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Core Practical Considerations Flashcards

1
Q

Outline a brief method of CP1 (measuring molar gas volume)

A

-add a known volume and concentration of ethanoic acid to a conical flask with a bung attach feeding into a delivery tube and gas syringe
-add 0.05g calcium carbonate powder and quickly reveal the flask to prevent gas escaping
-measure the final volume of gas
-repeat, increasing mass of calcium carbonate by 0.05g each time
-plot graph of volume against CaCO3 mass

NB gas volume may also be measured by turning a measuring cylinder upside down in water, but this wont be effective for carbonates or sulphate as they are soluble in water

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2
Q

What errors can arise in measuring the molar gas volume (CP1)

A

-some gas could escape from the conical flask before the bung is replaced
-some gases are soluble in water so could dissolve (like CO2 and SO2) so the volume of gas obtained is too low
-the gas syringe may be stuck meaning it doesn’t get fully pulled out as gas enters

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3
Q

Briefly explain a method for removing the water of crystallisation of a hydrated salt

A

-add 2g of the hydrated salt to a dry crucible and weigh them together
-place a loose fitting lid over the crucible to prevent solid from escaping but still allow water vapour to escape
-heat strongly for a few minutes, then allow to cool and re-weigh
-repeat until the crucible has been heated TO A CONSTANT MASS (ensures all water has been lost)

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4
Q

How to calculate % uncertainty

A

Uncertainty of equipment used to make measurement/ measurement) x100

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5
Q

When does uncertainty need to be multiplied by two

A

The uncertainty of your final value will be twice the uncertainty of the equipment if two readings are taken

So this is true for burettes, balances and rulers

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6
Q

What do you rinse titration apparatus with before

A

You rinse the burette with what’s going in it, the pipette with what’s going in it and the conical flask with distilled water

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7
Q

Outline a brief method for making a volumetric flask

A

-add a desired mass of solid to a weighing boat and record the mass of the boat and its contents
-transfer the solid to a beaker and re-weigh the empty boat. Difference in mass= mass of solid
-add 100cm3 of distilled water to the beaker and stir with a glass rod to dissolve the solid
-using a funnel, transfer this solution to a 250cm3 volumetric flask
-wash the beaker and glass rod with distilled water several times, transferring the washings to the volumetric flask each time
-wash around the funnel, then make up to the mark with distilled water so the meniscus sits on the line
-mix flask to ensure even concentration

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8
Q

Outline the method for investigating the rate of hydrolysis of Halogenoalkanes

A

-add an equal volume (5cm3) ethanol to three test tubes and 4 drops of each primary haloalkane to each
-place a loose bung on each and place them all n the same water bath of around 50c
-pour an equal volume of silver nitrate solution (5cm30 into three different tubes and place them into water bath
-leave everything to Equilibria the, then add silver nitrate to each tube and record the time taken for a precipitate to form
-this can be repeated using a primary secondary and tertiary haloalkane

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9
Q

What are the expected results for hydrolysis of haloalkanes and why

A

-iodoalkanes have the fastest rate of hydrolysis because the C-I bond is weakest
-tertiary haloalkanes have the fastest rate of hydrolysis because the carbocation intermediate is most stable as alkyl groups are electron donating

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10
Q

Describe how to draw distillation apparatus

A

-round bottomed flask with heat source underneath and thermometer in the top
-a condenser feeding out of one side into a conical flask
-water drawn as entering the bottom of the condenser (the part closest to the collecting area) and leaving the top (closest to the round bottomed flask) ensuring water runs the length of the condenser to allow for efficient cooling)

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11
Q

Describe how to draw reflux apparatus

A

-round bottomed flask with heat source underneath
-vertical condenser attached with water entering at the bottom and leaving at the top
-there should be no seal at the top of the condenser

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12
Q

What’s the purpose of anti bumping granules

A

They promote smooth and controlled boiling, preventing the mixture boiling over when heating (they should be used in reflux and distillation)

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13
Q

Describe how to carry out a flame test

A

-dip a clean nichrome wire into concentrated HCl
-coat the wet wire in a layer of powdered solid containing the cation you wish to carry a flame test out on
-place into a roaring blue Bunsen burner flame

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14
Q

Li+ flame

A

Scarlet red

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15
Q

Na+ flame

A

Yellow

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16
Q

K+ flame

A

Lilac

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17
Q

Rb+ flame (Rubidium)

A

Red

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18
Q

Cs+ flame (caesium flame)

A

Blue

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19
Q

Mg2+ flame

A

No flame colour because it emits energy of a wavelength outside of that of the visible spectrum

20
Q

Ca2+ flame

A

Orange-red

21
Q

Sr2+ flame

22
Q

Ba2+ flame

A

Apple green

23
Q

How can you use NaOH to test for certain ions

A

Add NaOH drop wise to a metal ion solution until in excess. The colour of the precipitate formed indicates the metal ion present

24
Q

Colour of Ca2+ and Mg2+ precipitates when excess NaOH added

A

White precipitates

25
Colour of Sr2+ and Ba2+ precipitates when excess NaOH added
TRICK they don’t precipitates due to their high solubility (as you go down group 2, solubility of hydroxides increases and of sulphates decreases)
26
Colour of Cu2+ precipitates when excess NaOH added
Blue
27
Colour of Co2+ precipitates when excess NaOH added
Blue
28
Colour of Fe2+ precipitates when excess NaOH added
Dirty green
29
Colour of Fe3+ precipitates when excess NaOH added
Brown
30
Colour of Cr3+ precipitates when excess NaOH added
Green AND dissolves in excess NaOH to give a green solution
31
Test for ammonium ions
Add NaOH solution to the solution containing NH4+ in a test tube and gently heat using a water bath. Test the vapours that form by holding damp red litmus paper to them. A positive result will see the damp red litmus turn blue, as alkaline NH3 gas forms
32
Test for the sulphate ion
Add BaCl2 solution that has been acidified with HCl (the HCl is needed to react with any carbonate impurities) A white precipitate will form (BaSO4)
33
Test for Halide ions
Add silver nitrate solution that has been acidified with nitric acid (the nitric acid is needed to react with carbonate impurities) Cl- forms white precipitate Br- forms cream precipitate I- forms yellow precipitate
34
How is ammonia used to further test for halides
-AgCl dissolves in dilute ammonia -AgBr dissolves in concentrated ammonia -AgI doesn’t dissolve
35
Test for carbonate ions
Add any dilute acid and observe effervescence Bubble the gas formed through limewater and it will turn milky
36
Outline the method for measuring the enthalpy change of a reaction using calorimetry
-place a polystyrene cup into a beaker (provides insulation to minimise heat loss to surroundings) -add a known volume of liquid reactant to the beaker using a volumetric pipette -place a lid on the beaker and poke a hole through the top which a thermometer is placed into, ensuring the bulb of the thermometer touches the solution -for several minutes before the other reactant is added, record the temperature of the solution each minute -add the other reactant, mix and quickly replace the lid and thermometer, recording the temperature every minute for 10 minutes after addition
37
How to plot the graph and read maximum temperature in your calorimetry experiment
-Plot temperature against time -draw two lines of best fit; one joining the points before combining reactants and one after -extrapolate the line after adding reactants to the point when the reactants are immediately combined to determine the maximum temperature change
38
Sources of error in calorimetry experiment
-heat loss to the surroundings -approximation of specific heat capacity of solution (assumes 4.18 which is for water) -specific heat capacity of calorimeter isn’t accounted for (ignore any energy absorbed by the calorimeter) -density of solution taken as same as water
39
Outline the method for determining the Ka of a weak acid
-titrate 25cm3 (measured with volumetric pipette) against NaOH -use a pH meter to measure the initial pH of the solution, then add a small amount of alkali and measure the pH again -repeat this, adding NaOH in small quantities and recording pH at these regular intervals each time -plot a titration curve of pH against volume of naOH added -use the graph to find the pH at the half equivalence point -at the half equivalence point pH=pKa so Ka= 10-phase
40
Outline how to make an electrochemical cell
-obtain two solid metal electrodes and clean them with emery to remove any oxides on the surface -place each electrode into a 1m solution containing its respective ions. Each solution should be the same volume -place filter paper soaked in potassium nitrate solution between the beakers to form a salt bridge -connect the half cells by connecting the metal electrodes to a circuit with a voltmeter to take voltage readings NB some half cells may call for use of a platinum electrode if they involve two solutions mixed together or non metal components
41
Outline the method for preparing a transition metal complex (in this case solid Cu(NH3)4SO4.H2O)
-weigh approx 1.5g of copper sulphate crystals by measuring the mass of crystals + test tube and then the mass of the empty tube -place the crystals into a test tube with 4cm3 water and place this into a water bath, stirring to dissolve the copper sulphate -remove from the water bath and add 2cm3 concentrated ammonia in a fume cupboard, then place this solution into 6cm3 ethanol (causing the complex to crash out of solution) -cool in an ice bath and filter off crystals with a Büchner funnel -wash out test tube with cold ethanol and add washings to funnel -rinse crystals with cold ethanol and pat dry between 2 sheets of filter paper, record the mass of restarts made
42
How can you use gas volume to measure rate of reaction
-if the reaction results in a change in the number of gas moles, then a gas syringe can be used to measure the volume of gas produced at regular timer intervals. Then plot a graph of volume over time and rate=gradient of the graph (or take gradients at specific times using tangents)
43
Outline the method for using titration to follow the rate of the reaction between iodine and propanone (quenching)
-mix iodine and propnaone with a sulphuric acid catalyst in a beaker, mix well, and start a timer -at regular time intervals, use a volumetric pipette to take a sample of the reaction mixture out and quench it using sodium hydrogen carbonate (this will neutralise the acid catalyst so stop the reaction). Record the tie at which the mixture is quenched -titrate this sample against sodium thiosulfate solution using a starch indicator. The end point is when the starch changes colour from blue black to colourless -use the values obtained to calculate iodine concentration at the times of quenching and plot a graph of iodine concentration over time to determine order of reaction with respect to iodine (as propanone and acid are in large excess so their concentrations are effectively constant)
44
What is measured to determine rate in the iodine clock reaction
-in each run of the experiment, the only thing that is varied is their concentration of iodide ions -you are measuring the time taken for starch to turn blue black, as this indicates that thiosulphate ions have been completely used up and so iodine is present in the reaction mixture to react with starch and form a blue black solution -rate= 1/time -plot a graph of rate against concentration of iodine to determine order of reaction with respect to iodine
45
How does the iodine clock work like what’s actually happening
-two reactions are happening; the iodide ions first react with hydrogen peroxide to from iodine, which then reacts with thiosulphate ions to turn back into iodide ions. -when all of the thiosulphate ions are used up, excess iodine remains in solution, as it can no longer react with any thiosulphate to be turned back into iodide. -it is the presence of this iodine that causes the starch to change colour
46
Outline how you can experimentally find the activation energy of a reaction
-relies on the arrenhius equation and plotting in the form lnk=-Ea/RT + lnA -plot a graph of 1/T on x axis and lnk on y axis, then gradient= -Ea/R
47
Describe the process of recrystallisation
-dissolve your impure solid in the minimum volume of hot solvent -heat up gravity filtration apparatus and pass the hot solvent through it to remove insolvable impurities -allow the filtrate to cool so that the crystals can recrystallise out of solution -use a Büchner funnel to filter the solid crystals off of the solution to remove soluble impurities, then wash the crystals in cold distilled water and pat dry with filter paper

Chemistry (7 decks)

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