Kadir Titration process began by adding thiosulpahte

Kadir Alp Gunes

 

Experiment 3: The Determination of Hydrogen Peroxide
by Iodometric Titration

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Abstract:

Iodometry is a method of volumetric chemical analysis where
iodine reacts directly with organic and inorganic substances. For a purpose of
this experiment, a redox titration was performed in order to determine hydrogen
peroxide. Namely, potassium iodine was added into a flask containing sulphuric
acid. Once dissolved, hydrogen peroxide was added gradually until the solution
developed a brown colour. Titration process began by adding thiosulpahte into
the flask, making it more of a yellow colour. Starch solution was added in order
to make the end point sharper causing the solution to develop black colour. At
the end point, solution went colourless.

 

Introduction:

 

 

 

Peroxide is a compound that has oxygen-oxygen single bonds
and is a strong oxidizing agent. Its general formula is R2O2
where R can either be an oxygen atom or 1st column metal. There are
many inorganic peroxides, ionic and covalent. Ionic peroxides contain alkali
metal ions, while one of the covalent peroxides’ representative is hydrogen
peroxide.

Hydrogen peroxide, H2O2, is a simple peroxide compound –
corrosive, toxic liquid found as a main component in hair bleaches and is also
used as antiseptic in chemical industries.

 

In H2O2 the oxidation number of oxygen
is -1, in oxides it is -2 and O2 gas is 0. An oxidation number is unstable.

In this titration, the oxidation number of Hydrogen peroxide changes from -1 to
0, meaing that it is the substance oxidized (reducing agent).

 

Titrimetry is an analytical method where a certain solution
is treated with a reagent of a known concentration. This method is suitable
when a number of moles of a reagent that reacts with undetermined substance
needs to be obtained.

 

The aim of the experiment is to determine the concentration
of a hydrogen peroxide solution by using iodometric titration.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Materials and methods:

 

The materials used in this experiment were

 

Materials used in this
experiment were solutions; H2O2, sodium thiosulphate,
sulphuric acid of concentration 1.25 mol/dm3, as well as a solution
of potassium iodide.

 

 

10.00 cm3 of sulphuric acid was added in 250 cm3
conical flask. Exactly 1.00 g of potassium iodide was weighed on a small plastic
plate and was poured in flask. Flask was swirled gently until all of potassium
iodide can dissolve properly.  25.00 cm3
of hydrogen peroxide was added to the solution, when potassium iodide has
dissolved. The solution swirled constantly to mix it more effectively. Parafilm
is used to cover up the top of the flask, the solution left for 15 minutes.

Because of the presence of iodine, it turned dark black/orange. Sodium
thiosulphate poured into a burette. In order to remove bubbles sodium
thiosulphate is run through the burette once and is thoroughly checked for
bubbles. A funnel put on the burette to get précises readings. Initial volume
was noted down. Stopper valve was released and sodium thiosulphate passes into
the solution considering there were no colour changes in colour in the first phases.

The stopper valve slowed downed as the colour of iodine solution change more to
yellow. The flask was swirled during the titration process to increase the rate
of titration. When the solution converts to pale yellow a few drops of starch
solution is added as an indicator. The addition of thiosulphate continued until
the iodine solution becomes colourless. The reading in the burette was observed
and recorded. The experiment was repeated until there is three consistent
results. 

 

 

 

 

 

 

 

 

 

 

 

 

 

Results:

 

Table1: Titration results.

 

1

2

3

Initial volume (cm3)

0.00

0.00

0.00

Final volume (cm3)

24.8

24.9

24.9

volume
used (cm3)

24.8

24.9

24.9

 

 

The experiment has been repeated three times to get a
precise result. It was required to get ± 0.1
cm3 difference between the results as can be seen from Table 1.

 

 

The average volume used:

­­­

 

 

The average volume is
calculated from table 1

 

 

Equation 1:                  H2O2
+ 2H+ + 2I-  à
I2 + 2H2O

Reaction
of hydrogen peroxide with potassium iodine.

 

From Equation 1 it can be said that 1 mole on Iodine (I2)
can be created from 1 mole of hydrogen peroxide. This can be seen from the
ration of  H2O2 to
I2.

 

 

 

 

Equation
2:                    
I2 + 2S2O32-
à 2I- + S4O62

Reaction
of produce Iodine from Equation 1 react with Na2S2O3.

 

The equation shows that it 1 mole of iodine gives 2 moles of
thiosulphate.

 

 

 

Titration 1.

 

Volume used is 24.8

 

 

Z1 = 0.052 mole/L

 

Titration 2.

 

Volume used is 24.9 cm3

 

 

Z2 = 0.052 mole/L

 

Titration 3.

 

Volume used is 24.9 cm3

 

 

 

Z3 = 0.052 mole/L

 

Moles of H2O2 for each titration
reaction can be calculated by knowing concentration of H2O2  in every reaction.

Number of moles of thiosulhate =

 

Titration 1.

 

 

(25.00 x 0.0519312) / 1000 = 1.29 x 10-3 moles

 

Titration 2.

 

 

(25.00 x 0.0521406) / 1000 = 1.30 x 10-3 moles

 

 

Titration 3.

 

 

 

 

(25.00 x 0.0521406) / 1000 = 1.30 x 10-3 moles

 

 

 

The steps of
standard deviation. 

 

Standard
deviation is calculated using median.

 

Standard
deviation is calculated by subtracting the mean from each result, squaring thi
value, repeting this with each result and totalling the answers. There after we
divide the answer by the number of results taken minus one. Finally we square
root the value.

 

 

 

(24.80-24.87)2
+ (24.90-24.87)2 + (24.90-24.87)2 = 0.0067

 

0.0067/(3-1)
= 0.003

 

 = 0.06

  0.1

 

 

To calculate relative standard deviation:

RSD (stand. dev. x 100)/mean = (0.1 x 100)/24.87 = 0.40%

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Discussion and conclusion:

 

The experiment was done in 3 attempts to get precise results