Experimental purpose

To understand the production principle of extracting iodine from kelp.

Experimental principle

Kelp contains iodide, and I- can be oxidized to I2 by H2O2. In this experiment, dried kelp was incinerated to remove organic matter, and the residue was treated with H2O2-H2SO4 to oxidize I- to I2, which reacted with alkali.

2I-+H2O2+2H+ = I2+2H2O

3I2+6NaOH=5NaI+NaIO3+3H2O

Experimental supplies

Drugs: dried kelp, hydrogen peroxide, sulfuric acid (3 mol/L), NaOH solution, alcohol and starch solution.

Instruments: beaker, test tube, crucible, crucible pliers, iron frame, tripod, clay triangle, glass rod, alcohol lamp, measuring cylinder, rubber dropper, tray balance, brush, funnel, filter paper, matches and scissors.

Doubts and difficulties

Do not rinse the attachments on the surface of dried kelp with water to prevent the iodide in kelp from dissolving in water and causing losses.

Experimental demonstration and steps

1. Weigh 3g of dried kelp, and brush the attachment on the surface of dried kelp with a brush (do not rinse with water). Cut the kelp into sections, wet it with alcohol (easy to burn) and put it in a crucible.

2. Burn the crucible with kelp with alcohol lamp until kelp is completely ashed, stop heating and cool.

3. Transfer kelp ash to a small beaker, add 10ml distilled water to the beaker, stir and boil for 2-3 minutes to dissolve the soluble matter, and filter.

4. Drop a few drops of sulfuric acid into the filtrate, and then add about 1ml H2O2 solution. Observe the phenomenon.

5. Take a small amount of the above filtrate and drop a few drops of starch solution. Observe the phenomenon.

6. Add 1 ml starch solution to the remaining filtrate, shake well and let stand, and observe the phenomenon.

7. Add NaOH solution to the solution containing starch, and after fully shaking, pour the mixed solution into the designated container.