Question

When sending copper metal through a cycle of reactions, it is most important to have an idea how much of any given reagent is needed to bring each step of the cycleof reactions to completion. In order to assure a complete reaction, reagents are often added in excess (up to 10 fold), but too much as well as too little might hamper the course of a reaction. The five key steps of the copper cycle are shown below:

Step 1: 3 Cu(s) + 2NO3-+ 8H+ -> 3 Cu2+(aq) + 4 H2O + 2 NO

Step 2: Cu2+(aq) + 2 OH-(aq) -> Cu(OH)2(s)

Step 3:Cu(OH)2(s) -> CuO(s)+ H2O

Step 4:CuO(s) + 2 H+ ->Cu2+(aq) + H2O

Step 5: Cu2+(aq) + Zn(s) -> Zn2+(aq) + Cu(s)

Assume that you want to carry out a sequence of cycle reactions based on 1.00g of copper. In order to use the right amount of reagents, present answersto the following questions:

1.What volume of 16 M HNO3 is required to completely react with Cu in the first step of the cycle?

2. What volume of 3.0 M NaOH is required to precipitate all copper(II) cations as Cu(OH)2 in the second step of the cycle?

3. How many grams of copper(II)oxide will form when the third step of the cycle goes to completion?

4. What volume of 6.0 M H2SO4 is required to completely convert all copper(II)oxide to copper(II) cation in the fourth step of the cycle?

5. How many grams of zinc metal are needed to completely regenerate all copper in the fifth step in the cycle?

Answer 1

moles of copper= mass/atomic weight= 1/63.5 =0.016

the 1st reactino is 3Cu(s) + 2NO3-+ 8H+ -> 3 Cu2+(aq) + 4 H2O + 2 NO

3 mole of copper requires 2 mole of HNO3 to produce 3 moles of Cu+2

0.016 moles of copper requires 0.016*2/3=0.011moles of HNO3 and produce 0.016 moles of Cu+2

volume of HNO3 in L = moles/molarity =0.011/16 =0.0006875L=0.6875ml

mass of HNO3= moles* molar mass =0.011*63= 0.693 gm

from 2nd reaction, Cu+2+2OH- ---------->Cu(OH)2, 1 mole of Cu+2requires 2 mole of NaOH and produces 1 mole of Cu(OH)2

0.016 moles require 0.016*2=0.032 moles of NaOH. mass of NaOH= moles* molar mass of NaOH =0.032*40 = 1.28 gm. volume of NaOH in L= moles/Molarity =0.032/3= 0.011L= 0.011*1000ml=11ml

0.016 moles of Cu+2 produces 0.016 moles of Cu(OH)2

from reaction-3, Cu(OH)2-------->CuO+ H2O, 1 mole of Cu(OH)2 produces 1 mole of CuO. 0.016 moles of Cu(OH)2 produces 0.016 moles of CuO. molar mass of CuO= 63.5+16= 79.5, mass of Cu produced= 0.016*79.5 =1.272 gm

from reaction-4, CuO+2H+(H2SO4) ----->Cu+2+ H2O, 1 mole of CuO requires 1 mole of H2SO4 to produce 1 mole of Cu+2

0.016 moles of Cu requires 0.016 moles of H2SO4 and produces 0.016 moles of Cu+2

mass of 100% H2SO4 required = 0.016 moles

volume of H2SO4 =0.016/6 L =0.0027 L=0.0027*1000ml= 2.7 ml

from the reaction-5, Cu+2+Zn ------>Zn+2+Cu

1mole of Cu+2 requires 1 mole of Zn

0.016 moles of Cu+2 requires 0.016 moles of Zn. atomic weight of Zn=65.38 g/mole

mass of Zinc =0.016*65.38 gm =1.05 gm of Zinc