unit 5 practical Flashcards
1
Q
what are some common mistakes when making a standard solution?
A
- not weighing by difference
- not ensuring all your solid is dissolved before transferring to the flask
- forgetting to rinse your stirring rod/breaker/funnel
- not putting the washings into the volumetric flask
- filling the volumetric flask over the line
- failure to fully mix the solution (not inverting the flask enough times)
2
Q
what are tips to look out for when making a standard solution?
A
- write down all the possible numbers from your weighing in rough
- keep your weighing boat on your desk and dont let anyone touch ut
- only use 100cm^3 of water to dissolve your solid initially
- use a pasteur pipette to add the last few drops of water to your volumetric
- remember the miniscus should sit on the line
- put your palm over the flask’s lid when mixing to ensure you dont lose and solution
3
Q
what are some common mistakes when doing a titration?
A
- not conditioning your equipment with the correct solutions
- not eliminating bubbles from the burette
- filling the burette over your head
- not reading the burette at eye level
- titrating with the funnel in
- using your rough as an actual result
4
Q
what are tips to look out for when doing a titration?
A
- practice using your burette to let out one drop at a time when you are conditioning
- balance any equations before you start so that you’re ready to do your calculation as soon as you have your result
- check you know what the end point will look like before you start titrating
- add half drops near the endpoint
- complete your rough very quickly so that you’re ready can spend more time on your ‘real’ titrations
5
Q
what are some common mistakes when doing double titration?
A
- make sure you add the indicators in the right order - phenolphthalein is always first
6
Q
what are tips to look out for when doing double titration?
A
- double check the equations when doing your calculations
7
Q
what are some common mistakes when doing back titration?
A
- don’t forget its alkali in the burette, be especially careful to wear your goggles
- remember the colour changes will be the opposite to usual
8
Q
what are tips to look out for when doing back titration?
A
- if you only take a portion of your original reaction don’t forget to factor this into your calculation
9
Q
what are some common mistakes when doing redox titrations?
A
- forgetting to add acid if required
10
Q
what are tips to look out for when doing redox titrations?
A
- add water from a kettle if your titration has to be carried out hot
11
Q
what are some common mistakes when doing inorganic tests (precipitation reactions) ?
A
- failing to label all your test tubes at the start
- giving answers as ‘yes’ instead of stating what the observations are
12
Q
what are tips to look out for when doing inorganic tests (precipitation reactions)?
A
- work out which reactions will give precipitates before you start
- remember some substances are ‘sparingly soluble’ so may be inconclusive - it is fine to record this
13
Q
what are some common mistakes when doing gravimetric analysis?
A
- failing to test the filtrate with reagent to see if all the solid has precipitated
- forgetting to rinse the beaker into the filter paper
14
Q
what are tips to look out for when doing gravimetric analysis?
A
- you may have to repeat the precipitation several times but make sure all your solid ends up in the same filter paper (you can add a a second piece of filter paper under the first if needed)
15
Q
what are some common mistakes when measuring rate?
A
- taking too long, this allows the room temperature to change and will affect your results
- not measuring concentrations / volumes exactly
- writing down the tenths and hundredths of seconds from your stopwatch - dont do this
16
Q
what are tips to look out for when measuring rate?
A
- plot your graph for rate as you go along, this way you can immediately repeat any experiments you need to - your points should be really close to your line of best fit
17
Q
what are some common mistakes when using electrochemical cells?
A
- forgetting to soak your salt bridge
- putting the cells the wrong way round
18
Q
what are some common mistakes when doing melting point experiments?
A
-forgetting to seal the base of the tube
19
Q
what are some common mistakes when doing recrystallisation?
A
- using too much solvent
- putting into an ice-bath too quickly (you will only make tiny crystals)
20
Q
what are tips to look out for when doing recrystallisation?
A
- if you cant see any crystals forming, scratch the bottom of the glass with a stirring rod. alternatively, seed the crystals by dipping a glass stir rod in the hot solution. let the solvent dry, then dip the stir rod back into the cooled solution
- make sure the solution is fully cool before filtering
21
Q
what are some common mistakes when doing esterification?
A
- forgetting to add the concentrated acid
- forgetting to distil off the ester
22
Q
what are tips to look out for when doing esterification?
A
- use the acid anhydride for a larger yield
23
Q
what are some common mistakes when doing thermochemistry?
A
- taking the thermometer out to read the temperature
- forgetting to use a lid
- not taking enough readings before and after adding the reagent
24
Q
what are some common mistakes when doing organic synthesis?
A
- not refluxing for long enough
25
what are tips to look out for when doing organic synthesis?
- follow the instructions exactly
- record all distillation temperatures
26
what is a standard solution?
- one whose concentration and volume is known exactly
- this can then be used to calculate the concentration of other solutions
27
how to make a standard solution?
- standard solutions of solids can be prepared by weighing a mass of solid, and dissolving it in a known volume of solvent in a volumetric flask:
1. weigh out your solid (see weighing by difference)
2. carefully add a small amount of distilled water to the beaker, use a glass rod to stir until all the solid has dissolved
3. use a funnel to transfer the liquid into the volumetric flask, pouring down the glass rod
4. rinse out the beaker and funnel several times with distilled water. wash the glass rod. ensure that all washings go into the volumetric flask
5. top up to the mark on the volumetric flask
6. put the stopper in firmly and thoroughly mix the solution
7. label the flask with your name
28
how do you weigh by difference?
- put the bottle and top on the balance and press on
- add between 1.1 and 1.4g
- put the lid on and remove the bottle from the balance
- re-zero the balance
- add the full bottle (with the lid) and write down the weight to 3.d.p
- carefully empty the solid into a beaker
- put the bottle containing any residual solid and the lid back on the balance, write down the weight to 3.d.p
- calculate the accurate weight of the solid to 3d.p
results:
- weight of bottle + top + solid = ____ g
- weight of bottle + top + residual solid = ____ g
- accurate weight of solid (1-2) = ____ g
29
what is the test for ammonia (gas)?
- test with red litmus paper
- +ve result = litmus paper turns blue
30
what is the test for carbon dioxide?
- bubble through limewater
- +ve result = limewater turns milky as calcium carbonate is made
31
what is the test for hydrogen?
- test with a lighted splint
- +ve result = gas burns with a squeaky pop
32
what is the test for oxygen?
- test with a glowing splint
- +ve result = splint relights
33
what is the test for ammonium NH4+?
- heat with NaOH, test vapours with red litmus
- +ve result = litmus turns blue (from evolved ammonia gas)
34
what are the tests for magnesium Mg2+?
- flame test
- +ve result = no flame colour
- add NaOH
- +ve result = white ppt that is insoluble in excess
- add NH3 (aq)
- +ve result = white ppt that is insoluble in excess
- add Na2CO3 (aq)
- +ve result = white ppt
35
what are the tests for calcium Ca2+?
- flame test
- +ve result = brick red flame
- add NaOH
- +ve result = white ppt that is insoluble in excess
- add NH3
- +ve result = no reaction
- add Na2CO3
- +ve result = white ppt
36
what are the tests for copper (II) Cu2+?
- flame test
- +ve result = blue-green flame
- add NaOH
- +ve result blue ppt
37
what is the test for iron (II) Fe2+?
- add NaOH
- +ve result = dark green ppt
38
what is the test for iron (III) Fe3+?
- add NaOH
- +ve result = brown ppt
39
what is the test for potassium K+?
- flame test
- +ve result = lilac flame
40
what is the test for sodium Na+?
- flame test
- +ve result = yellow-orange flame
41
what are the tests for zinc (II) Zn+?
- flame test
- +ve result = no flame colour
- add NaOH
- +ve result = white ppt that is soluble in excess
- add NH3
- +ve result = white ppt that is soluble in excess
42
what is the test for aluminium Al3+?
- add NaOH
- +ve result = white pot that is soluble in excess hydroxide
43
what is the test for chromium (III) Cr3+?
- add NaOH
- +ve result = grey-green ppt forms, soluble in excess NaOH to give a dark green solution, but not soluble in excess NH3
44
what are the tests for strontium Sr2+?
- flame test
- +ve result = crimson flame
- add NaOH
- +ve result = Sr(OH)2 is sparingly soluble - ppt depends on the concentration of the solution
- add Na2CO3
- +ve result = white ppt
45
what is the test for manganese (II) Mn2+?
- add NaOH
- +ve result = off-white ppt (insoluble with excess NaOH or NH3) that rapidly turns brown
46
what are the tests for lead (II) Pb2+?
- add NaOH
- +ve result = a white ppt forms which is soluble in excess NaOH but insoluble in excess NH3
- add KI
- +ve result = yellow pot forms
47
what are the tests for barium Ba2+?
- flame test
- +ve result = apple green flame
- add NaOH
- +ve result = doesnt form a ppt
- add Na2CO3
- +ve result = white ppt
48
what is the test for bromide Br-?
- add nitric acid + silver nitrate
- +ve result = cream ppt (of silver bromide)
49
what is the test for carbonate CO3 2-?
- add acid
- +ve result = fizz of co2 produced (can be tested with lime water)
50
what is the test for chloride Cl-?
- add nitric acid + silver nitrate
- +ve result = white ppt of silver chloride produced
51
what is the test for iodide I-?
- add nitric acid + silver nitrate
- +ve result = pale yellow ppt
52
what is the test for sulphates SO4 2-?
- add solution of barium chloride
- +ve result = white ppt of barium sulphate
53
C4H3KO8.nH2O + 3NaOH —> C4Na3KO8.nH2O + 3H2O
- a student carries out a two-part experiment to determine the value of n in hydrated potassium textraoxalate
- in part 1, the student weighs exactly 1.78g of the solid and transfers all of it to a 250cm^3 beaker
- she adds 100cm^3 of deionised water while stirring to ensure that it all disolves
- describe, giving full practical details, how the volume is made up to exactly 250^3 [3]
- pour liquid from beaker —> 250cm^3 volumetric flask
- add washings to volumetric flask
- make up to 250
- invert to ensure mixture is homogenous
54
when making a standard solution, why put it in a beaker first?
- to avoid spilling because the neck of the volumetric flask if thin
- or solid can get stuck on the side
55
when making a standard solution,
why do you dissolve the solid in a small amount of water first?
- to avoid spilling
- to avoid going over 250cm^3
56
when making a standard solution, why do you wash out the beaker and add it to the volumetric flask?
- to ensure all the solid is tranferred
57
mostly all group 1s are soluble
58
all nitrates are soluble
59
what metal’s salt produces:
- a white ppt when reacted with H2SO4
- no visible reaction when reacting with NaOH
- an orange/brown solution when reacting with Cl2
barium
60
what metal’s salt produces:
- no visible reaction when reacted with H2SO4
- a white ppt when reacting with NaOH
- an orange/brown solution when reacting with Cl2
magnesium
61
compound w is a simple inorganic salt containing one d-block metal cation and one anion.
tests were carried out to identify compound W
- test - observation - inference
- add compound w to water - ________________ - Fe2+ or Cr3+ ions could be present
- add aq NaOH drop-wise to solution of compound W, then add excess NaOH - ___________ - confirm Cr3+ ions present
- add aq silver nitrate - cream ppt forms - __________
- green solution
- grey-green ppt
- Br-
so compound w = CrBr3
62
if something unknown is insoluble but know it’s either group 1 or group 2, it’s probably group 2 because most group 1s are soluble
63
a solution of an unknown salt containing one s-block metal cation and one anion was tested
- WHAT ARE THE CONCLUSIONS FOR EACH TEST AND OBSERVATION
- solution of unknown salt
- test 1 = add CO3 2- = white ppt formed = conclusion =
- test 2 = add OH- = no change observed = conclusion =
- test 3 = add Cl2 = grey solid/brown solution formed =
- test 4 = add Cu2+ = white ppt in brown solution = formula of white ppt =_________. brown colouration due to=_______
- test 5 = add sodium thiosulfate solution TO RESULTS OF TEST 4 = observation=
- group 2
- barium
- I- present
- CuI
- I2
- colourless
64
why is CuI (+1) a white ppt?
Cu+ = d^10 = no free d orbitals to promote electrons
65
explain the observation made in test 5. include an equation in your answer [2] (addition sodium thiosulfate solution to CuI)
2Cu2+ + 4I- —> 2CuI + I2
2S2O3 2- + I2 —> S4O6 2+ + 2I
(iodine is used up so colourless)
66
state the feature required for a molecule to show optical activity [1]
chiral centre
67
state two chemical tests that will give a positive result for 5-aminobenzene-1,3-dicarboxylic acid but not ethyl-4-nitrobenzoate
- Na2CO3
- NaNO2 + HCl (HONO) - warm HONO above 5°C
68
state three chemical tests that will give a positive result for 1-(4-hydroxy-3-nitrophenyl)ethanone but not ethyl-4-nitrobenzoate
- tests for phenols:
- iron (III) chloride - purple solution
- bromine water - white ppt
- iodoform - iodine + sodium hydroxide - yellow ppt of CHI3
69
what are the reagents when using iodoform?
iodine + sodium hydroxide
70
what is the end product when using the iodoform test?
- yellow ppt of CHI3
71
is PbCl2 soluble or insoluble?
insoluble
72
what are the only two soluble compounds of lead
- Pb(NO3)2
- Pb(CH3COO)2
73
- a student planned to distinguish between eight compounds:
• magnesium hydroxide
• iron (II) hydroxide
• chromium (III) hydroxide
• lead (II) hydroxide
• magnesium carbonate
• iron (II) carbonate
• chromium (III) carbonate
• lead (II) carbonate
- step 1 : add dilute acid until all the solid has disappeared. record any effervescence
- step 2: add 1cm^3 of NaOH solution to each solution formed in step 1. record any ppt observed
- the student plans to use dilute hydrochloric acid in step 1. his teacher tells him that this is not the correct acid to use. explain why hydrochloric acid should not be used and suggest an appropriate acid to use in its place
- PbCl2 is insoluble so wont be able to do step 2
- use nitric acid instead
- as Pb(NO3)2 is soluble
74
what are the 4 ions that redissolve in excess NaOH?
- Cr3+ —> grey-green —> dark green
- Pb2+ —> white ppt —> colourless
- Al3+ —> white ppt —> colourless
- Zn2+ —> white ppt —> colourless
75
why are the 4 ions that redissolve in excess NaOH the only ones that do?
because they are amphoteric
76
you are supplied with four unlabelled aqueous solutions containing the following species:
- carbonate CO3 2-, iodide I-, chlorine Cl2, thiosulfate S2O3 2-
you are also provided with the following reagents:
- dilute H2SO4 and AgNO3
- devise a scheme whereby all four of the unlabelled solutions could be positively identified
you should include observations and ionic equations for any reactions occuring [8]
- add AgNO3 to all 4
- one turns yellow ppt —> I-
- Ag+ (aq) + I- (aq) —> AgI (s)
- add H2SO4 to remaining 3
- fizz —> carbonate
- CO3 2- + 2H+ —> CO2 + H2O
- add I- (identified) to remaining 2
- one goes brown —> Cl2
- 2I- + Cl2 —> 2Cl- + I2
- add I2 to last solution
- brown —> colourless
- 2S2O3 2- + I2 —> S4O6 2- + 2I-
77
what is the enthalpy change equation?
∆H = -mc∆T / n
∆H = joules
m = g
