Mass-to-Mass Stoichiometry: Worked Examples

📚 Quick Study Guide

• ⚖️ Stoichiometry: The study of the quantitative relationships or ratios between two or more substances undergoing a physical change or chemical change.
• 🧱 Mass-to-Mass Stoichiometry: Involves calculating the mass of a reactant or product given the mass of another reactant or product in a balanced chemical equation.
• 📝 Steps:
  1. Balance the chemical equation.
  2. Convert the mass of the given substance to moles using its molar mass.
  3. Use the stoichiometric ratio from the balanced equation to determine the moles of the desired substance.
  4. Convert the moles of the desired substance back to mass using its molar mass.
• ⚗️ Formula: $moles = \frac{mass}{molar\,mass}$ or $mass = moles \times molar\,mass$
• 💡 Important Tip: Always double-check your units and make sure the chemical equation is balanced before starting any calculations!

🧪 Practice Quiz

1. What is the first step in solving a mass-to-mass stoichiometry problem?
   1. A. Convert mass to volume
   2. B. Balance the chemical equation
   3. C. Calculate the molar mass of the reactants
   4. D. Convert mass to moles
2. If 10.0 g of $CaCO_3$ decomposes according to the equation $CaCO_3(s) \rightarrow CaO(s) + CO_2(g)$, what mass of $CaO$ is produced? (Molar mass of $CaCO_3 = 100.09 \frac{g}{mol}$, Molar mass of $CaO = 56.08 \frac{g}{mol}$)
   1. A. 5.61 g
   2. B. 10.0 g
   3. C. 28.04 g
   4. D. 56.08 g
3. In the reaction $2H_2(g) + O_2(g) \rightarrow 2H_2O(g)$, how many grams of water can be produced from 4.0 g of $H_2$? (Molar mass of $H_2 = 2.02 \frac{g}{mol}$, Molar mass of $H_2O = 18.02 \frac{g}{mol}$)
   1. A. 9.0 g
   2. B. 18.0 g
   3. C. 36.0 g
   4. D. 72.0 g
4. What is the molar mass of $NaCl$? (Molar mass of $Na = 22.99 \frac{g}{mol}$, Molar mass of $Cl = 35.45 \frac{g}{mol}$)
   1. A. 11.7 g/mol
   2. B. 58.44 g/mol
   3. C. 12.46 g/mol
   4. D. 70.90 g/mol
5. If 5.0 g of $CH_4$ reacts with excess oxygen according to the equation $CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g)$, what mass of $CO_2$ is produced? (Molar mass of $CH_4 = 16.04 \frac{g}{mol}$, Molar mass of $CO_2 = 44.01 \frac{g}{mol}$)
   1. A. 6.86 g
   2. B. 13.7 g
   3. C. 11.0 g
   4. D. 5.0 g
6. For the reaction $N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$, if you start with 14.0 g of $N_2$, what mass of $NH_3$ can be produced? (Molar mass of $N_2 = 28.02 \frac{g}{mol}$, Molar mass of $NH_3 = 17.03 \frac{g}{mol}$)
   1. A. 8.52 g
   2. B. 17.0 g
   3. C. 34.1 g
   4. D. 14.0 g
7. How many grams of $O_2$ are required to completely react with 10.0 g of $Mg$ according to the equation $2Mg(s) + O_2(g) \rightarrow 2MgO(s)$? (Molar mass of $Mg = 24.31 \frac{g}{mol}$, Molar mass of $O_2 = 32.00 \frac{g}{mol}$)
   1. A. 6.58 g
   2. B. 10.0 g
   3. C. 13.16 g
   4. D. 20.0 g