Overview: In this module, we present the mole, a unit of measure the is used broadly in invernessgangshow.net. The interconversion in between mass, moles, number of atoms or molecules, and also volume is described.


identify the number of moles in a provided mass of a sample converting sample mass to the variety of molecules or atoms using the thickness to called volume to number of moles

new terms:

Mole Avogadro"s Number (NA) molecule mass molar mass density (r) MolesWhat is a mole? usually a mole is identified as Avogadro"s variety of anything. Avogadro"s number, denoted through the price NA is 6.022 x 1023.

You are watching: What is the molar mass of ethanol

Fine, but what walk this have to do through invernessgangshow.net? That"s a fair question. Perhaps this will help. Imagine the you room a chemist and also you would prefer to measure out 6.022 x 1023 molecules of ethanol. If girlfriend didn"t know better, you might think the you had actually to somehow counting out all of these molecules individually. But this is far too time consuming and expensive. Besides you probably wouldn"t live long enough to finish. (It would certainly take virtually 2 x 1016 years to execute this. Even if a billion civilization worked with each other to count out the molecule you wouldn"t be able to finish also close to within your lifetime.)

Since 6.022 x 1023 ethanol molecules are needed, we merely need to measure out one mole of ethanol, however how execute we do that? Let"s redefine a mole. A mole is any item that contains the same number of that item together the variety of atoms in specifically 12 g of 12C. This method that in 12 g of C over there are specifically 6.022 x 1023 atom of carbon. Every atom that C has a massive of 12 amu"s, which method that:


Now us are acquiring somewhere. Ethanol is CH3CH2OH. Its total mass is 46 u:


How does this aid us measure the end 6.022 x 1023 molecule of ethanol? together we stated before, 1 g = 6.022 x 1023 u.


Therefore us only need to measure 46 g the ethanol to obtain 6.022 x 1023 molecule or 1 mol the ethanol. This is a lot less complicated than counting the end all those molecules.

The molecular mass that a molecule is measured in g/mol. In this case, ethanol"s molecular mass is 46 g/mol. This method that in 1 mol that ethanol, there space 46 g, therefore the term molecular mass and also molar mass are regularly used interchangeably.

When thinking about a mole, think that it choose a dozen. A dozen of noþeles is 12 of the item:a dozen eggs = 12 eggsa dozen N atoms = 12 N atomsa dozen ethanol molecules = 12 ethanol molecules

The very same is true that a mole. A mole of something is 6.022 x 1023 of that item.a mol that ethanol molecules = 6.022 x 1023 ethanol moleculesa mol the N atom = 6.022 x 1023 N atomsa mol of eggs = 6.022 x 1023 eggs

Example 1.

How many molecules of ethanol space in 89.0 g the ethanol?


Here space a few hints to usage in addressing this form of problem:Start by creating the offered information, including the units.Next identify what you are trying to solve and also what systems it will certainly be in.Use conversion components to cancel out units and get to your last units.So in this example 89.0 g of ehtanol room given. We want molecules that ethanol come answer the question. Now we need to come up v conversion determinants to publication units and also get to the desired collection of units. Molecular mass is g/mol. This can be supplied to cancel out the given number"s units. In order to cancel units, main point by the reciprocal of the molecule mass. Avogadro"s number deserve to be used to cancel out the moles and also leaves molecules of ethanol units. This is why using units is really imporatant. Also, mental to use the exactly number of far-reaching figures.

Example 2.

How countless carbon atoms are in 89.0 g that ethanol (CH3CH2OH)?


Again, we used the same gram come mole switch factor, the molecular mass, and additionally Avogadro"s number to go from mole to atoms. Notice that there is an extra counter in this equation. In each molecule the ethanol there space two carbon atoms. This also method that for each mole that ethanol there are two mole of carbon.

Example 3.

How countless molecules of ethanol space in 1.0 l of ethanol in ~ 1 atm and 25oC?

To price this we will require a volume to mass counter factor. This is defined as density (denoted by the Greek letter rho, r) and is in units of g/mL. Density is both temperature and pressure dependent; both need to be specified to know the thickness for a given substance. In ~ 25oC and also 1 atm pressure, the density of ethanol is r = 0.789 g/mL. So ago to the question:

SummaryNow you have to see exactly how moles are related to mass, density, and variety of molecules or atoms. You have to now know what a mole is and also how that is associated with Avogadro"s number.

Practice Quiz: moles Note: you will need a pencil, scrape paper, calculator, regular table and also equation paper to work the exercise quiz. Quizzes room timed (approximately 4 minutes per question). We indicate that you publish out the periodic table and the constants/equations web page before beginning the quizzes.

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Open periodic Table in a separate web browser window.Open Equations/Constants page in a separate web browser window.Return come the invernessgangshow.net topic Index© Washington college in St. Louis, 2005.