Practice Problem 15.1 SET UP From the periodic table of the elements, we find th

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Practice Problem 15.1 SET UP From the periodic table of the elements, we find that the molar mass of hydrogen (jie., the mass per mole of hydrogen atoms) is 1.008 g/mol.The molar mass of oxygen is 16.0 g/mol, so the molar mass of O2 is 32.0 g/mol. Let's begin by using the molar mass to find the actual mass of an atom and a molecule. Specifically, we will use the peniodic table to find the mass of a single hydrogen atom and the mass of an oxygen molecule (consisting of two oxygen atoms and written 02) SOLVE We use equation M NATn. The mass m of a single hydrogen atom is MH 1.008g/mol 6.022x10 molecules/mol 1.674 × 10-24 g/atom = The mass of a single molecule of O2 is 32.0g/mol 6.022x10molecules/mol = 53.1x 10 2 g/molecule mo REFLECT A water molecule mass H2O) consists of one oxygen atom and two hydrogen atoms, but we can now see that the oxygen atom accounts for nearly 90% of its Part A- Practice Problem: Find the total mass of a molecule of carbon dioxide (CO2). Express your answer in grams per molecule to three significant figures. g/molecule Submit My Answers Give Up Part B Practice Problem: What fraction of this total mass is the mass of the carbon atom? Express your answer to two significant figures.

Explanation / Answer

1)

molar mass of Carbon C = 12.010 g /mol

molar mass of O2 = 32.0 g /mol :

Therefore molar mass of CO2 = 12.010 + 32.0 = 44.010 g/mol

1 mole consists of = 6.022*1023 molecules

i.e., 6.022 X 1023 molecules / mole, so use it as below,,

Therefore, mass of 1 molecule of CO2 = 44.010 g / mole = 44.010 / [ 6.022 X 1023 ] (g / 1 molecule of CO2 )  

= 7.308 X 10-23 (g / 1 molecule of CO2 )  

mass of 1 molecule of CO2 = 7.31 X 10-23 (g / 1 molecule of CO2 )  

2)

molar mass of Carbon = 12.010 g /mol -------------------(1)

and 1 mol = 6.022 X 10^23 atoms , so substitute it in (1)

we get, mass of C = 12.010 / [ 6.022 X 1023] ( g/ 1 molecule of CO2 )

= 1.99 X 10-23 (g / molecule of CO2)

Now, mass % of C in CO2 = [1.99 X 10-23 (g / molecule of CO2) ] X 100 / [ 7.31 X 10-23 (g / 1 molecule of CO2 ) ]

= 0.273 X 100

= 27 % ( since, two significant figures )

Mass of Carbon in total mass of CO2 is , 27 %

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