Sodium reacts with chlorine as shown in the equation below;
2Na(s) + Cl2(g) = 2NaCl(s)
The molar mass of sodium chloride is 58.44g/mol,
while that of sodium is 23 g/mol.
The moles of sodium cholride formed will be 351 g / 58.44 g = 6.006 moles
The mole ratio of sodium to Sodium chloride is 2 : 2,
therefore the moles of sodium used will be 6.006 moles,
Hence, mass of sodium used, 6.006 × 23 = 138.142 g or 0.1381 kg