Year 8 Chemistry

We have just started studying Chemistry, after we finished Physics. The Particle Theory of Matter helps us understand why solids, liquids and gases behave the way we do.

Yesterday we did the classic experiment with ammonia and hydrogen chloride where ammonia diffuses much faster than HCl because its particles have half the mass of hydrogen chloride particles.

This experiment was much better.

We were investigating diffusion in liquids.

Because the particles in liquids are close together, like lots of people in a party, diffusion should be a lot slower. (imagine trying to get to the door in a room full of people)

Also, using substances with different particle masses we should be able to show much more clearly the different speeds of diffusion.

A petri dish is half filled with deionised water.

A spatula of lead nitrate crystals (careful, toxic) is added on one side, and a spatula of potassium iodide is added to the other side at exactly the same time.

After just over a minute later, this happened:

A yellow band appeared. This is crystals of lead iodide that are formed when the different particles mix. They react.

It is nearer the left where the lead nitrate crystals were added.

This means that potassium iodide particles must have diffused much faster across the dish.

This is because potassium iodide particles have half the mass of lead nitrate particles.

Even so it still took over a minute to travel just a few centimetres.