Stoichiometry Lab: Calcium Carbonate Synthesis Notes

Thermal Decomposition of Sodium Bicarbonate

• Initial Reactant: Sodium bicarbonate ($NaHCO_3$), commonly known as baking soda.
• Chemical Reaction: $2NaHCO_3(s) \rightarrow Na_2CO_3(s) + H_2O(g) + CO_2(g)$.
• Purpose: To produce sodium carbonate ($Na_2CO_3$) for subsequent synthesis as it is not available in the stock room.
• Quantitative Check: Identifying completion happens when the thermal decomposition reaction stops producing gas/loses mass consistent with theoretical yields from an initial mass (e.g., $3.00\,g$).

Synthesis of Calcium Carbonate

• Double Replacement Reaction: $CaCl_2(aq) + Na_2CO_3(aq) \rightarrow CaCO_3(s) + 2NaCl(aq)$.
• Product: Calcium carbonate ($CaCO_3$), identified as the primary component of Chaulk.
• Solubility and Precipitation:
  • $Na_2CO_3$ and $CaCl_2$ are soluble.
  • $CaCO_3$ is insoluble (forming a solid precipitate).
  • $NaCl$ remains soluble in the aqueous phase.
• Excess Reactant: We use a $25\%$ excess of calcium chloride ($CaCl_2$) to ensure all sodium carbonate is consumed.

Experimental Procedures and Precision

• Solution Preparation: Both reactants must be dissolved in water before mixing.
• Volume Requirements: Precise water measurements are secondary to the mass of the solute, provided the solubility limit is not exceeded to ensure total dissolution.
• Separation: To obtain pure calcium carbonate powder, the mixture must be filtered, washed to remove $NaCl$, and dried.

Percent Yield Calculation Example

• Experimental Data:
  • Starting mass of sodium bicarbonate: $3.83\,g$.
  • Final mass of dry calcium carbonate powder: $1.86\,g$.
• Yield Assessment: The percent yield is calculated by comparing the actual recovered mass ($1.86\,g$) to the theoretical yield derived from the starting $3.83\,g$ of sodium bicarbonate.