Lessons 8–10 · 3 lessons · K. T. Suyarov, Z. B. Sangirova, M. T. Umaraliyeva, S. G‘. Xasanova, M. K. Yuldasheva, D. T. Hasanova. Natural Science, Grade 6 (new edition). Republican Education Centre, 2022
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Practical: Studying diffusion
Textbook, pp. 23–24
GoalExplain what diffusion is and how it proceeds in gases, liquids and solids and in hot and cold water.
New words
diffusion (particles of one substance mixing among another) · diffuziyarandom motion · tartibsiz harakattemperature · haroratsolution · eritma
Explanation
Diffusion (Latin “spreading”) is the mixing of the particles of one substance among the particles of another. It is evidence that particles move constantly and randomly. The smell of cooking spreading through the house and sugar dissolving in tea are diffusion. Diffusion is fastest in gases, slower in liquids and very slow in solids, because gas particles move fastest. As temperature rises, particles move faster, so diffusion speeds up: sugar dissolves faster in hot tea than in cold tea. Because of diffusion, harmful gases from factories and traffic mix into the air and pollute it.
Worked examples
After perfume is spilt in a room, the smell soon reaches every corner – diffusion in gases. A chalk mark left a long time on a board is hard to wipe off – even in solids a slow diffusion occurs.
Two glasses, one with warm and one with cold water. A drop of food colouring spreads faster in the warm water because the particles move faster.
Class activity
Experiment: pour the same amount of water into two clear glasses – cold in one, warm in the other (about 50 °C, prepared by the teacher, not boiling). With a dropper add one drop of food colouring to each and time with a stopwatch how long it takes for the colour to spread through the glass. Safety: never use boiling water; food colouring can stain clothes – wear an apron and wash hands afterwards.
Practice
1
What is diffusion?
The mixing of particles of one substance among the particles of another.
2
Where is diffusion fastest: in a gas, a liquid or a solid?
In a gas.
3
Give two everyday examples of diffusion.
The smell of food spreading; sugar dissolving in tea; smoke mixing into air.
4
Why does colouring spread faster in hot water, and what does this show about particles?
At a higher temperature particles move faster. It shows that particles move constantly and randomly.