A Standard Hydrogen Electrode is an electrode that scientists use for reference on all half-cell potential reactions. The value of the standard electrode potential is zero, which forms the basis one needs to calculate cell potentials using different electrodes or different concentrations. It is important to have this common reference electrode, just as it is important for the International Bureau of Weights and Measures to keep a sealed piece of metal that is used to reference the S.I. Kilogram.
The role of an electrode as cathode or anode depends on the nature and electrode potential of the other electrode with which it forms the complete electrochemical cell.
When a cell is to be made with zinc electrode and hydrogen electrode, the hydrogen electrode will behave as a cathode and the zinc electrode will behave as anode because zinc is present above hydrogen in the activity series. That is zinc is more electropositive than hydrogen.
If the cell is made with a copper electrode and hydrogen electrode, the hydrogen electrode will behave as anode and the copper electrode as a cathode. This is due to the fact that Cooper is present below hydrogen in the activity series. Copper is less electropositive than hydrogen.
When non metallic oxide for example SO2 dissolved in water it produces sulphurous acid. SO2 + H2O → H2SO3 When metallic oxide reacts with water it produces Metal hydroxides. Na2O + H2O → 2NaOH
It is important to know if a resource is renewable or non-renewable because renewable resources are self-sustaining (unlike non-renewable resources). If a non-renewable resource is used too often, that resource may eventually become non-existant. This can also happen to renewable resources, but it is more difficult.
