Sally and Sam reacted 20.0 mL of 1.0 M silver (I) chloride with metallic zinc in class. Sam and Sally collected 0.85 g of zinc chloride. What is the percent yield?

Question

Peyton Adams · Accepted Answer

#62%#

First, for this one replacement reaction, write a balanced chemical equation.

#"Zn"_text((s]) + color(red)(2)"AgCl"_text((aq]) -> "ZnCl"_text(2(aq]) + 2"Ag"_text((s])#

Notice that you have a #color(red)(2):1# mole ratio between silver chloride and zinc chloride. This tells you that the reaction should theoretically produce #1# mole of zinc chloride for every #color(red)(2)# moles of silver chloride that take part in the reaction.

Since the problem doesn't specify how much zinc metal was used in the experiment, you can assume that there is too much of it.

This indicates that the reaction will involve every mole of silver chloride.

Find the number of moles in that sample using the molarity of the solution.

#color(blue)(c = n/V implies n = c * V)#

#n_(AgCl) = "1.0 M" * 20.0 * 10^(-3)"L" = "0.020 moles AgCl"#

In theory, the reaction ought to result in

#0.020 color(red)(cancel(color(black)("moles AgCl"))) * "1 mole ZnCl"_2/(color(red)(2)color(red)(cancel(color(black)("moles AgCl")))) = "0.010 moles ZnCl"_2#

Use the molar mass of zinc chloride to convert this to grams.

#0.010 color(red)(cancel(color(black)("moles ZnCl"_2))) * "136.286 g"/(1color(red)(cancel(color(black)("mole ZnCl"_2)))) = "1.363 g"#

So, this tells you that the reaction's theoretical yield, which is what you get in the hypothetical case in which a reaction has a #100%# yield, is equal to #"1.363 g"# of zinc chloride.

However, you only recover #"0.85 g"# of zinc chloride. This is the actual yield of the reaction.

Thus, the yield percentage will be

#color(blue)("% yield" = "actual yield"/"theoretical yield" xx 100)#

Enter your values to obtain

#"% yield" = (0.85color(red)(cancel(color(black)("g"))))/(1.363color(red)(cancel(color(black)("g")))) xx 100 = color(green)("62%")#

Since you have two sig figs for both the mass of recovered zinc chloride and the molarity of the silver chloride solution, the answer must be rounded to two sig figs.

Cooper Anderson · Answer

undefined The percent yield of zinc chloride in this reaction is 67.7%.