SAT Subject Test Chemistry,10 edition

6 . E

Let n   be  the atomic  mass    of  element X.  The expression  for the percent composition of  X   in

CH 3 X  is:

This,   we  are told,   is  equal   to  32%.    Therefore

Answer  choice  E,  Li, has an  atomic  weight  of  7.

7 . 31 g, 25 g, 81%

According   to  the balanced    equation,   two moles   of  silver  should  react   with    one mole    of  sulfur

to  form    one mole    of  silver  sulfide.    The theoretical yield   is  the amount  of  product that    would   be

collected   if  all of  the limiting    reagent reacts. Using   a   stoichiometric  calculation,    the theoretical

yield   of  silver  sulfide if  27.0    g   of  silver  is  used    would   be  as  follows:

The actual  yield   is  the amount  of  product that    is  obtained    from    the experiment. It  is  usually

less    than    the theoretical yield   since   the reagents    may not react   completely, and the product

may be  difficult   to  collect.    In  this    experiment, the actual  yield   is  25.0    g   of  silver  sulfide.    Finally,

the percent yield   represents  the percentage  of  product actually    collected   in  reference   to  the

theoretical yield.  Thus,   the percent yield   for this    experiment  would   be