AROUND THE WORLD WITH COPPERName:

(1 lab grade and 1 test grade)

INTRODUCTION:

Reaction stoichiometry involves the mass relationships between reactants and products in a chemical equation. All reaction stoichiometry calculations start with a balanced chemical equation. This equation gives the relative number of moles of reactants and products. In this unit over stoichiometry you will master stoichiometric calculations using a given mass of reactant to yield a specific quantity of product. In this lab you will try to prove this by taking a precise quantity of copper (0.50 g) and performing the following series of consecutive transformations:

Cu(s)  Cu(NO3) 2 (aq)  Cu(OH) 2 (s)  CuO (s)  CuSO4 (aq)  Cu (s)

PURPOSE:

To prove the law of conservation of mass; to carry out chemical reactions; to develop lab skills in decantation; to use stoichiometry to predict the amount of substance formed and to predict percent yield of product.

SAFETY:

You must wear goggles and aprons at all times in the lab area. Do not bring chemicals out of the lab area unnecessarily. Nitric acid (16 M) is VERY CONCENTRATED! Avoid spills with this substance. If it comes in contact with your skin, flush immediately with water and notify your instructor. Use this acid ONLY IN THE FUME HOOD!! All acid spills should be neutralized with baking soda (sodium bicarbonate, NaHCO3). Spills of a base such as NaOH should be neutralized with acetic acid. If your skin comes into contact with a base, flush with water 2-3 minutes.

PRELAB QUESTIONS:

  1. Complete and balance the following chemical equations that correspond to procedures Parts A-E of the laboratory exercise. Write the type of reaction that occurred under reaction type (redox, double replacement, decompsotion, or single replacement). Reaction Type(s)

A. Cu +O2+ HNO3 Cu(NO3) 2 + NO2 + H2ORedox Reaction

B. Cu(NO3) 2 +NaOH

C. Cu(OH) 2 +heat 

D. CuO +H2SO4

E. CuSO4 +Zn

  1. Determine the theoretical mass of the copper product in each step. Start with 0.5000 grams of copper (which will be your initial mass of copper). SHOW WORK! An example of how each of your steps should look is done below:

Part A (preparation of copper (II)nitrate) 3Cu + O2 + 8HNO3  3Cu(NO3) 2 + 2NO2 + 4H2O

?g Cu(NO3)2 0.5000g Cu 1mol Cu 3mol Cu(NO3)2 187.54g Cu(NO3)2 = 1.476g Cu(NO3)2

63.54g Cu 3mol Cu 1mol Cu(NO3)2

Part B (preperationof copper(II) hydroxide) Cu(NO3) 2 + 2NaOH  2NaNO3 + Cu(OH)2

?g Cu(OH)2 1.476g Cu(NO3)2

Part C

Part D

Part E

3. Write a hypothesis for this experiment. (If………., then………..)

PROCEDURES: Cu  Cu(NO3) 2  Cu(OH) 2  CuO  CuSO4  Cu.

Prior to beginning label your beaker or flask with your name, period, and date, using a piece of masking tape and a sharpie.

Part A: Preparation of copper (II) nitrate:

CAUTION: keep all material in the hood until the END of PART A.

Place 0.50 g of copper in a small beaker or flask. Record the exact mass of copper under DATA. Place beaker in fumehood and carefully add approximately4 mL of concentrated nitric acid (HNO3). Move beaker to back of fumehood and allow others to use fumehood. Allow copper to react with the nitric acid in the fumehood for two minutes. Pour approximately 50 mL of distilled water into beaker, remove beaker from fumehood,and return to your lab bench. The resulting blue solution contains copper (II) nitrate. The brown fumes produced are toxic NO2 gas. Record observations.

Part B: Preparation of copper (II) hydroxide

To the blue solution of copper (II) nitrate slowly add, stirring constantly, approximately 30 mL of 3M NaOH. Record observations.

Part C: Preparation of copper (II) oxide

Boil solution, stirring constantly. The Cu(OH) 2 will decompose to give black copper (II) oxide. When the reaction is complete remove from heat. Setup a filter using filter paper and a funnel. Filter your mixture. Discard the liquid, KEEP the black precipitate. Record observations.

Part D: Preparation of copper (II) sulfate

Leave precipitate on filter paper in funnel and slowly add approximately15 mL of concentrated 6M H2SO4 to the precipitate on the filter paper. The blue liquid that forms contains copper (II) sulfate. Keep the blue liquid!! Discard the filter paper. Record observations.

Part E: Preparation of copper

In a fumehood add approximately2 grams of zinc metalto the beaker and stir for approximately 2 minutes. Obtain and record the mass of a clean, dry evaporating dish. Pour the mixture into the evaporating dish. Decant the liquid and keep the precipitate in the evaporating dish (the precipitate is the copper)! Pour approximately5 mL of methanol (keep the methanol away from flames – it is flammable) into the evaporating dish. Allow the precipitate to settle and decant the methanol. (Mehtanol is also extremely toxic; avoid breathing the vapors as much as possible.) Pour approximately 5 mL of acetone (Keep the acetone away from flames – it is extremely flammable)into the evaporating dish. Allow the precipitate to settle and decant the acetone. Prepare a steam bath and dry the precipitate on your steam bath for at about 5 min. Wipe the bottom of the evaporating dish with a towel and weigh the copper and evaporating dish.

Place as much copper as you can into a test tube. Label the tube neatly with your name, class period, mass of your copper, and percent yield. Submit copper to your instructor.

DATA:

Data Table 1: Copper Mass Recordings

Initial mass of copper
Mass of empty evaporating dish or watch glass
Mass of evaporating dish or watch glass + dry copper
Final mass of copper:

Data Table 2: Observations of Reactions

Chemical Reaction
/
Observations
Part ACu (s)+ O2 (g)+ HNO3 (aq)
Part B Cu(NO3) 2 (aq)+ NaOH (aq)
Part CCu(OH) 2 (s)+heat
Part DCuO (s) +H2SO4 (aq)
Part ECuSO4(aq)+ Zn (s)

CALCULATIONS and CONCLUSIONS:

1. Calculate the percent yield for your copper sample. Show work.

(initial mass of copper = theoretical yield and final mass of copper = actual yield)

2. According to the law of conservation of mass, what quantity of copper should you obtain for your product?

  1. List four possible places where an error could have occurred. Be specific.
  1. In Part E: Preparation of Copper, hydrogen gas was the gas that was produced, if the preparation of copper reaction is CuSO4 + Zn  ZnSO4 + Cu, where did the hydrogen gas come from?
  1. Consider the initial reaction during this lab:

Cu +O2+ HNO3 Cu(NO3) 2 + NO2 + H2O

Suppose 4.5 mol of copper are allowed to react with 6.5 mol of nitric acid. (Make sure you balance the equation.)

(a). How many moles of nitrogen dioxide will form? (Show work)

(b). How many grams of copper (II) nitrate will form? (Show work)

(c). How many grams of the excess reactant will remain? (Show work)

6. Some students burned magnesium in excess oxygen, as described by the equation:

2Mg(s) + O2(g) → 2MgO(s)

Mass of Crucible / 35.84g
Mass of Crucible + Mg / 38.35g
Mass of Mg / ?
Mass of Crucible + MgO / 39.45g
Mass of MgO / ?

They recorded their data in the table.

______What is the percent yield of MgO in this reaction?