Asalt crystal has a mass of 0.18 mg . how many nacl formula units does it contain?

The molar mass of salt (NaCl) is 22.99+35.45 = 58.44 g/mol. If we have 0.18 mg of salt, this is equivalent to 0.00308 mmol NaCl, or 3.1E-6 mol NaCl. By definition, 1 mole contains 6.02E23 formula units, so multiplying this by the number of moles gives the answer, which is: 1.9E18 formula units.

Because electrons have negligible mass, to account for the mass of the isotope, there must be 16 neutrons, 16 neutrally charged, massive, fundamental particles present in the sulfur nucleus. and thus finally, if we have the 32s2− ion, there are 18 electrons, 16 protons, and 16 neutrons.

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