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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: jrrumfelt on September 25, 2006, 01:58:08 PM

Title: calculating the mass of zinc required to reduce copper
Post by: jrrumfelt on September 25, 2006, 01:58:08 PM
I was given four molecular equations to balance. the next question states, "based on your balanced equation in #1, if 0.150g of copper was used to begin the experiment, calculate the mass of zinc required to reduce the CuSO4 obtained.(assume 100% completion of all intermediate steps and that no Zn(s) is lost in competing reactions.) show all work."
the balanced equations are
#1. Cu(s)+4HNO3(aq)=Cu(NO3)2(aq)+2NO2(g)+2H2O(l)
#2. Cu(NO3)2(aq)+2NaOH(aq)=Cu(OH)2(s)+2NaNO3(aq)
#3. CuO(s)+H2SO4(aq)=CuSO4(aq)+H2O(l)
#4. CuSO4(aq)+Zn(s)=Cu(s)+ZnSO4(aq)

Idont even know how to start this problem can someone help.
Title: Re: calculating the mass of zinc required to reduce copper
Post by: Borek on September 25, 2006, 02:01:57 PM
http://www.chembuddy.com/?left=balancing-stoichiometry&right=stoichiometric-calculations
Title: Re: calculating the mass of zinc required to reduce copper
Post by: sdekivit on September 25, 2006, 02:02:26 PM
i don't get this question because of reaction #3. If you obtain CuSO4 according to these reaction how can CuO react with H2SO4 when in reaction #2 Cu(OH)2 is obtained ?
Title: Re: calculating the mass of zinc required to reduce copper
Post by: Alberto_Kravina on September 25, 2006, 02:04:16 PM
Quote
Idont even know how to start this problem can someone help.
Well, start with the reaction equation. Copper(2+) + Zink ? Zink(2+) + Copper

If you have the reaction equation calculate how many moles of Zn you need to reduce a mole of copper. Then convert moles in mass (n=m/M)

Edit: Borek was faster :(

2nd Edit:

Quote
i don't get this question because of reaction #3. If you obtain CuSO4 according to these reaction how can CuO react with H2SO4 when in reaction #2 Cu(OH)2 is obtained ?
I think that you should focus on reaction #1 and forget the others.

Title: Re: calculating the mass of zinc required to reduce copper
Post by: sdekivit on September 25, 2006, 02:10:03 PM
Quote from: jrrumfelt on September 25, 2006, 01:58:08 PM
(assume 100% completion of all intermediate steps and that no Zn(s) is lost in competing reactions.) show all work."
the balanced equations are
#1. Cu(s)+4HNO3(aq)=Cu(NO3)2(aq)+2NO2(g)+2H2O(l)
#2. Cu(NO3)2(aq)+2NaOH(aq)=Cu(OH)2(s)+2NaNO3(aq)
#3. CuO(s)+H2SO4(aq)=CuSO4(aq)+H2O(l)
#4. CuSO4(aq)+Zn(s)=Cu(s)+ZnSO4(aq)

do you think you should forget all the other reactions ? From this quote i think we need to take into account all the reactions that yield CuSO4 in this process. And thus then i'm stuck on reaction #3.
Title: Re: calculating the mass of zinc required to reduce copper
Post by: Borek on September 25, 2006, 03:02:55 PM
Looks like it is a "process" where next step starts with the product of the previous one. Cu(OH)2 -> CuO is missing, but my take is that it doesn't matter.

jrrumfelt: assuming every next reaction uses product from the previous one, how much copper is used as a reactant in the 4th reaction?
Title: Re: calculating the mass of zinc required to reduce copper
Post by: sdekivit on September 25, 2006, 04:51:11 PM
Quote from: Borek on September 25, 2006, 03:02:55 PM
Looks like it is a "process" where next step starts with the product of the previous one. Cu(OH)2 -> CuO is missing, but my take is that it doesn't matter.

i agree with this. Overall stoichiometry Cu : CuSO4 will be 1:1.