Stoichiometry & Percent Yield:

Stoichiometry & Percent Yield: Decomposition of Sodium Bicarbonate

Purpose

  • To determine the products, stoichiometry, theoretical yield, and percent yield of the decomposition of sodium bicarbonate.

  • To learn how to work with a Bunsen burner.

Background

  • Sodium Bicarbonate: A chemical commonly found in kitchens, also known as baking soda, used as a leavening agent in baking.

  • Decomposition Reaction: During baking, sodium bicarbonate undergoes decomposition to produce carbon dioxide, causing baked goods to rise.

  • Possible Decomposition Reactions:

    1. ext{sodium bicarbonate (s)}
      ightarrow ext{sodium hydroxide (s)} + ext{carbon dioxide (g)}

    2. ext{sodium bicarbonate (s)}
      ightarrow ext{sodium oxide (s)} + ext{carbon dioxide (g)} + ext{water (g)}

    3. ext{sodium bicarbonate (s)}
      ightarrow ext{sodium carbonate (s)} + ext{carbon dioxide (g)} + ext{water (g)}

  • Each reaction produces a solid product along with gaseous products that may be released due to heat.

  • Objective: To determine the mass of solid products generated and compare it with the theoretical yield of each reaction to identify which reaction occurred.

Procedure

Items Provided

  • Baking soda

Safety Note

  • The experiment involves the use of Bunsen burners. A demonstration on safe operation will occur during pre-lab lectures.

  • Crucible Handling:

    • Use crucible tongs to handle the hot porcelain crucible to avoid burns and contamination from skin oils, which can alter weight.

Part A: Mass of the Empty Crucible

  1. Setup:

    • Place a clean crucible and lid on a ceramic triangle atop an iron ring clamp attached to a ring stand (as shown in experimental setup figure).

  2. Heating:

    • Heat the crucible using a Bunsen burner for 5 minutes at a low temperature (outer flame).

  3. Cooling:

    • Remove the crucible and lid using crucible tongs and place it on wire gauze on the benchtop. Let it cool for approximately 10 minutes.

  4. Mass Measurement:

    • Record the mass of the empty crucible. Ensure the same balance is used for all mass measurements throughout the experiment.

Part B: Mass of the Crucible and Sodium Bicarbonate

  1. Addition of Sodium Bicarbonate:

    • Keeping the crucible on the balance, add approximately 5 g of sodium bicarbonate into the crucible.

  2. Mass Measurement:

    • Record the total mass of the crucible along with the sodium bicarbonate.

Part C: Decomposition of Sodium Bicarbonate

  1. Heating:

    • With the Bunsen burner, heat the crucible containing sodium bicarbonate at a low flame (outer cone) for 2 minutes and then switch to a high flame (tip of inner cone) for 8-10 minutes.

  2. Cooling:

    • After heating, remove the crucible and let it cool on wire gauze for 10-15 minutes. Record the mass of the crucible along with the resultant decomposition products.

  3. Reheating:

    • Repeat heating and cooling to ensure accuracy. If mass difference between cycles is greater than 0.1 g, continue heating to ensure all sodium bicarbonate is decomposed and any gaseous products are expelled.

Results

  1. Mole Calculation:

    • Determine the number of moles of sodium bicarbonate added to the crucible.

  2. Theoretical Yield Calculation:

    • Calculate the theoretical yield of solid products for each of the three reactions described in the background.

  3. Product Identification:

    • Based on theoretical yield calculations versus actual yield, identify the solid product formed.

  4. Balanced Reaction:

    • Write the balanced chemical reaction for the decomposition of sodium bicarbonate, based on the identified solid product.

  5. Percent Yield Calculation:

    • Use the formula to calculate percent yield:
      ext{percent yield} = rac{ ext{actual yield}}{ ext{theoretical yield}} imes 100

  6. Percent Error Calculation:

    • Use the formula for percent error:
      ext{percent error} = rac{ ext{theoretical yield} - ext{actual yield}}{ ext{theoretical yield}} imes 100

Postlab Questions

  1. If the percent yield for the reaction was determined to be 110%, what does this indicate about the execution of the experiment?

  2. List three possible reasons for the percent yield exceeding 100%.