Diffusion, solutions and solubility
Particles are in constant random motion. Diffusion and dissolving are both consequences of that motion, and the particle model explains every observation in this lesson.
Part of your national curriculum
- Chemistry: pure and impure substances: Understand diffusion in terms of the particle model, and the concepts of solutions, solvents, solutes and solubility
Lesson overview
What you'll learn in this lesson
Understand diffusion in terms of the particle model, and the concepts of solutions, solvents, solutes and solubility
Key learning points
- • Diffusion
- • Solutions vocabulary
- • Solubility
- • Speeding up dissolving
This lesson at a glance
- 28 minutes
- 21 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 21
Visual introductionPicture this
Diffusion, solutions and solubility
Particles are in constant random motion. Diffusion and dissolving are both consequences of that motion, and the particle model explains every observation in this lesson.
In a nutshell
Understand diffusion in terms of the particle model, and the concepts of solutions, solvents, solutes and solubility
Learning cycle
Part 2 of 21
Learning cycle 1 of 2
Part 1 · Diffusion
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 21
Learn
Diffusion
Diffusion is the net movement of particles from a region of higher concentration to lower concentration, caused by random motion. It happens fastest in gases, more slowly in liquids and effectively not at all in solids, where particles only vibrate in fixed positions. Raising the temperature speeds diffusion because particles move faster.
Reset break
Part 4 of 21
Pause
That's sitting 1 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 5 of 21
Learn
Solutions vocabulary
A solute dissolves in a solvent to form a solution. Salt is the solute, water the solvent, and salty water the solution. In a solution the solute particles are spread between the solvent particles, which is why the total mass is conserved and the mixture looks transparent.
Quick check
Part 6 of 21
Quick check
Part 7 of 21
Reset break
Part 8 of 21
Pause
That's sitting 2 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 9 of 21
Learning cycle 2 of 2
Part 2 · Solubility
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 21
Learn
Solubility
Solubility is the mass of solute that dissolves in a fixed volume of solvent at a given temperature, usually grams per 100 g of water. Most solids dissolve better in hot water, while gases dissolve less as temperature rises, which is why a warm fizzy drink goes flat sooner.
Explore the idea
Part 11 of 21
Learn
Speeding up dissolving
Stirring, heating and grinding into smaller pieces all speed dissolving because they increase the frequency of contact between solvent particles and the solute's surface. None of them change how much can dissolve in the end: that is set by solubility at that temperature.
Reset break
Part 12 of 21
Pause
That's sitting 3 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 13 of 21
Quick check
Part 14 of 21
Explore the idea
Part 15 of 21
Worked example
Worked answer: explain why a coloured crystal spreads through still water (3 marks)
Particles in the water and the dissolved crystal are in constant random motion (1). The coloured particles move from where they are highly concentrated, near the crystal, to where they are less concentrated, in the surrounding water (1). Over time this random movement spreads them evenly through the water, so the colour becomes uniform; heating would speed this up because particles move faster (1).
Reset break
Part 16 of 21
Pause
That's sitting 4 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 17 of 21
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 18 of 21
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
____ is the net movement of particles from a region of higher concentration to lower concentration, caused by random motion.
Challenge round
Part 19 of 21
Game · Recall cards
What causes diffusion?
Card 1 of 4
Mastery quiz
Part 20 of 21
Marked quiz
End of lesson quiz: Diffusion, solutions and solubility
4 questions, marked with the reasoning shown. No timer.
1. What causes diffusion?
2. In a solution of salt water, what is the solute?
3. What generally happens to the solubility of a solid as temperature rises?
4. Diffusion is fastest in
Lesson round-up
Part 21 of 21
Lesson round-up
Ready when you are
Quiz score
Not sat
Games
Not played
Points this lesson
0
Best run
0 in a row
Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?
Ask LunaPart 1 of 21 · Watch & discover
How this is going
- Not looked at yet
Understand diffusion in terms of the particle model, and the concepts of solutions, solvents, solutes and solubility