GCSE Chemistry

This word document contains some information needed for the UNIT 2 Chemistry exam in OCR 21st Century Science

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  • Created by: gabriele
  • Created on: 30-05-11 17:33
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LIGHT SPECTRA
Every atom gives off light when heated (sometimes this light is not visible to the human eye). Prisms can be
used to split this light to form a spectrum, and each element has its own distinctive line spectrum. This
technique is known as spectroscopy
Scientists have used line spectra to discover new elements. Some of these elements are rubidium, caesium
and helium.
GAS TESTS
There are different ways for testing if a certain gas is present.
Hydrogen-A lit wooden splint makes a popping sound in a test tube containing hydrogen.
Oxygen-A glowing wooden splint relights in a test tube of oxygen.
Carbon dioxide-A lighted wooden splint goes out in a test tube of carbon dioxide however this happens with
other gases too. It is better to bubble the test gas through limewater - calcium hydroxide solution. Carbon
dioxide turns limewater cloudy white.
Ammonia-There are several ways to test for ammonia. Ammonia has a characteristic sharp, choking smell. It
also makes damp red litmus paper turn blue. In addition ammonia forms a white smoke of ammonium
chloride when hydrogen chloride gas (from concentrated hydrochloric acid) is held near it.
Chlorine-Chlorine has a characteristic sharp, choking smell too. It also makes damp blue litmus paper turn
red, and then bleaches it white. Chlorine makes damp starch iodine paper turn blue to black.
DISPLACEMENT REACTION
A displacement reaction is when a more reactive element displaces a less reactive element from a
compound
HAZARD SYMBOLS
SYMBOL NAME EXPLANATION EXAMPLE
Corrosive Attacks and destroys Concentrated sulphuric
living tissue, including acid
yes and skin
Irritant Not corrosive but can Bleach
cause reddening or
blistering of the skin
Toxic Can cause death, either Hydrogen Cyanide
by swallowing, breathing
in or absorption through
the skin.

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Harmful Like something toxic but Copper Sulphate
not quite as dangerous
Oxidising Provides oxygen which Liquid Oxygen
allows other materials
to burn more fiercely
Highly Flammable Catches fire easily. Petrol
PROPERTIES OF IONIC COMPOUNDS
High melting and boiling points because ionic bonds are very strong (a lot of energy is needed to break them)
Conductive when liquid because ions are charged particles, but ionic compounds can only conduct electricity
if their ions are free to move.…read more

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