Lab 9.2 (pg 1 of 2) Stoichiometry of a Single


Introduction: In this lab, mole-mole relationships in chemical reactions will be inspected in an attempt to verify that the theoretical stoichiometry of balanced ...

Lab 9.2 (pg 1 of 2) “Stoy-key-aw-met-tree”

Stoichiometry of a Single Replacement Reaction % Yield of a Product

Introduction: In this lab, mole-mole relationships in chemical reactions will be inspected in an attempt to verify that the theoretical stoichiometry of balanced equations actually occurs in the laboratory. A single replacement reaction will occur when a piece of copper is placed in aqueous silver nitrate. Since copper can form either a +1 or +2 charge, there are two possible equations that could describe this reaction. Further, the mass of one of the products will be measured and a % yield will be calculated.

Pre-lab: Must be done BEFORE class 1.

Write out the two possible balanced chemical equations that could describe the reaction that occurs in this lab. ______________ + ______________ --> ______________ + ______________ ______________ + ______________ --> ______________ + ______________

Procedure Day 1

Goggles must be worn.

A. Mass of the labeled small 50 ml beaker ______________ B. Mass of the silver nitrate within the beaker ______________ C. Mass of the copper wire ______________ Detailed OBSERVATIONS the silver crystals forming. ____________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________

Detailed OBSERVATIONS of the color of the water solution. What is causing this? ____________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________

Day 2 D. Mass of the dried wire ____________ E. Mass of the second small 100 ml beaker ___________

Day 3 F. Mass of the dried silver crystals in the 50 ml beaker. ___________ Detailed OBSERVATIONS: Is there any blue substance dried in the beaker with the silver crystals. what does this mean? ____________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________ ____________________________________________________________________________________________________________________

G. Measure the mass of the dried blue copper(?) nitrate in the 100 ml beaker. ________

Disposal: • •

The remaining copper wire should be put on the tray. The beakers with the dried silver crystals and the dried blue crystals should be left on the tray on the center lab bench.

LAD 9.2 (pg 2 of 2)

Stoichiometry of a Single Replacement Reaction “Stoy-key-aw-met-tree” % Yield of a Product

Processing the data Part 1 - Stoichiometry mole ratios a. Initial mass of silver nitrate ___________ (from the first page) b. Final mass of silver formed___________ (from the first page) c. moles of silver (b./108g/mole)_____________ d. Initial mass of copper wire____________ (from the first page) e. Final mass of copper wire _____________ ((from the first page) f. Mass of copper reacted __________ g. Moles of copper (f/64g/mole)_____________ h. Ratio of moles of silver nitrate reacted to moles copper reacted.(c/g) _____________: 1

Based on your data, choose which reactio you believe occured in the lab: the 1st or 2nd from the first page, Based on the stoichiometry of the possible reactions between cooper and silver, which suggests a ratio similar to the one you’ve calculated above? Copper ions reating as Cu+1 or Cu+2 ions __________ Part 2 – Percent yield of a the silver nitrate product i. The experimental mass of silver crystals that formed is _____________ j. The theoretical mass of silver that should have formed is _____________. (begin your stochiometry prediction using the mass of Cu that reacted in this experiment) k. Determine the % yield of silver formed (Experimental Mass / Theoretical mass x 100) = ____________ Part 3 – Law of conservation of mass l. Determine the sum of the mass of the reactants that reacted.____________ m. Determine the sum of the mass of the products.___________ n. Calculate % error. (l - m / m) x 100 ___________ (Answer must be an Absolute Value)

Post Lab Questions Part 1 - Stoichiometry 1. Explain what causes the solution with the copper strip in to become blue/green in color. Give other examples of where you have seen this blue color in relation to copper ________________________________________________________________________________________________________ ________________________________________________________________________________________________________ 2.

How can you tell (while you are washing) when you have washed the silver crystals enough? What evidence was there after the crystals were dried if they had not been washed enough? ________________________________________________________________________________________________________ ________________________________________________________________________________________________________ 3. Why must all the wash water get into the beaker? What are you washing off and where do you want it to go? ________________________________________________________________________________________________________ ________________________________________________________________________________________________________ 4.

Explain how the ratio of moles silver nitrate reacted to moles copper reacted dictates which equation is the most dominant equation that occurs in this experiment? ________________________________________________________________________________________________________ ________________________________________________________________________________________________________

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