Exercises

Exercise 1. How many carbon dioxide, CO₂, molecules are in 0.845 moles?

\(\displaystyle 0.845 mol\times\frac{6.02\times 10^{23}\;molecules}{1\;mol}\;=\;5.09\times 10^{23}\;CO_2\;molecules\)

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Exercise 2. A sample contains 255.25 g of FeCl₂. How many Fe²⁺ ions are in this sample?

\(\displaystyle 255.25\;g\;FeCl_2\times\frac{1\;mol\;FeCl_2}{126.751\;g/mol}\times\frac{1\;mol\;Fe^{2+}}{1\;mol\;FeCl_2}\times\frac{6.02\times 10^{23}\;ions}{1\;mol\;Fe^{2+}}=\)
= 1.21 x 10²⁴ ions

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Exercise 3. How many sodium ions and how many phosphate ions are in 22.65 g of Na₃PO₄?

\(\displaystyle 22.65\;g\;Na_3PO_4\times\frac{1\;mol\;Na_3PO_4}{163.94\;g}\times\frac{3\;mol\;Na^+}{1\;mol\;Na_3PO_4}\times\frac{6.02\times10^{23}Na^+}{1\;mol\;Na^+}=\)
2.50 x 10²³Na⁺ ions

\(\displaystyle 22.65\;g\;Na_3PO_4\times\frac{1\;mol\;Na_3PO_4}{163.94\;g}\times\frac{1\;mol\;PO_4^{3-}}{1\;mol\;Na_3PO_4}\times\frac{6.02\times10^{23}PO_4^{3-}}{1\;mol\;PO_4^{3-}}=\)
8.32 x 10²² PO₄^3- ions.

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Exercise 4. How many oxygen atoms are in 45.52 g of Al₂(CO₃)₂?

\(\displaystyle 45.52\;g\;Al_2(CO_3)_3\times\frac{1\;mol\;Al_2(CO_3)_3}{96.09\;g\;Al_2(CO_3)_3}\times\frac{9\;mol\;O}{1\;mol\;Al_2(CO_3)_3}\times\frac{6.02\times 10^{23}\;O\;atoms}{1\;mol\;O}\)
= 2.57 x 10²⁴ O atoms

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Exercise 5. A sample of MgS has 2.64 x 10²⁴ sulfur ions. What is the mass of the original sample of MgS?

\(\displaystyle 2.64\times 10^{24}\;S ions\times\frac{1\;mol\;S}{6.02\times 10^{23}\;S\;ions}\times\frac{1\;mol\;MgS}{1\;mol\;S}\times\frac{56.38\;g}{1\;mol\;MgS}=247\;g\;MgS\)

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