to until there is a color changing

RESULT

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4. The Effect of Adding Strong Bases


TUBE 1 :2 ml

CH3COOH + 2 ml

CH3COONa

TUBE 2 :2 ml NH4OH

+ 2 ml NH4Cl

TUBE 3 :2 ml NaCl +

2 ml HCl


TUBE 5 :4 ml

pineapple solution

TUBE 6 :4ml orange

solution

TUBE 7 :4ml tomato

solution

TUBE 8 :4 ml

cucumber solution

TUBE 9 :4 ml sprite

TUBE 10 :4 ml

aquades

Added 2 drops of universal indicatorShake and noted the color of the solution and also pH rangeAdded drops of HCl until there is color changingCounted total drops of HCl to until there is a color changing

RESULT

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F. EXPERIMENT RESULT :

NO PROCEDUR RESULT HYPOTESIS CONCLUSIONBEFORE AFTER

1. The Effect of Adding Strong Acid Tube I :Collorless

Tube II :Collorless

Tube III :Collorless

Tube IV :Collorless

Tube V :Yellow

Tube VI :Turbit

Tube I :UI : yellowpH : 6HCl :Drops: 28pH : 2

Tube II :UI : bluepH : 8HCl : Drops :25pH : 3

Tube III :UI : orangepH : 3HCl : smooth

orangeDrops: 40pH : 2

Tube IV :UI : purplepH : 11HCl : smooth purpleDrops: 42pH : 10

Tube V :UI : orangepH : 4HCl : yellowDrops :45pH : 2

Tube VI :UI : smooth yellowpH : 3HCl : smoth yellowDrops : 73pH : 3

If we add a lot

of strong acid, it

will be occur

the change of

pH.

Buffer is the

solution if we

added a little

strong acid the

pH is settled.


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Tube VII :Red

Tube VIII :Turbid

Tube IX :Colorless

Tube X :Colorless

Tube VII :UI : orangepH : 4HCl : smooth yellowDrops : 40pH : 3

Tube VIII :UI : yellowpH : 5HCl : yellowDrops :pH : 5

Tube IX :UI : orangepH : 3HCl : smooth orangeDrops :42pH : 2

Tube X :UI : greenpH : 7HCl : pinkDrops : 23pH : 4


TUBE 1 :2 ml

CH3COOH + 2 ml

CH3COONa

TUBE 2 :2 ml NH4OH

+ 2 ml NH4Cl

TUBE 3 :2 ml NaCl +

2 ml HCl


TUBE 5 :4 ml

pineapple solution

TUBE 6 :4 ml orange

solution

TUBE 7 :4 ml tomato

solution

TUBE 8 :4 ml

cucumber solution

TUBE 9 :4 ml sprite

TUBE 10 :4 ml

aquades

Added 3 drops of universal indicatorShake and noted the color of the solution and also pH rangeAdded drops of NaOH until there is color changingCounted total drops of NaOH to until there is a color changing

RESULT

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NO PROCEDUR RESULT HYPOTESIS CONCLUSIONBEFORE AFTER

2. The Effect of Adding Strong Bases Tube I :Collorless

Tube II :Collorless

Tube III :Collorless

Tube IV :Collorless

Tube V :Yellow

Tube VI :Turbit

Tube I :UI : yellowpH : 5NaOH: dark purpleDrops: 6pH : 14

Tube II :UI : purplepH :12NaOH:smooth

purple Drops : 44pH : 14

Tube III :UI : orangepH : 4NaOH:smooth

purpleDrops: 34pH : 12

Tube IV :UI : dark bluepH : 11NaOH :blue Drops: 42pH : 10

Tube V :UI : orangepH : 4NaOH: brownDrops :7

Tube VI :UI : smooth orangepH : 3NaOH:smooth

yellow

If we add a lot

of strong bases,

it will be occur

the change of

pH.

Buffer is the

solution if we

added a little

strong bases

the pH is

settled.


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Tube VII :Red

Tube VIII :Turbid

Tube IX :Colorless

Tube X :Colorless

Drops : 50

Tube VII :UI : orangepH : 4NaOH : dark redDrops :21pH :

Tube VIII :UI : smooth greenpH : 5NaOH: dark purple

Drops : 3

Tube IX :UI : orangepH : 3HCl : blueDrops : 15

Tube X :UI : greenpH : 7NaOH :purple

Drops : 2


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G. DATA ANALYSIS :

1. Effect of adding strong acid

In the first experiment, we react CH3COOH + CH3COONa that colorless and

after drop two drops of universal indicator the solution become green so pH = 6

and after we drop HCl until 28 drops pH change become 2. It means that it is a

buffer solution because buffer solution is a solution of a weak acid and its salt

and able to keep value of pH upon the addition of small amounts of either strong

acid.

For the second experiment, it is about NH4OH react with NH4Cl that colorless

and directly become blue after added by universal indicator it show that the pH is

8 and after added of HCl 25 drops the color become orange and the pH decrease

until become 2. It is include in buffer solution especially in base.

In the third experiment, we react NaCl with HCl that colorless and become

orange after added by universal indicator and the pH is 3 although after add by 40

drops of HCl color become smooth orange and the pH is 2. It is not buffer

solution because buffer is a solution that formed if one of them is weak acid or

base, but in this reaction is contain of strong acid and strong base.

In the fourth experiment, we react NaCl with NaOH that are colorless and

become purple after we add by universal indicator with the pH is 11, but after we

added by 42 drops of HCl the color become smooth purple and the pH decrease

become 10. It is not a buffer solution.

For the fifth experiment, when pineapple solution that are dark yellow react

with universal indicator the color become orange and the pH is 2 after added by

45 drops of HCl, the color is smooth orange and the pH is 4. It is a buffer solution

especially in acid because it can resist changes in pH upon the addition of small

amounts of either acid


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In the sixth experiment, it is about orange solution that are turbid react with

universal indicator is become orange with the pH is 3, after added by 73 drops of

HCl the color changed become smooth orange and the pH is 3. Same with the fifth

experiment, it is include in buffer solution.

In the seventh experiment, tomato solution that are red react with universal

indicator the color become orange with the pH is 4, after added by HCl 40 drops

the color changed become smooth orange and the pH is 3. It is include buffer

solution like orange and pineapple.

In the eighth experiment, cucumber solution that are turbid when added by

universal indicator is yellow and the pH is 5 but after added by 60 drops of HCl

the color still yellow and the pH is 5 too. It is include buffer solution.

In the ninth experiment, soft drink that are colorless react with universal

indicator the color become orange and the pH is 3, after add by 42 drops of HCl,

the color become smooth orange and the pH is 2. It means that it is a buffer

solution because buffer is a solution that able to resist changes in pH upon the

addition of small amounts of either acid or base.

In the tenth experiment, aquades that are colorless react with universal

indicator the color become green and the pH is 7, after added by 23 drops of HCl

the color become pink and the pH is 4. Based on our result, the aquades that we

use is not include as buffer solution.

2. Effect of adding base strong.

In the first experiment, we react CH3COOH + CH3COONa that

colorless and drop universal indicator and the solution become green with

pH = 5 and after we drop with 6 drops of NaOH the color changed become

dark purple. It means that it is not a buffer solution because buffer solution

is a solution of a weak acid or a weak base and its salt and able to resist

changes in pH (we can see from our experiment if there is not change, it’s

means the value of pH is keep)upon the addition of small amounts of either

acid or base, so it solution is Buffer because in the first step we proven that

solution is Buffer


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For the second experiment, it is about NH4OH react with NH4Cl that colorless

and directly become purple after we add by universal indicator it show that the pH

is 12 but after we add by 44 drops of NaOH the color change become dark purple.

It is include in buffer solution especially in base.

In the third experiment, we react NaCl with HCl that colorless and become

orange after we add by universal indicator and the pH is 4, and after we added 34

drops of NaOH the color become smooth purple. It is not buffer solution because

buffer is a solution that form if one of them is weak, but in this reaction is contain

of strong acid and strong base.

In the fourth experiment, it is about react NaCl with NaOH that are colourless

and become dark blue after we add by universal indicator with the pH is 11, but

after we add 10 drops of NaOH the color become blue Same with the third

experiment, it is not a buffer solution.

For the fifth experiment, when pineapple solution that are yellow react with

universal indicator the color become orange and the pH is 4. But after added by

NaOH 7 drops the color directly change become brown. It is a buffer solution

especially in acid because it can resist changes in pH upon the addition of small

amounts of either acid

In the sixth experiment, it is about orange solution that the first colour is

turbid react with universal indicator is become smooth orange with the pH is 3,

but after added by NaOH 50 drops the color change become smooth yellow. Same

with the fifth experiment, it is include in buffer solution.

In the seventh experiment, tomato solution that first color is red react with

universal indicator the color become orange with the pH is 4, after added by

NaOH 21 drops the color change become dark red and the pH is 13. It is include

buffer solution like orange and pineapple because in first step it can resist changes

in pH upon the addition of small amounts of either acid.

In the eight experiment, cucumber solution when add by universal

indicator is red and the pH is 4 but after add by 3 drops of HCl the color change

become pink and the pH is 3. after add by NaOH 1 drop the color directly change

become purple and the pH is 13.


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In the ninth experiment, soft drink react that are colorless with universal

indicator, the color become orange and the pH is 2, after added by NaOH 15 drops

the color changed become blue. It means that it is a buffer solution because buffer

is a solution that able to resist changes in pH upon the addition of small amounts

of either acid or base.

In the tenth experiment, aquades that first color is colorless react with

universal indicator the color become green and the pH is 7. After added by NaOH

2 drop the color directly change become purple. Based on our result, the aquades

that we use is not include as buffer solution.


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H. DISCUSSION :

The experiment in accordance with definition of Buffer, buffer solution is a

solution of a weak acid or weak base and its salt and able to keep value of pH

upon the addition of small amounts of either strong acid or strong base.

In adding of Strong Base, CH3COOH + CH3COONa, orange and cucumber

do not need many drops of NaOH. Although it give the good result in HCl

addition that proven they are buffer solution because a large amount of HCl drops,

it does not work in NaOH adding. The possibility, we washed the reaction tube

unclearly. So, there is another substances that reacted, so it can disturb the

reaction.


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I. CONCLUSSION :

Base of the experiment we have done, we can conclude that :

Buffer solution is a solution of a weak acid or weak base and its salt

and able to keep value of pH upon the addition of small amounts of

either strong acid or strong base.

After we did buffer solution experiment we get that

CH3COOH+CH3COONa solution, NH4OH+NH4Cl solution,

pineapple, orange, tomato, cucumber and soft drink are buffer

solution, because they can maintain their initial pH although after

dropped by HCl or NaOH.

NaCl+HCl, NaOH+NaCl, and aquades are not buffer solution

because they can’t maintain their initial pH after dropped by HCl or

NaOH and because HCl is strong acid and NaOH is strong base.


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J. ANSWER of QUESTION :

QUESTION

1. Based on the third and fourth experiment, which one that you think is the

buffer solution?

2. What will happen if the solution of CH3COOH + CH3COONa and NH4OH

+ NH4Cl are added by HCl into aech solution?

3. Just like the quastion number 2. But we replace the addition of HCl by

NaOH, what wil happen?

ANSWER

1. Based on the 3rd and 4th experiment, we get that the buffer solution

are: CH3COOH+CH3COONa solution, NH4OH+NH4Cl solution,

pineapple, orange, tomato, cucumber and soft drink

2. If we add HCl into solution of CH3COONa + CH3COOH there will be

only a little changing of the pH after and before addition of HCl (it is

hard to change). And there will be pH changing but we need a lot of

HCl to be added. And it also happen when we add HCl into solution

of NH4OH + NH4Cl. It could happen because both of the solutions are

buffer. So the addition of HCl will change the pH hardly.

3. If we add NaOH into solution of CH3COOH + CH3COONa there will

be only a little changing of pH after and before addition of NaOH (it

is hard to change). And there will be pH changing but we need alot of

NaOH to be added. And it also happen when we add NaOh into

solution of NH4OH + NH4Cl. It could happen because both of the

solutions are buffer. So the addition of NaOH will change the pH

hardly


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BIBLIOGRAPY :

Tim Kimia Dasar.2013.Petunjuk Praktikum Kima Lanjut.Unesa:Unipress.

Brady, James E. 1990. General Chemistry:Principle and Structure 5 thed. United

State of America.

Chang, Raymond.General Chemistry: The Essential Concept/Raymond Chang-

3rded.America:Von Hoffman Press, Inc.

Svehla,G. 1979. Vogel:Longman Group Limited. London.


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ATTACHEMENT

Picture Explanation

The material to do the experiment.

The 3rd experiment, before adding some universal indicator.

The 3rd experiment, when adding some universal indicator.

The 3rd experiment, after we shake and adding some universal indicator.

The 3rd experiment, after we shake and adding some HCl.


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The 4rd experiment, before adding some universal indicator.

The 4rd experiment, after we shake and adding some universal indicator.

The 4rd experiment, after we shake and adding some NaOH.


Buffer Solution

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