Experiment 8: Limiting Reactant

Pre: What are the reactants in the experiment?

- Calcium Chloride Dihydrate (Ca2Cl2 x 2H2O) - Potassium Oxcelate Monohydrate (K2C2O2 x H2O)

How is the limiting reactant determined in the experiment?

Once you filter the solution, you centrifuge it and take out the supernatant to get the reagent.

A couple of drops of water were accidentally placed on the properly folded filter paper before its mass was measured. However, in Part A.6, the Ca2C2O4 x H2O precipitate and the filter paper were dry . Ass a result of this sloppy technique, will the mass of the limiting reactant be reported too high, to low, or remain unaffected? Explain.

The mass of the limiting reactant will be too low.. The water will add more mass to the filter paper. Once the filter paper and precipitate has dried, there will be a greater loss in mass; however, the loss in mass will be attributed to the precipitate and not the filter paper.

Excessive quantities of wash water are added to the CaC2O4•H2O precipitate. Will the mass of the CaC2O4•H2O be reported too high, too low, or remain unaffected? Explain.

The reported mass of CaC2O4xH2O will be too low. Every time the precipitate is washed the CaC2O4xH2O dissolves. With excessive amounts of wash water there will be a bigger loss of CaC2O4xH2O precipitate.

The CaC2O4•H2O precipitate is not completely air-dried when its mass is determined. Will the reported mass of the limiting reactant in the original salt mixture be reported too high or too low? Explain.

The reported mass of the limiting reactant in the original salt mixture will be too high. Since it is not completely dry there is water still in there which adds mass. This larger mass will result in a larger number when calculating the limiting reactant.

The drying oven, although thought (and assumed) to be set at 125°C, had an inside temperature of 84°C. How will this error affect the reported percent by mass of the limiting reactant in the salt mixture . . . too high, too low, or unaffected? Explain.

The reported mass of the limiting reactant in the original salt mixture will be too high. The mass recorded will be too high if it is not completely dry. This larger mass will result in a larger number when calculating the limiting reactant.

If the step for digestion the precipitate were omitted, will the reported "percent limiting reactant" in the salt mixture be too high, too low, or unaffected? Explain.

The reported percent limiting reactant would be too low. The purpose of digesting the participate is so that the filtering process will be more efficient. If we omitted this step, the amount of product collected would be smaller. This would decrease the amount in the limiting reactant.

Because of the porosity of the filter paper some of the CaC2O4•H2O precipitate passes through the filter paper. Will the reported percent of the limiting reactant in the original salt mixture be reported too high or too low? Explain.

The reported percent of the limiting reactant will be too low. The loss of the precipitate will lower the amount reported since it passed through the filter and was not collected. Therefore, lowering the percent of the limiting reactant of the original salt.

Because of the small particle size of the CaC2O4 x H2O precipitate, some of it passes through the filter and is not collected. How does this loss of precipitate affect the reported percentage of the limiting reactant in the salt mixture?

The reported percentage of the limiting reactant will be less because of the loss precipitate.

What does the expression, "digesting a precipitate" mean?

To heat up the precipitate at 75 degrees C for 15 minutes so that the bigger crystals can form resulting in more efficient filtering.

A reagent bottle on the shelf labeled 0.5 M NaCl was used in place of the 0.5 M CaCl2. Assuming C2O42- to be in excess, what would be observed as a result of using this wrong reagent in this test? Explain.

You would not be able to tell what was in excess since there would be both Ca2+ and C204^2- in both of the volumes.

In a hurry to complete the experiment, Anna withdrew two volumes of solution from Part A.2 before the precipitate had settled. As a result, what dilemma might she have encountered in Part B? Explain.

You would not be able to tell what was in excess since there would be both Ca2+ and C204^2- in both of the volumes.