BIOSCIENCE EDUCATION

DETERMINATION OF DISSOLVED OXYGEN IN WATER (WINKLER METHOD)

AIM:
To determine the dissolved oxygen (DO) content in water.

APPARATUS:
BOD bottles, burette, pipette.

REAGENT:
Manganese sulfate, alkaline iodide, starch, sodium thiosulphate.

PRINCIPLE:
DO oxidizes Mn²⁺ to Mn⁴⁺, which liberates iodine that is titrated.

PROCEDURE:

• Add MnSO₄ and alkaline iodide to water sample.

• Allow precipitate to form and settle.

• Add H₂SO₄ to dissolve.

• Titrate liberated iodine with sodium thiosulphate using starch as indicator.

CALCULATION:
DO (mg/L) = Volume of thiosulfate used × Normality × 8

DETERMINATION OF CITRIC ACID IN FRUIT JUICE

AIM:
To estimate citric acid content in fruit juice.

APPARATUS:
Burette, conical flask, pipette.

REAGENT:
0.1M NaOH, phenolphthalein.

PRINCIPLE:
Citric acid neutralized by NaOH; endpoint indicated by pink color.

PROCEDURE:

• Pipette 10ml of juice into a flask.

• Add 2–3 drops phenolphthalein.

• Titrate with NaOH to pink endpoint.

CALCULATION:
% Citric Acid = Titre × 0.064 × 100 / Volume of sample

DETERMINATION OF CHLOROPHYLL IN LEAF EXTRACT

AIM:
To estimate chlorophyll content in a leaf sample.

APPARATUS:
Spectrophotometer, centrifuge, test tubes.

REAGENT:
80% acetone.

PRINCIPLE:
Chlorophyll is extracted and measured at specific absorbance values.

PROCEDURE:

• Grind 1g of leaf in 10ml acetone.

• Centrifuge and collect supernatant.

• Measure absorbance at 645 nm and 663 nm.

CALCULATION:
Use Arnon's formula:
Chlorophyll a = 12.7(A663) – 2.69(A645)
Chlorophyll b = 22.9(A645) – 4.68(A663)

DETECTION OF BORIC ACID IN FOOD

AIM:
To detect boric acid in food samples (e.g., milk, jaggery).

APPARATUS:
Test tubes, turmeric paper.

REAGENT:
None (turmeric paper acts as indicator).

PRINCIPLE:
Boric acid turns turmeric paper red, which turns green on ammonia exposure.

PROCEDURE:

• Dip turmeric paper in food extract.

• Dry and observe color.

• Expose to ammonia vapor for confirmation.

RESULT:
Red to green color change confirms boric acid.

TEST FOR SULPHUR DIOXIDE IN DRIED FRUITS

AIM:
To detect presence of SO₂ preservative in food.

APPARATUS:
Test tubes, beaker.

REAGENT:
Pararosaniline hydrochloride, formaldehyde.

PRINCIPLE:
SO₂ reacts with dye and formaldehyde to form pink/magenta color.

PROCEDURE:

• Boil fruit sample in water, cool extract.

• Add 2ml dye reagent + formaldehyde.

• Observe color change.

RESULT:
Pink color indicates presence of sulphur dioxide.

ALCOHOL DETECTION IN HAND SANITIZERS

AIM:
To determine the presence and concentration of alcohol in hand sanitizer.

APPARATUS:
Test tube, alcohol hydrometer or colorimeter.

REAGENT:
Potassium dichromate + sulfuric acid.

PRINCIPLE:
Alcohol reduces orange dichromate to green chromium ions.

PROCEDURE:

• Add 2ml sanitizer to test tube.

• Add dichromate reagent.

• Shake and observe color change from orange to green.

RESULT:
Color change confirms alcohol; intensity can indicate concentration.