Hardware Models: Limiting Reagents and Theoretical Yields

1. Hardware Models: Limiting Reagents and Theoretical Yields Lab 4

2. Outline • Reactions in Chemistry • Moles • Limiting Reagents • Theoretical Yield • Using Analytical Balances • Points of Interest • Next Assignment

3. Reactions in Chemistry • Reactions are complex • Gases, solids and liquids all react differently • What you will be learning today are the basics only • Always work with balanced reactions • Balanced reactions provide us with molar ratios of reagents to products

4. Moles • We cannot make direct comparisons in chemistry using concentration or mass - we use moles instead. • A mole is 6.022 x 1023 of anything. • This concept is similar to that of a dozen. • We will be using the concept of a dozen today since 6.022 x 1023 are too many items to count out.

5. Limiting Reagent • A limiting reagent is the reagent you run out of first in a reaction. • The reagent that is in excess is called, excess reagent. • You must determine the limiting reagent of a reaction before you can determine the theoretical yield of product. • You will be limited by mass and number of items in some of your questions today to demonstrate this point.

6. Theoretical Yield • Theoretical yield is calculated to predict how much product can be produced based on the limiting reagent calculation. • You will use your predicted masses (theoretical values) to do your ratio calculations today. • After the theoretical yield is established, and the actual yield obtained, one can calculate percent yield.

7. Using Analytical Balances • Each balance auto-calibrates • Carefully open a door and make sure the basket is fully hinged • Place a blue weigh boat on the basket • Close the door completely and without slamming it • Tare the boat • Add the hardware and close the door carefully • Record the mass to the closest 0.1 mg (0.0001 g) • Remove your hardware, close the door(s) carefully and push the zero button

8. Points of Interest • Collect the required pieces of hardware from their containers. • Place these in a white plastic weigh boat. • The hardware may contain some oil. Wear gloves if you don’t want oil on your hands. • Use the plastic weigh boat to carry your hardware. It does not fit in the balance. • Use a blue plastic weigh boat in the balance to weigh your hardware. • Small pieces get lost easily. Please keep track of ALL your equipment.

9. Lab 5 Reminder • Read the required reading sections in your textbook and lab manual as you prepare for Lab 5. • Go through the significant figure molar mass tutorial in Blackboard before attempting the pre-lab questions. • Use the periodic table in your lab manual. • Complete and submit your pre-lab questions by the deadline. • Study for the quiz. • Submit your Lab 4 Report at the start of next week’s lab.

10. In Two Weeks - Lab 6 • Read the lab write-up in your manual (pp151 - 174). • Complete the pre-lab questions (pp. 174 - 188) in MicroLab™ in the SCICom lab (NSB 204), Chemistry Resource Center (CPSB 302K) or on your personal computer if you download the program. The program may be downloaded from http://www.microlabinfo.com under the Downloads link. • Take this exercise seriously. You will be required to complete a similar exercise in lab in two weeks without help from your lab manual.