CHEMISTRY LAB



LAB: Stoichiometry of a Reaction between Vinegar and Baking Soda

Introduction

The reaction you will be working with in this lab should be very familiar. It is often the source of the "eruption" of a volcano in an elementary school project. You will be mixing NaHCO3 (sodium bicarbonate or baking soda) and CH3COOH (acetic acid or vinegar). The reaction will generate H2CO3 (carbonic acid, which breaks up into water and carbon dioxide gas) and NaCH3COO (sodium acetate), which is a food preservation additive.

Pre-lab Questions: Computing amounts of reactants that we need

In this lab, you will be reacting NaHCO3 (sodium bicarbonate) with an excess of CH3COOH (acetic acid). By doing this you will ideally ensure that you will get 100% yield for the reaction.

For our reaction we will need to use 0.0130 moles of sodium bicarbonate and an excess of acetic acid. By doing this you will ideally ensure that you will get 100% actual yield for the reaction.

1. Calculate how many grams of sodium bicarbonate we will need for this lab by converting 0.0130 moles of sodium bicarbonate to grams. Show your work.

Teacher Initials: ___________

2. Using the information given in the introduction, write the balanced chemical equation for the reaction between NaHCO3 (sodium bicarbonate) and CH3COOH (acetic acid) below.

Part 1: Running the Reaction

3. Measure out the mass of sodium bicarbonate that you calculated you would need in Question #1 of this lab using a plastic weigh boat. Make sure that the amount you use is as close as you can make it to this calculated amount. Write the exact mass of sodium bicarbonate that you used here:

Mass of sodium bicarbonate used: _____________________ g

4. Mass a 250 mL beaker. You will need the mass of the empty beaker at the end of the lab.

Mass of the empty beaker: _____________________ g

5. Add the sodium bicarbonate to the 250 mL beaker.

6. Measure 25 mL of acetic acid into a graduated cylinder and then SLOWLY add it to beaker with the sodium bicarbonate. You will observe the formation of bubbles. Wait until the bubbling subsides before adding more acetic acid. When all of the acetic acid has been added, stir for two minutes before moving on to step 7.

7. Find the mass of one boiling chip and then add it to the beaker. You will be boiling away the liquid portion of this solution. The boiling chip will help to prevent the contents of the beaker from boiling over.

Mass of the boiling chip: _____________________ g

8. Place the beaker with the liquid and boiling chip over a heating source in order to evaporate off the liquid. Be patient – this can take some time.

9. When all of the liquid in the solution has boiled away, turn off the heat source. The powder that you observe inside is one of the products of the reaction, sodium acetate (NaCH3COO). Once the beaker has had a few minutes to cool down to room temperature, measure and record its mass.

Mass of the beaker, after the reaction: _____________________ g

10. Rinse out the beaker and any other glassware you used. All waste (except the boiling chip) can go down the drain.

Part 2: Analysis Questions

11. Copy down the balanced chemical equation from Question #2 and the exact mass of sodium bicarbonate that you measured in Question #1 into the appropriate box below.

|grams | | | | |

|molar mass | | | | |

|moles | | | | |

12. Calculate the theoretical yield of the mass of sodium acetate (NaCH3COO) in this reaction using the box above.

13. Calculate the actual yield of the mass of sodium acetate (NaCH3COO) that you recovered in this lab (this is the solid remaining in the beaker). To do this, you will need to use the mass of the empty beaker, the mass of the boiling chip, and the mass of the beaker after the reaction. Show your work.

In class you have learned how to calculate how much of a chemical product you can make when you mix measured amounts of chemical reactants. Using stoichiometry, you calculated the theoretical yield of one of the products of this reaction. The theoretical yield is the maximum amount of product that can be formed. You then did the lab and measured the actual yield of product made. Knowing these two values allows you to calculate the percent yield of your reaction.

[pic]

14. Using the actual yield of sodium acetate that you measured in Question #13 and the theoretical yield of sodium acetate that you calculated in Question #12, calculate the percent yield of sodium acetate recovered in this lab. Show your work.

15. Was your percent yield of sodium acetate 100%? List at least two factors that you think caused your percent yield to be greater or less than 100%.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download