Chemistry Paper 1 Practicals

• Sous Solution


  water, you need to tik
• ge products will be
• ctrolysis


  e ions in the elect
• l be some Hand O
• this situation, the pe


  ts involved are,
• ons are present, fem
• than hydrogen
• he more likely ista
• metal is less reactie
• Example 2


  • Asolation of sodium chloride (NaCl contaim
• Asolation of sodium chloride (NaCl contaim


  1. Som metal is more reactive than hydrogen. So, at the cathode, hydrogen gas is produced 2H+2e-H

  2. Charide ions are present in the solution. So, at the anode, chlorine gas is produced 2010, 2e.
• Exam Tip
• (Cl, Br, are pe
• will be formed if she
• d oxygen and water vily
• NaCl solution


  • hyalogen ion-
  • sodium ion
  • hydioside ion c
• NaCl solution


  1. So at the cathode, cappe

  2. anode oxygen and wa
• Investigating electrolysis of an aqueous solution

  • You need to be able to identify what's been made in an dectrolysis experiment.
  • Here's how you set up the electrolysis of an aqueous solution:
• Get two inert electrodes (eg, platinum or carbon


  1. Clean the surfaces of the electrodes using a piece of emery paper (or sandpaper)

  2. from this this point on, be careful not to touch the surfaces of the metals with your hands- you could transfer grease back onto the electrodes.

  3. Place both electrodes into a beaker filled with your electrolyte and position them so they are inside inverted test tubes containing the aqueous solution.

  4. Connect the electrodes to a power supply using crocodile clips and wires.

  5. As the reaction progresses, gases may form and collect inside the test tubes
• Topic 4 Chemical Chan
• BP = high
• 10. Electrolysis of Aqueous Solutions
• When you electrolyse substances dissolved in water, you need to think abo the ions in the water when working out what the products will be.
• Predicting the products of electrolysis


  Sometimes there are more than two types of free ions in the electrolyte. For example, if a salt is dissolved in water there will be some H and OH ions a well as the ions from the salt in the solution. In this situation, the producs of electrolysis depend on how reactive the elements involved are.
• At the negative electrode, if metal ions and H ions are present


  the metal im will stay in solution if the metal is more reactive than hydrogen.
• At the positive electrode, if OH and halide ions (Cl, Br, I) are present


  then molecules of chlorine, bromine or iodine will be formed. If no halide is present, then the OH ions are discharged and oxygen and water willbe formed.
• Example 1


  • A solution of copper(II) sulfate (CuSO,) contains four different ions: Cu, SO, H and OH.
• Example 2


  • A solution a four differen Sodium me gas is produc Chloride ion produced:
• Example 2


  negative electr (cath
• lead bromide done lead atom on te Manced. needs to be balanc erall charge of both quation for the reactise right so there needs balance the equation eeds to be balanced side, so that the 2-). So the half ve electrode is side to give both ation: se (-2)-(-2) ions in the e of graphite rode.
• Electrolysis of Metal Ores
• Next up the electrolysis of aluminium oxide to get pure aluminium. The basics s are all the same here, but there are a few twists to learn..
• Extracting metals using electrolysis


  Fa metal is too reactive to be reduced with carbon (see page 163), then electrolysis can be used to extract it. Extracting metals via this method is very expensive as lots of energy is needed to melt the ore and produce the current
• Extracting aluminium by electrolysis


  The main ore of aluminium is bauxite, which can be mined and purified to gie aluminium oxide, Al,O,. Aluminium is then extracted by electrolysis.
• Numinium oxide (Al,O,) has a very high melting point of over 2000 "C-30 meting it would be very expensive. Instead, the aluminium oxide is dissolved in maten cryolite (a less common ore of aluminium). This brings the melting point down to about 900 °C, which saves energy, making the process cheaper and easier. The electrolysis of aluminium oxide is shown in Figure 1.
• The electrodes are made of carbon (graphite), a good conductor of electricity


  • The positive Al ions are attracted to the negative electrode where they each pick up three electrons and turn into neutral aluminium atoms. These sink to the bottom of the electrolysis tank. The negative O ions are attracted to the positive electrode where they each lose two electrons. The neutral oxygen aloms combine to form O, molecules. Some of the oxygen produced reacts with the carbon in the electrode to produce carbon dioxide. This means that the positive electrodes gradually get 'eaten away and have to be replaced every now and again.
• The overall equation for the reaction is: 2A1,0,-
• Half equations Higher


  4Al+30,
• The half equations for the reactions taking place at the electrodes when aluminium oxide is electrolysed are:


  • Negative electrode: Al" + 3e → Al
  • Positive electrode: 200,
• Practice Questions