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A-level Chemistry > Required Practicals > Flashcards

Required Practicals Flashcards

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1
Q

Determination of the composition of copper (II) carbonate

A
  1. Set up the apparatus as shown in the diagram (https://i.imgur.com/WEupgMl.png) using a 250cm^3 measuring cylinder and a
    250cm^3 conical flask.
  2. Weigh 1.5 g of CuCO3.Cu(OH)2 and add it to the conical flask.
  3. Measure 50cm3 of H2SO4 into a measuring cylinder.
  4. Add the H2SO4 into the conical flask and immediately insert the stopper. The gas will collect
    in the measuring cylinder.
  5. Record the final volume of carbon dioxide in the measuring cylinder.
  6. Calculate the amount of carbon dioxide collected.
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2
Q

Determination of the concentration of hydrochloric acid

A
  1. Make a 0.10 dmmol^-3 standard solution of sodium hydrogencarbonate
  2. Use a pipette and pipette filler to transfer 25 cm3 of the standard NaHCO3 solution to a 250
    cm3 conical flask.
  3. Add two or three drops of methyl orange to the flask.
  4. Fill the burette with hydrochloric acid (ensuring there is no air bubble) and record the initial
    burette reading
  5. Add the hydrochloric acid from the burette to the conical flask until the end point is reached.
    At the end point, the solution will be orange in colour.
  6. Record the final burette reading. The volume of HCl added is the difference between the
    initial and final readings.
  7. Repeat until two concordant results are obtained.
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3
Q

Determination of the enthalpy change of neutralisation

A
  1. Measure 25 cm^3 1 molar hydrochloric acid using a measuring cylinder and add it to a polystyrene
    cup. (https://i.imgur.com/xHqwsg1.png)
  2. Place the cup in a 250 cm^3 glass beaker.
  3. Construct a suitable table to record the temperature of the acid at minute intervals for up to
    10 minutes
  4. Measure 25 cm^3 of 1 molar sodium hydroxide into a measuring cylinder.
  5. Start the timer and record the initial temperature of the hydrochloric acid in the cup.
  6. Continue to record the temperature each minute for three minutes.
  7. At the fourth minute, add the sodium hydroxide to the cup. Do not record the temperature.
  8. At the fifth minute, continue recording the temperature up until 10 minutes. Stir the solution
    in the cup each time the temperature is recorded.
  9. Use the data to work out the T value in q = mcT
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4
Q

Identifying the negative ions (anions) present in mixture A

A
  1. Add 25 cm^3 of distilled water into a 100 cm^3 beaker.
  2. Add mixture A into the water and stir with a glass rod, until most of the solid has dissolved.
  3. Filter the mixture into a conical flask.
  4. Add about 2 cm^3 of the filtrate to a test tube.
  5. Add 5 drops of HNO3 followed by 10 drops of AgNO3 to the test tube. Record any
    observations.
  6. To the same test tube, add NH3 dropwise until there is no further colour change. Record any
    observations.
  7. Add 1 spatula of the residue from step 3 to a test tube. Add about 2 cm3 of HNO3 to this test
    tube. Continue adding HNO3 dropwise until there is no further reaction. Record any
    observations.
  8. Add about 2 cm3 of the filtrate from part 1, step 3 to a test tube. Add about 2 cm3 of sulfuric
    acid to this test tube and record any observations.
  9. In a new test tube, add 2 cm3 of the filtrate from part 1, step 3 followed by about 2 cm3 of
    K2CrO4. Record any observation
  10. Check if your observations match the standard observations for common ions
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5
Q

Synthesis of a liquid haloalkane

A
  1. Pour about 6.5 cm3 of 2-methylpropan-2-ol into a 50 cm3 separating funnel and calculate the mass of 2-methylpropan-2-ol used
  2. Measure 20 cm3 of concentrated hydrochloric acid and gradually add the acid to the
    separating funnel.
  3. Place the stopper on the separating funnel and shake it vigorously for 20 minutes, releasing
    the pressure when required.
  4. Allow the mixture to separate. Once separated, remove the stopper and open the tap to collect the bottom aqueous layer.
  5. Weigh an empty sample tube.
  6. Set up the apparatus as shown in the
    diagram. (https://i.imgur.com/bQ7D7xk.png)
  7. Add the organic sample from the conical
    flask to the round bottom flask and add
    some anti bumping granules.
  8. Collect the liquid impurities that come
    through the condenser below 48°C in a
    small beaker.
  9. When the temperature reaches 48℃, collect the
    liquid from the condenser in the weighted sample tube until no more liquid comes through
    the condenser.
  10. Weigh the sample tube and calculate the mass of the product.
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6
Q

7A: Identification of an alkene

A 
Chemicals provided for the experiment
● Heptane
● Cyclohexane
● Cyclohexene
● Limonene
● Bromine water
  1. For each of the organic substances, in a separate test tube
  2. Add 10 drops of bromine water to 1 drop of the substance.
  3. Mix the contents of the test tube thoroughly.
  4. Record any observations.

Heptane: orange, cyclohexane: top layer orange and bottom layer water, others: colourless

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7
Q

7B: Identification of a haloalkane

A 
Chemicals provided for the experiment:
● 1- chlorobutane
● 1- bromobutane
● 1 -iodobutane
● Ethanol
● Aqueous silver nitrate
  1. Set up a water bath in a beaker.
  2. Heat each haloalkane separately under reflux with sodium hydroxide to release the halide
    ions.
  3. For each of the haloalkane, in a separate test tube:
  4. Add five drops of the refluxed haloalkane
  5. Add 1 cm3 of both ethanol and silver nitrate solution to the test tube.
  6. Mix the solution well and place the test tube into the water bath.
  7. Record any observations after 3 minutes.
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8
Q

7C: Identification of Aldehydes

A 
Chemicals provided for the experiment:
● Fehling’s solution
● Tollens’ reagent
● Brady’s reagent
● Ethanal
● Propanone
  1. In separate test tubes, heat propanone and ethanal with Fehling’s reagent. Make a note of
    any observations.
  2. In separate test tubes, heat propanone and ethanal with Tollens’ reagent. Record any
    observations.
  3. In separate test tubes, add Brady’s reagent to propanone and ethanal. Note any
    observations.

https://i.imgur.com/j8UeRo1.png

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9
Q

7D: Identification of Alcohols

A

Chemicals provided for the experiment:

● Butan-1-ol
● Butan-2-ol
● 2-methyl-propan-2-ol
● Phenol
● Acidified potassium dichromate solution
● Bromine water
  1. Heat the butan-1-ol under reflux with the acidified potassium dichromate and make a note
    of any observations.
  2. Repeat for butan-2-ol and 2-methyl-propan-2-ol.
  3. Add bromine water to a sample of phenol and note any changes

(https://i.imgur.com/EKqiPHQ.png)

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10
Q

7E: Identification of Carboxylic Acids

A

Chemicals provided for the experiment:
● Ethanoic acid
● Dilute sodium carbonate solution
● Limewater

  1. Add some sodium carbonate solution to the sample being tested.
  2. Bubble the gaseous product through limewater using a bung and delivery tube.

The ethanoic acid reacts with the sodium hydroxide producing carbon dioxide. Effervescence will
be observed. CO2 turns limewater cloudy

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11
Q

Making an electrochemical cell

A
  1. Clean a piece of copper and a piece of carbon using emery paper or fine grade sandpaper.
    Rinse the copper and carbon with distilled water then dry them.
  2. Place the copper into a 100 cm3 beaker with about 50 cm3 of 0.1 mol dm-3 CuSO4 solution.
  3. Using a crocodile clip, connect the copper electrode to the negative terminal of the voltmeter.
  4. Place the carbon electrode into a beaker containing about 50cm3 of a mixture of aqueous
    ammonium iron (II) sulfate: iron (III) chloride (1:5 ratio).
  5. Using a crocodile clip, connect the carbon electrode to the positive terminal of the
    voltmeter.
  6. Make a salt bridge by soaking a piece of filter paper in saturated potassium nitrate solution.
    Place the ends of the filter paper into the solutions in the beakers.
  7. Measure and record the voltmeter readings in a suitable format.

Clean electrodes with sandpaper
Place into solutions (100cm^3 beaker, 50cm^3 of 0.1mol)
Connect to voltmeter
Make salt bridge
Usually copper in CuSO4, carbon in 1:5 Ammonium iron(II) sulfate to iron(III) chloride

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12
Q

Rate of reaction between magnesium and hydrochloric acid

A

Method
1. Assemble the apparatus as shown in the picture above (https://i.imgur.com/74aBEEV.png)
2. Add 50cm3 of HCl to the conical flask add a 6cm strip of magnesium to the conical flask and
immediately insert the bung. Start the timer.
3. Record the volume of gas at 15 second time intervals for 2.5 minutes.
4. Repeat for different concentrations of HCl as advised by your teacher.
Analysis
1. For each HCl concentration: Plot a graph of time (sec) on the X-axis against volume of H2
gas produced (cm3) on Y-axis.
2. Draw a line of best fit for your time-points on graph.
3. Draw a tangent at time = 0 and use the gradient to find the initial rate for each
concentration of HCl.

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13
Q

Determination of enthalpy changes of combustion

A
  1. Accurately measure 100 cm^3 of water into a calorimeter/beaker.
  2. Accurately weigh a spirit-burner containing one of the alcohols.
  3. Arrange the apparatus in such a way that the spirit-burner can be used to heat the water in the
    calorimeter/beaker.
  4. Take the temperature of the water before you start heating.
  5. Use your spirit-burner to heat the water. Stop heating when you have heated the water enough to give a
    reasonable temperature rise (15°C). Stir the water thoroughly and measure the final temperature of the
    water.
  6. Reweigh the spirit-burner.
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14
Q

Determination of a enthalpy change of reaction by Hess’ Law

A
  1. Measure 30 cm^3 (an excess) of 2.00 mol dm^3 hydrochloric acid into a polystyrene cup and place inside a 250 cm^3 beaker.
  2. Accurately weigh a sample bottle containing between 2.5g and 3.0g of potassium carbonate, K2 CO3 .
  3. Measure the temperature of the acid and record this value.
  4. Carefully add the K2CO3 to the acid. Continually stir the mixture, measure the highest or lowest
    temperature and record this value.
  5. Reweigh the sample bottle and record this value.
  6. From your results, calculate the heat absorbed or evolved by the solution.
  7. Repeat the first experiment using between 3.2g and 3.7g of KHCO3 instead of K2CO3.
  8. Calculate the amount, in mol, of KHCO3 that reacted and determine the enthalpy change of reaction for the equation above.
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15
Q

Investigating iron tablets

A
  1. Grind 5 iron tablets into a powder
  2. Use a weighing boat to determine the mass of the tablets
  3. Put the iron tablets in a 100cm^3 conical flask
  4. Add 50cm^3 sulfuric acid and stopper the flask
  5. Shake the flask until the solution dissolves
  6. When the residue settles, filter the solution into a volumetric flask
  7. Add the washings from the filter paper to the volumetric flask
  8. Fill the volumetric flask with sulfuric acid up to the mark, to create an acidified solution of iron(II) sulfate
  9. Fill a burette with potassium permanganate solution
  10. Pipette 25cm^3 of the acidified solution with 25cm^3 sulfuric acid into the 250cm^3 flask
  11. Titrate until the solution turns light pink permanently

The equation is 5Fe(2+) + MnO4(-) + 8H(+) => 5Fe(3+) + Mn(2+) + 4H2O

Tablets in 50cm^3 sulfuric acid in flask
Shake and filter solution into vol. flask
Add washings to vol. flask
Fill vol. flask with sulfuric acid
Titrate 25cm^3 of this + 25cm^3 sulfuric acid in a 250cm^3 flask against potassium permanganate until light pink

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16
Q

Preparation of benzoic acid by alkaline hydrolysis of an ester

A 
Add sequentially to a round-bottom or pear-shaped flask (100 cm^3):
2.0 cm^3 of methyl benzoate
10.0 cm^3 of 2.0 molar NaOH
10.0 cm^3 of ethanol
A few anti-bumping granules

Fit the condenser to the flask in preparation to heat the mixture under reflux

Heat the flask gently, without allowing the contents to boil, for about 5 minutes, followed by gentle boiling under reflux for a further 15 minutes.

Allow the contents of the flask to cool. Remove the condenser and decant the solution from the anti-
bumping granules into a beaker.

Rinse the flask with distilled water, adding the rinsing solution into the beaker.

Add ten drops of methyl orange indicator to your solution and then acidify with 2.0 molar HCl. Solid benzoic acid will crystallise.

Filter the mixture using Buchner to obtain impure benzoic acid, washing the crystals with ice cold distilled/deionized water.

Recrystallise the impure benzoic acid (see “Recrystallisation of an organic solid”)

Measure the melting point of the pure crystals (see “Melting point analysis”)

Summary: in 100cm^3 RB add 2.0 methyl benzoate, 10 ethanol, 10 2 molar NaOH, and bumping granules
Heat gently without boiling for 5, then reflux for 15. Cool, decant into beaker along with washings. Add ten drops of methyl orange and acidify with 2 molar HCl. Filter using Buchner to obtain impure benzoic acid, then wash, recrystallise and measure the melting point

17
Q

[OAC3] Recrystallisation of an organic solid

A

Heat 10cm^3 of solvent to 60 degrees

Dissolve impure compound in minimum hot solvent

Filter hot solution to remove insoluble impurities

Leave filtrate to cool

Pour filtrate into Buchner funnel with moistened filter paper. The Buchner funnel should be connected to a Buchner flask

Turn on the vacuum and let the filtrate be sucked through the filter

Wash the crystals with distilled water

Leave the vacuum on for several minutes to dry the crystals

18
Q

[OAC3] Thin layer chromatography

A

Draw a line in pencil about 1 cm from the bottom of the TLC plate. Mark three equally spaced crosses along the line, to indicate the starting positions of the samples.

Use a capillary tube to spot the 3 chemicals on the TLC plate. Each spot should be as small as possible and the spot should be left to dry before the sample is spotted again on top.

Add about 10 cm^3 of solvent into a 100 cm^3 beaker and cover with a watch glass. The watch glass will prevent evaporation of the solvent.

Place the TLC plate into the beaker, making sure that the level of the solvent is below the pencil line. Make sure the watch glass is placed on top of the beaker.

When the solvent is about 1 cm from the top of the plate, remove the TLC plate and mark the solvent front with a pencil. Leave the plate to dry in a fume cupboard.

Place the plate in a beaker with iodine crystals and cover with a watch glass. Once the spots become visible mark them lightly with pencil.

Summary: Draw pencil line and crosses on plate, spot chemicals on plate, leave to dry and add 10 solvent to 100 beaker and cover with watch glass. Place plate in beaker and remove when solvent is 1cm from top. Mark solvent front, dry and use iodine crystals to make chemical visible

Calculate the Rf values of the observed spots.

19
Q

[OAC3] Melting point analysis

A

Seal the end of a melting point tube by rotating it in a Bunsen flame, then leave to cool

Place a small amount of the crystals on a watchglass

Fill the tube with the crystals to a depth of 5mm, and then tap the tube to the solid falls down to the sealed end

Use the melting point apparatus to slowly heat the benzoic acid until it melts

Note the range over which the solid melted

20
Q

Making methyl 3-nitrobenzoate from methyl 3-benzoate

A

Pipette 2.5cm^3 M3B into a small conical flask and mix it with 5cm^3 concentrated sulfuric acid

Cool the mixture in a 250cm^3 beaker ice/water bath

Add 2cm^3 concentrated H2SO4 to 2cm^3 concentrated HNO3 to a test tube and cool in a 75cm^3 ice/water bath

Add the nitrating mixture to the first mixture drop by drop

Stir the mixture with a small thermometer and keep the temperature below 10 degrees. Allow the mixture to stand at room temperature for 15 minutes

Pour ice into the conical flask and stir until it has melted and precipitation is complete

Filter the mixture using Buchner to obtain impure M3NB, washing the crystals with ice cold distilled/deionized water.

Recrystallise (see “Recrystallisation of an organic solid”)

21
Q

Complete oxidation of ethanol to a carboxylic acid

A

Add 4.0 g Na2Cr2O7 to a round-bottomed flask

Slowly add 20cm^3 3 molar sulfuric acid to the flask, then add a few anti-bumping granules

Swirl the flask in an ice water bath for 2-3 minutes until it’s below 10 degrees

Add 0.5cm^3 ethanol to the flask dropwise while swirling in the ice water. You will observe a temperature increase

When the maximum temperature has been reached, repeat these steps again with another 0.5cm^3 ethanol

Clamp the flask, put it into the heating mantle and arrange a condenser above the flask.

Turn on the heat and water flow, and heat under reflux for 20 minutes

Dry the outside of the flask with a paper towel

Heat using a Bunsen flame (see diagram) until you have distilled off 2-3cm^3 of distillate

22
Q

Complete oxidation of ethanol to an aldehyde

A

Add 2.0 g Na2Cr2O7 to a round-bottomed flask

Slowly add 20cm^3 2 molar sulfuric acid to the flask, then add a few anti-bumping granules

Swirl the flask in an ice water bath for 2-3 minutes until it’s below 10 degrees

Add 0.5cm^3 ethanol to the flask dropwise while swirling in the ice water. You will observe a temperature increase

When the maximum temperature has been reached, repeat these steps again with another 0.5cm^3 ethanol

Clamp the flask, arrange the Quickfit apparatus as shown in the diagram, and turn on the condenser water flow

Heat gently with a Bunsen flame until you have distilled off 2-3cm^3 of ethanal into a test tube

23
Q

Preparation of cyclohexene

A

Add 10cm^3 cyclohexanol to a small round-bottom flask

Slowly add 4cm^3 of concentrated phosphoric acid and mix thoroughly

Add a few anti-bumping granules, then set up the apparatus for reflux as shown in the diagram

Heat the mixture under reflux at about 70 degrees for 15 minutes. Adjust the heating and cooling rates to make sure all of the condensation occurs in the bottom half of the condenser

Stop heating and allow to cool for a few minutes

Arrange the apparatus for distillation

Raise the temperature and distil slowly, collecting the distillate that comes over between 70 and 90 degrees

See “purification of an organic liquid”

24
Q

[OAC3] Purification of an organic liquid

A

Add an equal volume of sodium chloride solution to the distillate in a separating funnel, shake gently and release any pressure build-up

Allow the layers to separate and discard the lower aqueous layer

Wash the organic layer with an equal volume of water and discard the lower aqueous layer

Run the remaining organic layer into a small conical flask.

Add a few lumps of anhydrous calcium chloride and swirl the mixture, and decant the clear liquid into a container

25
Q

Synthesis of a haloalkane from an alcohol (2-chloro-2-methylpropane)

A

Pour about 6.5 cm^3 of 2-methylpropan-2-ol into a 10 cm^3 measuring cylinder and measure the mass of cylinder and contents

Pour the 2-methylpropan-2-ol into a 50 cm^3 separating funnel

Measure the mass of the empty measuring cylinder and use this to record the exact mass of 2-
methylpropan-2-ol you have put in the separating funnel

Using a 50 cm^3 measuring cylinder, measure about 20 cm^3 of concentrated hydrochloric acid

Over a period of about 2 minutes, add the concentrated hydrochloric acid gradually to the 2-methylpropan-2-ol in the separating funnel.

Place the stopper in the separating funnel and gently shake the mixture every few minutes for 20 minutes. After shaking, carefully release any pressure inside the separating funnel.

When the layers have separated, remove the stopper and release and discard the aqueous layer

Slowly add 10cm^3 of 5% NaHCO3 solution to the organic layer in the funnel. Stopper and shake the contents gently.

Keep shaking the contents and releasing the pressure until no more gas is given off.

Add 10cm^3 distilled wate, shake and release the lower aqueous layer again

Run the organic layer into a 100cm^3 conical flask. Add small amounts of anh Na2SO4 and swirl until the liquid is clear

Distill and stop distilling at 53 degrees

A-level Chemistry (8 decks)

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