what i got wrong in the past papers

Question 1

which reagent is most suitable for the gravimetric determination of magnesium ions in water?

Answer 1

sodium carbonate

Question 2

are Fe3+ more stable than Fe2+ ions

Answer 2

yes

Question 3

what is the oxidation state of Cr2O7 ions

Answer 3

+6

Question 4

what is the oxidation state of MnO4 ions

Answer 4

+7

Question 5

what is the oxidation state of VO2+ ions

Answer 5

+4

Question 6

what is the oxidation state of Sn4+

Answer 6

+4

Question 7

what are the units for a second order reaction

Answer 7

l mol-1 s-1

Question 8

what are the units for a first order reaction

Answer 8

s-1

Question 9

what are the units for a zero order reaction

Answer 9

mol l-1 s-1

Question 10

what are the units for a third order reaction

Answer 10

mol -2 l2 s-1

Question 11

what does it mean if n=2 (principle quantum number)

Answer 11

electron is in shell 2

Question 12

what does it mean if l = 1

Answer 12

electron is in the p subshell

Question 13

what does it mean if ml = -1

Answer 13

electron is in the orbital of -1

Question 14

how can you work out the order of a reaction from the rate determining step

Answer 14

look at the number of moles of each of the reactants involved. 1 mole = first order etc

Question 15

why may you dilute a sample for the colorimeter

Answer 15

becase the absorbance levels must not be outwith the calibration range

Question 16

how can you find out the pKa values

Answer 16

the data booklet!

Question 17

what is a cause for electrons becoming excited

Answer 17

heat/high temperatures

Question 18

electron transitions involving the d-subshell can give rise to colour in transition metal complexes. why does a solution of an ion colourless

Answer 18

no d-d transitions are possible, so it does not absorb visible light

Question 19

why may you use E=hf and not E=hlf

Answer 19

if the units in the question are J and not J mol or KJ mol

Question 20

why may an experimentally determined value differ from the actual value, other than issues with the apparatus or transfer errors

Answer 20

impurities present in the substances

Question 21

explain how the line of red light is produced

Answer 21

• an electron is excited and promoted to a higher energy level
• when it falls back down to a state, energy corresponding to the red light is emitted

Question 22

why is recrystallisation necessary

Answer 22

to purify

Question 23

describe how a mixed melting point experiment would be carried out and the result used to confirm the product was pure

Answer 23

sample mixed with pure substance
melting point of the mixture will be the same as the pure if the sample is pure

Question 24

suggest an analytical technique which could be used to indicate whether the final sample is pure

Answer 24

thin layer chromatography

Question 25

state the value of the m orbital which contains the tenth electron

Answer 25

-1 0 1

Question 26

explain how unpaired electrons can arise in a complex ion

Answer 26

less energy is required to promote an electron. electrons can be promoted between energy levels

Question 27

suggest an analytical techniwue that could be used to determine the presence of copper in spiders blood

Answer 27

atomic absorption

Question 28

state the oxidation number of vanadium in VO2

Answer 28

4

Question 29

explain why a substance may be described as a homogenous catalyst

Answer 29

same state as the ions in the reaction

Question 30

describe fully the procedure required to obtain results that would allow a calibration graph to be drawn

Answer 30

standard solutions prepared suitable wavelength filter used use of a blank absorbance of each solution measured and noted

Question 31

the quantum number which specifies the shape of the orbital is the

Answer 31

angular momentum

Question 32

why may a spectrum have multiple lines

Answer 32

many different electron transitions in the visible region

Question 33

what piece of apparatus may be used to separate two immiscible layers

Answer 33

separating funnel

Question 34

state one way in which the identity of the product could be confirmed

Answer 34

mixed melting point analyis

Question 35

suggest how a student might test that no silver is remaining in the solution

Answer 35

add aldehyde to show a silver mirror

Question 36

how would an acidic buffer resist change in pH if a few more drops of the potassium hydroxide solution were added

Answer 36

the hydroxide ions would remove hydrogen ions from the solution these hydrogen ions would be replaced by the dissociation of ethanoic acid molecules into ethanoate and hydrogen ions

Question 37

21 Which of the following would not be suitable as a buffer solution? A Boric acid and sodium borate B Nitric acid and sodium nitrate C Benzoic acid and sodium benzoate D Propanoic acid and sodium propanoate

Answer 37

B

Question 38

20. Which of the following salts will form a solution with the lowest pH? A Potassium chloride B Potassium ethanoate C Ammonium chloride D Ammonium ethanoate

Answer 38

C

Question 39

9. Which of the following solids would form a colourless aqueous solution? A ZnSO4.7H2O B NiSO4.6H2O C K2CrO4 D CoCl2

Answer 39

A

Question 40

8 What is the co-ordination number of the transition metal in [Co(NH3)4(H2O)2]Cl3? A 3 B 4 C 6 D 9

Answer 40

C

Question 41

what is meant by the term degenerate

Answer 41

contains the same energy

Question 42

explain whether visible light would provide sufficient energy to ionise gaseous sodium atoms

Answer 42

no because the wavelength required is too short

Question 43

what is a back titration

Answer 43

substance is not titrated itself but insteaed a compound is reacted with the substance and then the remaining compound is titrated to see how much did not react

Question 44

suggest a good control experiment that could be used for a back titration

Answer 44

repeat with a known volume of reactant rather than an excess

Question 45

what structural feature of indigo dye allows it to absorb light within the visible region of the electromagnetic spectrum

Answer 45

alternating double and single bonds

Question 46

why does a dye like indigo appear blue when viewed in daylight

Answer 46

red and green absorbed, blue transmitted

Question 47

how could filtration be sped up

Answer 47

vacuum filtration

Question 48

when is the use of an indicator in a titration not required

Answer 48

when the reactants are methanoic acid solution and ammonia solution

Question 49

22. Which of the following statements about benzene is not true? A It is planar. B It is susceptible to attack by electrophilic reagents. C Its carbon to carbon bonds are equal in length. D It is readily attacked by bromine

Answer 49

D

Question 50

what does vacuum filtration use

Answer 50

buchner, hirsch or sintered glass funnel

Question 51

what does heating under reflux use

Answer 51

heating mantle water bath or bunsen burner

Question 52

what does distillation alloq

Answer 52

separation of liquids with similar boiling points

Question 53

how does distillation asses purity

Answer 53

by looking at the point at which a substance is separated by distillation

Question 54

Outline the steps for producing a calibration curve in colourimetr

Answer 54

A range of samples are prepared of known concentration*Colorimeter readings are taken with the wavelength that is most appropriate (i.e. has the greatest absorbance –look for the opposing colour on the colour wheel from what you see)*Dilutions to get samples are generally linear, but can be serial to give range. Burette and pipette are used for accuracy

Question 55

what is the criteria for solvent extraction

Answer 55

he solvent used must be immisciblewith the liquid mixture or solution (usually water) The solvent must also be one which the solute is moresoluble in than the liquid mixture or solution, volatileto allow the solute to be obtained by evaporation of the solvent and unreactivewith the solute.Extracting with multiplesmall volumes of solvent will extract a greater volume of solute than singleextraction.

Question 56

what is the purpose of recrystallisation

Answer 56

to purify an impure solid

Question 57

what are the steps involved in recrystallisation

Answer 57

dissolving an impure solid gently in a minimum volume of a hot solvent *hot filtration of the resulting mixture to remove any insoluble impurities *cooling the filtrate slowly to allow crystals of the pure compound to form, leaving soluble impurities dissolved in the solvent *filtering, washing and drying the pure crystals

Question 58

if the partition coefficient is high, which layer is the solute most soluble in

Answer 58

upper solvent

Question 59

Explain with 1moll-1of a strong acid has a lower pH than 1moll-1of a weak acid.

Answer 59

Since all of the ions dissociate in the strong acid there is a higher concentration of H+= lower pH

Question 60

what is an indicator

Answer 60

A substance with a clear colour change caused by distinct colours on each side of an equilbrium

Question 61

what is the colour of an indicator determined by

Answer 61

ratio of [HIn] to [In-