10 L of hard water required 5 .6 g of lime for removing hardness. Hence temporary hardness in ppm of CaCO3 is :

Temporary hardness is due to Ca(HCO3)2 (Mw of Ca(HCO3)2 and CaO = 162 and 56 g respectively) CaHCO32+CaO→CaCO3+H2O162                  56 g16.2                  5.6g 162 g CaHCO32=100 g CaCO3 Mw of CO3=100g16.2 g CaHCO32=10 g CaCO3 Temporary hardness = Mass of CaCO3 Mass of water ×106                              =10104×106=1000ppm(Since 10 L = 104 mL = 104 g of H2O)(∴dH2O=1)