Which of the following substances contains the greatest mass of chlorine? (a) \(5.0 \mathrm{~g} \mathrm{Cl}_{2},\) (b) \(60.0 \mathrm{~g}\mathrm{NaClO}_{3}\) (c) \(0.10 \mathrm{~mol} \mathrm{KCl}\), (d) \(30.0 \mathrm{~g} \mathrm{MgCl}_{2}\), (e) \(0.50 \mathrm{~mol} \mathrm{Cl}_{2}\).

Look up the atomic weights of the elements. Chlorine's atomic weight is approximately \(35.45 \mathrm{~g/mol}\). Then, calculate the molar mass for the compounds \(\mathrm{NaClO}_{3}, \mathrm{KCl}, \) and \(\mathrm{MgCl}_{2}\) , which are approximately \(106.44 \mathrm{~g/mol}\), \(74.55 \mathrm{~g/mol}\) and \(95.21 \mathrm{~g/mol}\) respectively.

Calculate the mass of chlorine in each substance. For (a), the mass is directly given as \(5.0 \mathrm{~g}\). For (b), the mass of chlorine is \(\frac{1}{3} \times 60.0 \mathrm{~g} = 20.0 \mathrm{~g}\), since \(\mathrm{NaClO}_{3}\) contains one chlorine atom per every three atomic units. For (c), the mass of chlorine is \(0.10 \mathrm{~mol} \times 35.45 \mathrm{~g/mol} = 3.545 \mathrm{~g}\). For (d), the mass of chlorine is \(\frac{2}{3} \times 30.0 \mathrm{~g} = 20.0 \mathrm{~g}\), since \(\mathrm{MgCl}_{2}\) contains two chlorine atoms per every three atomic units. For (e), the mass of chlorine is \(0.50 \mathrm{~mol} \times 70.90 \mathrm{~g/mol} = 35.45 \mathrm{~g}\), since molecular chlorine contains two chlorine atoms.

Compare the masses calculated in step 2. The substance with the greatest mass of chlorine is (e) \(0.50 \mathrm{~mol} \mathrm{Cl}_{2}\) with a mass of \(35.45 \mathrm{~g}\), followed by (a), (b) and (d) with masses of \(20.0 \mathrm{~g}\). The substance with the least mass of chlorine is (c) \(0.10 \mathrm{~mol} \mathrm{KCl}\) with a mass of \(3.545 \mathrm{~g}\).