FE 211 01.11.2004

EXPERIMENT 5

LAB REPORT

Submitted By : Mutlu DEMİREL Group: 3

MATERIALS:

HCl , , , , , , Zimmermann-Reinhardt reagent , Distilled water , Buret , Erlenmayer Flask , Graduated Cylinder , Pipet , Bunsen Burner.

PURPOSE:

Our purpose is to determine the iron by permanganete titration.

METHOD:

Gravimetric Analysis

THEORY:

Iron is an abundant element in the earth’s crust, but exists generally in minor concentrations in natural water systems. The form and solubility of iron in natural waters are strongly dependent upon the pH and the oxidation- reduction potential of the water. Iron is found in the +2 and +3 oxidation states. In a reducing environment, ferrous (+2) iron is relatively soluble. An increase in the oxidation-reduction potential of the water readily converts ferrous ions to ferric (+3) and allows ferric iron to hydrolyse and precipitate as hydrated ferric oxide. The precipitate is highly insoluble. Consequently, ferric iron is found in solution only at a pH of less than 3. The presence of inorganic or organic complex- forming ions in the natural water system can enhance the solubility of both ferrous and ferric iron.

PROCEDURE:

Standardization of Permanganate Solution with Sodium Oxalate: 10 ml of sodium oxalate ( ) was put into a flask and 25 mL was added to it. Then solution was heated nearly to boiling. Then the solution was titrated with permanganate until the pink color was observed. Finally the molarity of permanganate solution was calculated.

Iron Determination:

5 mL of HCI was added to 10 mL sample in a flask. Then the solution was heated. After , stannous chloride ( ) was added to the hot solution drop by drop until the yellow color changes to light green and two drops of excess was added. Then the solution diluted to 100 mL and allowed to cool at room temperature. After that 10 mL was added to this solution rapidly with stirring. When the white ppt was observed. The solution diluted to 300 mL and 25 mL Zimmermann – Reinhardt reagent was added to it. Finally the solution was titrated with permanganate ( ) .Untill the ping color was observed and %Fe was calculated in the sample.

RESULTS AND CALCULATION :

Standardization of Permanganate with Sodium Oxalate:

the volume of = 10 mL

the of = 20 g/L

the volume of permanganate = 38 mL

the molecular weight of =134 g

weight of =

Mole of =

Molarity =

Percentage of Fe ion:

the volume of sample = 5 mL

the of sample = 60 g/L

the volume of permanganate = 13 mL

the molarity of permanganate = 0.02 M

the mole of permanganate =

weight of =

weight of sample =

DISCUSSION:

Volumetric determination of iron is basicly based on the dissolution of the sample reduction of to , addition of special reagent and titration with standart permanganate. But instead of permanganate we should use create or dichromate solution as titrant. Firstly we calculated the molarity of permanganate which we used as standart solution during the determination of Fe. Later we prepared the titrand. During the experiment we heated the sample solution but didn’t boil it. This is because the prevent the loss of as vopar. Then we added stannous chloride to the solution. Our aim was to reduce ions into .Because is more soluble form of . We added 1-2 drops more to minimaze the air oxidation of and to eleminate the interference of impurities. After that we added 10 mL to the solution to oxidize the excess according to reaction: A small quantity of silky white precipitate of was appeared. İf the precipitate was gray it means that the was to much and changed the to Hg This Hg ions reacts with with slow rate , consuming more than required to reach the end point .İt means you failed the experiment . For this reason after adding white precipitate should be observed. In this case of no precipitation formation , after addition of it is observed that the was not in excess and most probably reduction of to is incomplete. Therefore , the sample solution should be discarded. If either gray precipitate formed or no precipitation observed. In our experiment white precipitate was observed. Soon we added 25 mL Zimmermann-Reinhardt reagent this reagent eliminates the interference of chloride with titration , Finally we titrated the sample solution with permanganate solution untill the pink color observed.

MnO4

Fe2+

MnO4

5Fe2+

(aq) + 5e-
MnO4

+ 5e-

+ 8H+

–

(aq) Fe3+

+ 8H+

+ 5e-

–

(aq) 5Fe3+

+ 8H+

+ 5Fe2+

–

Mn2+

Mn2+

Mn2+

+ 4H2O

(aq) + e

+ 4H2O

+ 5Fe3+ + 4H2O

…