Every card in Particles and states of matter, Year 8: evidence and solutions
The whole deck, in order — so you can read it through before your child ever sees it.
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- The random, jittery movement of tiny visible grains, such as smoke specks in air
Brownian motion
HintIt is named after a nineteenth-century botanist who saw it in grains from pollen.
WhyRobert Brown described it in 1827 while looking at tiny grains in water. Decades later it was explained by collisions with particles too small to see.
- In a smoke cell, what makes the smoke specks jiggle?
Collisions with moving air particles
HintThe cause is far too small to see, even under the microscope.
WhyAir particles move fast in every direction and keep striking each speck. The speck is light enough for these knocks to push it about.
- Why can the air particles in a smoke cell not be seen through the microscope?
They are far too small
HintCompare their size with a speck of smoke.
WhyA smoke speck is made of a huge number of particles. A single air particle is far smaller than anything a light microscope can show.
- Why does a smoke speck in Brownian motion keep changing direction?
It is hit unevenly from different sides
HintAt any instant, the knocks do not balance out.
WhyBy chance, more particles strike one side than the other, so the speck is pushed that way. An instant later the imbalance is somewhere else.
- Brownian motion is evidence for which idea about matter?
That it is made of tiny, moving particles
HintSomething unseen must be doing the knocking.
WhyNobody can see the particles of air, but the jiggling of the specks is exactly what the particle model predicts.
- A solution that can dissolve no more solute at that temperature
A saturated solution
HintThink of a sponge that can soak up no more.
WhyEvery solvent has a limit. Once it is reached, any extra solid simply stays undissolved at the bottom.
- Sugar sits undissolved at the bottom of a cup of cold tea. What happens to it when the tea is warmed?
More of it dissolves
HintCompare how sweet you can make hot tea and iced tea.
WhyFor most solids, solubility rises with temperature. The cold tea was saturated; warm tea has room for extra sugar.
- The solubility of a salt is 36 g per 100 g of water. What is the greatest mass of the salt that will dissolve in 200 g of water? (number only, in grams)
72
HintYou have twice as much water.
WhySolubility is given for each 100 g of water. Twice the water can hold twice the solute: 36 × 2.
- Why is the start line on chromatography paper drawn in pencil, not ink?
Pencil does not dissolve in the solvent
HintThink about what would happen to a line drawn in ink as the liquid rises.
WhyPencil 'lead' is graphite, which stays where it is drawn. An ink line would separate into its own dyes and spoil the result.
- On a chromatogram, ink A gives the same pattern of spots at the same heights as ink B. What does this tell you about the two inks?
They are made of the same dyes
HintEach dye travels its own fixed distance.
WhyA dye always travels the same distance under the same conditions, so matching patterns mean matching mixtures of dyes.
1★ KS3-CHEM-PAR-0013
2★ KS3-CHEM-PAR-0014
3★ KS3-CHEM-PAR-0015
4★ KS3-CHEM-PAR-0016
5★ KS3-CHEM-PAR-0017
6★ KS3-CHEM-PAR-0018
7★ KS3-CHEM-PAR-0019
8★ KS3-CHEM-PAR-0020
9★ KS3-CHEM-PAR-0021
10★ KS3-CHEM-PAR-0022
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