Chemistry Limiting Reactant Lab

0.018 ± 9 x 10-4mol Na2CO3(aq) : 0.018 ± 9 x 10-4mol CaCO3(s)                  0.013 ± 7 x 10-4mol CaCl2(aq)  : 0.013 ± 7 x 10-4mol CaCO3(s)        

 CaCl2(aq) is the limiting reactant and Na2CO3(aq) is excess

2. Theoretical yield:                                 Percentage Yield:

                   

Follow Up Questions

1. If you were to evaporate the filtered solution to dryness, would you be left with only solid NaCl? Explain.

If the filtered solution was evaporated to dryness, one would not be left with only solid NaCl(aq) as there would also be Na2CO3(aq) and maybe some residual CaCO3(s). It is determined that sodium carbonate is excess because there are more moles of it (0.018 ± 9 x 10-4mol) than of calcium chloride (0.013 ± 7 x 10-4mol) in the reaction. Because sodium carbonate is the excess reactant, not all of it is used in the reaction. This means that 0.005 ± 2 x 10-3mol of the excess reactant would also be found in the filtered solution as it did not react with the calcium chloride and is soluble. Therefore, when evaporating the filtered solution to dryness, there would also be sodium carbonate.

Furthermore, the filter paper is not completely efficient in obtaining the calcium carbonate precipitate as the percentage yield is only 92 ± 9%. This means that the actual yield does not equal the theoretical yield. This leaves room for the other approximately 8% of the precipitate to be left in the filtered solution. Furthermore, because two funnels were used due to the fact that the filter paper was not the correct size, may lead to some solution not being filtered through the filter paper due to human error. This may also account for the CaCO3 that would be found if the filtered solution was evaporated to dryness. Therefore, one would not be left with only solid NaCl if the solution were evaporated.

2. What theoretical volume of the Na2CO3 solution used in this experiment would result in no excess reactant?

Therefore, the theoretical volume of the Na2CO3 solution is 19 ±2mL.

3. A precipitation reaction occurs when 50.0mL of 0.50M BaCl2(aq) is mixed with 75.0mL of 0.75M of Na2CO3(aq). The only precipitate is the BaCO3(s) formed.

1. Write the balanced equation that describes this reaction.

BaCl2(aq) + Na2CO3(aq) → BaCO3(s) + 2NaCl(aq)

2. Which chemical is the limiting reactant?

BaCl2(aq) + Na2CO3(aq) → BaCO3(s) + 2NaCl(aq)

V=0.0500mL V=0.0750mL    MM=197.34g/mol

Assume BaCl2(aq) is limiting                         Assume Na2CO3(aq) is limiting

                 

1 mol BaCl2(aq) : 1 mol BaCO3(s)                              1 mol Na2CO3(aq): 1 mol BaCO3(s)        

0.025 mol BaCl2(aq) : 0.025 mol BaCO3(s)               0.056 mol Na2CO3(aq): 0.056 mol BaCO3(s)

 BaCl2(aq) is the limiting reactant and Na2CO3(aq) is excess.

3. Predict the theoretical mass of BaCO3(s) that should form.

 The theoretical mass of BaCO3(s) is approximately 4.9g

4. This experiment was conducted and the percent yield was found to be 82%. What was the actual mass of BaCO3(s) that formed?

Percentage Yield:

82%

Conclusion and Evaluation

        In conclusion, the reaction between sodium carbonate and calcium chloride results in sodium chloride and a calcium carbonate precipitate. The limiting reactant is deduced to be calcium chloride and the excess reactant is sodium carbonate. By using the chemical equation and the mass of the precipitate to find the limiting and excess reactants and the percentage yield, one reaches this conclusion. Calcium chloride appears to be the limiting reactant because there are fewer moles present in the reaction compared to sodium carbonate. Furthermore, because the percentage yield is 92 ± 9% instead of 100%, there is room for error and weaknesses in the experiment.

        Some weaknesses found in the experiment include the fact that some of the precipitate may not have been caught on the filter paper as the filter paper is not completely efficient. As well, the filter paper was not the same size as the funnel, thus two funnels were used one within the other leaving room for some of the solution to escape the filter paper. This may account for the difference in the theoretical yield and actual yield. Furthermore, because there are uncertainties in all the equipment used, there is a margin of error associated with each apparatus. Nevertheless, the margin of error increases when performing various calculations such as concentration and volume. Therefore all calculations will not be perfectly accurate resulting in discrepancies in comparison to theory. Moreover, some of the calcium carbonate precipitate coated the bottom of the beaker. Because of this fact, some of the mass of the precipitate may have been lost as the coating of the precipitate could not be removed. Using another object such as a cleaning rod would bring other factors into the experiment as some of the precipitate may have coated the cleaning rod which would lead to more inefficiencies. Lastly, human error is another weakness associated with this experiment. This could account for any spillage or human mistakes that may have been made throughout the course of the experiment.

        In order to improve the investigation one can use filter paper that is the same size as the funnel as this will omit room for human error. This will prevent some solution from being poured into the second funnel that was used in the experiment not allowing the precipitate to be filtered correctly. In addition, after filtering the solution through once and rinsing the beaker with distilled water, the solution should be filtered through the filter paper once again in order to increase the efficiency. Thus, if some precipitate went through once, it may be able to be caught on the filter paper the second time.

        In conclusion, the experiment proved to be quite successful with a percentage yield of 92 ± 8%. In order to improve the experiment further, the improvements suggested above can help ensure a more accurate experiment.