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Chemistry core practicals II - Coggle Diagram
Chemistry core practicals II
Electrolysis
Copper (II) chloride
Pour the copper sulphate solution in a beaker
Add two copper electrodes which have been cleaned with emery paper, measure their weight and connect them to a power supply
Turn on the power and adjust the variable resitor to give a current of 0.2 A
After 20 minutes, turn off the power and remove the electrodes
Gently rinse the electrode with distilled water and dip them in propanone, then remove them and gently shake until the propanone evapourates
Measure the mass of the electrodes and record the change in mass
Repeat using different currents
Important points
Increasing the current increases the change in mass
Cathode should increase as Cu2+ ions are attraced to the cathode where they are reduced
Anode should decrease as Cu2+ ions migrate from it to the cathode
Cathode also gains mass from the electrolyte
Inert electrodes
Pout a solution of copper sulfate in a beaker
Add two graphite electrodes and connect to a power supply
Cathode - copper forms a layer as copper ions are reduced
Anode - Oxygen forms, hydroxide ions are oxidised
Important points
Wear goggles as copper sulphate is an irritant
Clean the electrodes to scrape off any oxides
Propanone is used as it evapourates quickly, helping to dry the electrode
Propanone is highly flammable
Electrodes are washed to remove any copper sulphate
Changes in pH practical
Method
Add dilute HCl to the beaker and measure pH using universal indicator paper on a white tile using a glass rod (rinse after use)
Add weighed mass of calcium hydroxide and stir
Record the pH again
Keep adding weighed masses of calcium hydroxide until there is no more change to the pH
Important points
Wear eye protection as HCl is an irritant
control variables are the volume of HCl and mass of calcium hydroxide added each time
Independent variable is the total volume of calcium hydroxide
You can use a pH meter to make it more accurate
Preparing copper sulphate
Gently heat a beaker of sulfuric acid in a water bath, add an excess of copper oxide, the solution will turn blue
Stop adding copper oxide when the powder doesn't dissolve, showing that its in excess
Filter out the excess copper oxide using filtration
Pour the copper sulphate solution in an evapourating basin which is place over a beaker of water
Heat the soluiton until crystals start to form (when half the water has evapourated), and then leave for a couple of days in a cool palce
Gently dry the crystals
Important points
We reheat the mixture so that any acid left reacts with the excess copper oxide
This is a neutralisation reaction as it produces salt and water
Copper sulpahte is a salt as it formed in a reaction between an acid and a base
Copper oxide is left on the filter paper, it's too big to pass through
Reheat the mixture to mkae sure there is no acid left
Rates of reaction
Disappearing cross
Sodium thiosulfate solution reacts with hydrochloric acid to produce sulfur, it makes the solution go cloudy
Method
Add sodioum thiosulfate to a connical flask and place over a printed black cross
Add the HCl and start a stopwatch
Stop the clock when the cross is no longer visible
Repeat with different concentrations and calculate the mean
Same person has to decided when the cross disappears
Gas produced
Magnesium + HCl --> Magnesium chloride + Hydrogen
You can measure the volume of hydrogen produced
Method
Add HCl to a conical flask
Attatch the conical flask to a gas syringe
Add marble chips to the HCl
Measure the volume in the gas syringe until no more is produced
Repeat using different concentrations or different sized chips
Important points
Wear eye protection
Wear gloves when handling the acid, rinse if any spillages