1. #11.Puzzle in a beaker Maryia Valoshyna, Spectrum, Belarus

2. Problem situation 2 white layers number of bands

3. What is going on? MgSO ₄ + 2NH ₄ OH = Mg(OH) ₂ ↓ + (NH ₄ ) ₂ SO ₄ Mg ²⁺ + 2OH ⁻ = Mg(OH) ₂ ↓ 3 Gelatin forms a gel medium

4. Experimental part 4

5. Safety measures. Experiment methodic !All the experiments must be done in the draft hood! 20 ml 0,05M MgSO ₄ 20 ml gelatin Aqueous ammonia 38 ml H ₂ O → 0,6 g MgSO ₄ → 2,7 g gelatin → 1,54 ml 25% NH ₄ OH 5

6. Standard 6

7. Varying gelatin concentration 7 - 6% -10%, ___ - gelatin border,

8. Changing MgSO ₄ concentration 8 Two times lessTwo times more

9. Changing NH ₄ OH amount 9 Two times less Two times more

10. Changing both NH ₄ OH and MgSO ₄ 10 Two times more

11. Number and thickness of the layers 11

12. Distances between the layers 12

13. Existing models Prenucleation (Ostwald) Postnucleation 13

14. Liesegang rings 14 Raphael Eduard Liesegang

15. Various methods K ₂ Cr ₂ O ₇ + 2AgNO ₃ = Ag ₂ Cr ₂ O ₇ ↓ + 2KNO ₃ (with gelatin) K ₂ Cr ₂ O ₇ + CuSO ₄ = CuCr ₂ O ₇ ↓ + K ₂ SO ₄ (with H ₂ SiO ₃ ) 15 Co(OH) ₂

16. Petri dish 16

17. Natural examples 17 agate Blue agate Jasper

18. Results Plenty of experiments have been done, including varying concentrations of all the included reagents. More NH ₄ OH/MgSO ₄ → more rings The distance between the rings appeared to depend on the concentration of gelatin, MgSO ₄ and NH ₄ OH; More gelatin/MgSO ₄ / NH ₄ OH → distance less 18

19. Thank you for your kind attention! 19

20. Supplement 20

21. Safety measures Wear smock (+gloves, mask etc.) Make experiments in the draft hood Don’t place cold glasses onto the heated plate 21

22. Literature Воюцкий С.С. Курс коллоидной химии. Большая энциклопедия природы. Т. 12: Камни и минералы. http://biosurvey.ou.edu/oas/06/paper/weaver.pdf http://www.insilico.hu/index.html 22

23. The rope 23 The precipitate is shifted to the rope One of the layers is right on the knot

24. Calculations 40 ml of 6% solution of gelatin: 2,7 g of gelatin, 38 ml of water 10%: 4,58 g of gelatin, 35 ml of water C(MgSO₄)=0,05 M; m(MgSO₄)=Mn=0,6 g V(NH₄OH)=m:ρ=1,54 ml 24