For each of the following, determine: the limiting reactant the theoretical yiel

Question

For each of the following, determine: the limiting reactant

the theoretical yield of the given product

the mass of any exess reactants remaining

the percent yield

1.When powdered zinc is heated with sulfur, a violent reaction occurs and zinc sulfide forms. When 83.2 g of zinc reacts with 52.4 g of sulfur, 104.4 g of zinc sulfide is formed.

Zn (s) + S8 (s)      ZnS (s)

2.Aspirin (C9H8O4) is made by the reaction of salicylic acid (C7H6O3) with acetic anhydride ((CH3CO)2O). In one reaction, 3.077 g of salicylic acid and 5.50 mL of acetic anhydride (r = 1.080 g/mL) react to form 3.281 g of aspirin.

C7H6O3 (s) + (CH3CO)2O (l)      C9H8O4 (s) + CH3COOH (l)

3.When 36.5 g NH4CN is added to a solution containing 42.1 g Cd2+, a precipitate of Cd(CN)2 forms. The precipitate is found to have a mass of 29.4 g.

Cd2+ (aq) + NH4CN (aq)      Cd(CN)2 (s) + 2 NH4+ (aq)

Explanation / Answer

Q1.

mol of Zn = mass/NW= 83.2/65.38 = 1.27 mol of Zn

mol of S = mass/MW = 52.4/(32*8) = 0.20468

so...

ratio is

8Zn(s) + S(8) = 8ZnS

8:1

0.20468mol of S8 require 8*0.20468= 1.637 mol of Zn which we do not have so

Zn is limiting, since we have 1.27 mol only

expected mass to be:

1.27 mol of Zn --> 1.27 mol of ZnS

mol of ZnS = 1.27 *97.474 = 123.791 g of ZnS

mass of S8 left = 0.20468 - 1.27 /8 = 0.04593 mol of S8 left

mass = mol*MW = (0.04593)(8*32) =11.75808 g of S8 left

% yield = real/theoretical * 100 = 104.4/123.791 *100 = 84.335 %

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