A_-_102_F11_Notes

# 578gsampleofpuretinsnistreatedwithgaseousfluorineuntil

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Unformatted text preview: in “Per centum”  • means per 100 of something  • Percent composition can be given in terms of mass (sometimes “weight” is used),  volume, mols, etc  • To use this information, convert the percentage into a fraction or ratio  • A compound that is 7.2 mol% C could also be written as  mols C   mols compound     Question A4  € A fertilizer contains 21% nitrogen by mass.  What mass of this fertilizer, in kilograms, is  needed for an application requiring 225 g of nitrogen?      Avogadro’s Number  • The number of carbon atoms in exactly 12.0 g of 12C is called Avogadro’s number (NA).       NA = 6.022 x 1023  • The mole is a measurement of quantity:      1 ___‐mol = 6.022 x 1023 units      Molar Mass  • Molar Mass is the mass of one mol of a substance   • 6.022 x 1023 atoms (1 mol) of C weigh 12 g and therefore molar mass of C is 12 g/mol.  • 1 g‐mol of C = 12 g of C  • 1 lb‐mol of C = 12 lb of C  ChE102 Fall 2011 Class Notes ‐ Introduction  A ‐5   Question A5  Determine the name of the mystery element if a 2.80 x 1022 atom sample of the element  has a mass of 5.23g.      Molar Mass of Compounds  • Calculated from the molecular formula  • For example: Water (H2O)  • The molar mass of H is 1 g/mol and O is 16 g/mol  •      • Therefore, the molar mass of H2O is 18 g/mol        Question A6  You work for a copper mining company and are trying to decide which mine to buy.  One  mine is rich in chalcolite (Cu2S) and the other is rich in Athabascaite (Cu5Se4).  How  much more copper (in g) can be extracted from the chalcolite‐containing mine per kg of  mineral?    Composition of Compounds  • Calculating percent composition  • Determining empirical formulas for new compounds using combustion analysis  • Based on the knowledge of the products made when a substance is burned (...
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