We can argue that contemporary jiyuushikan.orgical science started as soon as researchers started exploring the quantitative and also the qualitative facets of jiyuushikan.orgistry. For instance, Dalton’s atomic theory was an effort to define the outcomes of measurements that permitted him to calculate the loved one masses of facets combined in various compounds. Understanding the relationship in between the masses of atoms and the jiyuushikan.orgical formulas of compounds enables us to quantitatively explain the complace of substances.

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Formula Mass

In an earlier chapter, we described the advance of the atomic mass unit, the principle of average atomic masses, and the use of jiyuushikan.orgical formulas to reexisting the elepsychological makeup of substances. These ideas deserve to be extended to calculate the formula mass of a substance by summing the average atomic masses of all the atoms stood for in the substance’s formula.

Formula Mass for Covalent Substances

For covalent substances, the formula represents the numbers and types of atoms writing a solitary molecule of the substance; therefore, the formula mass might be effectively described as a molecular mass. Consider chlorodevelop (CHCl3), a covalent compound when supplied as a surgical anesthetic and also currently mostly supplied in the production of tetrafluoroethylene, the building block for the “anti-stick” polymer, Teflon. The molecular formula of chlorodevelop shows that a single molecule contains one carbon atom, one hydrogen atom, and three chlorine atoms. The average molecular mass of a chloroform molecule is therefore equal to the amount of the average atomic masses of these atoms. Figure (PageIndex1) outlines the calculations provided to derive the molecular mass of chloroform, which is 119.37 amu.


Figure (PageIndex1): The average mass of a chlorodevelop molecule, CHCl3, is 119.37 amu, which is the amount of the average atomic masses of each of its constituent atoms. The version shows the molecular framework of chloroform.

Likewise, the molecular mass of an aspirin molecule, C9H8O4, is the sum of the atomic masses of nine carbon atoms, eight hydrogen atoms, and 4 oxygen atoms, which quantities to 180.15 amu (Figure (PageIndex2)).



Exercise (PageIndex1)

Acetaminophen, C8H9NO2, is a covalent compound and also the energetic ingredient in a number of well-known nonprescription pain medications, such as Tylenol. What is the molecular mass (amu) for this compound?


151.16 amu

Formula Mass for Ionic Compounds

Ionic compounds are composed of discrete cations and anions linked in ratios to yield electrically neutral mass issue. The formula mass for an ionic compound is calculated in the very same means as the formula mass for covalent compounds: by summing the average atomic masses of all the atoms in the compound’s formula. Keep in mind, yet, that the formula for an ionic compound does not recurrent the composition of a discrete molecule, so it might not appropriately be described as the “molecular mass.”

As an example, think about sodium chloride, NaCl, the jiyuushikan.orgical name for widespread table salt. Sodium chloride is an ionic compound created of sodium cations, Na+, and chloride anions, Cl−, merged in a 1:1 proportion. The formula mass for this compound is computed as 58.44 amu (Figure (PageIndex3)).


Exercise (PageIndex2)

Calcium phosphate, Ca3(PO4)2, is an ionic compound and a common anti-caking agent added to food commodities. What is the formula mass (amu) of calcium phosphate?


310.18 amu

The Mole

The identity of a substance is identified not just by the forms of atoms or ions it has, but by the amount of each form of atom or ion. For instance, water, H2O, and hydrogen peroxide, H2O2, are afavor in that their particular molecules are written of hydrogen and oxygen atoms. However before, because a hydrogen peroxide molecule includes two oxygen atoms, as opposed to the water molecule, which has actually just one, the 2 substances exhilittle bit incredibly various properties. Today, we possess advanced instruments that enable the straight measurement of these specifying microscopic traits; yet, the exact same traits were initially derived from the measurement of macroscopic properties (the masses and quantities of bulk amounts of matter) using relatively basic devices (balances and also volumetric glassware). This speculative approach required the introduction of a new unit for amount of substances, the mole, which continues to be indispensable in modern jiyuushikan.orgical scientific research.

The mole is an amount unit comparable to acquainted devices choose pair, dozen, gross, etc. It gives a details measure of the number of atoms or molecules in a mass sample of issue. A mole is defined as the amount of substance containing the very same variety of discrete entities (such as atoms, molecules, and ions) as the variety of atoms in a sample of pure 12C weighing specifically 12 g. One Latin connotation for the word “mole” is “huge mass” or “bulk,” which is consistent through its use as the name for this unit. The mole offers a link in between an conveniently measured macroscopic building, bulk mass, and also a very vital fundamental residential or commercial property, number of atoms, molecules, and also so forth.

The number of entities writing a mole has actually been experimentally established to be (6.02214179 imes 10^23), a standard constant called Avogadro’s number (NA) or the Avogadro continuous in honor of Italian scientist Amedeo Avogadro. This consistent is correctly reported with an explicit unit of “per mole,” a conveniently rounded version being (6.022 imes 10^23/cemol).

Consistent with its meaning as an amount unit, 1 mole of any type of element has the same variety of atoms as 1 mole of any type of other facet. The masses of 1 mole of various elements, yet, are different, given that the masses of the individual atoms are considerably various. The molar mass of an element (or compound) is the mass in grams of 1 mole of that substance, a residential or commercial property expressed in systems of grams per mole (g/mol) (Figure (PageIndex4)).

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Figure (PageIndex6): Copper wire is written of many kind of, many kind of atoms of Cu. (credit: Emilian Robert Vicol)


The number of Cu atoms in the wire may be conveniently derived from its mass by a two-action computation: initially calculating the molar amount of Cu, and also then utilizing Avogadro’s number (NA) to convert this molar amount to variety of Cu atoms:


Considering that the offered sample mass (5.00 g) is a small much less than one-tenth the mass of 1 mole of Cu (~64 g), a reasonable estimate for the number of atoms in the sample would be on the order of one-tenth NA, or around 1022 Cu atoms. Carrying out the two-action computation yields:

The factor-label approach yields the desired cancellation of units, and the computed outcome is on the order of 1022 as meant.

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The molar mass of glycine is required for this calculation, and also it is computed in the exact same fashion as its molecular mass. One mole of glycine, C2H5O2N, contains 2 moles of carbon, 5 moles of hydrogen, 2 moles of oxygen, and also 1 mole of nitrogen: