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The molar mass of any substance is its atomic mass, molecular mass, or formula mass in grams per mole.

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The periodic table lists the atomic mass of carbon as 12.011 amu; the average molar mass of carbon—the mass of 6.022 × 1023 carbon atoms—is therefore 12.011 g/mol:


Substance (formula) Atomic, Molecular, or Formula Mass (amu) Molar Mass (g/mol)
carbon (C) 12.011 (atomic mass) 12.011
ethanol (C2H5OH) 46.069 (molecular mass) 46.069
calcium phosphate 310.177 (formula mass) 310.177

The molar mass of naturally occurring carbon is different from that of carbon-12 and is not an integer because carbon occurs as a mixture of carbon-12, carbon-13, and carbon-14. One mole of carbon still has 6.022 × 1023 carbon atoms, but 98.89% of those atoms are carbon-12, 1.11% are carbon-13, and a trace (about 1 atom in 1012) are carbon-14. (For more information, see Section 1.6 ) Similarly, the molar mass of uranium is 238.03 g/mol, and the molar mass of iodine is 126.90 g/mol. When we deal with elements such as iodine and sulfur, which occur as a diatomic molecule (I2) and a polyatomic molecule (S8), respectively, molar mass usually refers to the mass of 1 mol of atoms of the element—in this case I and S, not to the mass of 1 mol of molecules of the element (I2 and S8).

The molar mass of ethanol is the mass of ethanol (C2H5OH) that contains 6.022 × 1023 ethanol molecules. As you calculated in Example 1, the molecular mass of ethanol is 46.069 amu. Because 1 mol of ethanol contains 2 mol of carbon atoms (2 × 12.011 g), 6 mol of hydrogen atoms (6 × 1.0079 g), and 1 mol of oxygen atoms (1 × 15.9994 g), its molar mass is 46.069 g/mol. Similarly, the formula mass of calcium phosphate is 310.177 amu, so its molar mass is 310.177 g/mol. This is the mass of calcium phosphate that contains 6.022 × 1023 formula units.

The mole is the basis of quantitative beer-selection.comistry. It provides beer-selection.comists with a way to convert easily between the mass of a substance and the number of individual atoms, molecules, or formula units of that substance. Conversely, it enables beer-selection.comists to calculate the mass of a substance needed to obtain a desired number of atoms, molecules, or formula units. For example, to convert moles of a substance to mass, we use the relationship


( (moles)(molar ; mass) ightarrow mass ag1.71 )


or, more specifically,

( molesleft ( dfracgramsmole ight ) = grams )​


To convert from mass to number of particles, mass is multipled by (1/molar mass) to get the number of moles which is then multiplied by AvogadroHow To Pronounce Fart In Spanish, How To Say Fart In Spanish

The mass of 1.75 mol of S2Cl2 is calculated as follows:

( moles; S_2Cl_2 left = mass; S_2Cl_2 )

( 1.75; mol; S_2Cl_2left ( dfrac135.036; g; S_2Cl_21;mol;S_2Cl_2 ight )=236;g; S_2Cl_2 )

B The formula mass of Ca(ClO)2 is obtained as follows:

1Ca (1 atom )(40.078 amu/atom) = 40.078 amu
2Cl (2 atoms)(35.453 amu/atom) = 70.906 amu
2O (2 atoms)(15.9994 amu/atom) = 31.9988 amu
Ca(ClO)2 formula mass of Ca(ClO)2 = 142.983 amu

The molar mass of Ca(ClO)2 is 142.983 g/mol

( moles; Caleft ( ClO ight )_2left < dfracmolar; mass; Caleft ( ClO ight )_21; mol; Caleft ( ClO ight )_2 ight >=mass; Caleft ( ClO ight )_2 )

( 1.75; mol; Caleft ( ClO ight )_2left < dfrac142.983; g Caleft ( ClO ight )_21; mol; Caleft ( ClO ight )_2 ight >=250.; g; Caleft ( ClO ight )_2 )​

Exercise

Calculate the mass of 0.0122 mol of each compound.

Si3N4 (silicon nitride), used as bearings and rollers (CH3)3N (trimethylamine), a corrosion inhibitor

Answer: