Card Set Information
Chemistry - First term
What is an atom?
type of particle
cannot be broken down chemically
no nett charge
What is a molecule?
type of particle
2 or more atoms
usually non metals
What is an ion?
type of particle
has an electric charge
either single or in a group
What are the three states of matter?
Describe the characteristics of a solid.
-has a definite shape / volume
-atoms close together
: fixed pattern
: particles vibrate in place
: Close together
Describe the characteristics of a liquid.
-has a definite volume
-takes shape of container
: no fixed position
: particles flow/slide passed each other
: Further apart (still close)
Describe the characteristics of a gas.
-no definite volume/shape (unless in closed container)
: randomly arranged
: random movement, moves everywhere rapidly
: Far apart
Why do solids have low movement?
They have low energy and strong attractive forces.
Why do gases have high movement?
They have high energy and weak attractive forces.
What are the changes of state?
Melting, boiling/evaporation, condensing, freezing.
What is sublimation?
When a solid becomes a gas.
What is deposition?
When a gas becomes a solid.
Name a few endothermic processes.
Melting, boiling, evaporation, sublimation.
Name a few exothermic processes.
Freezing, condensing and deposition.
Describe how a solid is heated.
solid is heated
particles gain energy and vibrate
forces of attraction weakens
(there's no temperature change at the melting point as energy is absorbed to overcome attractive forces)
How does temperature and pressure affect gases?
The higher the temperature, the higher the volume (particles move more rapidly)
The higher the pressure, the lower the volume (compressed)
The random movement and collision of particles in a medium which causes the particles to spread / mix.
What is the kinetic particle theory?
The theory that particles are constantly moving.
How does relative molecular mass affect diffusion?
The higher the relative molecular mass, the heavier the molecule and the slower the rate of diffusion.
What are the factors which affect diffusion?
: Higher the temperature, higher the rate of diffusion
: Higher the mass, lower the rate of diffusion
Size of particle
: Higher the size, lower the rate of diffusion
What is paper chromatography?
A method for separating and purifying coloured compound based on solubility.
When would paper chromatography work?
When the pigments have different solubilities in the solvent
When the pigments have different degrees of attraction for the filter paper
What are the steps for a paper chromatography?
Base line is drawn in paper
Colour dye is transferred
Paper is dipped into solvent
Beaker is closed
Draw line at solvent front
Calculate retention values
How do you calculate retention value?
distance from base line to centre of spot
distance of solvent front from base line
What solvents could you use for paper chromatography?
Water, ethanol, propanone
What's the use of paper chromatography?
To identify substances in mixture
To separate out substances in a mixture (thereby purifying them)
How do you conduct paper chromatography for a colourless substances?
Paper is dried and sprated with a locating agent (
in amino acids - reacts with substance to form colour compound)
Paper is shone under UV light / warmed in oven
What is chemical purity?
When only one substance is present.
What is the importance of purity?
Impurities in food additives / medical drugs have harmful effects on health
In computer chips (supposed to be pure silicon) the chips will not work properly
How do you identify pure substances?
Using their distinct / sharp
melting and boiling points
The more imipurities, the wider the range of temperatures
Boiling point is increased by impurities
Melting point is decreased by impurities
What is decanting?
Pouring off the solid from a solution.
What is filtration?
Separating an undissolved solid (solute) from a solution (solvent) by passing it through filter paper
Simple / Büchner filter
What is centrifugation?
A centrifuge spins the solution at a high speed. The denser substance will be collected at the bottom. (can then be followed by
What are the steps for crystallization / evaporation?
in evaporating dish to concentrate
till crystallisation point
3) leave to
What is a separation funnel?
A funnel which separates two
solutions (liquids that don't mix)
Could also be used with two solutes dissolved in a single solvent (useless if
- evaporates easilly)
What is distillation?
A method of separating a liquid from a mixture by boiling the mixture then condensing the vapours.
: Mixture of solid and liquid (salt in water)
: Mixture of liquids at different boiling points (ethanol and water)
What is an emulsion?
Tiny droplets of oil suspended in water
: oil and water mixed
: in the same phase, hard to separate
: different phases, easy to separate
What is an emulsifier?
Something which helps to mix liquids.
(eg: egg yolk in sald dressing)