Experimental Procedure

Materials

4 plastic bags (polyethylene, 2 kg)

1 black plastic bag

2 10-mL syringes

1 1-mL volumetric pipet

2 2-mL microburet

1 three-finger clamp 1 magnetic bar

1 magnetic stirrer

2 10-mL beakers

1 long wave UV pencil lamp 1 stop watch

3 10-mL Erlenmeyer flasks 1 propipet bulb

1 universal stand 1 ozone generator

Experiments

Reagents 0.3 MKI

0.0005 M Na2S203 • 5H20 CH2C12

0.5% starch solution concentrated H2S04

I) Ozone vs time

Connect the exit of the ozone generator to a plastic bag; close it perfectly in order to avoid any leaks.

This bag is protected of the light by covering it with a black bag. See Figure 1.

Start the ozone generator until the bag is filled (this takes around 3 min).

Sampling:

Simultaneously with filling the bag, prepare the reagent to detect the ozone: in a 10 mL Erlenmeyer flask pour an aliquot of 1 mL of KI solution and add 2 drops of acid and 2 drops of starch indicator. Suck this solution completely with the syringe.

Immediately after you have filled the bag, suck with the syringe 9 mL of the air in the bag. Shake

INNER BAG

BLACK OUTER BAG

OZONE GENERATOR

Figure 1. Experimental set-up.

INNER BAG

BLACK OUTER BAG

OZONE GENERATOR

Figure 1. Experimental set-up.

the syringe with the mixture for 1 minute, and return it to the Erlenmeyer flask and titrate it with the thiosulfate solution. Register the reading of the used volume.

Take six or seven samples in total, at different time intervals (every 4 minutes or so) up to 20-25 minutes.

II) Ozone + CH2C12 vs time

Connect the exit of the ozone generator to a plastic bag; close it perfectly in order to avoid any leaks. This bag is protected of the light by covering it with a black bag.

Start the ozone generator until the bag is filled (this takes around 3 min). Once the bag is filled with air/ozone introduce 1 mL of methylene chloride with a syringe.

In a 10-mL Erlenmeyer flask pour a lmL aliquot of KI solution and add 2 drops of acid and 2 drops of starch indicator. Suck this solution completely with the syringe.

Immediately after, take a 9-mL sample with a syringe containing 1 mL of the KI solution.

Shake the syringe with the mixture for 1 minute, return it to the Erlenmeyer flask and titrate it with the thiosulfate solution. Register the reading of the used volume.

Take six or seven samples in total, at different time intervals (every 4 minutes or so) up to 20-25 minutes.

Repeat the previous procedure, but now place the UV lamp inside the bag before introducing the ozone. Start the ozone generator until the bag is filled (this takes around 3 min); once the bag is filled, turn on the UV lamp.

In a 10-mL Erlenmeyer flask pour a 1-mL aliquot of KI solution and add 2 drops of acid and 2 drops of starch indicator. Suck this solution completely with the syringe and then suck 9 mL of the air that is in the bag.

Shake the syringe with the mixture for 1 minute, transfer its contents to the 10-mL Erlenmeyer flask and titrate it with the thiosulfate solution.

Register the reading of the used volume. Take six or seven samples in total, at different time intervals (every 4 minutes or so) up to 20-25 minutes.

Repeat the previous procedure for the filling of air/ozone in the bag. Once the bag is filled with air/ozone introduce 1 mL of methylene chloride with a syringe and turn on the UV lamp.

In a 10-mL Erlenmeyer flask pour a 1-mL aliquot of KI solution and add 2 drops of acid and 2 drops of starch indicator. Suck this solution completely with the syringe.

Immediately after, take a 9-mL sample with a syringe containing 1 mL of the KI solution.

Shake the syringe with the mixture for 1 minute, and return it to the Erlenmeyer flask. Then, titrate it with the thiosulfate solution. Register the reading of the used volume.

Take six or seven samples in total, at different time intervals (every 4 minutes or so) up to 2025 minutes.

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