Required Practicals (Paper 1)
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Suggest a method for obtaining pure crystal samples of copper oxide. [6]
• Heat hydrochloric acid [1] • Add copper oxide and stir till in excess [1] • Filter to remove excess copper oxide [1] • Place solution in a basin over a water bath and evaporate half of the liquid [1] • Pour solution into petri dish [1] • Leave to crystalize [1]
Suggest why a reaction with sodium nitrate would be unsafe to do in the lab.
• It is very explosive/reactive [1]
Suggest the reactants needed to form sodium nitrate. [2]
• Sodium [1] - Nitric acid [1]
Name the substance produced when copper oxide reacts with hydrochloric acid. [1]
• Copper chloride [1]
Describe an experiment to carry out an electrolysis of copper chloride. [6]
• Place carbon rods in copper chloride solution and attach croc clips [1] • Attach the croc clips to the power supply [1] • Turn on the power pack [1] • Use litmus paper to test for chlorine gas (goes clear when gas is present) [1] • After 5 minutes, switch off pack [1] • Check surface of electrodes for copper deposits [1]
Name the elements formed during the electrolysis of sodium chloride, and indicate the electrode at which each of them form at. [2]
• Chlorine, anode [1] - Sodium, cathode [1]
Suggest why lead bromide must be molten for an electrolysis to be successful. [2]
• When lead bromide is not molten, it cannot conduct electricity via it’s lattice of electrons. [1] • When molten, electrons can move and conduct electricity. [1]
Suggest a method for performing a titration of sodium hydroxide. [6]
• Pour 25cm3 of sodium hydroxide into a conical flask [1] • Add indicator to the solution [1] • Add 50cm3 of HCl with a pipette filler [1] • Let the HCl flow, dropwise [1] • Swirl the flask and continue until colour change [1] • Obtain reading from the burette [1]
Explain how the burette is adapted to allow more accurate readings. [2]
• Contains precise measurements [1] - Allows more accuracy in readings [1]
Define precise [1]
• Measurement with little spread around the mean [1]
Suggest why the flask is swirled during the titration [2]
• HCl dissolves faster [1] - so more accurate results [1]
Describe an experiment to test variables which affect temperature change. [4] You should name a suitable acid and hydroxide.
• Measure 50cm3 of HCl in a polystyrene cup [1] • Measure 5cm3 of sodium hydroxide and record highest temp [1] • Repeat until 40cm3 of sodium hydroxide has been added [1] • Empty the cup and refill with HCl to retest again [1]
How is thermal energy loss minimised in this experiment? [1]
• Polystyrene as an insulator [1]
Predict the resolution of the measuring cylinder the student used to measure 5cm3 of sodium hydroxide. [1]
• Millimetres (accept 0.1cm or mm) [1]
(Use table 5 on pg 18 of RQP book as a reference) Explain how the results of 0.50M and 1.00M are very precise. [2]
• Little spread about the mean [1] - meaning results are accurate [1]