A drop of ink is put into a glass of water at 10 °C, and another drop into a glass of water at 60…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A drop of ink is put into a glass of water at , and another drop into a glass of water at . Nobody stirs either glass.
- In which glass does the colour spread faster? Give a reason.
- A teacher wants to show diffusion quickly in class. Which glass should she use?
- A student stirs the cold glass and says: Now the ink diffuses faster. Is stirring part of diffusion?
Need a reminder? The key ideaShow
The particles of matter are always moving. Diffusion is the spreading of one substance through another by itself, because of this motion. It is fastest in gases and faster at a higher temperature, because heated particles move faster.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) At the particles of water and ink have more energy and move faster, so they mix faster. The colour spreads faster in the warm glass.
Step 2. (b) The warm glass, at : the class sees the colour spread within a few minutes.
Step 3. (c) No. Stirring moves the water around and mixes it faster, but diffusion is the spreading that happens by itself, because the particles move. Stirring is a push from outside.
Answer: (a) The warm glass. (b) The warm glass. (c) Stirring speeds the mixing, but it is not diffusion.
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