ISA P revision AS

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ghoran
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296593
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ISA P revision AS
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2015-03-01 03:39:54
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isa tuesday 3rd march 2015
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revision
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  1. 1m3 =
    1X103dm3 = 1x106dm3
  2. calculate the % by mass of strontium chloride hexahydrate in the sample when given you've already calculated mr and moles of strontium chloride hexahdrate (sch) and you're given mass of sample
    • mass of sample / mr x moles (sch)
    • times 100
  3. explain why the solution of strontium chloride was filtered to remove soluble impurities before the addition of silver nitrate
    insoluble impurities would be added to mass of precipitate which would make the mass incorrect
  4. explain why the precipitate of silver chloride was washed several times with dionised water
    to remove soluble impurities
  5. if we are weighing a liquid we worry about
    soluble impurities
  6. if we are weighing a solid we worry about
    insoluble impurities
  7. we filter a liquid to
    remove insoluble impurities
  8. we wash a solid to remove
    soluble impurities
  9. other than cost explain one other advantage of using magnesium hydroxide rather than magnesium carbonate to reduce acidity in the stomach
    magnesium hydroxide produces less gas in the stomach so less wind
  10. calcium ethanoate (CH3COO)2Ca is used in the treatment of kidney disease . thermal decomposition of calcium ethanoate under certain conditions gives propanone and one other product . write an equation for the thermal decomposition of calcium ethanoate
    (CH3COO)2Ca --> CH3COCH3 + CaCO3
  11. salts containing the chromate (6) ion are usually yellow in color . 
    calcium chromate (6) is soluble in water 
    strontium chromate (6) is insoluble in water , but will dissolve in a solution of ethanoic acid 
    barium chromate (6) is insoluble in water and also insoluble in a solution of ethanoic acid 
    decsribe a series of tests using solutions of
    • first add sodium chromate 
    • calcium salt - no visible change as its soluble in water so yellow solution remains 
    • barium salt and strontium salt - both give ppt as they are insoluble 
    • add ethanoic acid to strontium chromate and calcium chromate 
    • strontium chromate dissolves (solution) whereas calcium chromate doesn't (ppt)
  12. insoluble always gives a
    ppt
  13. reactivity series
  14. explain why the use of a wet crucible would give an inaccurate result
    water would be lost when heating so mass incorrect
  15. give one reason why the use of a lid improves the accuracy of the experiment
    prevents loss of solid from the crucible
  16. state one reason why the use of a very small amount of potassium hydrogencarbonate could lead to a less accurate result
    errors in weighing are too high
  17. in this experiment the mass of solid remaining in the crucible was greater than expected , suggest one reason for this result
    incomplete decomposition
  18. acid + carbonate -->
    salt + carbon dioixde + water
  19. the equation for the reaction of potassium carbonate (7) with glucose is shown below 
    3KClO4 (s) + C6H12O6(s) --> 6H2O (g) + 6CO2 (g) + 3KI (s) 
    the reaction is very exothermic . suggest one reason why a mixture of potassium chlorate (7) and glucose is used as a propellant for a rocket
    large volumes of gas
  20. potassium chlorate (7) is a powerful oxidizing agent . suggest one precaution other than the use of safety equipment that you should use to minimize this hazard when using potassium chlorate (7)
    keep away from flammeable materials
  21. a solution of barium hydroxide is often used for the titration of organic acids . a suitable indicator for the titration is thymol blue . thymol blue is yellow in acid and blue in alkali . in the titration a solution of an organic acid added from a burette to a conical flask containing barium hydroxide and a few drops of thymol blue .
    describe in full the colour change at the end point of this titration
    blue to green
  22. a solution of barium hydroxide is often used for the titration of organic acids . a suitable indicator for the titration is thymol blue . thymol blue is yellow in acid and blue in alkali . in the titration a solution of an organic acid added from a burette to a conical flask containing barium hydroxide and a few drops of thymol blue .
    thymol blue is an acid . state how the average titre would change if a few cm3 rather than a few drops of the indicator were used by mistake in this titration
    decrease less acid would be needed
  23. a solution of barium hydroxide is often used for the titration of organic acids . a suitable indicator for the titration is thymol blue . thymol blue is yellow in acid and blue in alkali . in the titration a solution of an organic acid added from a burette to a conical flask containing barium hydroxide and a few drops of thymol blue 
    barium hydroxide is toxic suggest one safety precaution you would take to minimise this hazard when wiping up a spillage of barium hydroxide solution
    avoid skin contact
  24. suggest one reason why a 250cm3 conical flask is preferred to a 250cm3 beaker for a titration
    less chance of losing solution when stirring mixture
  25. suggest one reason why repeating  titration can improve its accuracy
    first titration is a rough titration
  26. solubility of calcium hydroxide 1.73 gdm-3 suggest one reason why calcium hydroxide isn't used in the titration of a 0.200moldm-3 solution of an acid
    dilution of acid needed
  27. in an experiment to determine the solubility of water , solid barium hydroxide was added to 100cm3 of water until there was an excess of the solid , the mixture was filtered and an excess of sulphuric acid was added to the filtrate , the barium sulphate produced was obtained from the reaction mixture , washed with cold water and dried . the mass of barium sulphate was then recorded .
    explain why the mixture was filtered before the addition of sulphuric acid
    to remove excess solid
  28. in an experiment to determine the solubility of water , solid barium hydroxide was added to 100cm3 of water until there was an excess of the solid , the mixture was filtered and an excess of sulphuric acid was added to the filtrate , the barium sulphate produced was obtained from the reaction mixture , washed with cold water and dried . the mass of barium sulphate was then recorded . why was the barium sulphate washed before it was dried
    to remove excess acid
  29. in an experiment to determine the solubility of water , solid barium hydroxide was added to 100cm3 of water until there was an excess of the solid , the mixture was filtered and an excess of sulphuric acid was added to the filtrate , the barium sulphate produced was obtained from the reaction mixture , washed with cold water and dried . the mass of barium sulphate was then recorded .
    state how the barium sulphate produced was obtained from the reaction mixture
    filtration
  30. why do you fill the burette to the bottom before titrating
    • space will fill during titration 
    • volumes too high
  31. why do u wash the sides of the flask with distilled water
    returns reagents to the sides of the flask to the reaction mixture (to ensure that all of the acid/alkali reacts)
  32. why does washing not impact the result
    doesn't change the number of moles of reagents
  33. why do we swirl the mixture
    ensures uniform conc in solution
  34. why don't we leave a funnel in the top when we are titrating
    makes titre lower
  35. co2 in air reacting with alkali can cause what problem
    increase titre
  36. things that dissolve create
    colourless solutions
  37. things that are insoluble or sparingly soluble create
    white ppt when put into water
  38. when filtering the residue its the solid that left in the
    filter paper . this is washed with water to remove any soluble impurities
  39. when filtering the filtrate is the
    solution thats left this contains the soluble solids
  40. the only ppt's that aren't white are
    • AgBr (cream) 
    • and AgI (yellow)
  41. magnesium hydroxide is sparingly
    soluble
  42. this makes it a good
    antacid
  43. because it is
    weakly alkaline and doesn't react strongly with stomach acid , in addition it doesn't produce CO2 gas hen it neutralises the acid
  44. the fact that magnesium hydroxide is sparingly soluble means we need to ...... and then do a titration
    react it with excess acid
  45. if we titrated it directly with an acid it would give
    an inaccurate results
  46. barium hydroxide would be a poor antacid because
    barium compounds are toxic and its a strong alkali that reacts strongly with acid .
  47. barium sulphate is
    insoluble and so it is safe to use in barium meals as it doesn't get into the blood stream
  48. a sealed aluminium tank exploded while being used by mistake for transporting conc sodium hydroxide suggest a reason why the tank exploded
    pressure build up due to the production of hydrogen gas
  49. a strong alkali such as potassium hydroxide is used as the electrolyte in some alkaline batteries for household use . the electrolyte will escape if the battery casing is broken suggest one reason why a leak of the electrolyte is hazardous
    alkali is corrosive
  50. ammonia is an alkaline gas describe how you would use a named indicator to show that ammonia gas is released from the flask in this reaction . state the colour change you observe
    • collect gas and place litmus paper in the collected gas
    • litmus paper turns from red to blue
  51. state an observation that implies magnesium ions are present 
    state an observation that implies barium ions weren't present explain your answer 
    • white ppt 
    • no change when con sulphuric acid added
    • barium sulphate is insoluble
  52. description of how ti make up a standard solution --> take a clean 250cm3 volumetric flask . use the balance provided and a clean dry container to weigh out the amount of solid required . tip the solid into a clean dry 250cm3 beaker and add about 100cm3 of distilled water . use a stirring rod to help the solid dissolve , carefully breaking up any lumps of solid with the rod . when the solid has dissolved pour the solution into the flask using a filter funnel . add water to the flask until the level rises to the graduation mark . suggest three further instructions that would improve the overall technique in this account
    • wash the solid from its weighing container into the beaker 
    • wash the wet solid into the beaker after use 
    • wash the wet beaker into the flask after transfer 
    • wash the filter funnel after transfer into the flask 
    • use a teat pipette to make up the mark on the volumetric flask 
    • ensure the bottom of the meniscus is on the graduation mark 
    • invert the flask
  53. state what this student must do in order to obtain an accurate average titre in this experiment
    do further titrations to obtain concordant results
  54. barium chloride solution was added drop wise to magnesium sulphate solution until no more white ppt was formed . the mixture was filtered give the formulae of two main ions in the filtrate
    Cl- and Mg2+
  55. explain why the use of a wet crucible would give an inaccurate result
    water would be lost when heating so mass incorrect
  56. sodium borate
    Na3BO3
  57. suggest one method to remove soluble impurities from the sample of magnesium hydroxide that has been separated
    wash with dionised water
  58. the experiment in task one was designed to allow you to determine the order or reaction with respect to iodide ions in the reaction below 
    H2O2 (aq) + 2H+ (aq) + 2I- (aq) --> I2 (aq) +2H2O (l) 
    outline the changes you would make to the task so the order of reaction with respect to hydrogen peroxide could be determined
    • varying the concentration of hydrogen peroxide and keeping the other reactant concentrations the same 
    • do this by using the same volume of sulphuric acid , iodide ions , potassium hydroxide solution but changing the volume of hydrogen peroxide and water but ensuring their combined volume = 25cm3
  59. we know student technique must be at fault when
    % error greater than apparatus error
  60. other than cooling suggest one method that would decrease the rate of hydrolysis of fats
    keep the foodstuff dry
  61. food can also acquire unpleasant flavours when the fatty acids produced by hydrolysis of fats are oxidised by air . this oxidation occurs by a free radical mechanism , chemicals called antioxidants can be added to food to slow down the oxidation . suggest why antioxidants are not regarded as catalysts
    • because antioxidants are used up in the reaction 
    • as they react with free radicals
  62. ammonia and methyl amine were dissolved in separate samples of water . the two solutions had equal molar concentrations . state one simple method , other than smell . of distinguishing these solutions state what you would observe
    • measure pH with a pH meter 
    • methyl amine would have a higher pH
  63. a student carried out an experiment using a flask on the lab bench . the student recorded the time taken for the reaction mixture to turn blue . state one way this method could be improved other than by repeating the experiment or by improving the precision of time or volume measurements . explain why the accuracy of the experiment would be improved.
    • do experiment in water bath - there will be a constant temp and temp impacts the rate of reaction 
    • use a colorimeter - eliminates human reaction time
  64. suggest a method of separating hydrogen peroxide from the reaction mixture in stage 2 
    stage 2 : BaO2 (s) + 2HNO3 (aq) --> H2O2 (aq) + Ba(NO3)2 (aq)
    fractional distillation
  65. apart from cost suggest one reason why nitric acid was eventually replaced by sulphuric acid in stage 2
    would end up with barium sulphate which is insoluble and can be removed by filtration
  66. suggest one reason why infra red spec cannot be used to indicate the presence of a small amount of water in hydrogen peroxide
    both have OH group
  67. suggest a reason why hydrogen peroxide decomposes more quickly if its not stored in brown bottles
    light would make decomposition faster
  68. despite the corrosive nature of hydrogen peroxide suggest a reason why a spillage of a dilute solution of hydrogen peroxide presents little long term danger  to the environment
    decomposes to water and oxygen which are harmless
  69. 1 chloropropane and ethanoyl chloride can be distinguished by the addition of an aqueous solution of silver nitrate state what you would observe with each
    • 1 chloropropane - covalent bonding so nvc
    • ethanoyl chloride - white ppt
  70. state why it is necessary to maintain a constant temp in an experiment to measure an equilibrium constant
    kc is temp dependent
  71. suggest one method for maintaing a constant temp in an experiment
    water bath
  72. preparation of salicylic acid 
    0.5 g of an impure sample of salicylic acid was placed in a weighing bottle 
    the contents were tipped into a beaker and and 100cm3 of distilled water were added 
    salicylic acid doesn't dissolve well in cold water so the beaker and its contents were heated gently until all the solid had dissolved 
    the solution was poured into a 250 cm3 graduated flask and made up to the mark with distilled water 
    improvements
    • inert the flask
    • use a stirrer
    • rinse the beaker and add washing to flasks
    • rinse the weighing bottle and it to the beaker
  73. method for recrystallisation 
    1) the sample is dissolved in minimum volume of hot water
    to create saturated solution and increase yield
  74. 2) the solution is filtered hot
    to remove insoluble impurities
  75. 3) the filtrate is cooled in ice to form crystals
    this increases the amount of crystals
  76. 4) the crystals are collected by filtration , washed with cold water and left to dry
    to remove insoluble impurities
  77. why is the purified yield of aspirin less than 100%
    • crystals lost when filtering 
    • other reactions occurring
  78. if sodium thiosulphate was added sooner then
    would react with iodide ions before stoplock started so we would have shorter times and therefore the calculated rate of reaction would be quicker than it should be . this means we add sodium thiosulphate at the end
  79. volume is .. to conc
    proportional
  80. rate = K(A)m turn into y=mx +c
    • log rate = logK + mlogA 
    • y = c + mx 
    • gradient = m = order of reaction
  81. state how an aldehyde could be tested to show whether it is contaminated with traces of uncreacted acyl chloride state what you would observe
    • silver nitrate 
    • white ppt
  82. suggest one reason why tollens reagent used as the oxidising agent in the specific test for aldehydes rather than the less expensive acidified potassium dichromate
    potassium dichromate oxidises alcohols too
  83. an aldehyde or ketone is reacted with an alkaline solution of iodide . triiodomethane is formed as a precipitate . compounds that contain a group oxidised to the CH3CO group will also give a positive result in this test . state with a reason whether or not ethanol will give a positive result in the triiodomethane reaction
    • positive result 
    • ethanol is oxidised to ethanal that contains CH3CO group
  84. triiodomethane can be separated from the reaction mixture by filtration . state one reason why the solid residue is then washed with water after the filtration
    removes soluble impurities
  85. state one reason other than cost or availability why water is suitable for washing the solid residue after the filtration
    water doesn't dissolve the solid
  86. salicylic acid C6H4(OH)COOH reacts with magnesium to produce magnesium salicylate and hydrogen complete an equation for this reaction
    2C6H4(OH)COOH + Mg --> (C6H4(OH)COO)2Mg + H2
  87. q=mc∧T if the reaction is exothermic must have a
    - sign
  88. suggest one improvement that would reduce errors due to heat loss in the students experiment
    • using a draught screen around spirit burner
    • reduce distance between flame and beaker 
    • add a lid 
    • use a copper calorimeter rather than a beaker
  89. suggest one source of error in the students experiment . don't include heat loss , apparatus error or student error
    incomplete combustion
  90. a sample of 2methylpropan2ol was contaminated with butan2ol . the student separated the two alcohols using chromatography . identify a reagent or combination of reagents that the student could use to distinguish between these alcohols . state what would be observed for each alcohol
    • acidified potassium dichromate 
    • observation with 2methylpropan2ol no colour change stays orange 
    • observation with butan2ol colour change from orange solution to green solution

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