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PS 1 7 Percentage composition and moles Chem S Tree

 

A student reacted 1.5 g salicylic acid C7H6O3 with 2 g acetic anhydride C4H6O3  This yielded 1.5 g aspirin C9H8O4

C7H6O3    +    C4H6O3 --> C9H8O4 + HC2H3O7

 1.5 g                2 g

0.011 mol      0.020 mol

 

Need molar masses of reactants

Which is limiting reagent?  Find the number of moles 1 mole salicylic acid = 1 mole acetic anhydride

Salicylic acid is limiting

(0.009 mol acetic anhydride in excess)

Now find how much aspirin is needed?  find mol aspirin --> 1: 1 : 1 mole ratio, so 0.011 mol aspirin formed 

Mass aspirin = 

in grid

mol salicylic acid :  1 mol asp        :  180 g aspirin (mol mass)      = 1.98 g aspirin

                           1 mol sal acid   : 1 mol aspirin
1.50/1.98 = 76%

 

 

 

 

 

% yield example 

toy car: 4 wheels, 1 body, 3 stickers

You have enough parts to make 200 cars

BUT only 168 are made

The theoretical yield  =     (200)  Max possible amount that can be produced

the actual yield =       (168)   = Amount that IS produced 

the percent yield =   (84%)      = percentage of theoretical yield you actually produce                                        (actual yield/theoretical yield) x 100

5 mole H2 gas combine with 5 mole O2 gas to produce 4 moles H2O

What is the theoretical yield, actual yield and % yield

Write balanced equation

    2H2   +     O2   -->  2H2O                                                                                                                                            2 moles  1 mole       2 moles

 

= mole O2 needed  = 2.5 mole O2

To determine the limiting reagent, start with ONE of the amounts given—example here: 5 mole H2

5 mole H2            (amount available)

1 mole O2.          (amount in equation-theoretical)

 

2 mole H2.                   (amount in equation)

 

But there are 5 mole O2 available—so oxygen is in EXCESS

 

H2 is the LIMITING reagent

 

 

= mole H2O produced  = 5 mole H2O

With 5 mole H2, how many moles H2O are produced = theoretical yield

5 mole H2            (amount available)

2 mole H2O         (amount in equation)

  

2 mole H2.                   (amount in equation)

 

Theoretical yield =  5 moles H2O

actual yield (given in question)  = 4 moles H2O

 

Percentage yield  =    actual yield  x 100   %       = 4 moles x 100                                        

-                              theoretical yield                        5 moles

 

% yield = 80%

 

 

32g H2 gas with 96 g O2 to give 99 g water What is the percentage yield

STEP 1:   write equation

STEP 2:   convert O2 and H2  masses to moles                                                                                   STEP 3: determine the limiting reagent

96 g = 3 mole = limiting

32 g H2 = 16 moles  in excess.  

3 mol O2  :  2 mol H2O   :  10 g H2O      = 108 g H2O

                    1 mol O2         1 mol H2O.

STEP 4:  calculate the percentage yield

Theoretical (calculated) yield = 108g

Actual yield (given) = 99 g

 

Percentage yield  =    actual yield  x 100   %       =  99 g x100                                            

-                              theoretical yield                        108 g

 

% yield = 92%

 

 

 

 

Solve crime with this

Who killed Chem S. Tree?

4 suspects, all with a different herbicide residue

see free download of activity at https://www.teacherspayteachers.com/Product/CSI-Empirical-Formula-Who-Done-It-Activity-1065475

or go to https://chemsnyder.wikispaces.com/file/view/CSI+Empirical+Formula+Who+Done+It+Activity+Herbicide.pdf

 

+ dimensional analysis warm up with shapes (free download) at https://www.teacherspayteachers.com/Product/Dimensional-Analysis-Warm-Up-1065433