Particles and states of matter, Year 7: more practice

They are far apart, so there is lots of empty space to squeeze into

HintThink about the gaps between neighbouring particles.

The whyGas particles are spread out with large gaps between them, so pushing the plunger just moves them closer. Liquid particles are already touching, so there is almost no gap left to close.

The salt particles are dissolved and small enough to pass through the holes in the paper

HintCompare the size of the gaps in the filter with the size of a single grain of the solid once it has broken up.

The whyFiltering only holds back solid pieces too big to fit through the paper. Dissolved salt has been broken up into particles far smaller than the holes, so it runs straight through with the water.

They gain enough energy to break out of their fixed positions and slide past each other

HintNothing about the pieces changes; the pattern is what changes.

The whyIn a solid the particles vibrate in fixed places. Heating gives them more energy until the pattern gives way and they can move around, which is what makes it a liquid.

Water vapour (water in its gas state)

HintThey form inside the liquid itself, not from anything added to it.

The whyAt the boiling point, water particles throughout the liquid have enough energy to become gas. They collect as bubbles of vapour that rise to the surface and escape.

The smell in air, because gas particles are far apart and move faster

HintCompare how freely a gas and a liquid let things travel through them.

The whyGas particles have lots of space and little in their way, so they spread quickly. Liquid particles are packed together and keep bumping into each other, so diffusion is much slower.

It increases

HintThink about how the energy of the particles changes when they are heated.

The whyHeated particles move faster, so they hit the walls harder and more often. More force on the walls from the same space means higher pressure.

The dissolved particles are too small to block or scatter the light

HintThink about what has happened to the salt crystals.

The whyDissolving breaks the salt into particles far too small to see, spread evenly through the water. A solution may be coloured, but it is always see-through, unlike a cloudy suspension.

It contains many different substances mixed together

HintThink about everything that is found in the water in juice.

The whyJuice holds water, sugars, acids and flavour chemicals. In everyday language pure can mean nothing added, but in chemistry it means one type of particle only.

250

HintNothing has been added or taken away during dissolving.

The why50 + 200 = 250 g. The sugar is still there in the solution, so the total mass is the sum of the two masses.

The salt particles are all still there, just spread out among the water particles

HintOut of sight does not mean gone.

The whyDissolving only separates the particles and mixes them in. Because every particle is still in the beaker, the total mass is exactly what it was before.