This problem requires three conversions: 1) mass of margarine to mass of sodium, 2) mass of sodium to moles of sodium, and finally 3) moles of sodium to grams of sodium chloride (since moles of Na = moles of NaCl).
1) mass of Na = 10g marg • (0.70g Na / 100g marg)
2) moles of Na = mass of Na • (1 mol Na / 22.99g Na)
3) mass of NaCl = moles of Na • (58.5g NaCl / 1 mol NaCl)
Combining all three steps:
mass of NaCl = 10g • (0.70g / 100g) • (1 mol / 22.99g) • (58.5g / 1 mol) = 0.18g NaCl
If we check the units, we find that our final answer should be in units of grams, which it is.
