Core Practicals Flashcards
1
Q
1) Measure the volume of molar gas
A
Equations: mol = mass / Mr or mol = vol (dm³) / 24
Procedure:
- Place 30cm³ ethanoic acid in a boiling tube.
- Set up apparatus (1 on CPAC Apparatus Sheet).
- Place approx 0.05g calcium carbonate in a test tube and weight the contents and the test tube accurately.
- Quickly remove the bung on the boiling tube, add the test tube contents and replace the bung.
- The gas will be collected over the water in the measuring cylinder. Once the reaction is complete, measure the volume of gas collected.
- Reweigh the test tube that contained calcium carbonate.
- Repeat the experiment 6 more times, increasing the mass of calcium carbonate by approx 0.05g each time.
How can this procedure be improved?
- Use a gas syringe to measure the volume of the gas as some may be dissolved in the water
2
Q
2) Use a standard solution to find the concentration of a sodium hydroxide solution
A
Procedure 1: Standard solution
- Weigh an empty test tube. Add approx 2.5g of sulphamic acid to the test tube. Reweigh the test tube.
- Add the sulphamic acid to a 250cm³ beaker of 100cm³ of distilled water.
- Reweigh the test tube to see how much sulphamic acid has actually been added.
- Once the sulphamic acid has dissolved, add the solution to a 250cm³ volumetric flask. Rinse the beaker and add the washings to the volumetric flask. Then add distilled water until 250cm³ is reached.
- Stopper the flask and rotate upside down 15 times.
Procedure 2: Titration (2 on CPAC Apparatus Sheet)
- Using a volumetric pipette, transfer 25cm³ of sodium hydroxide solution into a conical flask. Add 4 drops of methyl orange indicator and note the colour.
- Fill a burette with the standard solution made earlier.
- Titrate the solutions until there is a distinct colour change. Record the results and repeat.
- The first result is rough, therefore the experiment must be repeated until concordant results are reached (±0.05cm³).
3
Q
3) Find the concentration of a solution of hydrochloric acid
A
Procedure:
- Transfer 25cm³ hydrochloric acid solution into a clean volumetric flask using a volumetric pipette and make up to the 250cm³ volume using distilled water.
- Transfer 25cm³ of this standard solution into a conical flask and add 3 drops of phenolphthalein indicator.
- Titrate the standard solution against standardised sodium hydroxide solution until the end-point is reached.
- Repeat until concordant results are reached.
4
Q
4) Investigation of the rates of hydrolysis in halogenoalkanes
A
Procedure 1:
- Make a 50ᵒc water bath. (This can be done with a beaker and hot tap water)
- Fill 3 test tubes with 5cm³ ethanol
- Add 4 drops of 1-chlorobutane to the first test tube, 4 drops 1-bromobutane to the second and 4 drops 1-iodobutane to the third, placing a loose bung on each.
- Fill 3 more test tubes with 5cm³ aqueous silver nitrate.
- Warm the 6 test tubes in the water bath for 5 mins.
- Add one test tube of silver nitrate to the 1-chlorobutane test tube and start a stop watch.
- Record the time taken for a precipitate to form. Then repeat with the 1-bromobutane and 1-iodobutane
Procedure 2:
- Repeat procedure 1 but with 1-bromobutane, 2-bromobutane and 2-bromo-2-methylpropane
5
Q
5) Investigation of the oxidation of ethanol
A
Intro:
Ethanol is heated under reflux to form ethanal (aldehyde), then condensed to form ethanoic acid (carboxylic acid). The ethanol is oxidised twice as it is a primary alcohol.
Oxidising Agent:
Acidified Sodium Dichromate
14H⁺(aq) + Cr₂O₇²⁻(aq) + 6e⁻ –> 2Cr³⁺(aq) + 7H₂O(l)
Procedure:
- Add 10cm³ of acidified sodium dichromate solution to a 50cm³ pear-shaped flask
- Add a few anti-bumping granules to the flask
- Set up the flask for heating under reflux as shown (5 on CPAC apparatus sheet)
- Mix 2cm³ ethanol with 5cm³ distilled water in a boiling tube
- Add the ethanol solution dropwise down the reflux condenser into the pear-shaped flask
- Once all the ethanol solution has been added, heat the contents of the pear-shaped flask carefully for about 30 mins using a micro-burner
- Once the apparatus has cooled sufficiently that it can be comfortably held by hand, re-configure the apparatus for distillation and collect the products that boil between 114ᵒc and 120ᵒc (5 on CPAC apparatus sheet)
Tests: To see if a carboxylic acid has formed
- Measure the pH of the distillate using universal indicator paper (orange colour equal to pH 3)
- Add a few drops of acidified potassium dichromate (no visible change)
- Add calcium carbonate (slight fizzing & cloudy solution)
- Add magnesium ribbon (slight fizzing)
- Add Fehling’s solution (clear blue - slight cloudy green precipitate formed)
6
Q
6) Chlorination of 2-methylpropan-2-ol using concentrated hydrochloric acid
A
Procedure:
- Pour 20cm³ of 2-methylpropan-2-ol and 70cm³ of concentrated hydrochloric acid into a large conical flask. Place a bung on the flask and swirl the contents to mix
- After about 30 secs, remove the bung to release any pressure that has built up
- Continue swirling and releasing pressure for 20 mins. After this time the contents should have split up into 2 layers
- Add 6g anhydrous calcium chloride to the mixture and swirl until dissolved.
- Transfer the flask contents into a separating funnel and allow the layers to separate. Then discard the lower aqueous layer.
- Add 20cm³ sodium hydrogen carbonate and place a bung on top
- Mix the contents by inverting the separating funnel, and constantly remove the bung to release pressure.
- Remove the bung and discard the lower aqueous layer that has formed.
- Repeat adding sodium hydrogen carbonate, mixing & discarding until no more gas is released.
- Pour the organic layer into a small conical flask and add a spatula of anhydrous sodium sulphate, swirl and then leave the sample overnight
- Once the liquid is clear, decant into a 50cm³ pear-shaped flask and distil the crude product, collecting the products that boil between 50ᵒc and 52ᵒc
Test:
- Add a small quantity of aqueous sodium hydroxide and ethanol to a sample of the distillate.
- Gently heat the mixture, then add silver nitrate solution.
- If a white precipitate has been formed, then the chlorination of 2-methylpropan-2-ol has been successful.
7
Q
7) Analysis of inorganic and organic unknowns
A
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8
Q
8) To determine the enthalpy change of a reaction using Hess’ law
A
Procedure:
- Place approx. 3g of potassium carbonate into a test tube. Accurately weigh the test tube and it’s contents to 2 d.p.
- Use a burette to add 30cm³ of 2 moldm⁻³ hydrochloric acid into a polystyrene cup (placed in a beaker for support)
- Measure and record the temperature
- Gradually add the potassium carbonate whilst stirring with the thermometer
- Once all the potassium carbonate has been added, record the maximum temperature. Then reweigh the empty test tube
- Repeat above with potassium hydrogen carbonate and record the lowest temperature
9
Q
9) Finding the Kₐ value for a weak acid
A
Procedure:
- Calibrate a pH meter using a pH 3 buffer solution
- Pipette 25cm³ of 0.1 moldm⁻³ weak acid into a conical flask. Record the pH to 2 d.p.
- Fill a burette with 0.1 moldm⁻³ sodium hydroxide
- Titrate 5cm³ of the NaOH solution into the conical flask and record the pH value
- Continue titrating in 5cm³ of NaOH until 20cm³ has been titrated. Recording the pH value after each addition
- Now start titrating in 1cm³ and record the pH value. When the pH rises above 7, recalibrate the pH meter with a pH 10 buffer
- Continue titrating in 1cm³ until 30cm³ has been added. At this point, titrate in 5cm³ until 50cm³ has been added
10
Q
10) Investigating some electrochemical cells
A
Half-cells:
- Zinc/Zinc Sulphate
- Copper/Copper Sulphate
- Iron/Iron Sulphate
- Silver/Silver Nitrate
Procedure:
- Clean strips of copper and zinc using sand paper.
- Set up a zinc half-cell by pouring 50cm³ zinc sulphate into a beaker, and then stand the cleaned zinc strip in the beaker.
- Set up a copper half-cell in the same way but using copper sulphate solution and copper instead.
- Prepare a salt bridge by soaking a folded piece of filter paper into potassium nitrate and place it in both half-cells.
- Connect the 2 metal strips to a voltmeter ensuring that the clips do not make contact with the solutions.
- Record the displayed voltage to 2 d.p. If there is a negative voltage, swap the wires to give a positive voltage.
- Repeat with the other combinations of metal/metal ion half-cells.
11
Q
11) Redox titration
A
Procedure:
- Crush 5 iron tablets and weigh the combined mass of the tablets and a weighing boat to 2 d.p. Empty the iron tablet powder into a beaker and reweigh the weighing boat.
- Add 100cm³ of 1.5 moldm⁻³ sulphuric acid to the beaker and stir to dissolve the iron tablet powder.
- Transfer the solution to a volumetric flask, with the washings and make up to 250cm³ with distilled water. Invert the flask 15 times to stir.
- Pipette 25cm³ into a conical flask.
- Fill a burette with standardised 0.005 moldm⁻³ KMnO₄.
- Titrate the iron solution until a faint pink colour stays for 30 secs or more.
- Repeat the titration until concordant results are reached.
12
Q
12) The preparation of a transition metal complex
A
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13
Q
13a) Following the rate of the iodine-propanone reaction by a titrimetric method
A
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14
Q
13b) Investigating a ‘clock reaction’ to determine a rate equation
A
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15
Q
14) Finding the activation energy of a reaction
A
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