Introduction – The objective of this lab is to better understand Stoichiometry by investigating sodium salts in carbonic acids. Stoichiometry is the study of the amounts of substances that are involved in reactions. This could be either before the reaction takes place or after the reaction takes place. For this lab the reactants are NaHCO3 + HCl and Na2CO3 + HCL and the products are NaCl + H20 + CO2 and CO2 + H2O + 2NaCl. Stoichiometry can be used to find the amount of products and the percent yield. Reaction stoichiometry describes the quantitative relationships among substances as they participate in chemical reaction. Composition stoichiometry describes the relationships of mass among elements in compounds. Mole relationships in a chemical reaction can be determined by looking at the balanced reaction equation. My hypothesis is that if we correctly do the step by step procedures then we will demonstrate Stoichiometry correctly.
My expected results are a 1 to 1 mole ratio for NaHCO3 and NaCl and a 1 to 2 mole ratio for Na2CO3 and NaCl. Procedure – Weigh a beaker and record its mass. Add approximately .15 grams of sodium carbonate into the beaker and record the mass of the beaker and sodium carbonate. Add 40 mL of water into the beaker. Stir the beaker to combine the sodium carbonate and water. Add HCl from a beret while stirring until the mixture turns slightly green. Put the beaker on a hotplate until it starts boiling. Take the beaker off the hotplate and let the beaker cool. Once the beaker is cool add more HCl until the mixture is yellow. Then put the mixture back on the hotplate. Once the liquid has dissolved measure the remaining substance. Minus this amount from the initial weight of the empty beaker. We will do this once more for unknown substance #1 and twice for unknown substance #2. Wear safety goggles, gloves, and lab coat while participating in this lab to minimize any safety risks. Results:
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The rates at which reactions occur depend on the composition and the temperature of the reaction mixture. Usually the rate of reaction is found to be proportional to the concentrations of the reactants raised to a power.1 There are many reactions that have a rate law in the form of: (1) v = k[A]a[B]b According to reference1 the power to which the concentration of a species (product or reactant) is ...
Though we were only able to obtain the final weight of unknown solid #2 trial #1 NaCl after evaporation the amount was .12 grams. The final weight of NaCl for unknown #1 after evaporation was .08 grams for trial 1 and .05 grams for trial 2. A trend noticed in this lab was that it took a higher volume of HCl to get to the yellow mixture for unknown substance #2 trial 1 and trial 2 compared to unknown substance #1 trial 1 and trial 2. There was also a negative trend for unknown substance #1 for the final weight of NaCl moving from .08 grams in trial 1 to .05 grams in trial 2. The percent yield for unknown substance #1 trial 1 was 53.086% and for trial 2 was 33.268%. Again, we were only able to obtain the final weight of unknown solid #2 trial #1 NaCl after evaporation the percent yield was 80%. Discussion:
The data is unreasonable, the reason being is that both unknown substances were below 100% percent yield making both of them NaHCO3. This shouldn’t happen in this lab, the reason being is that one of the unknowns should have over 100% yield and one should have under 100% yield. This would show which substance was NaHCO3 (Under 100% yield) and which substance was Na2CO3 (Over 100% yield).
The reason for this is that near the end of this lab we were rushing for time so this factor might have changed our results for the unknown substance #2. It also took an increased amount of titration for unknown substance #2 trial #1 and trial #2 in order to titrate completely. This could have also skewed our results for the unknown substance #2. Conclusion:
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In conclusion, even though the data was unreasonable. The main lesson was learned during the lab. This being that we learn chemical stoichiometry. We did this by first by balancing the chemical equations NaHCO3 + HCL = NaCl + H20 + CO2 and Na2CO3 + HCL = CO2 + H2O + 2NaCL during the pre-lab. Then we titrated unknown substance #1 and unknown substance #2 and this showed us the percent yield of NaCl. This percent yield was to show us the difference between NaHCO3 and Na2CO3. This didn’t happen; however, the reason being that all the yield percentage results were under 100% with unknown substance #1 trial #1 being 53.086% and trial #2 being 33.268% and unknown substance #2 trial #2 being 80%. This didn’t demonstrate what was supposed to happen in our lab but the main lesson was still learned during this procedure.
