Required practicals Flashcards
Practical 1 (simple distillation)
Aim: Investigate how simple distillation and paper chromatography can be used to separate and identify a mixture of food colourings.
Procedure - Ink consists of a solvent which has different dyes dissolved in it.
The investigation must thus include analysis of both the solvent and the dyes used.
The solvent must first be separated which can be done by simple distillation
Solvents tend to have low boiling points than the dyes which tend to be more viscous so it will evaporate first.
Add anti-bumping granules and heat gently so as not to go past the boiling point.
Record the temperature of boiling point.
Practical 1 (chromatography)
Aim: Investigate how simple distillation and paper chromatography can be used to separate and identify a mixture of food colourings.
Procedure - Use a ruler to draw a horizontal pencil line 2 cm from the end of the chromatography paper
Use a different capillary tube to put a tiny spot of each colouring A, B, C and D on the line.
Use the fifth tube to put a small spot of the unknown mixture U on the line
Make sure each spot is no more than 2-3 mm in diameter and label each spot in pencil.
Pour water into the beaker to a depth of no more than 1 cm and clip the top of the chromatography paper to the wooden spill. The top end is the furthest from the spots.
Carefully rest the wooden spill on the top edge of the beaker. The bottom edge of the paper should dip into the solvent.
Allow the solvent to travel undisturbed at least three quarters of the way up the paper.
Remove the paper and draw another pencil line on the dry part of the paper as close to the wet edge as possible. This is called the solvent front line.
Measure the distance in mm between the two pencil lines. This is the distance travelled by the water solvent.
For each of food colour A, B, C and D measure the distance in mm from the start line to the middle of the spot.
Practical 2 (investigating pH)
Aim: To investigate the changes in pH of a fixed volume of dilute HCl on addition of varying amounts of a solid base.
Procedure - Use a pipette to measure a fixed volume of dilute HCl into a conical flask.
Add one spatula of calcium oxide or calcium hydroxide to the flask and swirl
When all the base has reacted record the pH of the solution.
If using U.I. paper use the glass rod to extract a sample from the flask.
Repeat for different numbers of spatula (1-10) of solid but the same volume of HCl.
Record your results neatly in table format.
Practical 3 (copper sulphate)
Aim: To prepare a pure, dry sample of hydrated copper(II) sulphate crystals.
Procedure - dd 50 cm3 dilute acid into a beaker and warm gently using a Bunsen burner.
Add the copper(II) oxide slowly to the hot dilute acid and stir until the base is in excess (i.e. until the base stops dissolving and a suspension of the base forms in the acid).
Filter the mixture into an evaporating basin to remove the excess base.
Gently heat the solution in a water bath or with an electric heater to evaporate the water and to make the solution saturated.
Check the solution is saturated by dipping a cold glass rod into the solution and seeing if crystals form on the end.
Leave the filtrate in a warm place to dry and crystallise.
Decant excess solution and allow the crystals to dry.
Practical 4 (electrolysis of copper sulphate)
Aim: To electrolyse copper(II) sulphate solution using inert(graphite) electrodes.
Procedure - Pour copper sulphate solution into a beaker.
Place two graphite rods into the copper sulfate solution. Attach one electrode to the negative terminal of a DC supply, and the other electrode to the positive terminal.
Completely fill two small test tubes with copper sulphate solution and position a test tube over each electrode as shown in the diagram.
Turn on the power supply and observe what happens at each electrode.
Test any gas produced with a glowing splint and a burning splint.
Record your observations and the results of your tests.
Practical 4 (Electrolysis with Active Electrodes)
Aim: To electrolyse copper(II) sulphate solution using active( copper) electrodesDiagram.
Procedure - Pour copper sulphate solution into a beaker.
Measure and record the mass of a piece of copper foil. Attach it to the negative terminal of a DC supply, and dip the copper foil into the copper sulphate solution.
Repeat with another piece of copper foil, but this time attach it to the positive terminal.
Make sure the electrodes do not touch each other, then turn on the power supply.
Adjust the power supply to achieve a constant current and leave for 20 minutes.
Remove one of the electrodes and wash it with distilled water, then dip it into propanone.
Lift the electrode out and allow all the liquid to evaporate. Do not wipe the electrodes clean. Measure and record the mass of the electrode.
Repeat with the other electrode making sure you can identify which electrode is which.
Repeat the experiment with fresh electrodes and different currents..
Practical 5 (acid alkali titration)
Aim: analyse the concentration of a solution
Procedure - Use the pipette and pipette filler and place exactly 25 cm3 sodium hydroxide solution into the conical flask.
Place the conical flask on a white tile so the tip of the burette is inside the flask.
Add a few drops of a suitable indicator to the solution in the conical flask.
Perform a rough titration by taking the burette reading and running in the solution in 1 – 3 cm3 portions, while swirling the flask vigorously.
Quickly close the tap when the end-point is reached (sharp colour change) and record the volume, placing your eye level with the meniscus.
Now repeat the titration with a fresh batch of sodium hydroxide.
As the rough end-point volume is approached, add the solution from the burette one drop at a time until the indicator just changes colour
Record the volume to the nearest 0.05 cm3.
Repeat until you achieve two concordant results (two results that are within 0.1 cm3 of each other) to increase accuracy.
Practical 6 (Measuring the Production of a Gas)
Aim: To investigate the effect of changing surface area of marble chips in the reaction between marble chips and hydrochloric acid.
Procedure - Add hydrochloric acid into a conical flask.
Use a delivery tube to connect this flask to an inverted measuring cylinder.
Add marble chips into the conical flask and close the bung.
Measure the volume of gas produced in a fixed time using the measuring cylinder.
Repeat with different sizes of marble chips .
Practical 6 (Observing a Colour Change)
Aim: To investigate the effect of changing concentration in the reaction between sodium thiosulphate and hydrochloric acid.
Procedure - Measure 50 cm3 of sodium thiosulfate solution into a flask.
Measure 5 cm3 of dilute hydrochloric acid into a measuring cylinder.
Draw a cross on a piece of paper and put it underneath the flask
Add the acid into the flask and immediately start the stopwatch.
Look down at the cross from above and stop the stopwatch when the cross can no longer be seen.
Repeat using different concentrations of sodium thiosulfate solution (mix different volumes of sodium thiosulfate solution with water to dilute it).
Practical 7 (Heat of Combustion of Alcohols)
Aim: To investigate the heat of combustion of four alcohols.
Procedure - Using a measuring cylinder, place 100 cm3 of water into a copper can.
Record the initial temperature of the water and the mass of the empty burner.
Fill the burner with the test alcohol and record its new mass.
Place the burner under the copper can, light the wick and place the lid on.
Stir the water constantly with the thermometer (calorimeter lids allow for this) and continue heating until the temperature rises by 25 ºC.
Immediately extinguish the flame and measure and record the mass of the spirit burner.
Repeat procedure for other alcohols, making sure the variables are kept the same.
Practical 8 (identifying ions)
Aim: To use chemical tests to identify the ions in unknown binary ionic compounds.
Procedure - There are a number of strategies you could choose in order to identify the ions in unknown salts.
Common analysis strategies include flame tests, and tests for sulphate, carbonate and halide ions.
They can be carried out in any particular order, and you will probably not need to carry them all out on any one sample
Only small amounts of each sample and reagent are needed.
You may need to dissolve a sample of salt in a little distilled water if the salt you are given is in the solid state.
Record your observations carefully in a table of results as you work through the tests.
Repeat any tests that do not provide a clear result i.e. a colour change that was difficult to identify.
