edexcel chem guide

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Chemical detection
Qualitative and quantitative chemistry
1 mole of gas occupies 24 000 cm3 (24 dm3) at room temperature (25OC) and pressure (1 atm).
Equal volumes of gases at the same temperature and pressure contain the same amount
of molecules
Concentration of solutions
The concentration of a solution can be measured in g/dm3 or mol/dm3.
When 1 mole of solute is dissolved in water and the solution made up to a volume of 1.0
dm3 the solution has the concentration of 1 mole per dm3. This is written as 1.0mol/dm3
or 1.0M. it is called a molar solution
Titrations
In titration experiments, the volume of solution required to completely react with a known
volume of another solution is determined
Titrations involving an acid and an alkali are called acid base titrations
I. A known amount of alkali (usually 25.0 dm3) is placed in a conical flask using a pipette.
II. Two drops of an indicator ( phenolphthalein or methyl orange)
III. An acid of known concentration is put in a burette
IV. The acid is added until the solution just change colour.
V. The volume of the acid used is read and recorded
VI. The experiment is repeated until at least the last two readings are the same or within 0.05
cm3 of another.
Qualitative analysis
Cation : Reaction with sodium hydroxide
Al3+ White precipitate soluble in excess
sodium hydroxide
Ca2+ A white precipitate
insoluble in excess sodium hydroxide
Cu2+ A light blue precipitate,
insoluble in excess sodium hydroxide
Fe2+ A green precipitate
insoluble in excess sodium hydroxide
Fe3+ A reddish brown precipitate
insoluble in excess sodium hydroxide

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Mg2+ A white precipitate
insoluble in sodium hydroxide
NH4+ No precipitate is formed
On heating ammonia gas is given off
Cation: Colour of flame:
Ba2+ Apple green
Ca2+ Brick red
Cu2+ Green/blue
K+ Lilac/purple
Na+ Bright orange / yellow
Food label
Risks in food:
Benefits Risks
Animal drugs Helps the animal grow Small amount of drugs
more and faster may remain in the food
keeping costs down
Keeps the animals
disease free
Genetically modified food Improves the No risks known to date
nutritional content
Pesticides…read more

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Chemistry working for us
Contact process
Fertilizers
Element Importance to growing Natural sources Artificial source
plant
Nitrogen For growth of stems Manure, dried bird Ammonium nitrate,
and leaves droppings, dried ammonium sulphate,
blood Urea
Phosphorus For root growth Bone meal Ammonium phosphate
Potassium For flowers and fruit Wood ash Potassium sulphate…read more

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Soap and detergent
Washing powder contains:
Active detergent- does the cleaning
Water softener
Bleaches to remove coloured stains
Optical brighteners
And sometime enzymes used in low temp. washes to remove food stains
Soaps can be made by reacting fat with sodium hydroxide. The fat is placed in a beaker and sodium
hydroxide solution added slowly with stirring. The mixture is heated. When the reaction is complete,
sodium chloride is added (soap is less soluble in a sodium chloride solution).…read more

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Soapless detergents
The molecules of soapless detergents have a long hydrocarbon tail and an ionic SO4-2 head.
Crude oil + concentrated sulphuric acid soapless detergent + water
Soap Detergents
Hard water Give scum No scum
Conditions Do not clean well in acidic No condition required
conditions
Biodegradable Yes No ­ they pollute water
Hard water contains Ca+ ions and Mg+ ions; these react with sodium stearate to form insoluble
calcium or magnesium stearate (scum).…read more

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Oil paints
Have pigment dispersed in oil
And often a solvent that dissolves in oil
Dyes are chemical compounds that can attach themselves to textiles, leather, paper and
other surfaces and give them colour
Other pigments
Thermionic pigment change colour when heated or cooled. Thermionic pigment can be added to
acrylic paints to give even more colour changes.
Phosphorescent pigments can glow in the dark. These pigments absorb energy and then release it as
light over a period of time.…read more

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Reduce
inflammation
Side effect Gastric irritation Overdose can cause liver Gastric irritation
damage
Average cost (32 tablet) 0.55 p 0.45 p £ 3.42
Maximum dose 4g daily 4g daily 2.4 g daily
Synthesis of aspirin
Salicylic acid is added to the mixture and heated to about 900C for about 24 hours. The mixture is
cooled and aspirin crystallises out. The aspirin is washed to remove impurities then purified by
recrystallization. The equation is the same for the laboratory preparation.…read more

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