Problem Set 4 Answer Key (PDF)

Chemistry Lesson: Steemit Edition Problem Set 4

1.) Balance the following chemical reaction: Fe2O3 (s) + Al (s)  Al2O3 (s) + Fe (s)
This reaction is the thermite reaction, it was used in the 1800’s to weld railroads together before
the advent of the modern welding techniques, it is my personal favorite chemical reaction
because of how it looks! For reference check out this video of it:
(https://youtu.be/M3ZkoNF2ybg)

Fe2O3 (s) + 2 Al (s)  Al2O3 (s) + 2 Fe (s)

2.) Using the balanced reaction above. We reacted 0.7 mol of Fe2O3 with 1 mol of Al, and obtained
41 g of iron (Fe). What is our percent yield from the thermite reaction we performed?

0.7 𝑚𝑜𝑙 𝐹𝑒2 𝑂3 𝑥

1 𝑚𝑜𝑙 𝐴𝑙 𝑥

1 "𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠"
= 0.7 𝑚𝑜𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠
1 𝐹𝑒2 𝑂3

1 "𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠"
= 0.5 𝑚𝑜𝑙 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠
2 𝐴𝑙

Thus alumimum (Al) is our limiting reagent.
1 𝑚𝑜𝑙 𝐴𝑙 𝑥

2 𝐹𝑒
55.8 𝑔 𝐹𝑒
= 1 𝑚𝑜𝑙 𝐹𝑒 𝑥
= 55.8 𝑔 𝐹𝑒 (𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑌𝑖𝑒𝑙𝑑)
2 𝐴𝑙
1 𝑚𝑜𝑙 𝐹𝑒

% 𝑌𝑖𝑒𝑙𝑑 =

41 𝑔
𝑥 100% = 73.4% 𝑦𝑖𝑒𝑙𝑑
55.8 𝑔