Experiment 7_ Determination Of Bleaching Power By Iodimetry

Name: Eldee R. Balolong Student Number: 2007-58545 Class-Section: Chem 28.1-1 Date Performed: August 28, 2008 Date Submitted: August 15, 2008 I.

TITLE. Determination of Bleaching power by Iodometry

II.

RESULTS. Sta ndar dizat ion of Sodi um T hios ulf ate Sol utio n Primary Standard used:

K2Cr2O7

Formula mass of 1O standard: % Purity of 1O standard:

Trials Mass of K2Cr2O7 (g) Corrected Mass of K2Cr2O7 (g) Final Reading Na2S2O3 (ml) Initial Reading Na2S2O3 (ml) Volume Na2S2O3 (ml) Molarity of Na2S2O3 Average Molarity of Na2S2O3

294.07 g/mol 99.80%

1

2

3

0.1007 0.1005 20.40 0.000 20.40

0.1009 0.1007 41.00 20.40 20.60

0.1008 0.1006 20.65 41.00 20.30

0.1005

0.09970 0.1004

0.1011

Sa mple Ana lysis Brand of Bleaching Solution:

ZONROX

Trials Mass of the sample (g) Final volume Na2S2O3 (ml) Initial volume Na2S2O3 (ml) Net Volume Na2S2O3 (ml)

1

2

3

0.1447 9.500 0.000 9.500

0.1447 32.90 21.10 11.80

0.1447 21.10 9.500 11.60

mg Cl2 in sample % Cl2 in sample

0.2385 0.01648

0.2962 0.02047

0.2912 0.02013

Average % Cl2 in sample

III.

0.01903

Sample Calculations A. Corrected Mass of K2Cr2O7 (g) Masscorrected=MK2Cr2O7 * 0.9980 Masscorrected=0.1007 g * 0.9980 Mass

corrected

=0.1 005 g

B. Net Volume Na2S2O3 Vnet of Na2S2O3=(Vfinal Na2S2O3)-(Vinitial Na2S2O3) Vnet of Na2S2O3=(20.40 mL)-(0.000 mL) V net

of Na2S2O3

=20 .40 mL

C. Molarity Na2S2O3 Molarity

Na2S2O3=[((Masscorrected of K2Cr2O7 x 1000)mg/294.18 mg K2Cr2O7/mmol of K2Cr2O7)) x (3 mmol I2/1 mmol of K2Cr2O7) x (2 mmol Na2S2O3/1 mmol I2)]/ V Na2S2O3 used =[(1.005 g x 1000) mg/294.18 mg K2Cr2O7/mmol K2Cr2O7 x (3 mmol I2/1 mmol of K2Cr2O7) x (2 mmol Na2S2O3/1 mmol I2)]/ 20.40 mL Na2S2O3

Molarit y

Na2S2O3

=0 .100 5 mmo l Na 2 S 2 O 3 /mL Na 2 S 2 O 3

D. Average Molarity Na2S2O3 MolarityAve=(0.1005 M + 0.09970 M + 0.1011 M)/3 Molarit y iodine =0 .100 4 M

** for the sa mp le analy sis A. Net volume of Na2S2O3 Vnet=9.5 mL- 0.0 mL V net =9 .5 mL B. Mg Cl2 in sample MgCl2=(VNa2S2O3)(MNa2S2O3)(1 mmol I2/2 mmol Na2S2O3)(1 mmol OCl-/1 mmol I2)(1 mmol Cl2 /2 mmol OCl-)

MgCl2=(9.5 mL Na2S2O3)*(0.1004 mmol Na2S2O3/mL Na2S2O3)* )(1 mmol I2/2 mmol Na2S2O3)(1 mmol OCl-/1 mmol I2)(1 mmol Cl2 /2 mmol OCl-)

Mg Cl2 =0.2 385 mg C l 2

C. % Chloride in sample % Chloride=(Mg Cl2/(mass of sample *1000))*100% % Chloride=(0.2385 mg Cl2/(0.1447 g *1000))*100% % C hloride= 0.0 1648 % is chlor ide in the sa mple

D. Ave. % chloride in sample Ave % Chloride= (0.01648% + 0.02047% + 0.02013%) Ave % Chlor ide= 0.0 1903 % E. Mass of the sample

***The mass of the sample was taken with respect to the density of the given compound; liquid bleach was used, thereby mass of the sample at first cannot be taken.

Mg sample=(Vliquid bleach used)*(Densityliquid bleach)*(1 mmol OCl-/(51.45 mg OCl/mmol OCl-))(1 mmol Cl2/1 mmol OCl-)(70.91 mg Cl2/mmol Cl2) Mg sample=(2 mL)*(5250mg/100mL)*(1/51.45)*(1/1)*(70.91/1) Mg sample =144. 7 m g or 0.1 447 g

*the same mass of sample was used throughout the experiment where there was equal volume of ZONROX used. IV.

Discussion

Potassium Dichromate is a fairly strong oxidizing agent. It is not however as strong as potassium permanganate or the Cerium (IV) ion. It has the advantages of being inexpensive, very stable in solution, and available in sufficiently pure form for preparing standard solutions by direct weighing. Amidst its level of being an oxidizing agent and its slowness, still this was used in the above experiment possibly because of economical purposes. Most of the time, this kind of primary standard is principally used in the titration of iron in hydrochloric acid solutions.

In analytical processes, iodine is used as an oxidizing agent(iodimetry) and iodide ion is used as a reducing agent(iodometry); in the experiment, iodometry was used to determine the bleaching power by iodometry; and the Cl 2 content is a way to determine it.

Bleaching is the process of whitening, or removing the natural color of textile fibers and many other materials through the treatment with chemicals or by exposure to the sun, heat or water. Oxidizing agents play a huge part in this bleaching process and a lot of pigments and dyes are changed into substances of little or no color. Because of this, substances such as CHLORINE compounds, hydrogen peroxide, sodium perborate, and potassium permanganate are most commonly used as bleaches. Many pigments and colored substances can be decolored by such reducing agents as sulfur dioxide; and decoloration through the use of reducing agents is referred

to as stripping, particularly, when used to remove artificial colorants such as dyes from textiles. Oxidizing agents usually produce more permanent whites than do reducing agents. Bleaching was practiced already before in some parts of Asia, Europe and Africa. In 1785, the powerful bleaching properties of Chlorine were discovered by Berthollet. Bleaching powder, produced by the reaction of chlorine gas on slaked lime, with the same effect as chlorine, was introduced in 1799 by the Scottish chemist Charles Tennant. Bleaching powder is a mixture containing calcium hypochlorite (Ca[OCl] 2) as the active bleaching agent. Bleaching powder was used as the standard bleaching agent until about 1925. Since that time the use of so-called liquefied chlorine, a solution of sodium hypochlorite (NaOCl), has largely replaced bleaching powder. Liquid household bleaches are commonly based on sodium hypochlorite as the active ingredient at a concentration of 5.25 percent. Industrial strength versions are often several times more concentrated. ("Bleaching." Microsoft® Student 2008 [DVD]. Redmond, WA: Microsoft Corporation, 2007. ) With Chlorine being a so much important chemical in the industry makes it so much in demand in the textile industry being a huge compartment in bleaches. With Iodine here being the titrant, it is reduced to I2 and in turn reacts with thiosulfate ion; thereby oxidizing it in this step. With a lesser value of I2 produced, there would already be a fading of color in I3-. COMMENT: With the given experiment, I being one of the experimenters experienced a lot of difficulties facing this experiment; with so much vague terms pushes me further to stop reading in advance the experiment itself. Our school of course is undeniably the best in instruction; but I hope packaged in this ‘title’ is a huge responsibility to help students be stimulated by the experiment and on how we can apply this later in life.