Practicals Flashcards
Practicals 1-16 (18 cards)
State key points for CPR 1: Finding the molar volume of any gas
1) Always use a weak acid - slows the reaction
2) Don’t use too many marble chips (CaCO3)
3) Weigh by difference
4) Carbon dioxide is slightly soluble in water so exact volume of gas produced is not measured
5)Wait until no effervescence is observed before weighing the conical flask
State the method for CPR 2: Preparation of a standard solution for titration
1) Weigh out mass of required acid salt
2) Transfer salt to beaker
3) Add a known volume of distilled water to the solid
4) Stir with a glass rod until dissolved
5) Transfer solution to graduated volumetric flask using funnel
6) Wash down the filter paper of the funnel and the sides of the rod in the volumetric flask with distilled water
7) Fill with water until you reach the mark (250cm^3)
8) Place a stopper on the flask
9) Mix thoroughly by inverting the flask/shaking it
State key points for CPR 2: Preparation of a standard solution for titration
- Be careful not to lose any solid when transferring salt from the weighing boat and to the beaker
- Make sure to weigh by difference when measuring out the solid i.e. the difference between the total mass of the weighing boat + salt and the original mass of the weighing boat itself
- Acid should have a high molar mass to reduce weighing errors
- Sample must be pure
- Sample must not be air sensitive or react with air components e.g. absorbing CO2/H2O
Name the colours of phenolphthalein and methyl orange in conditions : acidic, neutral, basic
Phenolphthalein:
Acids –> Colourless
Neutral –> Colourless
Basic –> Pink
Methyl Orange:
Acids –> Red
Neutral –> Orange
Basic –> Yellow
State key points for CPR 3: Titration to find the concentration of an acidic or alkaline solution
1) Initially rinse the glass pipette with the analyte (e.g. NaOH)
2) Ensure there are no air bubbles at the tip of the pipette
3) Add a few drops of indicator to conical flask
4) Regularly swirl the flaks to thoroughly mix contents
5) Use a white tile to make the colour change/end-point more visible
6) Phenolphthalein may turn colourless at end-point if you leave the solution to stand because the NaOH reacts with CO2 in the air to form Na2CO3
State the method for CPR 4: Rates of hydrolysis of halogenoalkanes
1) Set up 3 test tubes by adding 1cm^3 of ethanol and two drops of a halogenoalkane (iodo/bromo/chloro alkanes)
2) Place test tubes in water bath (approx. 60 degrees Celsius) AND a test tube with just 0.1 moldm-3 of silver nitrate
3) Allow them all to reach the same temperature
4) Immediately add 1cm^3 of silver nitrate to each test tube containing the haloalkane
5) Start the stopwatch
6) Measure and record the time taken for precipitates to form in each test tube (i.e. measures the rate of the reaction)
What colour are the precipitates formed in separate reactions between the halogenoalkanes (chloro/bromo/iodo alkanes) and silver nitrate? Also, what do these results show us?
Chloroalkane: White precipitate formed slowly
Bromoalkane: Cream precipitate forms faster than chloroalkane but slower than iodoalkane
Iodoalkane: Yellow precipitate forms the fastest
–> These results demonstrate the relative carbon-halogen bond strengths with C-I being the weakest bond in the series so the reaction is the quickest
What type of experiment is required for the oxidation of ethanol to:
1) Ethanal
2) Ethanoic acid
Ethanol –> Ethanal (aldehyde) :
Distillation Apparatus
Ethanol –> ethanoic acid (carboxylic acid):
Reflux Apparatus
State the method for CPR 5: Oxidation of ethanol to produce ethanal and ethanoic acid
1) Place acidified potassium dichromate solution in pear-shaped flask
2) Cool down the flask using ice bath
3) Add a few anti-bumping granules
4) Add ethanol (drop-wise) to the pear-shaped flask
5) Stir to ensure complete mixing of contents
6) Warm up flask to room temperature
7) Set up reflux apparatus
8) Place flask in a water bath
9) Heat using a Bunsen burner for around 5-10 minutes
10) Allow some time for apparatus to cool down
11) Collect product via distillation
- Use a thermometer here to prevent temperature from rising too high
- Ensure to keep the bulb in vapours, never the solution
12) To prepare the aldehyde, conduct the same reaction under distillation conditions without the reflux process
State the colour change between ethanol –> ethanal/ethanoic acid
In both reactions, the colour changes from orange (Cr2O7 (2-) ) to green (Cr(3+))
State the method for CPR 6: Chlorination of 2-methylpropan-2-ol.
1) Add concentrated HCL and tertiary alcohol to a conical flask
2) Swirl gently
3) Put rubber bung in and swirl the flask gently
4) Every now and then, ensure to open the bung to release the pressure
5) Repeat this regularly for around 20 minutes
6) Add some anhydrous CaCl2 and shake
7) At this point, there should be two distinct layers
- Upper organic layer: Contains desired product
- Lower aqueous layer
8) Transfer contents of flask to separating funnel
9) Allow layers to separate and discard the lower aqueous layers
10) Close the tap to keep the organic layer in the separatory funnel
11) Add solution of NaHCO3 to remove the unreacted HCL
12) Swirl gently
13) Stopper the separating funnel and shake it
14) Invert the separatory funnel and open the tap to release the pressure due to CO2 being formed and repeat
15) Another aqueous layer is formed which is run off once the tap is opened again
16) Run off the remaining organic layer into a conical flask
17) Add some anhydrous Na2SO4
18) Swirl the contents and allow the flaks to stand for a bit
19) Distil to purify the product
What is the purpose of adding anti-bumping granules?
Prevents the formation of large gas bubbles that could cause violent boiling
What is the function of anhydrous NaSO4?
Acts as a drying agent
Why is a weak base used in CPR 6?
Prevents the hydrolysis of halogenoalkane - NaOH could react with the product via nucleophilic substitution
What is an error that most commonly occurs in CPR 6?
Some product is lost when transferring liquids between vessels
What does the simple distillation of ethanol produce?
Ethanal
What does the oxidation of ethanal produce?
Ethanoic acid
