required practicals Flashcards
(32 cards)
1
Q
how to make up a volumetric solution of known concentration
A
- calculate mass required
- weigh weighing boat with balance
- add powder and reweigh
- pour powder into a clean dry beaker
- reweigh weighing boat
- calculate mass of solid transferred
- add approx 100cm3 deionised water to beaker
- stir with glass rod until fully dissolved
- using a funnel, transfer into volumetric flask
- rinse glass rod, beaker and funnel with deionised water into the flask
- make up to line
- add stopper and invert to mix
2
Q
how to carry out a titration to calculate unknown concentration
A
- fill burette with solution of known concentration
- transfer 25cm3 of unknown solution to a conical flask using a pipette and pipette filler
- add 3 drops of indicator and record initial colour
- record initial volume of burette
- titrate until colour change is observed
- record end point of burette and calculate titre
- repeat until concordant (within 0.1 cm3 of each other)
3
Q
how to measure the enthalpy change of a reaction
A
- weigh 4g of anhydrous copper (II) sulfate in a dry weighing boat
- use a measuring cylinder to measure 25cm3 of distilled water and pour into polystyrene cup
- record initial temperature
- begin a timer and record temperature every minute for 3 minutes
- stir continuously
- at the 4th minute, pour the powdered anhydrous copper (II) sulfate
- do not record temperature, just stir
- at 5th minute, resume recording temperature every minute until 15 mins.
- plot the graph of temperature (y) against time (x)
- plot results and draw two lines of best fit
- extrapolate to 4 min and calculate enthalpy change
4
Q
how to investigate how temperature impacts rate of reaction
A
- add 10cm of 1M HCl to a test tube
- place test tube into plastic container
- add 10cm of 0.05M sodium thiosulfate
- place this tube into the plastic container with a cross underneath it
- place a thermometer in this tube
- record start temperature
- add 1cm of acid to thiosulfate solution and start timing
- record time for cross to disappear
- record final temperature and pour clody contents into sodium carbonate solution
- now add hot water to the plastic container (no hotter than 55)
- measure another 10cm of 0.05 thiosulfate solution and place above cross
- leave tube to warm up for about 3 mins
- repeat with alternative temperatures
5
Q
testing for group 2 ions with sodium hydroxide
A
- 10 drops of sample
- 10 drops of 0.6M NaOH solution and mix
- record observations
- add NaOH dropwise until in excess + gently shake
- record observations
Mg - slight white, white
Ca - slight white, slight white
Sr - slight white, slight white
Ba - colourless, colourless
6
Q
test for group 2 ions (dilute sulfuric acid)
A
- 10 drops sample
- 10 drops 1M sulfuric acid
- record observations
- add sulfuric acid until in excess
- record observations
Mg - slight white, colourless
Ca - slight white, slight white
Sr - white, white
Ba - white, white
7
Q
test for ammonium ions
A
- 10 drops ammonium chloride
- 10 drops NaOH
- heat in water bath
- test fumes using damp red litmus paper
- turns blue if ammonium present
8
Q
test for halide ions (aqueous solution)
A
- add small volume of dilute nitric acid to solution to remove other ions
- add 2cm3 silver nitrate
- observe and record
- split into two test tubes
- one with dilute ammonia
- one with concentrated ammonia
chloride - white ppt, dissolves in dilute and conc ammonia
bromide - cream ppt, only dissolves in conc ammonia
iodide - yellow ppt, doesn’t dissolve
9
Q
test for halide ions (solid salts)
A
- add a small spatula of salt in a clean dry test tube
- add conc sulfuric acid
- record observations
- test gas evolved using damp blue litmus paper
chloride - steamy white fumes, paper turns red
bromide - orange fumes, paper turns red
iodide - purple fumes and black solid, paper turns red
10
Q
tests for hydroxide ions
A
- 1cm depth
- red litmus paper turns blue
11
Q
test for carbonate ions
A
- 2 cm of dilute HCl to 2 cm of sample
- use delivery tube to tramsfer gas evoved into test tube with limewater
- add stopper and shake - turns cloudy if carbonate present
12
Q
test for sulfate ions
A
- 2cm of dilute HCl and 2cm of barium chloride
- forms barium sulfate ppt if present
- add 2cm of dilute HCl
- if it doesn’t redissolve, sulfate or hydrogen sulfate ions are present
13
Q
how to prepare cyclohexene
A
- pour 20cm3 of cyclohexanol into a 50cm3 pear shaped flask that has been weighed
- reweigh flask and record mass of cyclohexanol
- use a plastic pipette to add 8cm of conc phosphoric acid
- add anti bumping granules to the flask
- distill and heat gently
- pour distillate into separating funnel
- add 50cm of saturated sodium chloride solution
- shake and allow to separate
- run off lower layer into beaker and transfer upper layer into conical flask
- add anhydrous calcium chloride to remove water
- stopper, shake and allow to stand until liquid is clear
- decant into previously weighted sample container
- reweigh container and calculate mass of dry sample
- test with bromine water
14
Q
how to prepare ethanal
A
- make oxidising agent by dissolving potassium dichromate in dilute sulfuric acid
- use a 25cm measuring cylinder to measure 12cm of oxidising agent in a boiling tube
- cool in cold water (avoids loss of ethanal)
- measure 2cm of ethanol
- add dropwise to oxidising agent shaking gently
- set up distillation process so delivery tube goes to a test tube immersed in cold water
- heat gently and distill
- use tollens reagent to test for aldehyde (silver mirror)
15
Q
testing for alcohol with metal
A
- add a small piece of metallic sodium to sample
- test gas using squeaky pop test (hydrogen)
- dispose of excess sodium in ethanol, if in contact with water its a fire hazard
16
Q
testing for alcohol NOT with metal
A
- add 3cm acidified potassium dichromate
- primary and secondary go from orange dichromate ion (VI) to green chromium (III)
- tertiary doesnt oxidise, so remains orange
17
Q
test for aldehydes
A
- in a clean test tube, mix equal volumes of Fehling’s A (blue) and B (clear)
- this produces Fehling’s test (dark blue)
- add 5 drops to a test tube with anti bumping granules
- add sample
- warm for 2 mins in beaker of water
- bring water to a boil and maintain for 5 mins
- remove from water and allow to stand
- if present, brick red ppt forms
18
Q
test for alkenes
A
- add 1cm3 bromine water to 2 drops of sample
- shake vigorously
- if discoloured, alkene present
19
Q
test for carboxylic acid
A
- add spatula of solid sodium carbonate and 2cm of sample
- collect gas evolved and bubble through limewater
- if present, CO2 is produced, and water turns cloudy
20
Q
test for halogenoalkane
A
- 5 drops of sample
- 1 cm3 of sodium hydroxide (replaces halogen)
- warm at 60 degrees in water bath for 4 minutes
- add 2cm dilute nitric acid
- add 1cm silver nitrate
- if present, a ppt will form
21
Q
measuring initial rate of reaction
A
iodine clock reaction
- put 10cm of hydrogen peroxide in an 100 beaker
- fill burette with potassium iodide solution
- in a 250cm beaker, add 25cm sulfuric acid, 20cm deionised water, 1cm of starch solution, 5cm potassium iodide and 5cm of sodium thiosulfate
- pour the hydrogen peroxide in and start a timer
- top timer when solution turns black
- repeat with changing concentrations of potassium iodide
- plot a graph of rate (y) against concentration (x)
22
Q
measuring rate of reaction (continuous monitoring)
A
- 50cm of 0.8M HCl to conical flask
- set up gas syringe
- add 6cm strip of magnesium ribbon
- attach bung and start timer
- record the volume of hydrogen collected every 15 seconds for 3 minutes
- repeat with different concentrations
23
Q
how to measure EMF of an electrochemical cell (beakers)
A
- clean a piece of copper and zinc using fine grade sandpaper
- degrease using propanone and cotton wool
- place copper into 100cm beaker with 50cm of 1M copper sulfate solution
- place zinc into a 100cm beaker with 50cm of 1M szinc sulfate solution
- plug one end of a U-tube with cotton wool and fill with 2M NaCL solution and plug other side
- join the two beakers with U-tube so both ends are in the separate beakers
- connect the half cells with wires and record voltmeter reading
24
Q
how to measure EMF of an electrochemical cell ( no beakers)
A
- clean a piece of copper and zinc using fine grade sandpaper and propanone
- use a crocodile clip and connect copper to positive terminal of voltmeter
- cut a piece of filter paper to similar size as copper metal and add sodium chloride solution
- place it on top of copper
- connect negative terminal to zinc
- hold zinc against filter paper and record voltmeter reading
25
how to calibrate a pH probe
- rinse with deionised water and gently shake to remove excess
- place probe in standard buffer solution of pH 7.00.
- record reading
- repeat with pH 4.00 and 9.00 buffer solutions
- record readings
- plot graph of recorded readings (x) against buffer pH (y)
26
how to measure pH with a probe
- rinse burette with 0.1M ethanoic acid, then fill and label
- use the burette to transfer 20cm3 of ethanoic acid to an 100cm beaker
- rinse and fill another burette with 0.1M sodium hydroxide solution and label
- rinse pH probe with distilled water and clamp in ethanoic acid beaker so the bulb is fully immersed
- use a glass rod to stir and record the intial pH
- add 2cm of NaOH from burette at a time.
- stir and record pH each time
- near the end point, use 0.2cm NaOH instead
- after end point, return to 2cm
- plot graph
27
how to produce aspirin
- 20g of 2-hydroxybenzoic acid (salicylic acid) into a pear shaped flask
- add 40cm of ethanoic anhydride
- add 5 cm of concentrated phosphoric acid
- heat and reflux for 30 mins
- add water to hydrolyze any unreacted ethanoic anhydride to ethanoic acid
- pour into 400g of crushed ice in a beaker
- allow to crystalize
- remove crystals by suction filtration
- dissolve crystals in a minimum volume of hot solvent like ethanol
- filter with gravity (funnel and filter paper)
- allow to cool
- filter with Buchner funnel
- wash with distilled water and dry between filter paper
28
how to determine the melting point of a solid
- place solid into melting point tube and into apparatus
- gently heat and record initial melting temperature
- record final temperature
- repeat and calculate averages
- a higher range = less pure
- range below 2 degrees = fairly pure
29
test for transition metals with sodium hydroxide
- 10 drops of sample
- add NaOH until in excess
- record observations
- allow to stand in boiling water for 10 min
- record observations
Iron II = green ppt that goes brown upon standing. no change in excess
Copper II = blue ppt. no change in excess
Iron III = orange brown precipitate. no change in excess
Aluminium III = white ppt, in excess redissolves to form colourless solution
30
test for transition metals with sodium carbonate
- 10 drops sodium carbonate
- 10 drops sample
Iron II = green ppt
Copper II = blue green ppt
Iron III = brown ppt + CO2 gas
Aluminium III = white ppt + CO2 gas
31
test for transition metals with ammonia solution
- 10 drops ammonia solution to sample
Iron II = green ppt that goes brown on standing. no change in excess
Copper II = blue ppt that redissolves in excess to form deep blue solution
Iron III = brown ppt, no change in excess
Aluminium III = white ppt, no change in excess
32
