Culinary Chemistry: Stoichiometry Made Simple

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1 Culinary Chemistry: Stoichiometry Made Simple Background Stoichiometry is based on the law of conservation of mass which states that the mass of the reactants in a chemical reaction equals the mass of the products. Stoichiometry provides a means for researchers to use calculations in order to predict the amount of product (mass, moles, volume) that can be produced by a given quantity of reactants as well as the percent yield for that chemical reaction. This would be important in the manufacturing of drugs in determining a quantity of substance needed and, keeping in mind that medication may react or change in accordance with other metabolic processes of the body, may require an additional amount to compensate for these effects. Both pharmaceutics and pharmacokinetics address quantifying the amount of drug necessary for each patient, with a unique weight, and how to best deliver that drug. You will play the role of pharmacologist by reacting baking soda and vinegar and using stoichiometry to calculate quantity of product yield. CH3COOH + NaHCO3 NaCH3COO + H2O + CO2 Objective: To predict the amount of carbon dioxide gas expected as a product and to calculate percent yield. Materials: Vinegar (acetic acid) Baking soda Sodium acetate water Carbon dioxide 4 g baking soda 50 ml vinegar 1 ml disposable pipette ml beakers 50-mL graduated cylinder digital balance Procedure 1. Weigh a clean, dry 250-mL beaker on the digital balance. Record the mass (g) of this empty beaker. 2. Mass out 4 g of baking soda (NaHCO 3 ) in the 250-mL beaker that you weighed in #1. Calculate the number of moles in 4 g of baking soda (NaHCO 3 ). Show your work. 3. Measure 50 ml of vinegar (CH 3 COOH) using the 50-mL graduated cylinder. Using the second 250-mL beaker, record the mass (g) of the vinegar. 4. Using a 1-mL disposable pipette, add 1 ml of vinegar to the baking soda. What observations provide evidence that a chemical reaction is occurring?

2 5. Continue adding vinegar to the baking soda 1 ml at a time until the chemical reaction no longer occurs. How will you know that a chemical reaction is no longer occurring? 6. When your group is confident that there is no longer a chemical reaction, weigh the beaker with the new products. Record the total mass (g). 7. Calculate the mass (g) of the products only by subtracting the weight of the beaker that you recorded in #1. Name Period Date 8. Record the final weight (g) of the unused vinegar. 9. Based on your measurements, calculate the amount of carbon dioxide (CO 2 ) that was released as a product. 10. Calculate the expected amount of carbon dioxide that would be produced by the chemical reaction. 11. How does your expected CO 2 produced compare to the actual CO 2 produced? Can you explain any possible sources of error? 12. Calculate percent yield of CO 2. actual yield X 100% = theoretical yield 13. Calculate percent error. actual yield theoretical yield theoretical yield percent yield X 100% = percent error 14. The law of conservation of matter and energy states that matter is not created nor destroyed during a reaction. If this is true, then explain why the mass of the products is less than the total mass of the reactants.

3 Part B. Root Canal Stoichiometry Calcium hydroxide is sometimes used in dentistry to temporarily fill the space left by a root canal. The equation for the formation of calcium hydroxide can be found below. Balance the chemical equation by placing the appropriate coefficients on the lines. CaCl 2 + NaOH Ca(OH) 2 + NaCl Molar Mass (g/mol) 1. Calculate the molar mass of the reactants and the products in the chemical reaction above. Reactants CaCl 2 NaOH Product Ca(OH) 2 NaCl Imagine that a dentist performs this reaction four times using different amounts of the reactants. Fill in the missing information below. Reactants Products Reaction Quantity CaCl 2 NaOH Ca(OH) 2 NaCl 1 Moles 1.00 mol 2.00 mol 1.00 mol 2.00 mol 2 Moles mol 55.5 g 37.0 g 58.5 g 3 Moles mol mol 4 Moles 10.0 g 2. How many moles of Ca(OH) 2 are formed for every mole of NaOH used? 3. For every 0.50 mol of Ca(OH) 2 formed, how many moles of NaCl are formed? 4. How many grams of calcium chloride (CaCl 2 ) do you need to make 20.0 g of calcium hydroxide (Ca(OH) 2?

4 Part C. Human Bones Stoichiometry The chemical equation for the reaction that forms calcium phosphate, the main ingredient in human bones, can be found below. Balance the chemical equation by placing the appropriate coefficients on the lines. CaCl 2 + Na 3 PO 4 Ca(PO 4 ) 2 + NaCl Molar Mass (g/mol) 1. Calculate the molar mass of the reactants and the products in the chemical reaction above. Reactants CaCl 2 Na 3 PO 4 Product Ca(PO 4 ) 2 NaCl Imagine that a physician performs this reaction four times using different amounts of the reactants in order to develop human tissue for bone grafting. Fill in the missing information below. Reactants Products Reaction Quantity CaCl 2 Na 3 PO 4 Ca(PO 4 ) 2 NaCl 1 Moles 3.00 mol 2.00 mol 1.00 mol 6.00 mol 2 Moles 2.00 mol 666 g 620 g 702 g 3 Moles mol mol 4 Moles 9.92 g 2. For every mole of Na 3 PO 4 used, how many moles of Ca 3 (PO 4 ) 2 are formed? 3. For every mol of Ca(PO 4 ) 2 formed, how many moles of CaCl are used? 4. How many grams of calcium chloride (CaCl 2 ) do you need to make 20.0 g of human bone?

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VOCABULARY Define. 1. stoichiometry. 2. composition stoichiometry. 3. reaction stoichiometry. 4. unknown. 5. mole ratio

VOCABULARY Define. 1. stoichiometry. 2. composition stoichiometry. 3. reaction stoichiometry. 4. unknown. 5. mole ratio CHAPTER 9 HOMEWORK 9-1 (pp. 275 279) Define. 1. stoichiometry 2. composition stoichiometry 3. reaction stoichiometry 4. unknown 5. mole ratio SKILL BUILDER On a separate sheet of paper, write five possible