Hydrogen

• Hydrogen occurs in free & combined states
• Combined hydrogen can be found in water (H2O), acids (HCl, HNO3 etc.) and ammonia (NH3).
• Hydrogen with steam:

  $Zn +$$H2O -> ZnO +$$H2$
• Hydrogen with dilute acid:

  $Zn +$$H2SO4 -> ZnSO4 +$$H2$
• Hydrogen with Alkali:

  $Zn +$$2NaOH -> Na2ZnO2 +$$H2$
• What is electrolyte?

  A chemical compound which in the molten or solution state can conduct an electric current & undergo chemical decomposition due to flow of current.
• What is electrolysis?

  The process of decomposition of a chemical compound [electrolyte] in the fused [molten] or solution state by passage of an electric current resulting in the dissociation of the chemical compound into ions which are discharged as neutral atoms at the respective electrodes.
• Name the electrode:

  Anode

  Cathode
• In free state -

  • In trace: occurs in minutes traces in earth's crust, atmosphere and in volcanic gases.
  • In & around the sun: occurs in the interior of the sun which consists mainly of hydrogen which is converted to energy released as heat & light.
• In combined state -

  • HCl, H2O, KOH are the three compounds containing hydrogen in combined state.
• It is colourless, odourless and tasteless.
• Very slightly soluble in water
• Blue litmus do not change the colour of hydrogen
• Hydrogen is explosive, so it is not used in hot air balloons
• The test to differentiate between pure hydrogen & other hydrogen mixture:

  • Pure hydrogen burns quietly with a pale blue flame forming water
  • Hydrogen air mixture explodes with a 'pop' sound