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Set Answer Questions for F334
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- 1describe what happens to the vapour when a mixture is heated under refluxvapours are condensed
- 2reasons why to refluxmixture needed to be heated for a long time
no reactants or products are lost
high temperature required for reaction - 3describe and explain the process of recrystallisation using a suitable solvent. Include an explanation for the choice of solvent used and how impurities are removeddissolves salt well at higher temp but very little at room temp
dissolve in minimum volume of hot solvent
leave to cool so crystals form
filter off crystals, (soluble) impurities are left in filtrate
wash with minimum volume of cold solvent
leave to dry in air or dessicator - 4explain why a substance produces a spectrum showing absorption peaks when irradiated with infrared frequenciesbonds in molecule absorb
specific IR frequencies
absorbing different frequencies
causes different bonds to vibrate - 5give the meaning of the term Tgtemperature below which polymer turns brittle
- 6the less crystalline the polymer the more flexible - explain whychains are further apart
so weaker intermolecular forces of attraction
so chains can slide over each other easily - 7when using potassium manganate (VII) in a titration why do you not need to add an indicator?MnO4–(aq) is coloured
so colour change in the reaction
pink to colourless - 8as a reaction progresses, ions are formed which acts as a catalyst. explain the changes in the reaction rate as the reaction progressesincreases
rate speeds us as ion catalyst formed
then decreases
rate slows down as reactants used up - 9suggest a method that can be used to measure the concentration of a substance other than by titrationcolorimetry
visible spectroscopy - 10explain the term zwitteriona species with both a positive and negative charge
- 11drug x has many adverse side effects. suggest why it is still used to treat a diseaseless side effects than other drugs
more effective than other drugs - 12explain why with 1,2-diaminocyclohexane, you may have two different isomersC-C bond between the chiral atoms prevented from rotating by the ring structure
- 13describe the three levels of protein structureprimary - order of amino acids
secondary - folding of chains into alpha helices or beta pleated sheets
tertiary - overall 3D shape - 14what data would you need in order to be able to comment on the effect of temperature on the value of the equilibrium constant?enthalpy change of the reaction
is the reaction endothermic or exothermic? - 15explain why, in a reversible reaction in which a solid is formed, the reaction almost goes to completionsolid formed so no homogeneous system
precipitates out which shifts equilibrium to the right - 16what feature of d-block metal ions enables some to be coloured in solution?partially filled d sub shell
- 17name a suitable acid to acidify a sample for titration purposes(dilute) sulphuric acid
- 18suggest one advantage natural fibres have over polymers in terms of the method of disposalbiodegradable
- 19explain why hydrogen bonding is strong when there are benzene rings in the chainbenzene rings have flat molecules
so allows chains to get close together
so H-bonds act over shorter distances
so are stronger - 20explain why transition metals can act as catalystsform ions in different oxidation states
oxidation states can interconvert during the reaction
so remain unchanged at end
activation energy lowered - 21suggest four possible ways of monitoring the rate of a reactioncolorimetry because colour change
pressure measurements because decrease/increase in moles of gas in the reaction
pH measurement because solution of gases becomes more/less acidic as reaction proceeds
bubble gases through limewater measure rate of cloudiness occurring - 22when concentrated sulphuric acid is used to catalyse a reaction, the yield of the product increases - why?conc. sulphuric acid absorbs water
shifts equilibrium to the right - 23explain why the polymerisation of compound D proceeds without the loss or gain of water moleculeswater formed in condensation when repeating units join together
replaces water used in hydrolysis of compound D
so no net gain or loss of water - 24suggest why the purified crystalline solid is used rather than amphetamine itsleftablets easier for controlling dosage
soluble so quicker acting
may not have amphetamine's side effects - 25explain why enzyme reactions speed up as the temperature is increased but stop altogether if the temperature is too highat higher temperatures there's more energy
to overcome the activation energy
if temp too high the interactions holding the enzyme structure are broken down
active site changes shape - 26write an ionic equation, including state symbols for the precipitation reaction that forms a pale blue precipitateCu2+(aq) + 2OH-(aq) --> Cu(OH)2(s)
- 27what happens if excess ammonia is shaken with Cu(OH)2precipitate dissolves
dark blue solution - 28in terms of crystallinity and melting point suggest how the properties of a cis-trans mixed chain polymer differ from the properties of an all trans chain polymercis structures would make the chains less regular
so less crystalline
IMFs act over longer distances
IMFs are weaker
so MP lower in cis-trans mixed chain - 29name a chemical method which chemists can use to produce a polymer with slightly different propertiescopolymerisation
plasticisers - 30explain how zwitterions are formedcompound contains both basic and acidic group (e.g. amine and carboxylic acid)
proton transferred from acid to basic group
acid group deprotonated
basic group protonated - 31in living cells only one isomer can act as a substrate for enzymes, explain whyactive site in enzyme has specific shape
only one isomer has correct shape to fit - 32explain why it is important for the pH to be controlled in an enzyme-catalysed reactionChange of pH changes the nature of the amine and acid groups in
amino acids/proteins and changes hydrogen bonding in enzymes
So alters tertiary structure, changing shape of active site
substrate can no longer bind - 33suggest and explain why you would expect he voltage of a cell to be different from a calculated valueexperiment may not have been done under standard conditions - 1atm, 1moldm-3, 298K
E cell different under different conditions - 34describe one property that steel has as a result of containing chromium and nickelresistant to corrosion
stainless
hard
lustrous
high strength - 35other than recycling materials, what important role does adding scrap steel servecoolant
reduces thermal shock - 36in the production of steel what elements are removed by direct oxidation with gaseous oxygen?carbon
phosphorous
manganese
silicon - 37describe how ninhydrin should be used as a locating agentspray with ninhydrin
and heat - 38what happens to molecules when they absorb infrared radiationmore vigorous
bond vibrations
molecules move to higher
vibrational level - 39coating steel with zinc prevents rusting in a different way than coating with an organic polymer, explain the differencorganic polymer prevents air and water reaching metal - barrier
zinc more reactive than steel
so loses electrons and is oxidised
so zinc = sacrificial method - 40describe some factors that would be investigated in human clinical trialseffective does
toxicity
side reactions
how long drug lasts in body
formulation - 41explain how condensation polymerisation is different from addition polymerisationcondensation small molecule eliminated
addition - nothing eliminated in addition
and double bond is opened up - 42describe and explain how the properties of polymers change at low and high temperaturesat low temperatures below Tg polymer becomes brittle
at higher temperatures above Tm polymer melts
at low temperatures (not enough energy for) chains to slide over one another
applied force causes chains to break
at high temperatures chains (have enough energy to) move freely - 43what is meant by the term heating under reflux?heating with a vertical condenser
vapour condensed and returned to flask
no loss of volatiles - 44explain why a compound may have a geometric isomerrestricted rotation around C=C bond
so groups can be on same or opposite sides - 45what are two methods of measuring H+ concentrationtitrate with (standard) alkali
or
use a pH meter - 46how could you use a graph to show how the rate of reaction varies during the course of the reactionmeasure gradient
at different time intervals - 47explain why an enzyme is specific for the reaction it carries outenzymes form active site in their structure
which has a specific shape
in which the substrate can fit - 48give the reagent used to convert sodium salts into the corresponding acidsexcess hydrochloric acid
- 49what interactions can hold the tertiary structure of a protein together?ID-ID
ionic bonds
disulphide bridges
hydrogen bonding - 50why is chromium classed as a transition metal?chromium can form a stable ion with a partially filled d sub shell allowing variable oxidation states
- 51what tests will have to be done before a complex is allowed to be added to bottled drinks?Find the maximum dose of the complex which is safe
check that the complex used is pure
measure its toxicity - 52suggest a method for the disposal of plastic waste and explain the advantage of this methodburning
energy released can be used and saves landfill space
recycling
oil resources saved - 53what are some differences between DNA and RNA molecules?different bases
RNA has single chain
different sugar - 54outline how DNA is able to replicate genetic informationhydrogen bonds between DNA strands break
DNA unwinds
each strand acts as a template for a new strand - 55explain how organic nitrogen-containing compounds act as baseslone pair of electrons on nitrogen
can accept a proton - 56why is it important to add scrap steel?acts as a coolant as oxygen blow is very exothermic
- 57in a blast furnace apart from oxides and oxygen, what else is lost? what's put in?magnesium sulphide
magnesium, scrap steel and oxygen - 58a molecule with an asymmetric carbon atom exists as two enantiomers. explain why these are different compoundsthe mirror images are non-superimposable
- 59explain how molecular formula can be determined from an accurate mass:charge ratio for the M+ peak in its mass spectrummasses are measured relative to C-12
compare Mr with database - 60give three questions that clinical trials are designed to answeris the drug safe?
does it do what it was designed to do?
is it better than the standard treatment being used? - 61why are carboxylic acids soluble in alkaline solution?carboxylic acid reacts with alkali to form ions in solution
- 62how would you use concentrations of solutions measured at different time intervals to show that the reaction taking place is first order with respect to the compound?plot graph of concentration versus time
measure half lifes
constant half life = first order - 63explain why enzyme activity is less when the temperature is higher than the optimumat high temperatures hydrogen bonds break
active site changes shape
substrate can no longer fit - 64explain why enzyme activity is less when the pH is changed slightly from its optimum valuecauses ionisable groups to be altered
prevents ionic interactions between enzyme and substrate - 65explain why at low concentrations of P the reaction is first order with respect to Pthe rate determining step is the formation of the P-enzyme complex
when conc low not all active sites are filled
as P increases, rate increases in PROPORTION - 66explain why at high concentrations of P the reaction is no longer first order with respect to P. what is the new order of the reaction (w.r.t.P)?all active sites are filled
rate determining step is breakdown of enzyme-substrate complex
this doesn't depend on P
0 order with respect to P - 67give five ways in which enzymes may increase the efficiency of an industrial processspeeds up reaction rate
reduces amount of energy/heat required
can be reused/recycled
improves the atom economy
easier separation methods - 68explain the disadvantage associated with the formation of HCl in a condensation reactionHCl is toxic
HCl needs to be disposed of - 69explain why dilute hydrochloric acid will react with zincOxidising agent = H+
standard electrode potentials are measured with respect to the
(standard) H2/H+ half-cell
Eө H2/H+ = 0
metals with a negative electrode potential value will be
oxidised by H+ ions - 70suggest and explain why a student didn't form an aldehyde but a carboxylic acid instead when and primary alcohol was oxidisedheated under reflex so alcohol/aldehyde oxidised further
use of excess acidified potassium dichromate so alcohol/aldehyde oxidised further
acidified potassium dichromate not added slowly so alcohol/aldehyde oxidised further - 71describe and explain how an alteration in the sequence of bases can result in enzymes becoming less effective for a particular reactionenzymes are proteins with a specific sequence of amino acids
if DNA damaged, primary structure (order of AA) is changed
so tertiary structure will also change
active site is where reaction with substrate takes place
active site shape changes - no more complementary to substrate
substrate can't fit
enzyme doesn't work - 72explain why phenols are able to dissolve in water if a little aqueous alkali is added to the mixture of phenol and waterphenol forms ion
ions form bonds with water molecules
ions more soluble in water - 73explain how transition metal ions such as Cu2+ are able to increase the rate of a redox reactiontransition metal ion / Cu2+ reacts with one of reactants to form a product
oxidation state of the transition metal ion / Cu2+ changes
new ion then reacts to reform the original transition metal ion / Cu2
forms original oxidation state at end of reaction
activation enthalpy for this reaction is lower than without the transition metal ion / Cu2+ - 74describe and explain two methods of protecting copper from corrosionbarrier protection:
Paint / grease / plastic coating
prevents copper reactingwith oxygen and water
sacrificial protection:
coat with/strap on blocks of Mg or Zn / galvanise
the more reactive Mg or Zn corrodes/reacts instead of Cu - 75when determining the rate of reaction w.r.t substance x, why use an excess of other substances?so only the concentration of substance x is effectively changing
- 76explain why 1,2-dichloroethene shows E/Z isomerism whereas E300 does not. [E300 has a pentene ring, and two -OH groups attached to the C=C bond in the ring]restricted rotation around the C=C bond
each C atom (in C=C bond) has two different groups attached to it
the two –OH groups can only be on the same side of the C=C bond because the ring structure will not allow them to be on
opposite sides / rotate - 77describe and explain one difference between heating under reflux and distillationHeating under reflux:
the condenser is vertical
mixture is evaporated and condensed and
returned to mixture
no reactants/products is lost from the mixture
Distillation:
the condenser is horizontal
mixture is evaporated and condensed and collected
mixture is separated - 78explain in terms of structure and bonding why amino acids have a high melting pointit forms a zwitterion which has both a negative charge and a positive charge
zwitterions attract each other very strongly
high energy/heat required to separate particles - 79BrO3- ions can react with Br- in acidic solution to form bromine. Explain why colorimetry can be used to follow this reactionBrO3¯ and Br¯ are colourless but Br2 is brown
change in colour in the reaction
change in absorbance in a colorimeter in the
reaction - 80explain how the orders of reaction support the chemists' suggested rate-determining stepslow step of the reaction / rds depends upon the species given in the rate equation
- 81explain, in terms of fixed frequencies of light, why some transition metal ions in solution are colouredions absorb specific
frequencies of visible light
transmits complementary colour - 82give the meaning of the term crystallinitychains are highly ordered
how polymer chains are packed together in
an orderly regular way - 83suggest one reason why PLA - a polymer made from corn starch is 'greener' than poly(ethene)manufactured from a renewable resource
- 84suggest a method for removing Fe2O3 from a mixturefiltration
- 85give the meaning of the term electronegativityability of atom to attract eletrons in a covalent bond
- 86explain the term tertiary structurethe three dimensional structure of the protein
folding of the secondary structure - 87what does the colour that a transition metal absorbs depend on?oxidation state of the ion
the type of ligand
coordination number/shape of complex - 88explain why a protein with a tertiary structure is affected by pH changechanging pH affects the ionic attractions
and charges on polarisable side groups
lowering pH NH2 -> NH3+
(gets protonated)
lowering pH -COO- -> COOH
(gets protonated) - 89why was a black card placed behind the test tubes?help judge the disappearance of the suspension
- 90describe how you would use a rate of reaction vs temperature graph to find the relative rates of reaction at two different temperaturesread off rate on y-axis for a particular temperature on x-axis
- 91when the substrate concentration is high state the order of reaction with respect to the substrate. explain your answerzero order
all the active sites are full
max number of E-S complexes formed - 92what properties should a solvent have to achieve efficient recrystallization?solvent should dissolve solute at higher temperatures
solute is insoluble at room/lower temperature - 93explain why phenols react with aqueous sodium hydroxide and suggest why the products are soluble in waterphenol groups
phenols are acidic
neutralised by NaOH
ions form
ions / salts are soluble - 94why is it necessary to measure the rate of reaction when the amounts of reactants used up were small in comparison to the total quantities of reactants present?as reactants are used up the rate will change
concentrations remain (almost) constant
rate measured will be for the initial concentrations - 95explain how cross-links are formedC=C bonds on side chains (in different polymer chains) break/open up and form a (covalent) bond/link
- 96cross-linked poly(acrylic acid) does not dissolve when water is added. Poly(acrylic) acid without cross-links eventually dissolved when sufficient water is added. Suggest and explain a reason for this difference in propertiescrosslinks will prevent chains moving apart (sufficiently to dissolve) / held in position (so it does not dissolve)
without crosslinks water will force polymer chains apart (and so polymer will dissolve) - 97describe how the student used a colorimeter to find out how the concentration of the blue dye changed when added to the polymerSelect orange/red/complementary colour for filter
2. Make up/use dye solutions of different known/standard concentrations
3. Measure the absorbance/transmission/transmittance of the dye solutions of different known concentrations
OR absorbance/transmission/transmittance of the blue dye solution AW
4. Plot calibration graph of absorbance( or alternative see 3 above) readings v concentration
5. Add the polymer (known mass) to the dye solution and measure the new absorbance
6. Repeat/take measurements until no further change in absorbance/transmission / over a period of time AW
7. Use the calibration curve to find out how the concentration of the blue dye changes / to find the concentration of the blue dye at different times - 98suggest why scientists once thought that proteins were more likely to transmit genetic dataproteins have more amino acids than the bases/nucleotides in
DNA
from which to construct many unique
structures and to carry genetic data - 99stronger oxidising agents....have a more positive SEL
have a greater tendency to attract electrons
are reduced
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- A Level Chemistry Fichas sobre Set Answer Questions for F334, creado por ify.ezeps el 22/05/2015.
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