Elements of life

Question 1

how does a time of flight mass spectrometer work?

Answer 1

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.

Question 2

how do you work out relative atomic mass from a mass spectrum?

Answer 2

sum of (mass x charge) /100

Question 3

describe a test for sulfates

Answer 3

dilute HCl + barium chloride

-white precipitate of barium sulfate forms

Question 4

why does the melting point of metals increase across periods?

Answer 4

• increasing number of delocalised electrons, decreasing atomic radius
• higher electron density

Question 5

what is meant by the term ‘first ionisation enthalpy’?

Answer 5

the energy needed to remove one electron from the outer shell of one mole of gaseous atoms

Question 6

name the factors which cause ionisation enthalpy to be lower

Answer 6

• higher atomic radius

- more shielding

Question 7

name the factors which cause ionisation enthalpy to be higher

Answer 7

-positive charge

Question 8

describe and explain what an absorption spectrum looks like

Answer 8

• black lines on a coloured background

- energy corresponding to gaps between energy levels that is absorbed when an electron is excited

Question 9

what shape does a molecule with 4 groups of electrons, including 3 bonding pairs and 1 lone pair take?

Answer 9

trigonal planar, 120 degree bond angle

Question 10

what effect does a lone pair have on a bond angle?

Answer 10

decreases it by 2.5 each lone pair

Question 11

define relative atomic mass

Answer 11

average mass of an atom on a scale where carbon 12 is 12

Question 12

define nuclear fusion

Answer 12

when two small nuclei combine under high temperature and pressure to form a larger nucleus

Question 13

why do ionic substances have high melting points?

Answer 13

-strong electrostatic attractions between positive and negative ions

Question 14

how does the solubility of group 2 ions change down the group?

Answer 14

• singly charged anions (OH-) increase in solubility down the group
• doubly charged anions (CO3)2- decrease in solubility down the group

Question 15

how do you prepare a pure salt from a metal and acid?

Answer 15

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

Question 16

what is the reaction trend with group 2 elements and water?

Answer 16

increase in reactivity down the group, forms metal hydroxides

Question 17

why does first ionisation enthalpy decrease down the group?

Answer 17

amount of shielding inceases/less attraction of outer shell electrons to the nucleus

Question 18

why do first ionisation enthalpies increase across a period?

Answer 18

number of protons is increasing

Question 19

describe which colour corresponds to each silver halide precipitate (AgI, AgBr, AgCl)

Answer 19

Cl- = white
Br- = cream 
I- = yellow

Question 20

give the colours of the metal ions

Answer 20

Li+ = crimson 
Na+ orange-yellow
K+ = lilac
Ca2+ = brick red
Ba2+ = green 
Cu2+ =blue-green

Question 21

what order should tests for ions be done in?

Answer 21

carbonates -> sulfates -> halides

Question 22

what is the equation you use to calculate the energy given out by an ion?

Answer 22

deltaE = hv or deltaE/hv

where deltaE is energy, h is plancks constant and nu is frequency

Question 23

what is the equation which relates speed and frequency to wavelength?

Answer 23

c= vLambda

Question 24

why does ionisation enthalpy increase across a period?

Answer 24

outermost electrons are more strongly attracted to more protons in the nucleus

Question 25

why do group 2 carbonates increase in thermal stability down the group?

Answer 25

smaller ions have a higher charge density, and distort the large carbonate ion, causing it to decompose at a lower temperature

Question 26

briefly summarise why the geiger marsden experiment proved that the atom was mostly empty space

Answer 26

• fired alpha (+) particles at a thin sheet of gold

- if the plum pudding model was right, they’d have been deflected, but most of them passed straight through