STOICHIOMETRY Assessment

GATHER YOUR SUPPLIES

• Calculator

• Balance

• Cup

• Graduated cylinder

• Alka-seltzer-2 tablets

• Water

• Alka seltzer is a combination of citric acid, sodium bicarbonate and aspirin. The 3 compounds are pressed together and will not react until added to water.

• The objective is to calculate the mass and volume of carbon dioxide that is released into the atmosphere (actual) and compare it to what you will calculate (theoretical).

PRE LAB QUESTIONS

• 1) Write a equation for the following:

• Sodium bicarbonate (NaHCO3) reacts with citric acid (H3C6H5O7)

• To produce salt (Na3C6H5O7) and H2O and carbon dioxide (CO2)

• Notice how there are 3 Na on right... What would you put in front of sodium on left?

• Now balance the water and carbon dioxide

• _NaHCO3 +H3C6H5O7 ➡️Na3C6H5O7+ _H2O +_CO2

MOLAR MASS

• Calculate the molar mass of _NaHCO3

THE AMOUNT OF SODIUM

BICARBONATE IS 1.916G IN ONE TABIf you had 2 tabs, how much sodium bicarbonate would

you have?

MOLES OF SODIUM BICARBONATE

• Take the amount of 2 tabs of sodium bicarbonate and divide by the molar mass.

WHAT IS THE MOLE RATIO BETWEEN• 3NaHCO3 and 3CO2

• 3NaHCO3 +H3C6H5O7 ➡️Na3C6H5O7+ 3H2O +3CO2

CALCULATE THEORETICALLY

• How many moles of CO2 should be produced using the mole ratio from sodium bicarbonate?

• 3NaHCO3 +H3C6H5O7 ➡️Na3C6H5O7+ 3H2O +3CO2

WHAT IS THE MOLE RATIO BETWEEN

• 3NaHCO3 +H3C6H5O7

• 3NaHCO3 +H3C6H5O7 ➡️Na3C6H5O7+ 3H2O +3CO2

SOLVE GRAM H3C6H5O7TO GRAM_CO2

2 g• 3NaHCO3 +H3C6H5O7 ➡️Na3C6H5O7+ 3H2O +3CO2

?

2 g

• 3NaHCO3X 3CO2 =

SOLVE GRAM NAHCO3 TO GRAM_CO2

• Mass of bicarbonate in 2 tabs ?

• 3NaHCO3 +H3C6H5O7 ➡️Na3C6H5O7+ 3H2O +3CO2

From question 6

LAB INSTRUCTIONS• 1. Take 2 alka seltzer tabs

• 2. Mass the 2 tabs ______

• 3. Take 100 ml of water and pour it into cup.

• 4. Mass the cup and water____

• 5. Add #2 and #4 _______

• 6. Take the temperature of water_____ add 273 to convert it to K_______

• 7. Drop the 2 tabs into water

• 8. Let reaction happen until no bubbles are left.

DON'T SHORTCUT THIS STEP

Wait until there are no more bubbles.

INSTRUCTIONS CONT.

• 9. Now weigh the mixture of the dissolved tabs._____

• 10. To determine the grams of CO2 lost, subtract the value of #9 from #5. ______

HOW MANY GRAMS WAS THAT?From #10

MOLES OF CO2

• Convert the grams of CO2 from #9 to moles_____ by using the molar mass.

LITERS OF CO2

• You determined the amount of moles of CO2 that went into atmosphere. If 1 mole = 22.4 L. How many liters of CO2 were produced?

USE THE IDEAL GAS LAW TO SOLVE FOR VOLUME

• Pressure= 0.98 ATM

• Temperature =

• R=0.821

• N=

• Solve for v

PERCENT YIELD

• % yield = experimental (#13)\theoretical (from pre lab#7

PERCENT ERRORSubtract percent yield from 100%