Lecture notes
GCSE Chemistry notes revision
This provides a detailed description of various subjects that are tested in GCSE chemistry.
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general information• water boils at 100 degrees Celsius
• sodium chloride melts at 801 degrees Celsius.
Definitions of terms:
Compound – a compound is a pure substance made from more than one type of element
that is chemically bonded together.
Mixture – a mixture is made from two or more elements or compounds being mixed, without
the formation of any chemical bonds.
Pure substance - contains only one type of compound or element. Melts and boils at
specific temperatures
Impure substance - doesn’t have a specific melting and boiling point. They melt and boil
over a range of temperatures, depending on how much of each substance there is in the
mixture.
Formulations - Mixtures that have been prepared using a specific formula (they contain
precise amounts of different components and have a particular formula). can be used for a
specific purpose like fuels, cleaning agents, paint, medicines, alloys, fertilisers, and even
food and drink
Solvent - the liquid in which a substance is dissolved.
Chromatography:
Chromatography is a general analytical technique used to separate the different substances
in a mixture so that we can then identify them. There are lots of types of chromatography.
Paper chromatography can be used to separate the different dyes in an ink.
Testing for gases:
Learning how to test for four common gases: Chlorine, Oxygen, Hydrogen, and Carbon
Dioxide.
chlorine - have a test tube with sample gas in it, in which you think there might be chlorine in.
get a blue litmus paper. put the paper into the test tube. If chlorine is present, the paper turns
from blue to white. something to be aware of though is that you might sometimes find that
the paper briefly turns red before turning white. This is because the chlorine dissolves in the
water on the damp paper and forms hydrochloric acid, which because its acidic will turn the
blue litmus paper red. however the paper will then quickly go white as it gets bleached by the
chlorine.
oxygen - have a glowing splint (so one without a flame but which is still glowing red at the
end). then get a sample of a gas and then place the splint into the tube. If the gas is oxygen,
then the glowing splint will relight because burning requires oxygen and so if we supply
loads of oxygen to the splint the reaction will spark up again.
Hydrogen - this involves a test tube containing hydrogen and a burning splint. When we
move them close enough together, we will suddenly hear a squeaky pop as the heat energy
provided by the flame causes the hydrogen to burn with the oxygen in the air to form water.
Carbon dioxide - get a gas sample in one tube and an aqueous solution of calcium
(otherwise known as lime water) in another. We then bubble the gas sample through the
calcium hydroxide and if the gas is carbon dioxide this will cause the solution to go cloudy.
as the co2 and calcium hydroxide react to form calcium carbonate and water. The reason it
goes cloudy is because calcium carbonates us a solid and it's all these little solid particles
that make it appear cloudy.
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