paper 1 missed marks

Question 1

what are the stages in a catalytic converter that decrease emissions of gases such as carbon monoxide?

Answer 1

CO molecules adsorbed onto the catalytic surface
which weakens the bonds
CO2 is desorbed from the catalytic surface

Question 2

when would you expect ΔSsystem to be positive?

Answer 2

increase in number of moles from reactants to products
change of state from solid to liquid/gas/solution

Question 3

explain how a buffer solution works

Answer 3

large reservoir of both acid and base/ the buffer (name them if poss)
OH- + HA —> A- + H2O

H+ + A- —> HA

because [H+] and [A-] are in such large amounts the [H+][A-] ratio barely changes so pH hardly changes

Question 4

explain why the complex ions [Co(NH3)6]2+ and [Co(H2O)6]2+ are coloured and have different colours

Answer 4

d subshell splits into two different energies
difference in energy depends on the ligands
electrons undergo different d-d transitions requiring different energy
difference in energy leads to different frequencies
the unabsorbed frequencies are reflected

Question 5

EDTA4- factfile

Answer 5

hexadentate
coordination number = 6
can form dative covalent bond with cobalt (III) ion

Question 6

ethane-1,2-diamine factfile

Answer 6

bidentate
coordination number = 6
can form dative covalent bond with the cobalt (III) ion

Question 7

explain why there is a difference in experimental lattice energy and theoretical lattice energy for MgI2?

Answer 7

some covalent character
magnesium ion is small and highly charged
iodide ion has a large ionic radius
iodide ion is polarised by the magnesium ion

Question 8

make fc for hess cycles of hydration/solution!!

Answer 8

…

Question 9

what does atomic emission spec provide evidence for?

Answer 9

quantum shells

Question 10

what colour changes will be seen from universal indicator in a beaker of water containing water?

Answer 10

blue to purple

Question 11

why do disproportionation reactions that aren’t feasible sometimes react to a small extent?

Answer 11

disproportionation is an equilibrium system

Question 12

what type of reaction occurs when ammonia gas reacts with hydrogen chloride?

Answer 12

acid-base

Question 13

colours of copper (II) chromate (VI) at the positive and negative electrodes

Answer 13

positive - yellow
negative - blue

Question 14

why might a reaction carried out in a sealed container with a constant volume have different heat energy change to the enthalpy change?

Answer 14

system not at constant pressure due to gas produced increasing/changing the pressure

Question 15

why can chromium show variable oxidation numbers? (in terms of ionisation energies)

Answer 15

steady increase in successive ionisation energies

Question 16

potassium bromide and chlorine water equation

Answer 16

2KBr + Cl2 —> 2KCl + Br2

Question 17

why is there no reaction between potassium bromide and iodine?

Answer 17

iodine cannot oxidise bromide ions

Question 18

after using Q = mc^T what equation do you use to find enthalpy change?

Answer 18

^H = Q(in kJ) / number of moles

Question 19

why is the standard enthalpy change of neutralisation of ethanoic acid with sodium hydroxide -55.2kJ/mol and the value of HCl -57.1 kJ/mol?

Answer 19

HCl is a strong acid so more energy is needed to ionoise the ethanoic acid

Question 20

equation for decomposition of g1 compound NaNO3?

Answer 20

2NaNO3 —> 2NaNO2 + O2

Question 21

equation of decomposition of a g2 nitrate?

Answer 21

2X(NO3)2 —> 2XO + 4NO2 + O2

Question 22

why does magnesium carbonate decompose more readily on heating than barium carbonate?

Answer 22

Mg is smaller which polarises the carbonate ion and weakens the carbon-oxygen bond

Question 23

equations for iron(II) catalysing 2I- + S2O8^2- —> I2 + 2SO4^2-

Answer 23

2Fe^2+ + S2O8^2- —> 2Fe^3+ + 2SO4^2-
2Fe^3+ + 2I- —> 2Fe^2+ + I2

Question 24

equation for cobalt (II) catalysing SO3^2- + 1/2O2 —> SO4^2-

Answer 24

2Co^2+ + 1/2O2 + 2H^+ —> 2Co^3+ + H2O
2Co^3+ + SO3^2- + H2O —> 2Co^2+ + SO4^2- + 2H+

Question 25

is water acidic alkaline or neutral at 310K?

Answer 25

neutral
[H+]=[OH-]

Question 26

explain how the carbonic acid - hydrogen carbonate buffer system helps control the pH of blood when extra CO2 is present due to strenuous exercise

Answer 26

CO2 dissolved in blood forms carbonic acid therefore equilibrium will shift right producing more H+
large reservoir of HCO3^- combines with H+ ions

Question 27

how do you calculate the number of molecules present?

Answer 27

avogadro x number of moles