351 kg = 351 x 1000 = 351000 grams
number of moles can be calculated using the following rule:
number of moles = mass / molar mass
From the periodic table:
molar mass of calcium = 40.078 grams
Therefore, substituting in the above equation:
number of moles = 351000 / 40.078 = 8757.922 moles
