home > q&a board > chemistry > topic: percent yield

Q BgQuestion:

Rookie
Karma Points: 0
Respect (100%):
posted by  SueZ on 10/10/2008 12:14:19 AM  |  status: Live  

percent yield

Course Textbook Chapter Problem
N/A N/A N/A N/A
Question Details:
When powdered zinc is heated with sulfur, a violent reaction occurs, and zinc sulfide forms:
              8Zn(s) + S8 (s) ---> 8ZnS(s)
a) Some of the reactants also combine with oxygen in air to form zinc oxide and sulfur dioxide. When 83.2g of Zn reacts with 52.4g of S8, 104.2g of ZnS forms. What is this the percent yield of ZnS?ZnS=__________%
 
b)  If all the remaining reactants combine with oxygen, how many grams of each of the two oxides form
Mass ZnO:________g    and Mass SO2:_________g
Please help, Thank you.
 
Tags: Chemistry

AAnswers:

Answer Question
Mentor
Karma Points: 781
posted by ajw7989 on 10/10/2008 12:38:17 AM  |  status: Live
Asker's Rating: Lifesaver   
SueZ's comment:
"Thank you so much for answering my question."
Response Details:
percent yield = actual/theoritical
 
molar mass of:
Zn = 65.34g/mol
S8= 256.52g/mol
ZnS=97.405g/mol
 
convert each to moles(actual)
83.2g/65.34 = 1.27moles Zn
52.4g/256.52 = .204moles of S
104.2g/97.405 = 1.07moles of ZnS
 
(we see the amount of Zn is the same as ZnS so...)
 
1.07/1.27 = 84.3% ZnS
 
Zn is the limiting reactant so no ZnO will form and (1.27/8 = .125 so .204-.125 = .079moles of S left so)
 
.079 moles of SO2 form they want moles so times by molar mass 5.06g but since we need to write the equation we see we need to times it by 8 to get 40.48g
S8+4O2-->8SO2
 
 
 
 
Answer Question
Ask New Question

Join Cramster's Community

Cramster.com brings together students, educators and subject enthusiasts in an online study community. With around-the-clock expert help and a community of over 100,000 knowledgeable members, you can find the help you need, whenever you need it. Join for free today » How Cramster is different from tutoring »

Need Help In

Useful Links