Chemistry Flashcards
compounds and mixture
elements
An element only contains one type of atom. The atoms may occur individually, or bonded together to form molecules of that
element.
All elements appear in the Periodic Table.
compounds
A compound is a substance containing at least two different elements that are chemically bonded together. Compounds do
not appear in the Periodic Table.
All compounds are molecules, but not all molecules are compounds.
mixture
A mixture contains at least two different substances (elements and/or compounds) that are not chemically bonded together.
physical change
A physical change involves rearranging particles, but the individual particles are not changed in any way. Physical changes are reversible – it is
possible to put the particles back to the way they originally were.
chemical change
A chemical change involves the creation of at least one new chemical substance (so, the individual particles are now different).
naming compounds
The formula of a chemical compound tells you how many of each atom type are present.
making a solution
When making a cup of coffee (the
solution), we mix coffee powder (the solute) into the water (the solvent). A concentrated solution will have more solute; a dilute solution will have more solvent
dissolving and melting
…are not the same thing
While both dissolving and melting are physical changes, and both are reversible…
dissolving
…involves the particles of the solute
(which may already be a liquid, or even a gas) mixing with the particles of the solvent. The
solute particles are so small, they seem to disappear, but are ‘carried’ and spread out as they mix with the solvent particles.
melting
…melting only involves one substance, where the
arrangement of the particles changes from ‘solid’
to ‘liquid’.
insoluble substances
Substances that dissolve easily can be described as soluble, but substances that will not dissolve are referred to as insoluble.
Occasionally, you may discover a
sparingly soluble substance, which is very hard to dissolve.
different solvents
Water is the most common solvent we will use, but there are plenty of other solvents that may be used.
Some substances are insoluble in water, but may dissolve in other solvents, or have different solubilities.
solubility curve
A solubility curve is a type of
graph that shows how much
solute will dissolve in a given
solvent at different temperatures.
filtration
To separate an insoluble solid from a liquid (such as sand and water), we can decant the liquid (carefully pour it
away, leaving the solid behind)…
…or the mixture can be filtered through paper, using a filter funnel.
The water particles are small enough to fit through the fibres of the paper, but the sand particles are too big.
Evaporation
To separate a soluble solid from a liquid, you may evaporate the liquid; this may be done in an evaporating basin.
The water may be evaporated quickly (with the aid of a heat source), or slowly (by leaving the mixture for a few days).
