The purpose of today's lab is to look into the relationship between moles and mass in chemical reactions, and to find the percent yield of a product.
Equation of chemical reaction: NaHCO3 (s) + HCl (aq) ==> NaCl (aq) + CO2 (g) + H2O (g)
Using a known mass of sodium hydrogen carbonate, my lab partner, Orest, and I added hydrochloric acid and found the relationships within the equation above. Below are some questions regarding the lab with my answers.
Questions:
1) Which reactant is limiting? How do you know?
The limiting reactant in this lab is the sodium hydrogen carbonate. I know this because the hydrochloric acid was added until the substance stopped fizzing. As there was no limit to the HCl added until there was no NaHCO3 left for it to react with, the latter is limiting.
2) Find the theoretical yield of NaCl based on your limiting reactant. Show your work below.
(2.05g NaHCO3 / 1) x (1 mol NaHCO3 / 84.0g NaHCO3) x (1 mol NaCl / 1 mol NaHCO3) x
(58.4g NaCl / 1 mol NaCl) = 1.425 g
1.43g NaCl
3) Find the mass for the remaining solid product after the evaporation of water based on your experimental data. (Show work.)
45.48g - 44.23g = 1.25g NaCl
4) Find the percent yield for this experiment for the solid product. (Show work.)
(1.25g / 1.43g) x 100 = 87.4%
NaCl ultimately left in the dish:
There could be various reasons as to why our percent yield is 87.4% rather than 100%. Firstly, we noticed that some salt (NaCl) ended up on the lab desk, instead of in the evaporating dish. This could have been caused by our not holding the watch glass close enough to the rim of the dish, allowing some NaCl particles to fly onto the desk. Additionally, we may have kept the evaporating dish on the hot plate for too long on our last heating. It is faint in the photo above but in the lab, Orest and I noticed that there is some brown coloring in the center ring of the NaCl. We concluded that the salt may have burned. Therefore, the salt mass ended up being less than the theoretical yield.
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