2788642
| Questão | Responda |
| describe what happens to the vapour when a mixture is heated under reflux | vapours are condensed |
| reasons why to reflux | mixture needed to be heated for a long time no reactants or products are lost high temperature required for reaction |
| describe and explain the process of recrystallisation using a suitable solvent. Include an explanation for the choice of solvent used and how impurities are removed | dissolves 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 |
| explain why a substance produces a spectrum showing absorption peaks when irradiated with infrared frequencies | bonds in molecule absorb specific IR frequencies absorbing different frequencies causes different bonds to vibrate |
| give the meaning of the term Tg | temperature below which polymer turns brittle |
| the less crystalline the polymer the more flexible - explain why | chains are further apart so weaker intermolecular forces of attraction so chains can slide over each other easily |
| when 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 |
| as a reaction progresses, ions are formed which acts as a catalyst. explain the changes in the reaction rate as the reaction progresses | increases rate speeds us as ion catalyst formed then decreases rate slows down as reactants used up |
| suggest a method that can be used to measure the concentration of a substance other than by titration | colorimetry visible spectroscopy |
| explain the term zwitterion | a species with both a positive and negative charge |
| drug x has many adverse side effects. suggest why it is still used to treat a disease | less side effects than other drugs more effective than other drugs |
| explain why with 1,2-diaminocyclohexane, you may have two different isomers | C-C bond between the chiral atoms prevented from rotating by the ring structure |
| describe the three levels of protein structure | primary - order of amino acids secondary - folding of chains into alpha helices or beta pleated sheets tertiary - overall 3D shape |
| what 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? |
| explain why, in a reversible reaction in which a solid is formed, the reaction almost goes to completion | solid formed so no homogeneous system precipitates out which shifts equilibrium to the right |
| what feature of d-block metal ions enables some to be coloured in solution? | partially filled d sub shell |
| name a suitable acid to acidify a sample for titration purposes | (dilute) sulphuric acid |
| suggest one advantage natural fibres have over polymers in terms of the method of disposal | biodegradable |
| explain why hydrogen bonding is strong when there are benzene rings in the chain | benzene rings have flat molecules so allows chains to get close together so H-bonds act over shorter distances so are stronger |
| explain why transition metals can act as catalysts | form ions in different oxidation states oxidation states can interconvert during the reaction so remain unchanged at end activation energy lowered |
| suggest four possible ways of monitoring the rate of a reaction | colorimetry 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 |
| when 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 |
| explain why the polymerisation of compound D proceeds without the loss or gain of water molecules | water formed in condensation when repeating units join together replaces water used in hydrolysis of compound D so no net gain or loss of water |
| suggest why the purified crystalline solid is used rather than amphetamine itslef | tablets easier for controlling dosage soluble so quicker acting may not have amphetamine's side effects |
| explain why enzyme reactions speed up as the temperature is increased but stop altogether if the temperature is too high | at 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 |
| write an ionic equation, including state symbols for the precipitation reaction that forms a pale blue precipitate | Cu2+(aq) + 2OH-(aq) --> Cu(OH)2(s) |
| what happens if excess ammonia is shaken with Cu(OH)2 | precipitate dissolves dark blue solution |
| in 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 polymer | cis 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 |
| name a chemical method which chemists can use to produce a polymer with slightly different properties | copolymerisation plasticisers |
| explain how zwitterions are formed | compound 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 |
| in living cells only one isomer can act as a substrate for enzymes, explain why | active site in enzyme has specific shape only one isomer has correct shape to fit |
| explain why it is important for the pH to be controlled in an enzyme-catalysed reaction | Change 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 |
| suggest and explain why you would expect he voltage of a cell to be different from a calculated value | experiment may not have been done under standard conditions - 1atm, 1moldm-3, 298K E cell different under different conditions |
| describe one property that steel has as a result of containing chromium and nickel | resistant to corrosion stainless hard lustrous high strength |
| other than recycling materials, what important role does adding scrap steel serve | coolant reduces thermal shock |
| in the production of steel what elements are removed by direct oxidation with gaseous oxygen? | carbon phosphorous manganese silicon |
| describe how ninhydrin should be used as a locating agent | spray with ninhydrin and heat |
| what happens to molecules when they absorb infrared radiation | more vigorous bond vibrations molecules move to higher vibrational level |
| coating steel with zinc prevents rusting in a different way than coating with an organic polymer, explain the differenc | organic polymer prevents air and water reaching metal - barrier zinc more reactive than steel so loses electrons and is oxidised so zinc = sacrificial method |
| describe some factors that would be investigated in human clinical trials | effective does toxicity side reactions how long drug lasts in body formulation |
| explain how condensation polymerisation is different from addition polymerisation | condensation small molecule eliminated addition - nothing eliminated in addition and double bond is opened up |
| describe and explain how the properties of polymers change at low and high temperatures | at 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 |
| what is meant by the term heating under reflux? | heating with a vertical condenser vapour condensed and returned to flask no loss of volatiles |
| explain why a compound may have a geometric isomer | restricted rotation around C=C bond so groups can be on same or opposite sides |
| what are two methods of measuring H+ concentration | titrate with (standard) alkali or use a pH meter |
| how could you use a graph to show how the rate of reaction varies during the course of the reaction | measure gradient at different time intervals |
| explain why an enzyme is specific for the reaction it carries out | enzymes form active site in their structure which has a specific shape in which the substrate can fit |
| give the reagent used to convert sodium salts into the corresponding acids | excess hydrochloric acid |
| what interactions can hold the tertiary structure of a protein together? | ID-ID ionic bonds disulphide bridges hydrogen bonding |
| why is chromium classed as a transition metal? | chromium can form a stable ion with a partially filled d sub shell allowing variable oxidation states |
| what 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 |
| suggest a method for the disposal of plastic waste and explain the advantage of this method | burning energy released can be used and saves landfill space recycling oil resources saved |
| what are some differences between DNA and RNA molecules? | different bases RNA has single chain different sugar |
| outline how DNA is able to replicate genetic information | hydrogen bonds between DNA strands break DNA unwinds each strand acts as a template for a new strand |
| explain how organic nitrogen-containing compounds act as bases | lone pair of electrons on nitrogen can accept a proton |
| why is it important to add scrap steel? | acts as a coolant as oxygen blow is very exothermic |
| in a blast furnace apart from oxides and oxygen, what else is lost? what's put in? | magnesium sulphide magnesium, scrap steel and oxygen |
| a molecule with an asymmetric carbon atom exists as two enantiomers. explain why these are different compounds | the mirror images are non-superimposable |
| explain how molecular formula can be determined from an accurate mass:charge ratio for the M+ peak in its mass spectrum | masses are measured relative to C-12 compare Mr with database |
| give three questions that clinical trials are designed to answer | is the drug safe? does it do what it was designed to do? is it better than the standard treatment being used? |
| why are carboxylic acids soluble in alkaline solution? | carboxylic acid reacts with alkali to form ions in solution |
| how 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 |
| explain why enzyme activity is less when the temperature is higher than the optimum | at high temperatures hydrogen bonds break active site changes shape substrate can no longer fit |
| explain why enzyme activity is less when the pH is changed slightly from its optimum value | causes ionisable groups to be altered prevents ionic interactions between enzyme and substrate |
| explain why at low concentrations of P the reaction is first order with respect to P | the 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 |
| explain 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 |
| give five ways in which enzymes may increase the efficiency of an industrial process | speeds up reaction rate reduces amount of energy/heat required can be reused/recycled improves the atom economy easier separation methods |
| explain the disadvantage associated with the formation of HCl in a condensation reaction | HCl is toxic HCl needs to be disposed of |
| explain why dilute hydrochloric acid will react with zinc | Oxidising 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 |
| suggest and explain why a student didn't form an aldehyde but a carboxylic acid instead when and primary alcohol was oxidised | heated 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 |
| describe and explain how an alteration in the sequence of bases can result in enzymes becoming less effective for a particular reaction | enzymes 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 |
| explain why phenols are able to dissolve in water if a little aqueous alkali is added to the mixture of phenol and water | phenol forms ion ions form bonds with water molecules ions more soluble in water |
| explain how transition metal ions such as Cu2+ are able to increase the rate of a redox reaction | transition 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+ |
| describe and explain two methods of protecting copper from corrosion | barrier 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 |
| when 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 |
| explain 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 |
| describe and explain one difference between heating under reflux and distillation | Heating 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 |
| explain in terms of structure and bonding why amino acids have a high melting point | it 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 |
| BrO3- ions can react with Br- in acidic solution to form bromine. Explain why colorimetry can be used to follow this reaction | BrO3¯ and Br¯ are colourless but Br2 is brown change in colour in the reaction change in absorbance in a colorimeter in the reaction |
| explain how the orders of reaction support the chemists' suggested rate-determining step | slow step of the reaction / rds depends upon the species given in the rate equation |
| explain, in terms of fixed frequencies of light, why some transition metal ions in solution are coloured | ions absorb specific frequencies of visible light transmits complementary colour |
| give the meaning of the term crystallinity | chains are highly ordered how polymer chains are packed together in an orderly regular way |
| suggest one reason why PLA - a polymer made from corn starch is 'greener' than poly(ethene) | manufactured from a renewable resource |
| suggest a method for removing Fe2O3 from a mixture | filtration |
| give the meaning of the term electronegativity | ability of atom to attract eletrons in a covalent bond |
| explain the term tertiary structure | the three dimensional structure of the protein folding of the secondary structure |
| what does the colour that a transition metal absorbs depend on? | oxidation state of the ion the type of ligand coordination number/shape of complex |
| explain why a protein with a tertiary structure is affected by pH change | changing pH affects the ionic attractions and charges on polarisable side groups lowering pH NH2 -> NH3+ (gets protonated) lowering pH -COO- -> COOH (gets protonated) |
| why was a black card placed behind the test tubes? | help judge the disappearance of the suspension |
| describe how you would use a rate of reaction vs temperature graph to find the relative rates of reaction at two different temperatures | read off rate on y-axis for a particular temperature on x-axis |
| when the substrate concentration is high state the order of reaction with respect to the substrate. explain your answer | zero order all the active sites are full max number of E-S complexes formed |
| what properties should a solvent have to achieve efficient recrystallization? | solvent should dissolve solute at higher temperatures solute is insoluble at room/lower temperature |
| explain why phenols react with aqueous sodium hydroxide and suggest why the products are soluble in water | phenol groups phenols are acidic neutralised by NaOH ions form ions / salts are soluble |
| why 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 |
| explain how cross-links are formed | C=C bonds on side chains (in different polymer chains) break/open up and form a (covalent) bond/link |
| cross-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 properties | crosslinks 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) |
| describe how the student used a colorimeter to find out how the concentration of the blue dye changed when added to the polymer | Select 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 |
| suggest why scientists once thought that proteins were more likely to transmit genetic data | proteins have more amino acids than the bases/nucleotides in DNA from which to construct many unique structures and to carry genetic data |
| stronger oxidising agents.... | have a more positive SEL have a greater tendency to attract electrons are reduced |
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