what i got wrong in the past papers Flashcards
which reagent is most suitable for the gravimetric determination of magnesium ions in water?
sodium carbonate
are Fe3+ more stable than Fe2+ ions
yes
what is the oxidation state of Cr2O7 ions
+6
what is the oxidation state of MnO4 ions
+7
what is the oxidation state of VO2+ ions
+4
what is the oxidation state of Sn4+
+4
what are the units for a second order reaction
l mol-1 s-1
what are the units for a first order reaction
s-1
what are the units for a zero order reaction
mol l-1 s-1
what are the units for a third order reaction
mol -2 l2 s-1
what does it mean if n=2 (principle quantum number)
electron is in shell 2
what does it mean if l = 1
electron is in the p subshell
what does it mean if ml = -1
electron is in the orbital of -1
how can you work out the order of a reaction from the rate determining step
look at the number of moles of each of the reactants involved. 1 mole = first order etc
why may you dilute a sample for the colorimeter
becase the absorbance levels must not be outwith the calibration range
how can you find out the pKa values
the data booklet!
what is a cause for electrons becoming excited
heat/high temperatures
electron transitions involving the d-subshell can give rise to colour in transition metal complexes. why does a solution of an ion colourless
no d-d transitions are possible, so it does not absorb visible light
why may you use E=hf and not E=hlf
if the units in the question are J and not J mol or KJ mol
why may an experimentally determined value differ from the actual value, other than issues with the apparatus or transfer errors
impurities present in the substances
explain how the line of red light is produced
- 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
why is recrystallisation necessary
to purify
describe how a mixed melting point experiment would be carried out and the result used to confirm the product was pure
sample mixed with pure substance
melting point of the mixture will be the same as the pure if the sample is pure
suggest an analytical technique which could be used to indicate whether the final sample is pure
thin layer chromatography
state the value of the m orbital which contains the tenth electron
-1 0 1
explain how unpaired electrons can arise in a complex ion
less energy is required to promote an electron. electrons can be promoted between energy levels
suggest an analytical techniwue that could be used to determine the presence of copper in spiders blood
atomic absorption
state the oxidation number of vanadium in VO2
4
explain why a substance may be described as a homogenous catalyst
same state as the ions in the reaction
describe fully the procedure required to obtain results that would allow a calibration graph to be drawn
standard solutions prepared
suitable wavelength filter used
use of a blank
absorbance of each solution measured and noted
the quantum number which specifies the shape of the orbital is the
angular momentum
why may a spectrum have multiple lines
many different electron transitions in the visible region
what piece of apparatus may be used to separate two immiscible layers
separating funnel
state one way in which the identity of the product could be confirmed
mixed melting point analyis
suggest how a student might test that no silver is remaining in the solution
add aldehyde to show a silver mirror
how would an acidic buffer resist change in pH if a few more drops of the potassium hydroxide solution were added
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
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
B
- 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
C
- Which of the following solids would form a
colourless aqueous solution?
A ZnSO4.7H2O
B NiSO4.6H2O
C K2CrO4
D CoCl2
A
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
C
what is meant by the term degenerate
contains the same energy
explain whether visible light would provide sufficient energy to ionise gaseous sodium atoms
no because the wavelength required is too short
what is a back titration
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
suggest a good control experiment that could be used for a back titration
repeat with a known volume of reactant rather than an excess
what structural feature of indigo dye allows it to absorb light within the visible region of the electromagnetic spectrum
alternating double and single bonds
why does a dye like indigo appear blue when viewed in daylight
red and green absorbed, blue transmitted
how could filtration be sped up
vacuum filtration
when is the use of an indicator in a titration not required
when the reactants are methanoic acid solution and ammonia solution
- 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
D
what does vacuum filtration use
buchner, hirsch or sintered glass funnel
what does heating under reflux use
heating mantle water bath or bunsen burner
what does distillation alloq
separation of liquids with similar boiling points
how does distillation asses purity
by looking at the point at which a substance is separated by distillation
Outline the steps for producing a calibration curve in colourimetr
A range of samples are prepared of known concentrationColorimeter 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
what is the criteria for solvent extraction
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.
what is the purpose of recrystallisation
to purify an impure solid
what are the steps involved in recrystallisation
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
if the partition coefficient is high, which layer is the solute most soluble in
upper solvent
Explain with 1moll-1of a strong acid has a lower pH than 1moll-1of a weak acid.
Since all of the ions dissociate in the strong acid there is a higher concentration of H+= lower pH
what is an indicator
A substance with a clear colour change caused by distinct colours on each side of an equilbrium
what is the colour of an indicator determined by
ratio of [HIn] to [In-
