code: def alpha2_carbonate(pH):
      
      alpha2_carbonate = 1/(1+(invpH(pH)/K2_carbonate) *
                              (1+(invpH(pH)/K1_carbonate)))
      return alpha2_carbonate
docs: Calculate the fraction of total carbonates in carbonate form (CO3-2)
  
      :param pH: pH of the system
      :type pH: float
  
      :return: Fraction of carbonates in carbonate form (CO3-2)
      :rtype: float
  
      :Examples:
  
      >>> from aguaclara.research.environmental_processes_analysis import alpha2_carbonate
      >>> round(alpha2_carbonate(10), 7)
      <Quantity(0.359881, 'dimensionless')>