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Sample % composition problem #1

% composition problems: using mole concept to convert weights to formulas. Sample % composition problem #1. A compound of N and O contains 63.63 wt % N and 36.36 wt % O. What is the empiric formula of the compound ?. % composition Problem 1: empiric formula determination.

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Sample % composition problem #1

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  1. % composition problems: using mole concept to convert weights to formulas Sample % composition problem #1 A compound of N and O contains 63.63 wt % N and 36.36 wt % O. What is the empiric formula of the compound ?

  2. % composition Problem 1: empiric formula determination A compound of N and O contains 63.63% N and 36.36 %O. What is the empiric formula of the compound? let’s do it on the board…

  3. Sample problem #1; SUMMARIZED =Laughing gas OFFICIAL NAME… =>N2O Dinitrogen monoxide n nmin AW=Atomic wt (g/mol) n=w/AW moles w(g) 4.545 = 2 2.273 63.63/14= 4.545 63.63 14 36.36/16= 2.273 2.273 =1 2.273 36.36 16

  4. An oxide of nitrogen contains 46.7 wt. % N and 53.3 % O. What is it’s empiric formula ? (problem 35, page 417) • NO3 • NO2 • N2O • N3O7 • NO • None of the above

  5. % composition Problem 2: empiric formula determination with a twist A compound composed of C,H and O is 48.64% C and 8.16 % H and 43.2 % O by mass. What is the empiric formula ? Answer: C1.5H3O1 C3H6O2 x FACTOR 1.5*2= 3 48.64/12= 4.05 4.05/2.7= 1.5 ? 8.16/1= 8.16 3.0*2= 6 8.16/2.7= 3.0 43.2/16= 2.70 2.7/2.7= 1 1*2= 3

  6. A compound contains:0.3158 g C, 0.0526 g H and 0.631 g O. What is its empiric formula ? • C2H4O3 • C4H2O3 • CHO • CH2O • None of the above

  7. % composition Problem 3: empiric + molecular formula determination The previous empiric compound (C2H4O3) has a molecular weight of 228 g/mol. What is the molecular formula of the compound ? Let’s do this on the board…

  8. A compound with the empiric formula CH2O has a molecular weight of 180 g/mol. Given C=12 g/mol, H=1 g/mol and O=16 g/mol what is the molecular formula for the compound ? • CH2O • C3H6O3 • C6H12O6 • C12H24O12 • None of the above

  9. Chemical Compositions from Combustion Data 1) A 0.30 gram sample of carbon black is burned in a covered crucible. The collected gas weighs 0.70 grams. What is the empiric formula of the gas ? (C =12, O =16) ANSWER: CO

  10. Chemical Compositions from Combustion Data (continued) 2) A hydrocarbon sample (Cx Hy) is burned in oxygen producing 1.0 gram of CO2 and 0.4086 g H2O. What is the empiric formula for the hydrocarbon ? (C=12, O=16, H=1) ANSWER: CH2

  11. A similar text book problem to try: Page 418 Problem 51 Propane is a common hydrocarbon gas used for heating rural American homes. Complete combustion of a sample of propane produced 2.641 g CO2 and 1.442 g H2O. What is the empiric formula for propane ? (also called LNG=liquid natural gas) Answer: C3H8

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