Scientific ideas, concepts and processes
Solutions: Where does the solid go when it dissolves in a liquid?
A solute dissolved in a solvent makes a solution.
Gases can also dissolve in liquids.
When a solid dissolves in a liquid, the particles are too small to see, but are still there, so mass is conserved (the total stays the same).
Substances can be classified as soluble or insoluble.
Particle theory: Is everything made of moving particles?
Particles that make up a pure substance can be atoms or molecules.
Particles in a solid are strongly held together and vibrate about fixed positions.
As a solid is heated, the particles vibrate faster.
At absolute zero (-273°C) the particles stop moving.
Particles in a liquid are more weakly held together and move around.
Particles in a gas move around quickly and randomly, colliding and bouncing off each other and the walls of the container.
When a liquid or gas is heated, the particles move faster.
Particles are very small, and are not destroyed or made during physical changes, such as melting, boiling, solidifying, condensing or dissolving.
The overall mass of particles stays the same when a physical change happens.
Atoms, compounds and molecules: How do atoms make molecules?
(Almost) everything is made of atoms.
Atoms join together to make molecules.
Substances made of just one type of atom are elements.
Substances made of more than one type of atom joined together in a chemical reaction are called compounds.
All of the elements (types of atom) are listed in the periodic table.
Each element has a symbol, for example the symbol for Helium is He.
All of the elements in the universe are listed in the periodic table.
Each compound has a formula which says how many of each type of atom there are in the molecule. For example H2O is the formula for water, and a water molecule is made up of 2 hydrogen atoms and 1 oxygen atom.
Purifying water: What are the impurities in dirty water? How can we clean water to drink?
Dirty water can contain a mixture of insoluble pieces, soluble substances and pathogens (such as bacteria).
Water can be filtered using a filter funnel, filter paper and a conical flask. This separates out the insoluble substances.
Water can be evaporated and then condensed again to purify it. This technique removes dissolved substances and pathogens and is called distillation.
In high income countries, municipal water and sewerage systems provide clean water and remove waste water. The waste water is cleaned and put back into rivers and seas.
Around one billion people in the world do not have access to clean water.
One World Science 