Lab Chem 3

UNIVERSITI PENDIDIKAN SULTAN IDRIS

EXPERIMENT 3: ACID AND BASE TITRATION TKU 1033 BASIC CHEMISTRY 1

NAME: SAYIDAH NAFISAH BINTI MOHD SALIM MATRIC NO: D20081032338 LECTURER’S NAME: PN FARIDAH BT. YUSOF GROUP: 2 DATE: 14 AUGUST 2009

OBJECTIVE : •

To determine the concentration of sodium hydroxide solution through titration technique using hydrochloric acid and sulfuric acid.

CONCEPT : 1. To determine the concentration of acid and base solution through titration with standard solution. 2. To apply the correct technique in titration. 3. To carry out acid base titration using phenolphthalein as indicator. RESULT : Hydrochloric acid, HCl Erlenmeyer flask

Initial reading (ml)

Final reading (ml)

1

0.00

46.50

2

0.00

44.50

3

0.00

45.50

Erlenmeyer flask

Initial reading (ml)

Final reading (ml)

1

0.00

24.00

2

0.00

22.50

3

0.00

22.80

Sulphuric acid, H2SO4

CALCULATION Concentration of HCl

NaOH (l) + HCl (l)

NaCl (l) + H2O (l)

Average of HCl solution

= 44.50 ml + 45.50 ml 2 = 45.00 ml

Molarity of NaOH (C solution) M1V1 = M2V2 M1 (25 ml) = (1.00 x 10-2 M) ( 25 ml) M1 = (1.00 x 10-2 M) ( 25 ml) (25 ml) M1 = 0.01 M

Mole of NaOH = ( 0.01 M) (10 ml) = 0.1 mol

1 mole of NaOH = 1 mole of HCl 0.1 mole of NaOH = 0.1 mole of HCl

Molarity of HCl = 0.1 mol 45.00 ml

= 0.002 M Concentration of H2SO4

2NaOH (aq) + H2SO4 (aq)

Average of HCl solution

Na2SO4 (l) + 2H2O (l)

= 22.50 ml + 22.80 ml 2 = 22.65 ml

Molarity of NaOH (C solution) M1V1 = M2V2 M1 (25 ml) = (1.00 x 10-2 M) ( 25 ml) M1 = (1.00 x 10-2 M) ( 25 ml) (25 ml) M1 = 0.01 M

Mole of NaOH = ( 0.01 M) (10 ml) = 0.1 mol

2 mole of NaOH = 1 mole of H2SO4 0.1 mole of NaOH = 0.1 mole of H2SO4

Molarity of HCl = 0.05 mol 22.65 ml = 0.002 M

DISCUSSION : Quantitative studies of acid-base neutralization reactions are most conveniently carried out using a technique known as titration. In titration, a solution of accurately known concentration, called a standard solution, is added gradually to another solution of unknown concentration, until the chemical reaction between the two solutions is complete. To determine the concentration of a particular solute in a solution, chemists often carry out titration, which involves combining a sample of the solution with a reagent solution of known concentration, called a standard solution. If we know the volumes of the standard and unknown solutions used in the titration, along with the concentration of the standard solution, we can calculate the concentration of the unknown solution. Titrations can be conducted using acid-base, precipitation or oxidation-reduction reactions. Sodium hydroxide is one of the bases commonly used in the laboratory. However, it is difficult to obtain solid sodium hydroxide in a pure form because it has a tendency to absorb water from air, and its solution reacts with carbon dioxide. For these reasons, a solution of sodium hydroxide must be standardized before it can be used in accurate analytical work. In this experiment, we have NaOH solution of unknown concentration and an HCl solution we know to be 1.00 x 10-2 M. To determine the concentration of the NaOH solution, we take a specific volume of that solution, say 25.00 mL. We than slowly add the standard HCl solution to it until the neutralization reaction between the NaOH and HCl is complete. The point at which stoichiometrically equivalent quantities are brought together is known as the equivalence point of the titration. In this experiment, the concentration or molarity of Hydrochloric acid, HCl and sulphuric acid H2SO4 must determine. This molarity can be determined by use the molarity of Sodium Hydroxide, NaOH. To determine the concentration of NaOH we can use this formula:

M1 V1 M2 V2

=

1 1

M1 is a molarity of Sodium Hydroxide, while V1 is a volume of Sodium Hydroxide, NaOH. For M2 show the molarity and volume of Hydrochloric acid, HCl or sulphuric acid, H 2SO4. Base on this formula, we can get the molarity of NaOH. Before determine the molarity of Hydrochloric acid, HCl or sulphuric acid, H2SO4 the equation of the reaction of the acid and base must be balance to get the rate of solution. The accurate value of the molarity Hydrochloric acid, HCl or sulphuric acid, H2SO4 is 0.02M. In order to titrate an unknown with, there must be some way to determine when the equivalence point of the titration has been reached. In acid-base titration, dyes known as acidbase indicators are used for this purpose. For example, the dyes known as phenolphthalein are colorless in acidic solution but are pink in basic solution. If we add phenolphthalein to an unknown solution of basic, the solution will be in pink color. We can then add standard acid from a burette until the solution barely turns from pink to colorless. This color change indicates that the acid has been neutralized and the drop of the acid that caused the solution to become colorless has no base to react with. The solution therefore became acid, and the dye turns colorless. The color change signals the end point of the titration, which usually coincides very nearly with the equivalence point. Care must be taken to choose indicator whose end point corresponds to the equivalence point of the titration. There are many precautions when we do acid-base titration experiment. For example, in acid-base titration 3 aliquots of unknown concentration which is if we take three reading, we only take at 2 and three reading to calculate the average because at first reading its act as try and error. We must can to differentiate between equivalence point and an end point. Phenolphthalein is an indicator for acid-base titration that will show pink color for basic solution and colorless for acid solution.

CONCLUSION : As a conclusion, if we want to determine the concentration of unknown concentration either acid or base, we can do the titration process with apply the correct technique in titration. If we not use the correct technique, there must have some error in our result. REFERENCES : http://www.google.com.my/search?hl=en&q=function+of+phenolphthalein&meta=&aq=2&oq=f unction+of+pheno http://en.wikipedia.org/wiki/Acid-base_titration#Equipment Brown, T. L, LeMay, H.E & Bursten, B.E. (2005). Chemistry The Central Science (10th ed.). London: Prentice Hall. Raymond Chang (1998). Chemistry (6th ed.). New York: Mc Graw Hill.