Download - Aqa gcse chemistry c3 revision
C3 OVERVIEWWhat we have covered....
PERIODIC TABLE Early: arranged according to properties. Failed to take account of undiscovered
elements Mendelev’s table was the first to leave
gaps for unknown elements and formed the basis of the modern periodic table
Modern: arranged according to proton number
We can now explain the trends in groups due to electron number and shell energy
GROUP 1- ALKALI METALS Alkali metal + water metal hydroxide
+ H2
Reactivity increases as you go down the table
Form ions with 1+ charge
GROUP 7 - HALOGENS Diatomic molecules Form ions of 1- charge Form covalent compounds (share
electrons) with other non-metals Reactivity decreases as you go down the
group
THE TRANSISTION ELEMENTS Found in the middle of the periodic table High m.p’s and high b.p’s Good conductors of heat and electricity Do not react vigorously with oxygen or
water Compounds are usually coloured Can have a number of valencies (e.g
Fe2+, Fe3+)
Transition Metal electron config In an atom, as you get further from the nucleus
energy levels get closer together, until they start to overlap. This first happens between energy levels 3 and 4, and affects the way the shells fill up.
Potassium has 19 electrons, but the 19th goes in the 4th energy level not the 3rd.(2,8,8,1). Ca is 2,8,8,2.
The next ten elements (transition metals) put their electrons into the overlapping 3rd energy level until it is full.
Sc Ti V Cr Mn Fe Co Ni Cu2,8,9,2 2,8,10,
22,8,11,2
2,8,13,1
2,8,13,2
2,8,14,2
2,8,15,2
2,8,16,2
2,8,17,1
Sc Ti V Cr Mn Fe Co Ni Cu
2,8,9,2 2,8,10,2
2,8,11,2
2,8,13,1
2,8,13,2
2,8,14,2
2,8,15,2
2,8,16,2
2,8,17,1
STRONG AND WEAK ALKALIS Acids produce H+ ions in water Alkalis produce OH- ions in water
Strong acids/alkalis are 100% ionised (dissociated) in water – give more ions to solution
Weak acids/alkalis are only partly ionised in water – don’t give many ions to the solution.
Acids are proton DONORS Alkalis are proton ACCEPTORS
TITRATION Used to measure accurately how much
acid is need to completely neutralise an known amount of alkali (and vice versa).
Indicators are used to show the END POINT
TITRATION CALCULATIONS Mass = Mr x moles
Moles = concentration x volume
Use ratio of moles from the equation
Concentration units = mol/dm3
WATER AND SOLUBILITY Water evaporates from rivers and
oceans, and condenses in clouds, returning to the surface as rain (water cycle).
Most IONIC substances are soluble in water
Most COVALENT compounds are NOT soluble in water
A SATURATED solution contains the maximum amount of solute that will dissolve at that temperature.
SOLUBILITY CURVES The solubility of most solid solutes
INCREASES with temperature. The solubility of GASES DECREASES with
temperature.
Solubility curves show how the solubility changes with temperatureALWAYS CHECK AND STATE THE UNITS IN
ANSWERS!!
HARD WATER Dissolves metal compounds (usually
group 2) Mg and Ca make water hard Ca and Mg react with soap to form
SCUM Ca and Mg salts decompose on heating
leading to SCALE formation.
Hard water is good for your health!
REMOVING HARDNESS Soften water by removing the salts that
produce scum and scale
Washing Soda Ca2+ (aq) + CO3
2-(aq) CaCO3(s)
Ion Exchange columnExchanges Ca and Mg for softer Na ions.
WATER TREATMENT Making water safe to drink requires
removing microorganisms and decreasing levels of dissolved substances.
Filtering removes solids Adding chlorine kills bacteria
Pure water is obtained by DISTILLATION
COMPARING ENERGY CONTENT When fuels burn they react with oxygen
and release ENERGY – exothermic reaction.
A simple calorimeter can be used to measure the energy changes.However these will not give an ACCURATE
reading of energy released, they will allow different fuels to be compared.
TOO Much HEAT is lost to the surroundings
ENERGY CHANGES IN REACTIONS Energy is required to BREAK bonds Energy is RELEASED when bonds are
formed.
Exothermic reactions have a net energy RELEASE and are NEGATIVE in sign
Endothermic reaction have a net energy ABSORPTION and are POSITIVE in sign
Activation energy is the amount of energy required to START a reaction.
ENERGY CALCULATIONS E = mcT Where c is the specific heat capacity of
water 4.2 J/g/oC m is the mass of the liquids involved in
the reaction.
Remember: All energy must be quoted in kJ/mol!
TESTS FOR POSITIVE IONSUnknown
Red/brown
Cu 2+
Ammonia gasGiven off
Green/Brown
Add NaOH
NH 4+
Soluble
InsolubleColoured Ppt
Light blue
Fe 3+
Mg 2+Ca 2+
Fe 2+
Al 3+
Flame Test
Brick Red No colour
White Ppt
TESTS FOR NEGATIVE IONS
Add HCl
Fizzes
Add Warm NaOH
Add silver nitrateand dilute HNO3
No Fizz
Milky/Cloudy
LimewaterTest
No gasAmmoniasmell, turns Litmus blue
Cream ppt
Add Barium Chloride
CO3 -
White ppt
SO4 2-
Br -Cl - I -
White ppt Yellow ppt NO3 -
Add Al powder
and warmNH4
+
TESTING FOR ORGANIC SUBSTANCES Bromine water to test for saturation
Know how to determine the empirical formula from masses of carbon dioxide and water
produced through combustion of organic substances.
INSTRUMENTAL ANALYSIS
Some instrumental methods are suited to identifying elements, such as atomic absorption spectroscopy
used in the steel industry. Other instrumental methods are suited
to identifying compounds, such as infrared spectroscopy, ultraviolet
spectroscopy, nuclear magnetic resonance spectroscopy, and gas-liquid chromatography.
Some methods can be adapted for elements or compounds, such as mass spectrometry.