Karteikarten
F334 Past paper questions
Karten in diesem Stapel (122)
- 1Explain what is meant by crystalinePolymer chains are highly ordered
- 2PPA is more crystalline than nylon-6. This gives PPA a greater Tm than nylon-6. Explain the greater Tm in terms of intermolecular bonding involved (3)PPA chains closer together
Intermolecular bonds in PPA will be stronger/more intermolecular bonding
More energy required to break the intermolecular bonding, which allows chains to move over each other. - 3Suggest why scientists once thought that proteins were more likely to transmit genetic data (2)Proteins have more amino acids than the bases in DNA
From which to construct many unique/differnt structures to carry genetic data - 4What is meant by the secondary and tertiary structure of an enzyme (2)Secondary: folding of polypeptide chains
Tertiary: 3D shape/globular structure - 5Name the type of polymerisation reaction is needed to form nylon-6 (1)condensation and water is lost
- 6Name a process by which nylon-6 can be made more crysallinecold-drawing
- 7Give two successful outcomes of clinical trials that would be necessary before a drug can be classed as an effective drug (2)Non-toxic
No harmful side effects
Works better than standard medicines - 8Suggest why stereoisomers would be expected to have different activities in the body (2)They have different shapes
One would fit better in the active site of the enzyme than the other/ Only one will be able to form enzyme-substrate complexes. - 9What properties should a solvent have to achieve efficient recrystallisation (2)Solvent should dissolve solute at high temperatures.
Solute is insoluble at room temperature - 10Explain why resveratrol (contains 3 phenol groups) reacts with NaOH (aq) and suggest why the products are soluble in water. (4)1. Has phenol groups
2. the OH groups are acidic so react with NaOH
3. Forms ions
4. Ions are soluble - 11The rates of reaction are measured when the amounts of reactants used up are small in comparison to the total quantities of reactant present. Explain why it is necessary to do this. (2)As reactants are used up/ concentration changes, the rate will change.
Concentrations remain almost constant
Rate measured will be for initial concentrations - 12Explain the meaning of enantiomers (2)Isomers that structures are mirror images
which are non-superimposable - 13Explain how cross links in polymers are formedC=C bonds on side chains break open and form covalent bonds
- 14Name a suitable reagent for converting a carboxylic acid into a carboxylate ionSodium hydroxide
- 15A cross-linked polymer does not dissolve when water is added, a polymer without cross-links eventually dissolves when enough water is added. Suggest and explain a reason for this difference in properties. (2)Cross links prevent chains moving apart
Without cross links water molecules will force the chains apart. - 16The voltage of a battery measured with a high resistance voltmeter is less than the value of the batteries Ecell value. Suggest whyThe measured voltage or the electrode potentials are not recorded in standard conditions
Concentration of ions is not 1moldm-3 - 17Suggest and explain a reason why it is much easier to recycle super absorbent polymers than polymers from a mixture of used packaging,Used packagaing consists of many different polymers which need to be separated first
- 18What happens why sodium carbonate is added to a carboxylic acidfizzes,
- 19Why is it important that reactions have a high atom economy (2)Reduce waste products
Costs kept to a minimum/ less energy used - 20What are the conditions for an electrochemical cell25 degrees
1moldm-3 solution - 21State the colour of Cu2+ ions in water and explain why the solution has this colour. (2)Transmit blue, because absorbs orange light
- 22What is the colour of the [Fe(H2O)6]3+ ion in water?Yellow
- 23When conc HCl (aq) is added to a solution of Cu2+ ions, what type of reaction occurs, and give the formula of product containing the copper (2)Ligand substitution
[CuCl4]2- - 24Describe how colorimetry is used to determine the concentration of Cu2+ ions in an aqueous sample1. Make up standard solutions of known concentrations of Cu2+
2. Choose a suitable filter - set the colorimeter to a suitable wavelength
3. Zero the colorimeter
4. Measure absorbance of standard solutions
5. Plot calibration curve
6. measure the unknown solution.
7. Read off concentration from calibration curve - 25Many members of the public believe that the DNA fingerprints of the innocent should be removed from the DNA database. Others disagree with this view Give a reason for each of the two viewpointsFor removal: fingerprint not unique, only a probability
Techniques not foolproof
Against removal: Helps to solve crimes
Innocent till proved guilty
Future research into disease - 26Describe and explain the effect on the crystallinity of a polymer of changing the double bonds to 50% cis and 50% trans (2)Less trans (different sides) will make the chains less linear, less crystaline.
So the chains cannot line up as close together. - 27Materials made from nylon-6 can absorb moisture, but those made from neoprene cannot (no NH2 group). Explain these observations Describe how the effect of water absorption on the chain arrangement in nylon-6 and thus on its Tg (4)1. NH group allows hydrogen bonding with water molecules
2. No hydrogen bonding in neoprene
3. Water molecules will force chains further apart
4. Chains less crystaline, weaker IMforces so Tg will be lowered - 28High-resolution mass spec can be used to determine the molecular formula of a compound by measuring the mass:charge ratio of the M+ peak. Explain how the molecular formula of a molecule can be determined from an accurate mass:charge ratio for the M+ peak in its mass spectrumThe masses of the different types of atom present are not integers.. Masses are measured relative to carbon 12.
Different compounds with the same whole number molecular mass will have different Mr values from high resolution
spectra.
Comparison of Mr with database - 29Recrystallisation removes both soluble and insoluble impurities. Describe how a student would carry out this procedure using a suitable solvent (5)1. Heat the (impure) sample with solvent
2. with a minimum amount (of solvent)
3. filter
4. leave filtrate to cool so that it can crystallise
5. filter off crystals, wash and dry
AD for QWC mark:
*First filtration / filtration of hot solution removes insoluble impurities
OR after crystallisation soluble impurities stay in solution / - 30Give three questions that clinical trials are designed to answer (3)1. Is the drug safe to be used in humans?
2 Does it do the job it is designed to do?
3 Is it better than the standard treatment being used? - 31Explain how a student would use a colorimeter and calibration curve to determine the concentrations of 'compound B' as a purple colour faded in the titration flask. Explain how the student would use the results to show that the reaction taking place is in first order with respect to compound B (5)1. Use a suitable filter OR a filter having the complementary colour
2. sample of the reaction mixture into the colorimeter and) take absorbance readings at regular intervals
3. convert absorbance readings to concentrations using the calibration curve
4. plot graph of concentration v time
5. measure half-lives from graph
6. constant half-life = first order - 32Explain why the enzyme activity is less when the pH is changed slightly from its optimum value(change of pH) affects charges on polar side groups or active site
prevents correct interactions between enzyme and substrate - 33At low concentrations of amino acid P, the synthesis reaction is first order with respect to P and first order with respect to the enzyme. Give the rate equation for the reaction.Rate = K [P] [enzyme]
- 34Rate = K [P] [enzyme] Explain why at low concentrations of P, the reaction is first order with respect to PWhen [P] is low, not all enzyme active sites are filled.
Rate increases in proportion, so in first order - 35Rate = K [P] [enzyme] At high concentrations of P, the reaction is no longer in first order with respect to P Give the new order and how it arises (2)Order becomes 0.
Because all the active sites are filled - 36Give two ways that enzymes may increase the efficiency of an industrial processSpeed up reaction rate.
Reduce the number of steps in synthesis
Improves atom economy
Reduces the amount of heat required.
Can be reused
Fewer organic solvents used - reduces hazardous waste
Reduces use of more toxic catalysts/ - 37One way that DNA can be damaged is by alteration in the sequence of bases. Describe and explain how this damage could damage could result in enzymes becoming less effective for a particular reason. (6)1. enzymes are proteins with a specific sequence of amino acids
2. if the DNA is damaged order of the amino acids in the enzyme will be changed
3. so the tertiary structure of the enzyme will also alter change
4. the active site is part of the tertiary structure and is where the reaction with the substrate takes place
5. an altered active site will not have the correct shape
6. and will not be able to (interact with the substrate) by forming the correct intermolecular bonds - 38Give one way a polymer could be made more flexible (1)Plasticiser
- 39Solutions of Potassium manganite can be standardised against a measured volume of a standard solution of sodium ethanedioate, under acidic conditions. The contents of the titration flask have to be warmed to 60degrees before starting, otherwise the reaction is too slow. Describe how you would carry out this titration to get one result (5)1. (fill) burette with KMnO4 solution (unknown)
2. volumetric pipette for sodium ethanedioate (known)
3. to place solution in flask / beaker and then acidify (and warm flask)
4. then add KMnO4 solution slowly near end point
5. until permanent pink colour - 40Why do you add dilute sulphuric acid in a redox titration with managanate ions?Acid added to make sure that there are plenty of H+ ions to allow the oxidising agent MnO4- to be reduced
- 41Explain how transition metal ions such as Cu2+ are able to increase the rate of a redox reaction. (4)1. transition metal ion reacts with one of the reactants to form a product. Reacts to form an intermediate compound.
2. Oxidation state of the transition metal ion changes, the ion can be oxidised or reduced.
3. New ion then reacts to reform the original transition metal
4. Activation enthalpy for this reaction is lower than without the transition metal ion - 42What name is given to this type catalysis by aqueous transition metal ions?homogeneous
- 43Explain why copper is a transition metalIt forms an ion with an incompletely filled d orbital.
- 44Describe a method for protecting copper from corrosionPaint, grease, galvanising,
Prevents copper reacting/ reacting with oxygen and water
Sacrificial protection: Coat with blocks Mg or Zn. Galvanise.
The more reactive Mg or Zn corrodes instead of Cu - 45In a titration of sodium thiosulfate and iodine. The student went past the end point and added too much sodium sulcate. What effect would this have on their answer for the concentration of iodine. (2)The concentration of iodine will be too low
because it would appear as if there is more unreacted iodine - 46Describe one difference between heating under reflux and distillation (2)in heating under reflux the condenser is vertical.
mixture is evaporated and condensed/liquefied and returned to mixture no reactants is lost from the mixture in distillation
the condenser is horizontal mixture is evaporated and condensed and collected. The mixture is separated - 47Explain in terms of structure and intermolecular bonding why a molecule that can react with both alkali and acid has such a high melting point (3)it forms a zwitterion OR an ion which has both a negative charge and a positive charge
zwitterions attract each other very strongly zwitterions form a giant lattice
ionic bonding is (very strong)
high energy required to separate particles - 48Describe the properties of a polymer at temperatures above its Tm Describe and explain the properties of a polymer at temperatures below its Tg Suggest why the blended polymer has a higher Tm.above Tm: polymer becomes liquid
below Tg: polymer becomes brittle
because chains cannot move over each other so break when a force is applied (blended polymer is more crystalline) so intermolecular bonds are stronger
AND more energy is needed to separate chains. - 49Suggest a way of removing Fe2O3 from the mixture formed after the reaction with sulphuric acidFiltration
- 50explain the meaning f electronegativityability of atom to attract electrons
in a (covalent) bond - 51What makes an reaction an acid-base reactionexchange of protons
OR a proton is lost AND gained - 52What makes NH2CH2CH2NH2 a bidentate ligandit can donate both lone pairs
to form dative covalent/coordinate bonds with metal cation - 53Give the chemical reagent and conditions needed to break down a protein into amino acids in a labModerately concentrated HCl
Heat under reflux - 54Explain why a protein with a tertiary structure is affected by lowering the pH Give the groups that would be affected by lowering the pH (3)changing pH affects the ionic charges on side groups
so by lowering pH –COO- carboxylate can be protonated to form –COOH
lowering pH NH2 protonated to NH3+ - 55Explain why the curve on the graph (gradually increases then decreases) for rate of reaction using enzymes rises then falls sharply (4)1. as the temperature rises particles have more energy
2. more collisions have energy greater than the activation enthalpy/energy
3. graph falls because at high temperatures intermolecular bonds break
4. loss of active site as the shape changes, unable to form enzymes-substrate complexes. - 56Describe how thin-layer chromatography can be used to show that chemicals are present in cinnamon oil (5)1. draw pencil-line near bottom of plate and place 1 drop of mixture and a drop of each of the 3 compounds on the line.
2. place plate in solvent, line above solvent level AND add lid
3. when solvent nears top of plate, remove and dry plate
4. locate spots with UV light or iodine
5. compare position of spots from mixture with the 3 standard compounds
6. calculate Rf values of spots and compare with those of the standards - 57Describe what happens to vapour when it is heated under reflux and give one reason why reflux was used in this reaction1. Vapours are condensed
2. Mixture needed to be heated for a long time for reaction to occur.
No reactants or products are lost - 58Explain why a substance produces a spectrum showing absorption peaks when interacts with IR radiation (2)Bonds in a molecule absorb specific frequencies of IR, this causes different bonds to vibrate,
- 59Describe what would happen to a bottle made from PET if it was heated to 300degrees in the absence of airWould melt into a liquid
- 60Explain the term zwitter ionContains both a positive and negative charge
- 61A chemist wanted to make phenyl methyl ethanoate. Suggest three compounds that could be used to react with the alcohol to produce the ester.Ethanoic acid
Ethanoyl chloride
Ethanoic anhydride - 62What is combinatorial chemistrythe name given to the method for synthesising a larger number of analogues in a short time.
It is a technique used by pharmaceutical companies to make many related compounds in order to test them for pharmacological activity so that their potential as medicines can be assessed - 63What are the 4 different types of reactionrearrangement
Addition
substitution
elimination - 64What is a transition metal metal defined as?A d-block element that forms at lease one ion with a partially filled sub-shell of d electrons
- 65Why do scandium and zinc not display the chemical properties associated with transition metals?Their ions Sc3+ and Zn 2+ have electron arrangements 3d0 and 3d10
- 66Why do transition metals have variable oxidation states?The differences between successive ionisation enthalpies in the 3d and 4S sub-shells are small.
Multiple electron loss is possible - 67Suggest why certain properties are common to transition metals, but different from the properties of s-block metalsThe properties of elements are governed by the arrangement of electrons in the outermost incomplete shells. In the first row of the d block, the inner 3d
orbital is being filled and most elements have two electrons in the outer 4s shell, so they have essentially the same outer
electronic arrangement as each other, .
Metals in different groups in the periodic table have different numbers of outer electrons and hence different properties. - 68Explain why titanium (IV) oxide is not colouredTiO2(s) contains titanium with a 3d0 electron
configuration. It is white as no 3d electron transitions
are possible. - 69What is EDTA4- and what makes it a useful ion?A hexadentate ligand has 6 lone pairs of electrons - all of which can form dative covalent bonds with the same metal ion.
A complex of a metal ion with edta contains six 5-membered chelate ring systems
EDTA is used as a negative ion EDTA4-The co-ordination number is 6 because of the 6 co-ordinate bonds being formed by the central metal ion. - 70Describe how paper chromatography can be used to identify amino acids1. Peptide is hydrolysed under reflux
2. Product is compared to known samples of pure amino acids using chromatography - 71Complexes formed by EDTA involve pairs of electrons on nitrogen and oxygen atoms, in the same way as complexes formed by NH3 and H2O. Explain why stability constants of EDTA complexes in solution are generally much larger than those of corresponding complexes with NH3 and H2OA complex of a metal ion with edta contains six 5-membered chelate ring systems. The complex is much more stable than the corresponding complexes with NH3 or H2O which contain no chelate rings. The extra stability is due to the large increase in entropy when edta4– displaces six ligands.
- 72What is meant by the standard electrode potential of a half cell?The voltage measured under standard conditions when the half-cell is connected to a standard hydrogen electrode
- 73How do you work out the whole cell potential using a standard electrode potential?1. Hydrogen electrode potential always shown on the left.
2. The whole cell potential is right-left
3. Left is the hydrogen cell so will be 0V - so will be a number - 0
4. The reading can be negative or positive depending on which way electrons flow - 74When is a reaction feasible?If the standard electrode potential for what is being reduced is greater than the electrode potential for what is being oxidised
- 75Why might a reaction not happen even if it is 'feasible'The electrode potential doesn't tell you about the rate
The rate can be so slow that effectively the reaction doesn't happen.
Doesn't mean it will definitely happen. - 76Why does copper prefer to have a full 3d subshell with only one electron n the 4s shell?More stable
- 77Why is Sc not a transition metal?only forms one ion Sc3+
This has no electrons in its 3d sub-shell - 78Why is zinc not a transition metal?Only forms one ion, Nn2+ which has a full d sub-shell
- 79Why is there not much difference in energy between making the Fe2+ and Fe3+ ions?The 4s orbital and the 3d orbital are all at similar energy levels.
To make Fe2+ two 4s electrons are removed
To make Fe3+ two 4s and one 3d electron are removed.. - 80Why are transition metals good catalysts?They can change oxidation states by gaining or losing electrons within their d orbitals.
They can transfer electrons by taking electrons to speed up reactions - 81Why is the co-ordination number for some complexes 4 and 6 for others?If the ligands are small like H2O or NH3 6 can fit around the central metal ion
If the ligands are larger like Cl- only 4 can fit around - 82In a ligand substitution reaction, what can cause the complex to change shape?If the ligands that are substituted are different sizes e.g H2O and Cl-
- 83Transition metals in (aq) form complex ions e.g. [Fe(H2O)6]2+ Hydroxide ions remove H+ ions from water ligands. What happens when enough H+ ions have been removed?The complex ion becomes neutral and forms a precipitate
- 84What colour is the: Fe(OH)2 solid?GREEN
- 85What colour is the: Fe(OH)3 solid?ORANGE
- 86What colour is the: Cu(OH)2 solid?PALE BLUE SOLID
- 87What happens when you add a small amount of ammonia solution to [Cu(H2O)6]2+?Causes the same reaction as a OH- ion, so acts as a base, accepts protons to make it neutral then forms a pale blue solid
- 88What happens when you add excess ammonia solution to the Cu(OH)2?The precipitate dissolves and forms a dark blue/violet solution. This is because NH3 can now act as ligands forming
[Cu(NH3)4(H2O)2]2+ - 89Why are transition metals good heterogeneous catalysts?Weak interactions between thee 3d and 4s electrons of the transition metal keep the molecules in place while bonds are broken and formed
- 90What does the colour that a transition metal depend on?1. Oxidation state of the transition ion
2. The type of ligand
3. The co-ordination number/shape of the complex - 91Why use a filter on a colorimeter?Converts white light into monochromic light of only one frequency
- 92Ways to measure the rate of reaction:pH measurement
Gas volume
Loss of mass
Colour change
Quenching a titration - 93How can you use a graph to calculate the rate at one point of the in the reaction?The gradient
Or tangent if the graph is a curve is proportional to the rate - 94What does the order of reaction with respect to a particular reactant tell you?How the reactants concentration affects the rate
- 95What does the K in the rate equation tell you?The bigger it is the faster the reaction
- 96What does the order of reaction with respect to reactant show?The number of molecules of that reactant which are involved in the rate-determining step
- 97What forces can hold the tertiary structure together1. Id-id
2. ionic interactions
3. hydrogen bonding
4. Disulfide bridges - strongest, covalent bond between two sulphur-containing side groups. - 98What is a nucleotide made up of?1. A phosphate group
2. A pentose sugar
3. a base - 99What group on the base bonds to the sugar phosphate backboneN from the NH group.
- 100Arguments for storing genetic infoFOR: the information is useful to the police and has helped solve many crimes
AGAINST: concerns about who has access to the information - 101How is mRNA involved in protein synthesis1. DNA helix unwinds to expose a single strand
2. The DNA bases attract free RNA nucleotides with complementary bases
3. The RNA nucleotides are joined to each other by RNA polymerase, forms a strand of RNA
4. The DNA coils up again - 102Describe the process of translation1. Ribosome attaches to mRNA, finds start condon
2. tRNA with complementary anticodon bases pairs with the codon inside the ribosome. tRNA has an amino acid attached to it.
3. The ribosome then moves forward., and waits for the next for a new tRNA to bring another amino acid. The ribosome joins them together by a peptide bond.
4. The ribosome moves forward again, the first tRNA leaves. A new tRNA brings in the third amino acid of the chain.
5. process continues till a stop codon is reached.. The ribosome then releases the polypeptide chain - 103What determines whether a bond has a permanent dipoleits shape and polarity of tis bonds
- 104How can you neutralise an amine?By reacting it with an acid to make an ammonium salt
- 105How do you hydrolyse an amide?Mod conc sulphuric acid
- 106What do you need for making an ester?Conc sulphuric acid
- 107In recrystallisation, why so impurities stay in solution after dissolving?They're present in smaller amounts than the product so take longer to crystallise out
- 108What would happen if the solute is too soluble at room temp?Most of the solute will stay in solution, after cooling. So when you filter it, you'll los some of the solute
- 109Ways to make polymer production more green:- Use reactants a that are safe and environmentally friendly
-Renewable raw materials
- Energy use to a minimum
- Generate no waste products - 110What do thermoplastics have?no covalent bonds or cross-links between chains
Only intermolecular forces hold chains together - 111What is meant by an amorphous polymer?arrangement of chains is random, all run in different directions
- 112What affect does adding a plasticiser have?Makes polymer more bendy.
The molecules get between the chains and push them apart.
Reduces the strength of the intermolecular forces between the chains, so they slide about more.
Added to plastics with high Tg's to make them more flexible - 113How does cold drawing increase the crystallinity of a polymer?The chains of an amorphous polymer are randomly tangled, don't lie close to each other and intermolecular bonds are weak.
By pulling or drawing the polymer chains out in straight lines, they are forced to straighten out and lie close to each other.
The intermolecular forces increase between chains so polymer gets stronger - 114When are ions formed?When electrons are transferred from one atom to another
- 115Why use an acyl chloride to make an ester from a phenol?Phenols react very slowly with carboxylic acids
- 116How and why heat under reflux?1. Organic reactions are slow, substances flammable and volatile.
2. Mixture heated in a flask, fitted with vertical liebig condenser - condenses the vapours and recycles them back into the flask so that they can react. - 117Why does hydrogen cyanide partially dissociate in water?weak acid
- 118What is the stationary phase in TLCthin layer of silica or alumina fixed to a glass or metal plate
- 119How would you work out the Rf valueDistance travelled by spot/distance travelled by spot
- 120How can Rf values change?If the composition of the TLC plate, the solvent, or the temperature changes
- 121Why are fragmentation patterns useful?Use them to identify molecules and their structure
- 122Why are high-resolution mass spec usefulAllow you to compare elements and compounds relative isotopic masses.
Carbon 12 relative isotopic mass is 12, everything else is relative to this.
Only carbon 12 has a relative isotopic mass that is a whole number.
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- a level chemistry Karteikarten am F334 Past paper questions, erstellt von Clelia Serra am 26/05/2015.
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