☰ Contents · Physics

The three states of matter

Lessons 12–13 · 2 lessons · N.Sh. Turdiyev. Physics Grade 6, 3rd revised edition. Niso Poligraf Publishers, Tashkent, 2017
13

Studying diffusion in liquids (done at home)

Textbook, p. 28
GoalTest at home how the speed of diffusion in a liquid depends on temperature and calculate it using v = h : t.
New words
speed (rate) of diffusion · diffuziya tezligiheight h of the coloured layer · balandlik hobservation table · kuzatish jadvaliconclusion · xulosa
Explanation

This home experiment tests that diffusion goes more slowly in cold water and faster in warmer water. Pour equal volumes of water into two identical tall glasses: put one in the refrigerator and the other in a place at room temperature (or a bit warmer); it is important that only the temperature differs. Carefully place an identical small piece of coloured hard candy at the bottom of each glass and do not shake the water. Twice a day measure the height h of the coloured layer in millimetres with a ruler and write the time t. The speed of diffusion is calculated by v = h : t. Write the results in a table and compare: the expected conclusion is that the higher the temperature, the faster the molecules move and the faster diffusion goes.

Worked examples
Sample result: in cold water after 24 h h = 24 mm → v = 24 : 24 = 1 mm/h; in warm water after 24 h h = 72 mm → v = 72 : 24 = 3 mm/h.
Sample conclusion: “In warm water the speed of diffusion was 3 times that in cold water, so diffusion speeds up as temperature rises.”
Class activity

Home experiment (with an adult): prepare two glasses as described and draw a table: “time, h (mm), v (mm/h)”. Safety: do not use boiling water; do not use potassium permanganate — coloured candy or food colouring is enough; label the glasses “not for drinking”; wash your hands afterwards.

Practice
1
If the dye rose 48 mm in 24 hours, what is the diffusion speed in mm/hour?
2
Why are the volume of water and the dye the same in both glasses?
3
Why must the water not be shaken?
4
In which glass do you expect faster diffusion and why?