Stoichiometry: Calculating Chemical Amounts

8.1  Stoichiometry:  Calculating  Chemical  Amounts   (notes,  3  examples,  and  3  practice  problems)   If  you  have  internet  access,  there  is  a  video  on  my  website  explaining  these  notes!   When  potassium  iodide  (KI)  is  mixed  with  lead  nitrate   (Pb(NO3)2),  a  yellow  solid  is  formed.  This  yellow  solid  is  lead   iodide,  PbI2.  Lead  iodide  used  to  be  used  as  a  pigment  in   yellow  paint,  but  is  now  used  to  detect  gamma  and  x-­‐rays.     2  KI      +      Pb(NO3)2      à      PbI2      +      2  KNO3   Molar  Mass  KI:    166.0  grams  =  1  mol   Molar  Mass  Pb(NO3)2:    331.22  grams  =  1  mol   Molar  Mass  PbI2:      461.0  grams  =  1  mole   Molar  Mass  KNO3:      101.11  grams  =  1  mole   1. I  need  15.5  grams  of  PbI2.  How  many  moles  of  KI  do  I need  to  use  to  make  it? Given  (with  units!):  15.5  grams  of  PbI2 Desired  units:  moles  of  KI   Calculation:     15.5  grams  PbI2 1  mol  PbI2 2  mol  KI   =  0.0672  mol  KI   (remember:  nothing  goes   here!)   461.0  g  PbI2 1  mol  PbI2 (remember:  nothing  goes   here!)   Explanation  for  each  step:   Use  molar  mass  to  convert   grams  of  PbI2  to  moles  of   PbI2 Use  mole  ratio  to  convert   moles  of  PbI2  to  moles  of  KI   Calculate  by  multiplying  by   the  top/dividing  by  the   bottom  (15.5  ÷  461.0  x  2)   1   2. If  I  want  to  make  15.5  grams  of  PbI2,  how  many  grams  of  Pb(NO3)2  will  I  need  to  use? Given  (with  units!):  15.5  grams  of  PbI2   Desired  units:  grams  Pb(NO3)2   Calculation:     15.5  grams  PbI2   1  mol  PbI2 1  mol  Pb(NO3)2 331.22  g  Pb(NO3)2   =  11.1  g  Pb(NO3)2   (remember:  nothing   goes  here!)   461.0  g  PbI2 1  mol  PbI2 1  mol  Pb(NO3)2   (remember:  nothing   goes  here!)   Explanation  for  each   step:   Use  molar  mass  to   Use  mole  ratio  to   convert  grams  of  PbI2   convert  moles  of  PbI2   to  moles  of  PbI2 to  moles  of  Pb(NO3)2   Calculate  by   Use  molar  mass  to   multiplying  by  the   convert  moles  of   top/dividing  by  the   Pb(NO3)2  to  grams   bottom  (15.5  ÷  461.0  x   of  Pb(NO3)2   331.22)   3. If  I  use  4.8  x  1023  particles  of  KI,  how  many  grams  of  PbI2  can  be  made? Given  (with  units!):  4.8  x  1023  particles  of  KI   Desired  units:  grams  of  PbI2 Calculation:   4.8  x  1023  particles  KI   1  mol  KI 1  mol  PbI2 461.0  g  PbI2 =  180  g  PbI2 (remember:  nothing   goes  here!)   6.02  x  1023  particles   KI   2  mol  KI 1  mol  PbI2 (remember:  nothing   goes  here!)   Use  molar  mass  to   convert  moles  of   PbI2  to  grams  of   PbI2   Calculate  by   multiplying  by  the   top/dividing  by  the   bottom  (remember  to   put  Avogadro’s   number  in   parentheses!)   Explanation  for  each   step:   Use  Avogadro’s   number  to  convert   particles  of  KI  to   moles  of  KI Use  mole  ratio  to   convert  moles  of  KI   to  moles  of  PbI2   Try  these  problems  on  your  own,  then  check  your  answers.  The  answers  are  at  the  bottom  of  the  page.  If  you  have   internet  access,  there  is  also  a  video  showing  how  to  do  the  problems  on  my  website.     The  reaction  below  is  called  the  Haber  process.  It  was  developed  by  Fritz  Haber  in  the  early  1900s.  Ammonia,  NH3,  is  the   main  component  in  fertilizer;  this  is  the  main  use  of  the  Haber  process  today.  However,  ammonia  is  also  used  in  many   cleaning  products  such  as  Windex.     Balance:   ______  H2  +  ______  N2  à  ______  NH3   MM  H2:    2.016  grams  =  1  mol   MM  N2:  28.02  grams  =  1  mol   MM  NH3:  17.034  grams  =  1  mol   1. If  I  start  with  6.8  x  1023  particles  of  H2,  how  many  particles  of  N2  will  I  need  to  use? Given  (with  units!):  _________________________   Desired  units:  __________________________   Calculation:     2   2. If  I  start  with  3.78  grams  of  N2,  how  many  molecules  of  NH3  can  I  make? Given  (with  units!):  _________________________   Desired  units:  __________________________   Calculation:     Ammonia  should  never  be  mixed  with  chlorine  bleach  when  cleaning.  When  mixed,  the  following  reaction  happens:   NaOCl  (bleach)  +  NH3  (ammonia)  à  NaOH  +  NH2Cl   NH2Cl  is  a  substance  that  is  used  to  treat  water  in  very  small  amounts,  but  it’s  fumes  can  be  poisonous  or  even  fatal  if   inhaled.     3. A  lethal  dose  of  NH2Cl  is  approximately  65  grams  for  the  average  adult.  How  many  grams  of  bleach  (NaOCl) would  be  needed  to  generate  this  amount  of  NH2Cl? Given  (with  units!):  _________________________   Molar  Mass  NH2Cl:     Desired  units:  __________________________   Molar  Mass  NaOCl:     Calculation:   Answers  (problems  2  and  3  only):  2.3  x  1023  particles  N2,  1.62  x  1023  molecules  NH3,  94  grams  NaOCl   3   Assignment  8.2  Stoichiometry  Practice   Before you begin, make sure you have completed assignment 8.1. Please show your work. You must show your work in order to receive full credit. Use the mole Island Graphic Organizer (Page ) to guide you. A partial answer key is also included for you. YOU MUST SHOW YOUR WORK TO RECEIVE FULL CREDIT!!! Use the following balanced chemical equation to answer questions 1-4: C3H8 + 5O2 → 4H2O + 3CO2 1. If I want to make 3.00 moles of H2O, how many grams of C3H8 do I need? Given/start with units (X): 3 moles of H2O Desired/end with units (Y) : grams of C3H8 Step 1. Write what you start with in the top left, what you end with goes in the top right. Step 2. Make plan from start → end using mole island island moles of (X) → moles of (Y) → grams of (Y) Step 3. Using dimensional analysis and mole island, convert from X → Y Each mole island arrow will be one column of dimensional analysis You will have to calculate molar mass in some problems The molar ratio of C3H8 : H2O is 1 mol of C3H8 : 4 mol of H2O 3 moles of H2O (start) 1 mol of C3H8 44.097 grams of C3H8 = 33.1 grams of C3H8 (end) (This area remaines blank) 4 mol of H2O 1 mol of C3H8 (This area remaines blank) 2. If I use 50.0 grams of O2 , how many grams of C3H8 will I use? Given/start with units (X): 50.0 grams of O2 Desired/end with units (Y): grams of C3H8 Mole island pathway: grams of (X) → moles of (X) → moles of (Y) → grams of (Y) 50.0 grams of O2 = grams of C3H8 (This area remaines blank) (This area remaines blank) 4   3. If I want to make 12 moles of CO2, how many particles of C3H8 will I use? a. Given/start with units (X): ___________ b. Desired/end with units (Y): _____________ c. Mole island map: Moles of (X) → moles of (Y) → particles of (Y) (start) (end) 4. If I use 8.65 x 1023 particles of C3H8, how many grams of CO2 will I use? Use the following balanced chemical equation to answer questions 5-8: 2 Al + Fe2O3 → Al2O3 + 2 Fe 5. Mr. Lim is going to perform a thermite reaction. How many moles of Al should he use if he wants to make 123 grams Fe? 6. If Mrs. Macedo produces 1.01 x 1023 particles of Al2O3, how many particles of Fe2O3 were used? 7. How many grams of Al will Mrs. Meemari needs to make 4.80 moles of Al2O3? 8. If Mrs. Richardson produce 92 grams of Al2O3, how many grams of Fe2O3 did she use? 9. (Super) Challenge (Optional): 2 Al + Fe2O3 → Al2O3 + 2 Fe I have 2.000 pounds of Al and 5.000 pounds of Fe2O3, how many moles of Fe can I make? How many grams? (hint: 453.6 grams = 1 lb, there is a limiting reactant as well) 5   8.3  End  of  Year  Survey  Please answer the following questions:   1. If we could travel back in time and redo semester 2 (specifically the 4th quarter with distance learning) what should we add/change to make the experience better or more successful for you? 2. How "hard" was the workload this quarter on Distance Learning? Did you feel you had enough support and could successfully complete the assignments if you were actually trying? 3. On a scale of 1-5 (1 being the easiest and 5 being the hardest) - how hard was it to do the following: a. Access assignments? _____ b. Complete assignments? _____ c. Submit the distance learning assignments? _____ 4. How did the rest of this quarter end for you? A lot of news reports discussed "Distance Learning Fatigue" did you feel that way? Anything else you would like me to know about how you're doing right now? 5. What was your favorite memory from class this year? 6. If you had to describe your Chem Class in a tweet - what would the tweet say? 7. Which topic do you feel you never fully understood/still have questions about? 8. Which topic was your favorite to learn about this year? Why? 9. Anything else you would like to share with me or think would be helpful for me to change going forward? Please be honest (but make it Constructive Criticism). I would like to make this the best class possible and your feedback is super important to me. 6   7