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Determination of the concentration in oxigenated water (H2O2) using potassium iodine (KI)

Goal​

Find appropriate solutions concentrations of H2O2 and KI to realize experiments using the simple-spectro.

Caution: H2O2 is dangerous: it is really exothermic when mixed with acid. It can explode. Avoid contact with skin. On the contrary, KI is totally fine, since it is even sometimes ingested for medical purpose.

Principle​

Two solutions are required: a solution of H2O2 and a solution of KI. The goal is to mix them together having an excess of KI so that all the H2O2 reacts and results in iodine, which is brown and can be measured using a spectrophotometer.

First batch of solutions​

We realized solutions at 0.1 M. To do so, we placed 4.15 g (measured using a scale, precision: 0.001g) of KI in a 250 ml calibrated flask and completed with deionized water, agitating well to dissolve all the KI (room temperature is sufficient). Similarly, place 2.5 ml of 30% H2O2 in a 250 ml calibrated flask and complete with deionized water.

To measure the color, we mixed 4ml of the KI solution with 1 ml of the H2O2 solution.

Measures of absorbance:

  • red: 0.00
  • green: 0.04
  • blue: 0.06

Conclusion: Solutions were not concentrated enough. We tried with solutions 10 times more concentrated.

Second batch of solutions​

4 mL KI 1M 1 mL H2O2 1M

Second batch of solutions​

4 mL KI 0.1M 1 mL H2O2 0.1M 1 mL AcOH 1M

Measures of absorbance:

  • red: 0.10
  • green: 0.54
  • blue: 1.66

Third batch​

A : KI 0.1M B : AcOH 1M C : H2O2 0.1M D : H2O

expABCDRGB
14mL1mL500uL0 uL
24mL1mL400uL100 uL
34mL1mL300uL200 uL
44mL1mL200uL300 uL
54mL1mL100uL400 uL
64mL1mL0uL500 uL

5 min​

E R G B UV 12577193 387718 403065 384133 417 12594548 223065 55675 2758 546 12610603 232675 72691 5427 753 12626255 280567 117289 13706 814 12644618 339650 227652 57634 734 12660371 375441 333788 163714 392 12679335 388637 405498 383777 530

10 min​

E R G B UV 13061752 389020 407754 385773 402 13078204 156613 18952 386 418 13091850 173585 32390 1134 455 13105797 224915 61675 3716 475 13119242 318763 164851 21973 468 13134092 363637 286491 94578 431 13148340 382483 408947 382763 507

around 20 min​

E R G B UV 13474330 387667 402271 384342 406 13488975 117434 9789 77 363 13502019 138779 18208 395 396 13516167 186529 37383 1424 414 13531117 294999 119511 10251 383 13543759 351437 246161 58623 412 13556101 382648 408938 382256 473

Kinetic trial with AcOH​

A : KI 0.1M B : AcOH 1M C : H2O2 0.1M D : H2O

expABCD
14mL1mL60uL0 uL

Kinetic at 23°C shows a fast reaction (5 minutes) followed by a much slower reaction.

AcOH.svg

Kinetic trial with H2SO4​

A : KI 0.1M B : H2SO4 1M C : H2O2 0.1M D : H2O

expABCD
14mL1mL60uL0 uL

In presence of H2SO4 the reaction is much faster.

H2SO4.svg