Basic:
Oxidation of organic substances with potassium dichromate and silver sulfate excess in boiling sulfuric acid. The amount of potassium dichromate is not reduced during the oxidation reaction is determined by how titrimetrik with standard solution of ferrous ammonium sulfate (FAS) and indicators feroin. Chloride ion concentration above 1 mg / L is closed with mercury sulfate.
Reaction:
CxHyOz + Cr2O72-→ CO2 + H2O + Cr3+
Cr2O72-(excess) + Fe2 + → Fe3 + + 2Cr3+ + H2O
Reagents:
1. Examples
2. Sulfuric acid 98%
3. Silver sulfate solution
4. Mercury sulfate solution
5. Potassium dichromate solution
6. Ferrous ammonium sulfate solution
7. Solution of potassium hydrogen phthalate
8. Feroin indicator solution
Tools:
1. Pumpkin peck 50 ml, 100 ml, and 1000 ml
2. Goblets 250, 500, and 1000 ml
3. 25.50 measuring cup, and 100 ml
4. Watch glass
5. 25 ml Burette + clamp + Standards
6. The temperature of the appliance COD (cod tube, air condensers, equipment destruction, ice water bath, and shelves)
7. Electronic Scales 4 decimal places (Mettler AE 260)
8. Magnetic stir bar magnet and 2.5 cm
How it works:
1. In the pumpkin destruction COD included consecutive 20 ml sample or have been diluted, 5 ml of mercury sulfate. 10 ml of 0.1 N potassium dichromate and boiling stones
2. Air condenser mounted above the pumpkin COD then added 40 ml 98% sulfuric acid through the upper air condenser carefully
3. Destruction tool heated to the perfect red dots mark
4. Examples that have been prepared (no. 2) is inserted into the device destruction and didestruksikan for 120 minutes
5. When didestruksi / reflux lasted 10 minutes add 5 ml of silver sulphate through the upper condenser
6. Examples that have been didestruksi cooled in the open air to room temperature
7. Added 25 ml of distilled water through the upper air condenser as a rinse
8. Air condenser removed and cooled in ice water sample
9. Example titrated with 0.1 N ferrous ammonium sulfate with feroin indicator until the end point (color change from blue green to red brown)
10. Blank determination made by the same treatment as samples, but samples of distilled water replaced
11. Done setting the standard solution of potassium hydrogen phthalate with the same treatment as an example, but an example is replaced with a standard solution of potassium hydrogen phthalate
12. Added 10 ml of 0.1 N potassium dichromate solution into a flask COD sample / standard / blank that has been titrated to end point. Then titrated back with a solution of 0.1 N ferrous ammonium sulfate until the endpoint (this step for the determination of FAS solution of normality 0.1 N)
Calculation:
1. The calculation of the concentration of ferrous ammonium sulfate (FAS)
FAS = ml K2Cr2O7 N x N K2Cr2O7
ml Fas
1. COD value calculation COD (mg O2 / L) = (a-b) x c x 8000 x d
v
Description:
a = volume of FAS to titrate the blank. ml
b = volume umtuk FAS titration sample.
c = normality of FAS. N
d = dilution factor
v = volume of sample. ml
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