PAGs

Question 1

Errors in PAG 1.1 Composition of copper carbonate

Where you collect gas in a measuring cylinder

Answer 1

Some CO2 may have escaped before the bung is inserted.
Some copper carbonate may not react (so mix the carbonate flask to ensure the reaction goes to completion)
CO2 may dissolve in the water (use a gas syringe)
Some Copper carbonate may remain in the weighing boat meaning it wasn’t transferred to the conical flask (use another weighing method)

Question 2

Method for determination of the relative atomic mass of magnesium

Answer 2

1. Set up a conical flask with 10cm3 of sulphuric acid
2. Weigh 0.15g if magnesium. Add it to the acid and place the bung on
3. Record the final volume of gas collected
4. Weigh a clean evaporating basin.
5. Pour the solution in the basin.
6. Rinse the conical flask with some distilled water and add the washings to the basin
7. Evaporate the solution until a dry solution is left (using heat)
8. The mass of magnesium sulfate is the difference between the final and initial mass of the empty basin

Question 3

Determining the concentration of HCl

What are the 2 main parts?

Answer 3

1. making a 0.10 moldm-3 standard solution of NaHCO3

2. Finding the concentration of HCl by titration

Question 4

How to make a standard solution?

Answer 4

1. weigh a specific amount into a weighing boat and then transfer into a beaker
2. Add a small volume of distilled water to the beaker and stir until the solid completely
   dissolves (using a stirring rod).
3. Reweigh the boat. The difference of the 2 readings is the mass used up.
4. Transfer the solution to a 250 cm3 volumetric flask using a filter funnel.
5. Rinse the beaker and the glass rod with distilled water, adding the washings to the
   volumetric flask.
6. Fill the volumetric flask till it’s nearly to the graduation line.
7. Then, using a pipette, fill the the rest, till the bottom of the meniscus sits on the graduation line.
8. Stopper the flask and invert a several times to mix the solution.

Question 5

Second part of Determining the concentration of HCl

Answer 5

1. Use a pipette and pipette filler to transfer 25 cm3 of the standard NaHCO3 solution to a 250
   cm3 conical flask.
2. Add two or three drops of methyl orange to the flask.
3. Fill the burette with hydrochloric acid (ensuring there is no air bubble) and record the initial
   burette reading
4. 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.
5. Record the final burette reading. The volume of HCl added is the difference between the
   initial and final readings.
6. Repeat until two concordant results are obtained.

Question 6

Errors in Determining the concentration of HCl

Answer 6

Some of the NaHCO3 may not transfer from the weighing boat.
Take care not to spil any solid or solution (use a conical flask rather than a beaker)
During the titration, make sure to swirl to ensure that the reactants are mixed well together
The colour change may not be obvious (place a white tile)

Question 7

Determining the enthalpy change of neutralisation

Answer 7

Measure 25 cm3 hydrochloric acid using a measuring cylinder and add it to a polystyrene
cup.
2. Place the cup in a 250 cm3 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 cm3 of 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.

Question 8

Errors during the determination of enthalpy change of neutralisation

Answer 8

Heat may transfer to surroundings (use an insulator)

Use an electric thermometer.

Question 9

Preparation of cyclohexene part 1

Answer 9

Pour 10 cm3 of cyclohexanol into a 50 cm3 round-bottomed flask
2. Using a plastic graduated dropping pipette, carefully add approximately 4.0 cm3 of
concentrated phosphoric acid to the flask.
3. Add a few anti bumping granules to the flask and then assemble the reflux apparatus as
shown in the diagram
4. Heat the flask gently at about 70℃ for 15 -20 minutes
ensuring that all the condensation happens in the lower
half of the condenser.
5. Stop the heating and allow the apparatus to cool before
assembling for distillation as shown in the diagram.
6. Slowly heat the flask, collecting any liquid which boils
between 70℃ and 90℃.

Question 10

Preparation of cyclohexene part 2

Answer 10

1. Pour the distillate into a separating funnel and add an equal amount of saturated sodium
   chloride solution.
2. Shake the separating funnel then allow the two layers to separate.
3. Carefully run off the lower aqueous layer into a beaker. Collect the upper layer, containing
   the crude cyclohexene, in a small conical flask.
4. Add a few lumps of anhydrous calcium chloride to the crude cyclohexene to remove any
   traces of water.
5. Stopper the flask, shake the contents and allow this to stand until the solid settles.
6. Weigh a sample container then decant the liquid into this container.
7. Reweigh the container. Calculate the mass of dry cyclohexene produced and determine the
   percentage yield of the product.
8. Test the distillate using bromine water, to confirm that it contains an alkene. If an alkene is
   present, the bromine water will be decolourised.

Question 11

Key points to consider when the making of cyclohexene

Answer 11

Use a water bath or electric heater if there are flammable substances.

Question 12

Electrochemical cells

Answer 12

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.
8. Repeat the experiment with a different ratio of aqueous ammonium iron (II) sulfate: iron (III)
   chloride.

Question 13

Making a haloalkane part 1

Answer 13

1. Pour about 6.5 cm3 of 2-methylpropan-2-ol into a 10 cm3 measuring cylinder then weigh the
   measuring cylinder and its contents.
2. Pour the 2-methylpropan-2-ol into a 50 cm3 separating funnel.
3. Reweigh the empty measuring cylinder to deduce the mass of 2-methylpropan-2-ol used in
   the reaction.
4. Measure 20 cm3 of concentrated hydrochloric acid and gradually add the acid to the
   separating funnel.
5. Place the stopper on the separating funnel and shake it vigorously for 20 minutes, releasing
   the pressure when required.

Question 14

Making a haloalkane part 2

Answer 14

1. Allow the mixture to separate.
2. Once separated, remove the stopper and open the
   tap to collect the bottom aqueous layer.
3. One all the aqueous layer has been removed, close
   the tap and add 10 cm3 of 5% sodium
   hydrogencarbonate to the organic layer in the
   separating funnel.
4. Shake the mixture in the funnel gently, releasing the
   pressure when required.
5. Allow the mixture to separate and remove the
   bottom aqueous layer.
6. Repeat steps 3 to 5 until there is no pressure build
   up in the separating funnel.
7. Collect the organic layer into a 100 cm3 conical flask.
8. Add anhydrous magnesium sulfate slowly while swirling the conical flask, until the
   magnesium sulfate stops clumping.

Question 15

Making a haloalkane part 3

Answer 15

Weigh an empty sample tube.
2. Set up the apparatus as shown in the
diagram.
3. Add the organic sample from the conical
flask to the round bottom flask and add
some anti bumping granules.
4. Collect the liquid impurities that come
through the condenser below 48°C in a
small beaker.
5. When the temperature reaches 48℃, collect the
liquid from the condenser in the weighted sample tube until no more liquid comes through
the condenser.
6. Weigh the sample tube and calculate the mass of the product.

Question 16

Rate of reaction between magnesium and HCl

Answer 16

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 teach

Question 17

Errors in the rate of reaction between magnesium and HCl

Answer 17

Some gas may have escaped before putting the bung on.

Question 18

Comparing Thermal Stabilities of calcium carbonate and strontium.

Answer 18

heating carbonate and bubbling gas
into limewater / measuring volume of
gas / measuring mass loss. 
equal amounts/number of moles of
each carbonate heated. 
using the same Bunsen flame AW. 
the first to go cloudy has the lower
thermal stability (or alternative methods
based on amounts of cloudiness in
certain time etc). 
Co2 is given off is shown by the lime-water becoming cloudy.

Question 19

Manganate (VII) Titrations

- entire procedure

Answer 19

A standard solution of potassium magnate is added to the Burkett.
2. Using a pipettes, add a measured volume of the solution being analysed to the conical flask. An excess of dilute sulphuric acid is also added (to provide the H+ ions).
3. During the titration, the manganate solution reacts and is decolourised as it is being added.
The end point is a permanent pink colour.
4. Repeat the titration you obtain concordant results. .

Question 20

Manganate titration

Answer 20

They may be read from the top as it is hard to see the bottom of the meniscus due to the dark purple hue.

Question 21

How to calibrate a pH meter

Answer 21

Place the bulb of the pH meter into distilled water and allow the reading to settle. Adjust the reading on the pH meter so that it reads 7.0. Repeat these steps with a standard solution of ph 4 and 10, making sure to rinse the probe with distilled water between each reading.

Question 22

Where can iodine/ thiosulfate titration be used to determine

Answer 22

ClO- content in copper 2+ analysis in household bleach
Cu 2+ content in copper compounds
Cu content in copper alloys

Question 23

Procedure for analysis of oxidising agents

Answer 23

1. Add a standard solution of Na2S2O3 to the burette.
2. Prepare a solution of the oxidinsg agent to be analysed. Using a pipette, add this solution to a conical flask. Then, add an excess of potassium iodide. The oxidising agent reacts with iodine ions to produce iodine, which turns the solution a yellow- brown colour.
3. Titrate this solution with the Na2S2O3. During the titration, the iodine is reduced back to I- ions, and the brown colour fades slowly. When the end point is being approached, the iodine will change to a pale straw colour.
4. So then, add starch. It should change from a deep blue-black colour to colourless at the end point.

Question 24

Procedure for the analysis of household bleach

Answer 24

1. Using a pipette, add 10cm3 of the bleach into a 250cm3 volumetric flask. Add water to prepare 250cm3 of this solution.
2. Using a pipette, measure 25cm3 of this solution dn add to a conical flask. Then add 10cm3 of KI and 1 molar HCl to acidify the solution.
3. Using a burette, titrate this solution using a standard 0.05 molar solution of nA2s2o3.
4. Repeat this titration to obtain concordant results.
5. Finally, analyse your results to determine the concentration of chlorate (1) ions in the bleach.

Question 25

Measuring standard cell potentials

Answer 25

1. Prepare for the correct half cell.
2. Connect the metal electrodes of the half cells to a voltmeter using wires.
3. Prepare a salt bridge by soaking a strip of filter paper in saturated aq. solution of KNO3.
4. Connect the 2 solutions of the half cells with the bridge.
5. Record the standard cell potential from the voltmeter.

Question 26

How can you measure the standard cell potentials of a metal/ metal ion half cell?

Answer 26

The metal ion must have a concentration of 1.

Temperature of 298K.

Question 27

How can you measure the standard cell potentials of a ion/ ion half cell?

Answer 27

Both metal ions present in the solution must have the same concentration. There must be an inert electrode, such as Pt.
Temperature of 298K.

Question 28

How can you measure the standard cell potentials of a half cell containing a gas?

Answer 28

The gas must be at 100kPa, in contact with a solution with an ionic concentration of 1, and there must be an inert electrode.
Temperature of 298K.