Elements of life
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how does a time of flight mass spectrometer work?
1) gas is vaporised using electric heater 2) ionised by bombardment of high energy e- 3) acceleration using electric field 4) time taken for ions to reach magnetic field/detector measured.
how do you work out relative atomic mass from a mass spectrum?
sum of (mass x charge) /100
describe a test for sulfates
dilute HCl + barium chloride -white precipitate of barium sulfate forms
why does the melting point of metals increase across periods?
• increasing number of delocalised electrons, decreasing atomic radius • higher electron density
what is meant by the term ‘first ionisation enthalpy’?
the energy needed to remove one electron from the outer shell of one mole of gaseous atoms
name the factors which cause ionisation enthalpy to be lower
• higher atomic radius - more shielding
name the factors which cause ionisation enthalpy to be higher
-positive charge
describe and explain what an absorption spectrum looks like
• black lines on a coloured background - energy corresponding to gaps between energy levels that is absorbed when an electron is excited
what shape does a molecule with 4 groups of electrons, including 3 bonding pairs and 1 lone pair take?
trigonal planar, 120 degree bond angle
what effect does a lone pair have on a bond angle?
decreases it by 2.5 each lone pair
define relative atomic mass
average mass of an atom on a scale where carbon 12 is 12
define nuclear fusion
when two small nuclei combine under high temperature and pressure to form a larger nucleus
why do ionic substances have high melting points?
-strong electrostatic attractions between positive and negative ions
how does the solubility of group 2 ions change down the group?
• singly charged anions (OH-) increase in solubility down the group • doubly charged anions (CO3)2- decrease in solubility down the group
how do you prepare a pure salt from a metal and acid?
DFEE 1) add metal to acid and dissolve 2) filter the excess metal off 3) evaporate off some of the liquid, leave the rest to evaporate naturally
what is the reaction trend with group 2 elements and water?
increase in reactivity down the group, forms metal hydroxides
why does first ionisation enthalpy decrease down the group?
amount of shielding inceases/less attraction of outer shell electrons to the nucleus
why do first ionisation enthalpies increase across a period?
number of protons is increasing
describe which colour corresponds to each silver halide precipitate (AgI, AgBr, AgCl)
Cl- = white Br- = cream I- = yellow
give the colours of the metal ions
Li+ = crimson Na+ orange-yellow K+ = lilac Ca2+ = brick red Ba2+ = green Cu2+ =blue-green
what order should tests for ions be done in?
carbonates -> sulfates -> halides
what is the equation you use to calculate the energy given out by an ion?
deltaE = hv or deltaE/hv where deltaE is energy, h is plancks constant and nu is frequency
what is the equation which relates speed and frequency to wavelength?
c= vLambda
why does ionisation enthalpy increase across a period?
outermost electrons are more strongly attracted to more protons in the nucleus