Evidence for Moving Particles:
- Diffusion is the random movement of particles from a region of high concentration towards a region of lower concentration until their concentration is the same throughout.
Bromine:
- When a drop of bromine liquid is placed in the gas jar, it starts to go up the whole jar as it has turned into a gas and then starts to diffuse.
Comparison:
- First, the orange colour is deep at the bottom and pale at the top.
- After 30 minutes, the orange colour is the same throughout, as there is no concentration gradient.
- This experiment is carried out in a fume cupboard as bromine is toxic and volatile (goes from liquid to gas easily at room temperature), which means you could inhale the gas.
Potassium Manganate:
- When the crystals are added to cold water, they dissolve and diffuse slowly; however, when added to hot water, they dissolve, and diffusion is sped up. In hot water, there’s also a higher saturation point.
- The purple colour spreads through the water by diffusion.
- Potassium permanganate breaks down into individual particles when dissolved in water.
- How it would look tomorrow morning.
NH3 and HCl
- Ammonia and hydrochloric acid travel through the tube. The hydrochloric acid makes the indicator paper turn red, as it is acidic, while the ammonia makes the paper turn dark green, as it is alkaline.
- When the vapours meet ammonium chloride gas, white smoke is formed.
- The white smoke is formed closer to the cotton wool soaked in HCl because NH3 travels faster than HCl because it has a lower Mr. This means it is lighter and therefore can travel quicker.
- The heavier the molecule, the slower the diffusion.