TITLE EXPERIMENT 5 DETERMINATION OF THE MOLARITY AND CONCENTRATION OF SULPUHURIC ACID BY TITRATION WITH A STANDARD SOLUTION OF SODIUM HYDROXIDE.
INTRODUCTION
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 the volumes of the standard and unknown solutions used in the titration, along with the concentration of the standard solution, the calculate concentration of the unknown solution. Titrations can be conducted using acid-base, precipitation or oidation-reduction reactions. !odium hydroide is one of the bases commonly used in the laboratory. "owever, "owever, it is difficult to obtain solid sodium hydroide in a pure form because it has a tendency to absorb water from air, and its solution reacts with carbon dioide. In an acid-base titration one of the solutions is an acid and the other a base. #ne is placed in a flask. The other is placed in a burette, from which it is dripped dripped into the flask until the titration reaches its end point. $ suitable indicator needs to be chosen such that the end point shows accurately that all of the solution in the flask has reacted with the solution being dripped into it the point at which this happens is called the equivalence point. In a perfect titration the end point and equivalence point will be identical. If the indicator is not chosen well, the end and equivalence points will differ, and the titration will not produce accurate data about the solution of interest.
OBJECTIVES 1. To determine the molarity and concentration of sulphuric acid using titration technique.
APPARATUS
%. '. (. *. 0. 2. 4.
&urette &urette clamp )etort stand +olumetric pipette ' m/ 1ipette filler or suction bulb 3onical flask '0 m/ 5hite tile
CHEMICALS 1. !odium hydroide solution, 6a#" 2. 7ilute sulphuric acid, "'!#* of unknown molarity 3. 1henolphthalein PROCEDURE
%. The burette was washed with distilled water and then rinsed with about 0-% m of 6a#" solution, running the second rinsing through the burette tip. The burette was clamped to the retort stand. '. The burette was filled with the 6a#" solution. 8ake sure the tip was completely filled and contain no air bubbles. The initial reading was recorded to two decimal places. (. ' m " '!#* was transferred to a clean '0 m conical flask. ' or ( drops of phenolphthalein indicator. The conical flask was placed on a piece of white tile under the burette and lower the burette tip to the conical flask. *. The titration apparatus was set up. The "'!#* solution by adding 6a#" solution until the end point was reached. The conical flask was kept swirled during titration. The end was indicated when the entire solution retain a faint pink colour for at least ( seconds. The final burette reading was recorded. 0. The titration process was repeat until consecutive titrations. 2. The reading from all titrations was recorded in the space provided on the datasheet. 4. 5hen finished with the titration, the burette was empty and rinsed it at least twice with tap water and once with distilled water.
RESULTS
DATA Numb! "# $%$!&$%"' 9inal burette reading m/ Initial burette reading m/ +olume of 6a#" used m/
ROU(H T%$!&$%"' %:
T%$!&$%"' 1 %:.'
T%$!&$%"' 2 '.0
T%$!&$%"' 3 '.0
%:
%:.'
'.0
'.0
8olarity of standard 6a#" solution 8 b/ ; .' 8 +olume of "'!#* solution +a/ ; ' m $verage volume of 6a#" used + b/ ; ' m 19.2+20.5+20.5
) ' m
3
CALCULATIONS 1. D$!m%' $* u'+'",' m"-&!%$ "# $* H2SO/ 0M& "-u$%"'.
' 6a#" < " '!#* 8a ; = 8 b ; .' 8 +a ; ' m + b ; ' m
6a'!#* < ' "'
8a '/ ; % .' '/
'
* 8a ; * 8a ; .% 8
2. D$!m%' $* u'+'",' "''$!&$%"' %' 4L "# H2SO/ "-u$%"'.
3oncentration g>/; 8olarity ? 8olar mass
8olar mass "'!#* ; '%/<('<*%2/ ; :@ g>mole 3oncentration ; .% ? :@ ; :.@ g> DISCUSSION
In the titration by using " '!* as the acid solution and 6a#" as the base solution. . 9or this eperiment is the neutralization of sulfuric acid with sodium hydroide. The titration was repeated three times. The initial burette reading was remaining same but the final burette reading and the volume of sodium hydroide is increases. This result was obtained because there are some errors when handling the burette. The equation of the reaction isA 2 N&OH 6 H2SO/
N&2SO/ 6 2 H2
The molarity of 6a#" solution is .'8 and the volume of sulphuric acid used was ' m. The average volume of 6a#" used was calculated by adding the volume of 6a#" in titration %,' and (. Then, it was divided by (. There are many precautions when do acid-base titration eperiment. 9or eample, in acid-base titration ( aliquots of unknown concentration which is if take three reading, only take at ' and three reading to calculate the average because at first reading its act as try and error. The different between equivalence point and an end point must do. 1henolphthalein is an indicator for acid-base titration that will show pink colour for basic solution and colourless for acid solution. &y adding phenolphthalein to an acids, the solution will be colourless. Then, add standard base from burette until the solution barely turns from colourless to pink. This colour change indicates that the acid has been neutralized. The solution therefore becomes base, and the dye turns pink. 3are must be taken choose indicators whose end points correspond to the equivalence point of the titration.
!ome precaution during do this eperiment. 9irst, each apparatus must be rinse with the distilled water. 8easure the volume of the solution properly especially during make dilution solution. 8ake sure the solution from the burette flow very slowly to avoid some mistake during take the reading. 8ake sure there are no air bubble in the burette by open the stopcock for a while and let the solution flow a little bit. CONCLUSION
$s a conclusion, to determine the unknown molarity and unknown concentration of sulphuric acid, the titration process can be used with the correct technique in titration. If not use the correct technique, there must have some error in the result.
7UESTIONS 1. W* 8*'"-8*$*&-%' % u9 %' $*% :8!%m'$; It is a chemical used to indicate a change in p" during a titration. It turns colourless in an acidic solution, and it turns pink in a basic solution 2. N&OH % & *4!""8% "m8"u'9 &'9 &-- N&OH "-u$%"' mu$ b $&'9&!9%<9 b#"! %$ &' b u9 #"! &'&-%. U%'4 !#!'= :8-&%' $* 4%>' $!m? &. H4!""8% "ygroscopic substances absorb moisture from the atmosphere but do not change their state. b. S$&'9&!9%<&$%"' !tandardization is a process in which the value of a potential standard is fied by a measurement made with respect to a standard whose value is known.
REFERENCES
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