ch9 bs lab

STOCHIOMETRY LAB – CHANGING BS INTO SALT

PURPOSE: Measure how many grams of salt can be obtained from a measured amount of baking soda, then calculate how much was theoretically possible using stoichiometry; then calculate % yield.

DISCUSSION: When aqueous hydrochloric acid reacts with baking soda (sodium hydrogen carbonate), a gas, carbon dioxide, is produced, liquid water, and salt(which dissolves in the water). By using stoichiometry, and the mass of baking soda, we can predict how much salt is theoretically possible (theoretical yield). % yield is calculated by dividing the experimental yield (what we recovered in the experiment) by the theoretical yield.

PROCEDURE: Weigh an empty beaker, then add about 1/2 teaspoon of bs, weigh again. Weigh the beaker of acid . Place a paper towel under the beaker, then add hydrochloric acid with a dropper, stirring with the thermometer. (note room temperature before putting into solution). It will probably take about 2 droppers full. Test the gas by placing a flaming splint and glowing splint into the gas (not the liquid) in the beaker. Try not to add too much HCl, because we will have to evaporate the excess. When the solution looks clear, and a drop of HCl produces no reaction, note the temperature. Weigh the beaker of acid again. Place an identifying mark (initials) on the beaker , then evaporate the water by placing it in a drying oven overnight. The next day, remove and mass (use the same balance for all massing). Observe the shape of the crystals, then wash out the dish. Do another trial if directed; if not, remove your initials with alcohol. bold 1st day 7 data entries

mr j's data; everyone will use this for trial 2.

1. room temp 21.5 degrees C

2. empty beaker 57.31g

3. beaker and bs 59.17g

4. HCl & beaker before use 124.06g

5. HCl & beaker after use 117.68g

6. temp of solution after reaction 15 degrees C

7. mass of beaker and solution 64.45g

8. (next day) mass of beaker and solute. 58.65g

Data:

1. Room temp

2. Mass of beaker (put initials on the dish)

3. mass of beaker and bs

4. mass of HCl and beaker before use

5. mass of HCl and beaker after use

6. temp of the solution after reaction

7. mass of beaker and solution

8. The next day, mass of beaker and solute

Calculations:

CONCLUSIONS:

1. Was this an endothermic or exothermic reaction? What is your evidence?

2. Write the balanced chemical equation, including states.

3. What caused the bubbling? What were the bubbles? What is the flame test for this gas?

4. What will be in the beaker when the reaction is done, but before we heat it?

5. What will the heating remove?

6. What is the limiting reactant? What is the excess reactant? What is the evidence? Why don't we want a lot of the excess reactant remaining?

6a. Predict the grams (theoretical yield) of salt you expect by using your mass of bs and stoichiometry. (alligator stoichiometry)

6b. predict the theoretical yield in grams of carbon dioxide using the mass of bs and stoichiometry

6c find the actual mass of carbon dioxide produced (from lab data)

6d (not from lab) Write an equation for the combustion of octane (C8H18) , and calculate the theoretical yield in grams of water produced from the combustion of 57g of octane ( show da.)

7. What is the shape of the crystals? What are they? Look at sample in which the crystals are not like everyone else's. What was the limiting reactant in that case? Why are some crystals an unexpected color?

8a What was the actual yield? (mass of salt in dish) Find the %yield. of salt by dividing actual yield by the theoretical yield

8b (rchem may skip). find the % yield of carbon dioxide (to find the experimental mass of the carbon dioxide, add the mass of the bs used to the mass of HCl used; from that amount, subtract the mass of the solution; the missing mass is the mass of the carbon dioxide).

9. Ideally, what would be the percent yield? In reality, what do we usually expect? rchem may skip the next question. Why did the % yield for the carbon dioxide go over 100%?

10. What is a positive test for carbon dioxide gas?

11. Calculate the theoretical volume of carbon dioxide produced (using my data for mass of bs), given that the density of carbon dioxide is 1.25g/L. (rchem may skip this problem)

12. record results on this form

class data available day assignment due

Answer for #11: If I used 2.0grams of bs, this would result:

2.0g NaHCO₃ * 1mole NaHCO₃ / 84g NaHCO₃ * 1mole CO₂ / 1mole NaHCO₃ * 44g CO₂ / 1mole CO₂ * 1L / 1.25gCO₂ = .84LCO_{2 = 840mL carbon dioxide}