College Chemistry I Chem 1806 Lab Report 4 As

Name College Chemistry I Chem 1806lab Report 4 As

Complete the following table. (10 points) Data Table 1 Initial: CaCl2•2H2O (g) Initial: CaCl2•2H2O (moles) Initial: CaCl2 (moles) Initial: Na2CO3 (moles) Initial: Na2CO3 (g) Theoretical: CaCO3 (g) Mass of Filter Paper (g) Mass of Filter Paper + CaCO3 (g) Actual: CaCO3 (g) % Yield

2. A perfect percent yield would be 100%. Based on your results, describe your degree of accuracy.

3. Describe how conservation of mass could be checked in the experiment performed.

4. Determine the quantity of pure CaCl2 in 7.5 g of CaCl2•9H2O.

5. Is it possible to get a percent yield over 100%? Be sure to explain your reasoning behind your answer.

6. Provide a written summary of your results in your own words. Be sure to explain your results and provide an explanation if anything went wrong in your experiment.

Paper For Above instruction

The aim of this laboratory report is to analyze the stoichiometry of a precipitation reaction involving calcium chloride dihydrate (CaCl2•2H2O) and sodium carbonate (Na2CO3). The experiment focuses on quantifying the theoretical yields, measuring the actual precipitate formed, calculating the percent yield, and reflecting on sources of error and the conservation of mass principle.

Introduction

Stoichiometry provides the quantitative basis to predict the amounts of reactants and products in chemical reactions. Precipitation reactions, characterized by the formation of insoluble solids, serve as a practical demonstration of stoichiometric principles. The specific reaction examined involves calcium chloride dihydrate reacting with sodium carbonate to form calcium carbonate precipitate, sodium chloride, and water:

CaCl₂•2H₂O (aq) + Na₂CO₃ (aq) → CaCO₃ (s) + 2 NaCl (aq) + 2 H₂O (l)

This reaction illustrates the principles of molar ratios and hydration effects, which influence the calculation of theoretical yields and actual product recovery.

Methodology

The experiment begins with the accurate weighing of CaCl₂•2H₂O, followed by converting this mass into moles using the molar mass derived from the periodic table. Similarly, the molar amount of sodium carbonate is calculated from measured mass. The solutions are prepared by dissolving the prescribed amounts of reactants in distilled water, then mixed to precipitate calcium carbonate.

For precipitate collection, the solution is filtered through a pre-weighed filter paper, which is then dried overnight. Post-drying, the filter paper with precipitate is weighed, and the actual mass of calcium carbonate is determined by subtracting the weight of the dry filter paper. Theoretical yields are calculated based on molar ratios and limiting reactant considerations, while percent yield is obtained by comparing actual and theoretical masses of precipitate.

Results and Calculations

Suppose the initial mass of calcium chloride dihydrate (CaCl₂•2H₂O) used was 5.0 g. The molar mass of CaCl₂•2H₂O is approximately 147.01 g/mol (per IUPAC standards). The moles of CaCl₂•2H₂O in 5.0 g are calculated as:

n = 5.0 g / 147.01 g/mol ≈ 0.03402 mol

Since each mole of CaCl₂•2H₂O contains one mole of CaCl₂ (excluding water molecules), the moles of CaCl₂ are approximately 0.03402 mol. The molar mass of CaCO₃ (calcium carbonate) is about 100.09 g/mol, thus the theoretical maximum mass of CaCO₃ produced is:

mass = 0.03402 mol × 100.09 g/mol ≈ 3.404 g

In the experiment, after filtration and drying, suppose the dry precipitate mass measured was 3.2 g. The percent yield would be:

Percent yield = (actual yield / theoretical yield) × 100 = (3.2 g / 3.404 g) × 100 ≈ 94.0%

Discussion

The calculated percent yield of approximately 94% indicates a high level of experimental accuracy, though slight deviations could be attributed to procedural losses such as incomplete filtration, moisture retention, or weighing errors. A percent yield over 100% is theoretically impossible under perfectly controlled conditions, as it would suggest obtaining more product than the maximum predicted, possibly due to impurities, residual moisture, or measurement inaccuracies.

Conservation of mass can be confirmed by verifying that the combined mass of all reactants equals the total mass of precipitated calcium carbonate plus the remaining solution. In practice, some minor mass loss occurs through evaporation or incomplete transfer, but these should be minimal if procedures are carefully followed.

Furthermore, hydration water in CaCl₂•2H₂O does not participate in the precipitation reaction, emphasizing the importance of converting hydrate to anhydrous molar quantities for accurate calculations.

Conclusion

This experiment demonstrates the application of stoichiometry and the principles of conservation of mass in a precipitation reaction. The high percent yield affirms the reliability of the methods used, although minor sources of error such as incomplete drying or measurement inaccuracies can affect results. Understanding these factors is crucial for precise quantitative analysis in analytical chemistry.

References

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