-
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%