Required Practicals Flashcards
(RP.10) Draw the diagram for suction filtration
(RP.10) Write down the method for recrystallisation (6 steps)
prep: Filter solution gravity before
1) Dissolve impure crystals in the minimum volume of hot solvent
2) Filter off hot solution by gravity filtration , using a hot funnel and fluted filter paper - prevents precipitation of solid
3) Allow the solution to cool and crystallise - scratch side of flask with a glass rod
4) Filter off crystals formed using suction filtration under reduced pressure
5) Wash by pouring some iced cold solvent too remove aqueous impurities
6)Dry by sucking air over the crystals in the büchner flask then place in a low temperature oven
(RP.10) How do you check the purity of an organic solid (5 Steps) + (1 Explanation)
1)Place some of the solid in a capillary tube sealed at one end
2) Place in melting point apparatus and heat gently
3) Record the temperature at which the solid starts to melt and the temperature at which it finishes melting
4) Repeat steps 1-3 and average the temperatures
5) Compare the melting point with know value as in the data book
6) If the compound melts at a lower melting point and over a range of temperatures, it is impure
(RP.10) When prepping an organic solid why is the percentage yield less then 100%
. Some of the solid is lost in purification steps, some of the solid may still be dissolved in the solvent in recrystallisation
.Some of the product is lost ion transferring solids between vessels (solved by rinsing to minimise loss)
(RP.9) Why must your ph meter be calibrated
ensures your readings are accurate and repeatable
ph meter can be contaminated, so results tend to drift from their true value with further use
(RP.9) How do you calibrate a ph meter (3)
testing buffer solutions of known ph
using that data to form a calibration curve
map recorded ph’s to the calibration graph and read off their corrected ph values
(RP.7) How can the rate of the reaction be determined
Continuous monitoring method ie. Loss of reactant over time / Gain of product over time
Initial Rates method (Iodine clock)
(RP.7) What is the Initial Rates Method
Plot a graph for each of the experiments at different Conditions
Draw a tangent to the curve when x=0
Measure the gradient of this tangent
The gradient is the initial rate of reaction, compare values with other graphs at different temperatures
(RP.7) Describe the Iodine Clock Experiment. Include the Equations
The I2 produced reacts with the thiosulphate
Excess I2 that remains in solution then reacts with starch to form a blue black solution
Time how long it takes for the blue black colour to appear
Vary the [I-] to then determine the order of the reaction with respect to iodine ions
(RP.7) What are some issues surrounding the Iodine Clock Experiment
Some [I-] conc may take too long to react
Delayed stopwatch reactions makes readings inaccurate
Concentrations may not be exact due to measuring apparatus
What is a Continuous monitoring method?
Measuring change in concertation of reactant or product over time
Involves measuring a quantity such as volume at set time intervals
(RP.7) Describe the Magnesium ribbon experiment (6)
Continuous monitoring method
connect each end of rubber lead to a bung at one end and a gas syringe at the other
add 6cm strip of magnesium ribbon into a conical flaks containing HCL
quickly place a bung in the top of the flask and start the timer
Note down Volume of hydrogen gas collected every 15 seconds
Repeat using different Concentrations of HCl
(RP.7) How do you analyse data form the magnesium ribbon experiment
Plot a graph of volume gas produced (Y-axis) against time (x-axis) for each different concentation of HCl
Draw a tangent to the curve when x=0
Measure the gradient of this tangent
The gradient is the initial rate of reaction, compare values with other graphs at different Concentrations
(RP.7) what are some issues with the magnesium ribbon experiment
Some gas mat escape before the bung is added
Density of magnesium ribbon used maybe different for each experiment
(RP.8) What is an Electrochemical Cell? (2)
Two different half cells, connected by a salt bridge. with their electrodes connected by a high resistance voltmeter
It’s electric potential energy is generated by chemical redox reactions
(RP.8) What is a salt bridge
A connection between the half cells that allows the movement of ions, to complete the circuit.
Consist of a concentrated electrolyte that doesn’t react with wither half cell solution
(RP.8) if a half cell’s reaction consist of two aqueous ions what electrode would be used and why?
Graphite/ Platinum
Unreactive with solutions & a good electrical conductor so doesn’t affect voltmeter readings
(RP.8) How do you measure comparative electrode potentials of different metals? (6)
File the surface of a piece of copper & the other metal using emery paper
connect the filed copper to the positive voltmeter terminal
Cut a piece of filter paper, saturate it with KNO3 solution and place on top of copper covering it completely
Connect voltmeter to another piece of metal
Hold metal against the filter paper and record the voltmeter value , make sure none of the metals are directly touching
Repeat with different metals and record results
(RP.8) Why do you need to file the outer layer of the metal
Removes the oxide layer on the outside of the metal that is largely unreactive
(RP.9)
What is a brønsted-lowry acid
What is a brønsted-lowry bace
What is an Alkali
Proton Donor
Proton acceptor
A bace that dissolves in water
(RP.9) Why are acid bace indicators used
To detect when a reaction reaches the end point, usually by the presence of a distinct colour change
What is accuracy?
the more accurate the data, the closer it is to the true value
(RP.9) How can you investigate how a weak acids PH changes upon addition of a strong bace
Add 2Cm^3 of NaOH from a burette to ethanoic acid in a conical flask
Continue to add 2cm^3 of NaOH measuring the ph each time
(RP.9) why is it important to stir the solution each time bace is added
So all the acid and bace is thoroughly mixed
Makes sure ph doesn’t significantly vary at different areas within the solution
Gives a more accurate reading
(RP.9) how would you analyse the data from
how a weak acids PH changes upon addition of a strong bace
Plot a graph of Ph values (y axis) against volume of NaOH ( x axis)
You will see a curve with a stationary point of inflation
(RP.10) What are the 6 main steps in producing a pure organic solid?
Synthesis of the compound (usually with reflux disitialltiion ect.)
Recrystallisation:
Gravity filtration with hot saturated solvent
Leave for recrystallisation of the compound
Filtration under reduced pressure
Wash to remove soluble impurities
Dry in Büchner flask and warming oven
(RP.10) how do you use laboratory equipment to heat under reflux (4)
Use of a quick flit apparatus
Substance is boiled in a pear shaped or round-bottomed flask
As it evaporates its cooled by water in the liebig condenser in place of the fractionating column
Vapours condense back into a liquid and drips back into the falls to be reheated
(Rp.10) Why is heating under reflux used?
Allows heating for a long period of time
ensures even boiling
prevents volatile reactants or products from escaping
Prevents flask from boiling dry
(RP.10) Draw a diagram of the quick-fit apparatus for reflux
(RP.10) why are anti-boiling granules used under reflux and distillation?
To prevent uneven and vigorous boiling point
(RP.10) How do you filter under reduced pressure
Using a büchner funnel and büchner flask
Place a filter paper on the pours plate
Pour the substance onto the filter paper
Turn on the vacuum and the liquid will be sucked into the flask
Solid residue will remain in the paper
(RP.10) Draw a diagram of a set up to filter under reduced pressure
(RP.10) How do you purify a solid product? (6)
By recrystallisation
1) Dissolve impure crystals in the minimum volume of hot solvent
2) Filter off hot solution by gravity filtration , using a hot funnel and fluted filter paper - prevents precipitation of solid
3) Allow the solution to cool and crystallise - scratch side of flask with a glass rod
4) Filter off crystals formed using suction filtration under reduced pressure
5) Wash by pouring some iced cold solvent too remove aqueous impurities
6)Dry by sucking air over the crystals in the büchner flask then place in a low temperature oven
(RP.10) How do you purify a liquid product?
Use a separating funnel to isolate the organic layer form the aqueous layer
Add anhydrous MgSO4 drying agent to absorb all of the water in the organic layer
Purify the liquid by distillation, which separates d the substances by boiling point
How do you calculate % Yield
Actual yield / Theortical yield *100
(RP.11) What can be reacted with transition metals to form a metal hydroxide (precipitation reaction) ?
Aqueous Alkali/Alkaline earth metal Hydroxide
Ammonia
(RP.11) Describe the experiment to identify Transition metal ions
Test 1:
Place 10 drops of sample solution in a test tube
Add NaOH drop by drop until excess
Note Observations
Stand in Beaker of hot water for 10 minutes
Note Observations
Test 2:
Add 10 drops of fresh sample into a test tube with Na2CO3
Shake and Record observations
(RP.11) For the the experiment to identify Transition metal ions
What are the observations if the original sample contains Iron (III) ions
Test 1:
Initial - Yellow Solution
After NaOH - Orange/Brown Precipitate
On standing in hot water- No visible change
Test 2:
Orange/Brown Precipitate with effervescence
(RP.11) For the the experiment to identify Transition metal ions
What are the observations if the original sample contains Copper (II) ions
Test 1:
Initial - Light Blue Solution
After NaOH - Deep-Blue Precipitate
On standing in hot water- No visible change
Test 2:
Blue/Green Precipitate
(RP.11) For the the experiment to identify Transition metal ions
What are the observations if the original sample contains Iron (II) ions
Test 1:
Initial - Pale Green Solution
After NaOH - Grey/Green Precipitate
On standing in hot water- No visible change
Test 2:
Grey/Green Precipitate
(RP.12) What are the uses of thin layer Chromatography
Separates components of a mixture.
This allows for the identification of the components by calculating its RF value and comparing it to known values .
(RP.12) How do you calculate an RF value
Distance Travelled by component/ Distance travelled by solvent * 100
Both Distances are measured from the baseline
(RP.12) How do you carry out TLC (7 Steps)
Add solvent to a jar and seal it to create a saturated environment
Draw pencil line on TLC plate
Spot Samples along this line using a capillary tube
Add TLC plate to jar –> Making sure the Solvent is below the pencil line initially
The solvent rises up the TLC plate, different components have different retention time and are separated slowly .
Before the solvent reaches the top of the plate. Draw a pencil line where the solvent finished.
Allow to Dry
(RP.12) Why must pencil be used for marking on the TLC plate
Pen Ink will bleed and dissolve in the solvent, carrying it up the plate ,contaminating it, and affecting the results.
(RP.12) Why should the solvent be below the pencil line
If above the pencil line, the solvent will dissolve all samples, and they will not run up the plate
(RP.12) What happens if your sample is too Concentrated
Spots begin to overlap and unclear results form.
(RP.12) What happens if you use a high baseline and less solvents
Spots on the plate will be larger
(RP.12) How do you analyse the results of TLC via Iodine? (2)
Place chromatogram in a sealed jar with iodine crystals
-Iodine vapour (locating agent) sticks to the colourless spots turning them purple
(RP.12) How do you analyse the results of TLC via Ninhydrin? (2)
What can Ninhydrin analyse?
-Spray chromatogram with heated ninhydrin (developing agent)
-Ninhydrin turns amino acid spots from colourless to purple
-Amino acids
(RP.12) How do you analyse the results of TLC via UV Light? (4)
-Add fluorescent dye to silica/alumina
-Shine UV light onto plate
-Colourless spots on the chromatogram will block any glow from the fluorescent dye
-Draw round the spots to mark where they are
(RP.10) What is a common impurity within the synthesis of aspirin.
Water
Didn’t allow for the crystals to dry properly
Why doesn’t a reflux quick-fit set up have a lid on top of the condenser
to prevent the build up of pressure within the system
A graph question has appeared, what is the first thing you do.
Label the axis’
