Extra Percent Yield Problems

1. Phosphorous reacts with bromine to form phosphorous tribromide. If 35.0 grams of bromine are reacted and 27.9 grams of phosphorous tribromide are formed, what is the percent yield?

2 P + 3 Br2 ! 2 PBr3

35.0  𝑔  𝐵𝑟!1

 𝑥  1  𝑚𝑜𝑙𝑒  𝐵𝑟!

159.808  𝑔  𝐵𝑟!  𝑥  2  𝑚𝑜𝑙𝑒𝑠  𝑃𝐵𝑟!3  𝑚𝑜𝑙𝑒𝑠  𝐵𝑟!

 𝑥  270.686  𝑔  𝑃𝐵𝑟!1  𝑚𝑜𝑙𝑒  𝑃𝐵𝑟!

= 39.5  𝑔  𝑔  𝑃𝐵𝑟!

%  𝑦𝑖𝑒𝑙𝑑 =  27.9  𝑔  𝑔  𝑃𝐵𝑟!39.5  𝑔  𝑔  𝑃𝐵𝑟!

 𝑥  100 =  70.63%

2. Silver Nitrate reacts with Magnesium Chloride to produce Silver Chloride and Magnesium Nitrate. If 305 grams of silver nitrate are reacted in an excess of magnesium chloride producing 23.7 grams of magnesium nitrate, what is the percent yield?

2 AgNO3 + MgCl2 ! 2 AgCl + Mg(NO3)2

305  𝑔  𝐴𝑔𝑁𝑂!1

 𝑥  1  𝑚𝑜𝑙𝑒  𝐴𝑔𝑁𝑂!

169.872  𝑔  𝐴𝑔𝑁𝑂!  𝑥  2  𝑚𝑜𝑙𝑒𝑠  𝑀𝑔(𝑁𝑂!)!2  𝑚𝑜𝑙𝑒𝑠  𝐴𝑔𝑁𝑂!

 𝑥  148.313  𝑔  𝑀𝑔(𝑁𝑂!)!1  𝑚𝑜𝑙𝑒  𝑀𝑔(𝑁𝑂!)!

=  266  𝑔  𝑀𝑔(𝑁𝑂!)!

%  𝑦𝑖𝑒𝑙𝑑 =  23.7  𝑔  𝑀𝑔(𝑁𝑂!)!266  𝑔  𝑀𝑔(𝑁𝑂!)!

 𝑥  100 = 8.91%

3. Zinc is reacted with Hydrochloric acid to form zinc chloride and hydrogen gas. The reaction is carried out in a glass container that has a mass of 14.7 grams. After placing the zinc in the glass container, the mass is 29.5 grams. The hydrochloric acid is poured into the container and the zinc chloride is formed. The excess hydrochloric acid is removed leaving the glass container and the zinc chloride, which together have a mass of 37.5 grams. What is the percent yield?

Zn + 2 HCl(aq) ! ZnCl2 + H2(g)

𝐴𝑚𝑡  𝑍𝑛𝐶𝑙!  𝑎𝑐𝑡𝑢𝑎𝑙𝑙𝑦  𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑 = 37.5  𝑔𝑟𝑎𝑚𝑠 − 14.7  𝑔𝑟𝑎𝑚𝑠 = 22.8  𝑔𝑟𝑎𝑚𝑠  𝑍𝑛𝐶𝑙!    

𝐴𝑚𝑡  𝑜𝑓  𝑍𝑖𝑛𝑐  𝑟𝑒𝑎𝑐𝑡𝑒𝑑 = 29.5  𝑔𝑟𝑎𝑚𝑠 − 14.7  𝑔𝑟𝑎𝑚𝑠 = 14.8  𝑔𝑟𝑎𝑚𝑠  𝑍𝑛

𝐴𝑚𝑜𝑢𝑛𝑡  𝑜𝑓  𝑍𝑛𝐶𝑙!  𝑡ℎ𝑎𝑡  𝑐𝑜𝑢𝑙𝑑  ℎ𝑎𝑣𝑒  𝑏𝑒𝑒𝑛  𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑:

14.8  𝑔  𝑍𝑛1

 𝑥  1  𝑚𝑜𝑙𝑒  𝑍𝑛65.39  𝑔  𝑍𝑛

 𝑥  1  𝑚𝑜𝑙𝑒  𝑍𝑛𝐶𝑙!1  𝑚𝑜𝑙𝑒  𝑍𝑛

 𝑥  136.296  𝑔  𝑍𝑛𝐶𝑙!1  𝑚𝑜𝑙𝑒  𝑍𝑛𝐶𝑙!

= 30.8  𝑔  𝑍𝑛𝐶𝑙!

%  𝑦𝑖𝑒𝑙𝑑 =  22.8  𝑔𝑟𝑎𝑚𝑠  𝑍𝑛𝐶𝑙!30.8  𝑔  𝑍𝑛𝐶𝑙!

 𝑥  100 =  74.03%