Lab 6: Mole-Mass Relationships Lab

The purpose of this lab was to practice calculating both theoretical and percent yields, and look at the relationship between moles and mass. The reaction we investigated was NaHCO3 + HCl => NaCl + CO2 + H2O. My lab partner Leila and I predicted how much NaCl would remain at the end of the lab by using conversions to see how much NaCl would result as a product of two grams of the reactant NaHCO3. We had to convert two grams of NaHCO3 to moles, then used the mole ratio in the equation (1 NaHCO3 : 1 NaCl), and then converted to grams of NaCl. This helped us practice theoretical yield calculations. We then did the lab, boiling down the H2O in our evaporating dish until it was mostly evaporated and only the NaCl remained. After weighing the dish and the NaCl, we found the mass of the NaCl and used that and our theoretical yield to calculate our percent yield. 

Above is the product, NaCl, after the H2O was evaporated out of the dish. The yellow-green color on the top could have resulted due to contamination from the tongs used to lift the dish.

1. Which reactant is limiting? How do you know?

NaHCO3 is the limiting reactant. This is because we added as much of the other reactant (HCl) as needed to a measured amount of NaHCO3. We also didn't need to use of the 15 mL of HCl that we measured, showing that it wasn't limiting.

2. Find the theoretical yield of NaCl based on your limiting reactant. Show your work below.

(2.00g NaHCO3 / 1) * (1 mol NaCO3 / 84.006g NaCO3) * (1 mol NaCl / 1 mol NaHCO3) * (58.443g NaCl / 1 mol NaCl) = 1.3914 g = 1.39g NaCl

3. Find the mass for the remaining solid product after the evaporation of water based on your experimental data.

46.30g (mass of dish + remaining solid product) - 44.91g (mass of dish) = 1.39g

4. Find the percent yield for this experiment for the solid product.

(1.39g (actual) / 1.39g (theoretical)) * 100 = 100%

Since it was probably very unlikely to actually achieve a 100% yield, there are possible sources that would allow this to happen. While the NaCl began to pop after boiling, some of the product could have popped out of the dish, lowering the mass. However, we could have not boiled down all the H2O, which would increase the mass. These two factors could even out to produce a 100% yield. The scale also fluctuated, which could have lead to a reading that was not completely accurate.