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a-level chemistry > Practical Stuff > Flashcards

Practical Stuff Flashcards

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1
Q

how can % uncertainty of a burette be reduced & why?

A

decrease conc. of solution in burette
so a larger vol. is used so larger titre reading

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2
Q

how can % uncertainty for temp. change be reduced?

A

increase conc. of solution causing temp. change
so greater readings for change in temp.

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3
Q

how can the energetics experiment be improved? (6 marker)

A
  1. apparatus
    1a. use pipette instead of measuring cylinder
    1b. use polystyrene cup instead of beaker or insulate beaker
    1c. reweigh the watchglass after adding the solid
    1d. use powdered solid
  2. temp. measurements
    2a. measure initial temp. every minute before adding solid
    2b. measure temp. every minute for 10 mins after the addition
  3. analysis
    3a. plot graph of time vs temp.
    3b. extrapolate graph to the time of addition
    3c. find temp. change at the time of addition
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4
Q

describe a method to make a volumetric solution

A
  1. put weighing boat on mass balance & tare
  2. add a known mass of solid & pour into beaker
  3. reweigh mass of weighing boat to calculate the actual mass of the solid added
  4. add 100cm^3 distilled water & stir with a glass until all solid has dissolved
  5. transfer to a volumetric flask with washings
  6. add water up to the 250cm^3 line & invert the flask
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5
Q

describe the method for an acid-base titration

A
  1. fill a burette the standard/volumetric solution of a known concentration
  2. using a pipette filler, measure 25cm^3 of the solution with an unknown conc. & put it into a conical flask
  3. add 2-3 drops phenolphthalein indicator to the solution in the conical flask
  4. record the initial burette reading
  5. do a rough titration in which you add solution from the burette until the indicator changes colour, record the final reading & calculate the titre volume (change in vol. in burette)
  6. repeat, but adding dropwise near the end
  7. repeat until you get 2 concordant results
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6
Q

why do you rinse burette with the solution that will go in it?

A

to avoid diluting it/changing its conc.

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7
Q

describe a method to investigate enthalpy change (using copper sulfate)

A
  1. weigh out b/w 3.90 & 4.10g of anhydrous copper sulfate in a weighing boat & record the precise mass
  2. make a table of results to record temperatures at minute intervals over 15 mins
  3. using a measuring cylinder, measure 25cm^3 distilled water into a polystyrene cup
  4. record the initial temp. of the water & start the time & record temp. every minute for 3 mins
  5. at the 4th min, add the anhydrous copper sulfate to the water & stir but do not record the temp.
  6. at the 5th min, continue to record the temp. every min up to 15mins, constantly stirring
  7. repeat with 6.20-6.30g of hydrated copper sulfate & record precise mass
  8. plot a graph of time vs. temp. for each set of results, draw 2 straight lines of best fit 1 before & 1 after the addition. Extrapolate both lines to the 4th minute.
  9. use the graph to calculate the change in temp. at the time of the addition & use this to calculate energy change
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8
Q

describe a method to investigate how temperature affects the rate of reaction

A
  1. add 10cm^3 of 1moldm^-3 HCl to a small glass tube & place it in the plastic container
  2. use a measuring cylinder to add 10cm^3 of 0.05moldm^-3 sodium thiosulfate to another glass tube ‘reaction tube’, put a thermometer in it & place it in the plastic container above the cross
  3. record the start temp. in the reaction tube then add 1cm^3 HCl to sodium thiosulfate & start the stop clock
  4. watch the tube from above & record the time taken for the cross to disappear
  5. record the final temp. in the reaction tube then pour the contents of the reaction tube into a stop bath in the fume cupboard (sodium carbonate)
  6. add hot water, cold water or ice to the plastic container to get the desired temp.
  7. measure out another 10cm^3 sodium thiosulfate into reaction tube & leave both tubes in the water for 5 mins
  8. repeat for a range of temp. from 5C-50C
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9
Q

describe a method to test for group 2 ions with sodium hydroxide

A
  1. place 10 drops of the metal ion solution in a test tube
  2. add 12 drops NaOH solution & swirl
  3. continue adding NaOH dropwise until in excess
  4. record observations
    Mg2+ white ppt
    Ca2+ white ppt
    Sr2+ solution stays colourless
    Ba2+ solution stays colourless
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10
Q

describe a method to test for group 2 ions with sulfuric acid

A
  1. place 10 drops of the metal ion solution in a test tube
  2. add 12 drops H2SO4 solution & swirl
  3. continue adding H2SO4 dropwise until in excess
  4. record observations
    Mg2+ solution stays colourless
    Ca2+ slight white ppt
    Sr2+ white ppt
    Ba2+ white ppt
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11
Q

describe a method to test for ammonium ions

A
  1. place 10 drops of the ammonium chloride solution in a test tube
  2. add 8 drops NaOH solution & swirl
  3. warm in a hot water bath
  4. use tongs to hold damp red litmus paper over the mouth of the test tube
  5. record observations
    damp red litmus paper turns blue
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12
Q

describe 2 methods to test for hydroxide ions

A

first method:
1. place a few drops of sodium hydroxide on a watch glass
2. test the solution with a piece of red litmus paper & record observations
red litmus paper turns blue

second method:
1. place a few drops of ammonia solution on a piece of filter paper in petri dish
2. dampen red litmus paper & put on lid of petri dish
3. replace the lid & leave for a few minutes & record observations
damp red litmus paper turns blue

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13
Q

describe a method to test for carbonate ions

A
  1. put 2cm^3 lime water in a test tube
  2. in a different test tube, add a pipette-full of sodium carbonate solution, & prepare a delivery tube
  3. add a pipette-full of hydrochloric acid to the second test tube & quickly put in the delivery tube with the open end in the lime water
  4. Record any observations
    limewater turns from colourless to milky & white
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14
Q

describe a method to test for sulfate ions

A
  1. put about 1cm^3 zinc sulfate solution in a test tube
  2. add about 1cm^3 hydrochloric acid, then 1cm^3 barium chloride solution
  3. record any observations
    white precipitate forms
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15
Q

describe a method to test for aqueous halide ions

A
  1. put about 10 drops of the required halide ion solution in a test tube
  2. add 5 drops of nitric acid & swirl
  3. add 10 drops of silver nitrate solution
  4. add excess of dilute ammonia solution & mix
  5. repeat steps 1-3 with the same halide, then (working in the fume cupboard) add an excess of concentrated ammonia solution
  6. record any observations
    repeat steps 1-7 using the other two halides
    Cl- white ppt then solution turns colourless w dilute ammonia
    Br- cream ppt then no visible change w dilute ammonia then solution turns colourless w conc. ammonia
    I- yellow ppt then no visible change w dilute or conc. ammonia
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16
Q

describe a method to test for solid halide ions

A
  1. place a small sample of the required halide solid into a boiling tube
  2. slowly add 5 drops of conc. sulfuric acid
  3. test any gases evolved as follows:
    a. for potassium chloride: moist blue litmus paper turns red
    b. for potassium bromide: orange fumes
    c. for potassium iodide: purple fumes & black solid
17
Q

describe a method to distil ethanol to ethanal

A
  1. pour 20cm^3 ethanol into a pear-shaped flask that has been weighed & reweigh to calculate the mass of ethanol
  2. add 8cm^3 conc. phosphoric acid catalyst to the flask
  3. add a small spatula of anti-bumping granules to the flask so the ethanol boils more smoothly
  4. heat the flask using a heating mantle, distilling the ethanol, which boils under 100C
  5. distil about 5cm^3 of the liquid distillate into a test tube immersed in a beaker of ice-cold water
  6. test for ethanal using Tollen’s reagent
18
Q

describe a method to test for alcohol

A
  1. add a piece of sodium metal to 1cm^3 ethanol
  2. record observations
    fizzing, sodium sinks, solution stays colourless - sodium disappears
19
Q

describe 2 methods to test for an aldehyde

A
  1. add Tollen’s reagent
    silver mirror forms
  2. add Fehling’s reagent & warm in a hot water bath for 5mins
    blue solution turns to red ppt
20
Q

describe a method to test for an alkene

A
  1. put 1cm^3 bromine water in a test tube
  2. add 2 drops alkene
  3. put bung on test tube & shake
    solution will turn from orange to colourless
21
Q

describe a method to test for a carboxylic acid

A
  1. put a spatula of sodium hydrogen carbonate in a test tube
  2. slowly add ethanoic acid to the test tube
    bubbling –> solution stays colourless
22
Q

describe a method to test for a haloalkane

A
  1. put 1cm^3 sodium hydroxide solution in a test tube & add 5 drops of 1-bromobutane
  2. warm in a hot water bath for 5 mins
  3. add nitric acid & silver nitrate
  4. record observations
    cream precipitate

a-level chemistry (12 decks)

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