 ### Note the Pattern

The molar fixed of any substance is its atom mass, molecule mass, or formula mass in grams per mole.

You are watching: Calculate the formula weight of ethanol, c2h5oh

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

problem (formula) Atomic, Molecular, or Formula fixed (amu) Molar massive (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 fixed of naturally arising carbon is various from that of carbon-12 and is no an integer due to the fact that carbon occurs as a mixture the carbon-12, carbon-13, and also carbon-14. One mole of carbon still has actually 6.022 × 1023 carbon atoms, however 98.89% of those atoms space carbon-12, 1.11% space carbon-13, and a map (about 1 atom in 1012) space carbon-14. (For much more information, see ar 1.6 ) Similarly, the molar mass of uranium is 238.03 g/mol, and the molar fixed of iodine is 126.90 g/mol. When we address elements such together iodine and also sulfur, which occur as a diatomic molecule (I2) and a polyatomic molecule (S8), respectively, molar fixed usually refers to the massive of 1 mol of atoms the the element—in this case I and S, not to the fixed of 1 mol that molecules that the facet (I2 and S8).

The molar fixed of ethanol is the mass of ethanol (C2H5OH) that contains 6.022 × 1023 ethanol molecules. Together you calculated in example 1, the molecule mass that ethanol is 46.069 amu. Due to the fact that 1 mol that ethanol contains 2 mol of carbon atoms (2 × 12.011 g), 6 mol the hydrogen atom (6 × 1.0079 g), and also 1 mol the oxygen atom (1 × 15.9994 g), that is molar fixed is 46.069 g/mol. Similarly, the formula massive of calcium phosphate is 310.177 amu, for this reason its molar mass is 310.177 g/mol. This is the fixed of calcium phosphate that has 6.022 × 1023 formula units.

The mole is the basis of quantitative invernessgangshow.netistry. It gives invernessgangshow.netists through a way to convert easily in between the fixed of a substance and also the variety of individual atoms, molecules, or formula devices of that substance. Conversely, it permits invernessgangshow.netists to calculation the fixed of a substance essential to obtain a desired variety of atoms, molecules, or formula units. Because that example, to convert moles that a substance to mass, we use the relationship

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

or, more specifically,

( molesleft ( dfracgramsmole ight ) = grams )​

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### Example 1.7.2

For 35.00 g of ethylene glycol (HOCH2CH2OH), i beg your pardon is used in inks for ballpoint pens, calculate the number of

moles. Molecules.

Given: mass and also molecular formula

Asked for: number of mole and number of molecules

Strategy:

A use the molecule formula the the compound to calculation its molecule mass in grams every mole.

B transform from massive to mole by dividing the mass offered by the compound’s molar mass.

C transform from mole to molecules by multiply the variety of moles through Avogadro’s number.

Solution:

A The molecule mass that ethylene glycol have the right to be calculated from its molecular formula using the an approach illustrated in example 1:

 2C (2 atoms)(12.011 amu/atom) = 24.022 amu 6H (6 atoms)(1.0079 amu/atom) = 6.0474 amu 2O (2 atoms)(15.9994 amu/atom) = 31.9988 amu C2H6O molecular fixed of ethanol = 62.068 amu

The molar fixed of ethylene glycol is 62.068 g/mol

B The variety of moles the ethylene glycol current in 35.00 g have the right to be calculate by separating the massive (in grams) through the molar mass (in grams every mole):

( ; 35.00; g; ethylene glycolleft ( frac1; mol; ethylene; glycol; (g))62.068; g; ethylene; glycol ight )=0.5639; mol; ethylene; glycol)

It is always a great idea to estimate the prize before you perform the actual calculation. In this case, the mass offered (35.00 g) is less 보다 the molar mass, therefore the answer need to be less than 1 mol. The calculated answer (0.5639 mol) is undoubtedly less 보다 1 mol, therefore we have actually probably not made a major error in the calculations.

C To calculation the number of molecules in the sample, we multiply the number of moles through Avogadro’s number:

( molecules; of; ethylene; glycol=0.5639; molleft ( dfrac6.022 imes 10^231; mol ight ) )

( = 3.396 imes 10^23; molecules​ )

Exercise

For 75.0 g that CCl3F (Freon-11), calculate the number of

moles. Molecules.

0.546 mol 3.29 × 1023 molecules

### Example 1.7.3

Calculate the massive of 1.75 mol of each compound.

S2Cl2 (common name: sulfur monochloride; organized name: disulfur dichloride) Ca(ClO)2 (calcium hypochlorite)

Given: number the moles and also molecular or empirical formula

Strategy:

A calculate the molecular mass that the link in grams indigenous its molecule formula (if covalent) or empirical formula (if ionic).

B transform from mole to massive by multiply the mole of the compound provided by its molar mass.

Solution:

We start by calculating the molecular mass the S2Cl2 and also the formula mass of Ca(ClO)2.

A The molar fixed of S2Cl2 is acquired from its molecular mass together follows:

 2S (2 atoms)(32.065 amu/atom) = 64.130 amu 2Cl (2 atoms)(35.353 amu/atom) = 70.906 amu S2Cl​2 molecular mass of S2Cl​2 = 135.036 amu

The molar massive of S2Cl2 is 135.036 g/mol.

See more:

How Many Pounds Is 58 Kg ) Converts To 127, 58 Kg To Lbs

The mass of 1.75 mol the S2Cl2 is calculated together 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 derived 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 fixed of Ca(ClO)2 = 142.983 amu

The molar massive 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), provided as bearings and rollers (CH3)3N (trimethylamine), a corrosion inhibitor