Question

Calculate the percent yield if 31.6 grams of C4H8Br2 are produced when 10.0 grams of C4H8 are reacted with excess Br2. The reaction is C4H8 + Br2 ---> C4H8Br2

Answer 1

Molar mass of C4H8 = 4*MM(C) + 8*MM(H)

= 4*12.01 + 8*1.008

= 56.104 g/mol

mass of C4H8 = 10 g

mol of C4H8 = (mass)/(molar mass)

= 10/56.104

= 0.1782 mol

From balanced chemical reaction, we see that

when 1 mol of C4H8 reacts, 1 mol of C4H8Br2 is formed

mol of C4H8Br2 formed = moles of C4H8

= 0.1782 mol

Molar mass of C4H8Br2 = 4*MM(C) + 8*MM(H) + 2*MM(Br)

= 4*12.01 + 8*1.008 + 2*79.9

= 215.904 g/mol

mass of C4H8Br2 = number of mol * molar mass

= 0.1782*215.904

= 38.4828 g

% yield = actual mass*100/theoretical mass

= 31.6*100/38.4828

= 82.1 %

Answer: 82.1 %