Decomposition of Sodium Bicarbonate

1 Experiment 12: Decomposition of Sodium Bicarbonate Objective: To experimentally determine decomposition reaction of sodium hydrogen carbonate on reaction stoichiometry. Introduction: Chemicals can undergo many different reactions, such as synthesis reactions that create new substances, or combustion reactions, in which a substance usually reacts with oxygen and generates energy in the form of heat. Another reaction type is the decomposition reaction, which is the opposite of a synthesis reaction. When a chemical substance decomposes it breaks down to form two or more separate compounds. Sodium bicarbonate (N aHCO3 ) , or baking soda is a chemical that can undergo a decomposition reaction when heated. There are three theoretically possible chemical reactions that could occur during the thermal decomposition of baking soda. 1) sodium bicarbonate (s) → sodium hydroxide (s) + carbon dioxide (g) 2) sodium bicarbonate (s) → sodium oxide (s) + carbon dioxide (g) + water (g) 3) sodium bicarbonate (s)→ sodium carbonate (s) + carbon dioxide (g) + water (g) Procedure: In the lab, the decomposing of baking soda (sodium hydrogen carbonate or sodium bicarbonate) and use of the mass relationships were used to determine how sodium bicarbonate decomposes. By comparing the theoretical yields of the possible solid products with the actual experimental yield of the product, it was determined which of the above decomposition reactions 2 occurred. The products were from the thermal decomposition of sodium bicarbonate. A clean beaker was weighed and recorded. Four to five grams of sodium bicarbonate was added to the beaker and the weight was recorded. A hot plate was set at 20 ° C and the beaker was added to the hot plate for 15 minutes. The beaker was taken off the hot plate and cooled until it reached room temperature. The beaker was reweighed. A new clean dry beaker was weighed. Four to five grams of sodium bicarbonate and reweighed. The hot plate was set to 400 ° C . The beaker was put on the hot plate and heated for 15 minutes. The beaker was then removed from the hot plate and allowed to cool to room temperature. The beaker was reweighed. The waste was then disposed of in the waste container. Results: Mass of Test Tube: 43.29g Mass of test tube + Sodium bicarbonate: 48.87g Mass of Sodium bicarbonate: 5.58g Initial mass of test tube plus product after heating: 46.81g Mass of product (actual yield): 2.6 1) Balance the reactions for the three theoretical decomposition reactions. A. sodium bicarbonate (s) → sodium hydroxide (s) + carbon dioxide (g) _NaHCO 3 (s) → ___NaOH(s) + (Reaction A) ___ C O 2 (g) B. sodium bicarbonate (s) → sodium oxide (s) + carbon dioxide (g) + water (g) __2_ N aHCO 3 (s) → ___ N a 2O (s) + _2__CO 2 (g) + ___H 2 O (g) (Reaction B) 3 C. sodium bicarbonate (s) _2__NaHCO3(s) → → sodium carbonate (s) + carbon dioxide (g) + water (g) ___Na2CO3(s) + ___CO2(g) + (Reaction C) ___H2O(g) 2) Using the mass of sodium bicarbonate used, calculate the theoretical yield of solid products from each of the possible decomposition reactions, then calculate the percent yield by dividing your actual yield by the theoretical yield you calculate for each reaction. Percent yield = | 𝑎𝑐𝑡𝑢𝑎𝑙 𝑦𝑖𝑒𝑙𝑑 /𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑦𝑖𝑒𝑙𝑑 | x 100 Reaction A ___NaHCO3(s) → ___NaOH(s) + ___CO2(g) Initial grams of NaHCO3 = ___5.58____ Molar mass= 84.001 Initial moles = 0.0664 mols (5.58/84.001) 40 5 = .66g 2 Theoretical yield= 5.58 N aHCO 3 → 84 × .58 2.6 Percent Yield of NaOH= 2.7 × 100 = 96.2% Reaction B Initial grams of NaHCO3(s)= 5.58 Molar mass= 168g Initial moles = .033 moles 62 5 Theoretical yield= 5.58 N aHCO 3 → 168 ×.58 2.6 Percent Yield of NaOH= 2.1 × 100 =123% Reaction C Initial grams of NaHCO3(s)= 5.58 Molar mass= 168g Initial moles = .033 moles 106 5 Theoretical yield= 5.58 N aHCO 3 → 168 ×.58 2.6 × 1 = 00 Percent Yield of NaOH= 3.53 74.2% Discussion/ Conclusion: =2.05 = 3.52 4 Which reaction was closest to 100% yield? Reaction A is the closest to 100% yield Do you think that the sodium bicarbonate turned into NaOH, Na2O, or Na2CO3? Was this expected or unexpected? Explain briefly. I think sodium bicarbonate turned into Na2CO3. I feel as thought it was expected because during the heating process something was evaporating off.