F334 Past paper questions

Clelia Serra
Flashcards by Clelia Serra, updated more than 1 year ago More Less
Clelia Serra
Created by Clelia Serra over 4 years ago
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a level chemistry Flashcards on F334 Past paper questions, created by Clelia Serra on 05/26/2015.

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Question Answer
Explain what is meant by crystaline Polymer chains are highly ordered
PPA 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.
Suggest 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
What is meant by the secondary and tertiary structure of an enzyme (2) Secondary: folding of polypeptide chains Tertiary: 3D shape/globular structure
Name the type of polymerisation reaction is needed to form nylon-6 (1) condensation and water is lost
Name a process by which nylon-6 can be made more crysalline cold-drawing
Give 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
Suggest 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.
What properties should a solvent have to achieve efficient recrystallisation (2) Solvent should dissolve solute at high temperatures. Solute is insoluble at room temperature
Explain 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
The 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
Explain the meaning of enantiomers (2) Isomers that structures are mirror images which are non-superimposable
Explain how cross links in polymers are formed C=C bonds on side chains break open and form covalent bonds
Name a suitable reagent for converting a carboxylic acid into a carboxylate ion Sodium hydroxide
A 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.
The voltage of a battery measured with a high resistance voltmeter is less than the value of the batteries Ecell value. Suggest why The measured voltage or the electrode potentials are not recorded in standard conditions Concentration of ions is not 1moldm-3
Suggest 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
What happens why sodium carbonate is added to a carboxylic acid fizzes,
Why is it important that reactions have a high atom economy (2) Reduce waste products Costs kept to a minimum/ less energy used
What are the conditions for an electrochemical cell 25 degrees 1moldm-3 solution
State the colour of Cu2+ ions in water and explain why the solution has this colour. (2) Transmit blue, because absorbs orange light
What is the colour of the [Fe(H2O)6]3+ ion in water? Yellow
When 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-
Describe how colorimetry is used to determine the concentration of Cu2+ ions in an aqueous sample 1. 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
Many 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 viewpoints For removal: fingerprint not unique, only a probability Techniques not foolproof Against removal: Helps to solve crimes Innocent till proved guilty Future research into disease
Describe 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.
Materials 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
High-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 spectrum The 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
Recrystallisation 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 /
Give 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?
Explain 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
Explain 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
At 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]
Rate = K [P] [enzyme] Explain why at low concentrations of P, the reaction is first order with respect to P When [P] is low, not all enzyme active sites are filled. Rate increases in proportion, so in first order
Rate = 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
Give two ways that enzymes may increase the efficiency of an industrial process Speed 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/
One 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
Give one way a polymer could be made more flexible (1) Plasticiser
Solutions 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
Why 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
Explain 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
What name is given to this type catalysis by aqueous transition metal ions? homogeneous
Explain why copper is a transition metal It forms an ion with an incompletely filled d orbital.
Describe a method for protecting copper from corrosion Paint, 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
In 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
Describe 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
Explain 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
Describe 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.
Suggest a way of removing Fe2O3 from the mixture formed after the reaction with sulphuric acid Filtration
explain the meaning f electronegativity ability of atom to attract electrons  in a (covalent) bond
What makes an reaction an acid-base reaction exchange of protons OR a proton is lost AND gained
What makes NH2CH2CH2NH2 a bidentate ligand it can donate both lone pairs to form dative covalent/coordinate bonds with metal cation
Give the chemical reagent and conditions needed to break down a protein into amino acids in a lab Moderately concentrated HCl Heat under reflux
Explain 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+
Explain 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.
Describe 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
Describe what happens to vapour when it is heated under reflux and give one reason why reflux was used in this reaction 1. Vapours are condensed 2. Mixture needed to be heated for a long time for reaction to occur. No reactants or products are lost
Explain 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,
Describe what would happen to a bottle made from PET if it was heated to 300degrees in the absence of air Would melt into a liquid
Explain the term zwitter ion Contains both a positive and negative charge
A 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
What is combinatorial chemistry the 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
What are the 4 different types of reaction rearrangement Addition substitution elimination
What 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
Why 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
Why 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
Suggest why certain properties are common to transition metals, but different from the properties of s-block metals The 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.
Explain why titanium (IV) oxide is not coloured TiO2(s) contains titanium with a 3d0 electron configuration. It is white as no 3d electron transitions are possible.
What 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.
Describe how paper chromatography can be used to identify amino acids 1. Peptide is hydrolysed under reflux 2. Product is compared to known samples of pure amino acids using chromatography
Complexes 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 H2O A 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.
What 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
How 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
When 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
Why 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.
Why does copper prefer to have a full 3d subshell with only one electron n the 4s shell? More stable
Why is Sc not a transition metal? only forms one ion Sc3+ This has no electrons in its 3d sub-shell
Why is zinc not a transition metal? Only forms one ion, Nn2+ which has a full d sub-shell
Why 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..
Why 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
Why 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
In 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-
Transition 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
What colour is the: Fe(OH)2 solid? GREEN
What colour is the: Fe(OH)3 solid? ORANGE
What colour is the: Cu(OH)2 solid? PALE BLUE SOLID
What 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
What 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+
Why 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
What 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
Why use a filter on a colorimeter? Converts white light into monochromic light of only one frequency
Ways to measure the rate of reaction: pH measurement Gas volume Loss of mass Colour change Quenching a titration
How 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
What does the order of reaction with respect to a particular reactant tell you? How the reactants concentration affects the rate
What does the K in the rate equation tell you? The bigger it is the faster the reaction
What 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
What forces can hold the tertiary structure together 1. Id-id 2. ionic interactions 3. hydrogen bonding 4. Disulfide bridges - strongest, covalent bond between two sulphur-containing side groups.
What is a nucleotide made up of? 1. A phosphate group 2. A pentose sugar 3. a base
What group on the base bonds to the sugar phosphate backbone N from the NH group.
Arguments for storing genetic info FOR: the information is useful to the police and has helped solve many crimes AGAINST: concerns about who has access to the information
How is mRNA involved in protein synthesis 1. 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
Describe the process of translation 1. 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
What determines whether a bond has a permanent dipole its shape and polarity of tis bonds
How can you neutralise an amine? By reacting it with an acid to make an ammonium salt
How do you hydrolyse an amide? Mod conc sulphuric acid
What do you need for making an ester? Conc sulphuric acid
In recrystallisation, why so impurities stay in solution after dissolving? They're present in smaller amounts than the product so take longer to crystallise out
What 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
Ways 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
What do thermoplastics have? no covalent bonds or cross-links between chains Only intermolecular forces hold chains together
What is meant by an amorphous polymer? arrangement of chains is random, all run in different directions
What 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
How 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
When are ions formed? When electrons are transferred from one atom to another
Why use an acyl chloride to make an ester from a phenol? Phenols react very slowly with carboxylic acids
How 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.
Why does hydrogen cyanide partially dissociate in water? weak acid
What is the stationary phase in TLC thin layer of silica or alumina fixed to a glass or metal plate
How would you work out the Rf value Distance travelled by spot/distance travelled by spot
How can Rf values change? If the composition of the TLC plate, the solvent, or the temperature changes
Why are fragmentation patterns useful? Use them to identify molecules and their structure
Why are high-resolution mass spec useful Allow 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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