A Mole Of Carbon Weighs
The Mole
The content that follows is the substance of lecture viii. In this lecture we cover the Mole and Avagadro'south Number as well as the calculations for Tooth Mass and conversions using moles.
The MOLE (mol) is a unit of measurement that is the amount of a pure substance containing the same number of chemical units (atoms, molecules etc.) every bit in that location are atoms in exactly 12 grams of carbon-12 (i.e., 6.022 10 x23).
And so the mole is the title used for the amount half-dozen.022 x ten23 much the same manner the word "dozen" is used for the amount 12.
Then if y'all had a mole of donuts you would have vi.022 10 1023 donuts and a serious tummy anguish.
Nosotros use the mole (mol) to represent the corporeality of substances in chemistry because the numbers of atoms and molecules in each substance is then large. The value given six.022 ten 1023 is called Avagadro's number for the scientist that establish the number of atoms in 12 grams of carbon 12. Why utilize 12 grams? This is the theoretical diminutive mass of the Carbon-12 isotope (half-dozen protons and 6 neutrons). This means that the atomic mass or atomic weight (12 grams) of carbon is equal to exactly 1 mole of carbon.
Using carbon as a reference, the atomic weights you see in the periodic table are also equal to one mole of those substances:
Lithium for instance has an atomic mass of half dozen.941 grams and this is equal to one mole of lithium. This is why nosotros state the atomic and molecular masses in units of grams per mole or yard/mol.
What can nosotros do with moles? We use the unit to brand calculations based on balanced chemical equations. We use the stoichiometry (fancy way of saying mole ratios in an equation) to brand predictions most how much product will be made or reactant needed if we know i mole corporeality in a reaction.
Moles of a Substance and the Molecular Weight
The Tooth mass or Molecular Weight (interchangeable terms so long as we are on Earth) of a substance is the total of all the private masses of the elements information technology contains. To use our old friend h2o every bit an case:
Ane mole of Water is equanimous of 1 mole of Oxygen and ii moles of Hydrogen. The mass of oxygen equal to one mole of oxygen is xv.998 grams and the mass of one mole of hydrogen is 1.008 g. If we full up the gram amounts of each element in the water molecule = xv.998g/mol + ii(one.008g/mol) we get the molar mass of water = eighteen.014g/mol.
So if we had exactly 18.014g of water we would have 1 mole of water.
Exercise: Mole and Molar Mass
Mole Relationships
The reason the mole is so of import is because we use the mole every bit the unit for about of the relationships in chemistry. Reactions are counterbalanced based on the number of moles of each element in the reaction, solution concentrations are very often described in terms of moles per liter or moles per kg of solvent and we have already seen that the molecules or atoms of an chemical element are reported every bit moles of the substance rather than the individual count of their particles.
Allow's start the human relationship word with the relationship betwixt the mole and the AMU.
An AMU is 1/12 the mass of a Carbon-12 atom which according to the periodic tabular array weighs ~12g. This means that one AMU ≈ 1g right? and thus Carbon has a mass of 12amu, correct? Just look, this could not be the mass of a single carbon cantlet right? They are really, really tiny. And that is correct, the mass shown in the periodic table is actually the mass of 6.022 x 1023 carbon atoms or a mole of carbon atoms. And then in reality, i AMU = 1.66 x x-24m and while a carbon atom weighs 12 AMU, the mass shown in the periodic table is
12 atoms x one.66 ten x-24g 10 6.022 x 1023 atoms/ mol= 12 g/mol
Then a unmarried carbon atom weighs 12 amu while a mole of carbon atoms weighs 12.01g/mol.
Mole Calculations
There are plethora of calculations that tin exist conducted using the unit of moles as the intermediate. I am going to review a few of them now and then you will encounter as nosotros progress through later topics that moles are essential to those calculations too.
Typical mole calculations:
1) Adding of the Molecular Weight or Molar Mass of a compound
The molar mass of a chemical compound besides often called the molecular weight while on Globe, is only the sum of all the individual element masses in the compound. You lot use the periodic table as a reference for these masses and total them upwards:
For example, if we want to total the molar mass of Aluminum Sulfate Altwo(So4)iii , nosotros need to decide the number and mass of each element in the compound. For Aluminum Sulfate the totals are 2 Al, three S and 12 O. So here is the math using the atomic masses given in the periodic table:
2(26.98 m/mol) + 3( 32.07 1000/mol) + 12(16.00 thousand/mol) = 342.17 g/mol
2) Conversion from Grams to Moles or Moles to Grams
In one case you know the molar mass of a compound, you tin can use that mass to determine the amount of moles in a gram corporeality of the substance or conversely, you can summate the number of grams in a mole amount of the substance.
Here are some examples:
How many moles are in 55.4g of Aluminum Sulfate?
The calculation is set up like a conversion with the molar mass of Aluminum Sulfate as the conversion factor:
55.4g Al2(SO4)three 10 ane mol Altwo(SO4)iii/342.17 g Al2(SO4)3 = 0.162 mol Al2(So4)3
Or, How many grams of Al2(And then4)iii are in 6.34 moles of Altwo(SO4)iii?
half dozen.34 mol Al2(So4)3 x 342.17g Al2(And then4)3/ 1 mol Al2(SOiv)three = 2.17 x 103 Al2(SO4)iii
iii) Conversion to Molecules or Atoms
In add-on to being a unit for molar mass, the mole is besides the gateway betwixt the mass of a substance and its atoms or molecules.
For Example, if asked how many molecules of Al2(And then4)3 are in th 55.four g of Al2(And then4)three above we simply need to offset calculate the number of moles as before and and then utilize Avagadro'due south number to convert the moles to molecules:
55.4g Al2(SO4)three x i mol Alii(And so4)3/342.17 grand Al2(SO4)3= 0.162 mol Al2(And theniv)3
0.162 mol Al2(So4)three ten 6.022 ten 1023 molecules Al2(SOfour)iii/ one mol Al2(SO4)3 =
ix.76 x 1022 Molecules Al2(SOiv)3
Furthermore if nosotros continued the trouble and asked how many Aluminum atoms were in the 55.4 g of Al2(SOfour)3?
Well that is a simple continuation. We just demand to multiply by the number of atoms of Aluminum in the compound:
9.76 x ten22 Molecules Al2(SO4)three x ii atoms Al/ i molecule Al2(Then4)3 = 1.95 x 1023 Al atoms
Let's Practice some more than:
A Mole Of Carbon Weighs,
Source: https://chem.fsu.edu/chemlab/chm1045/mole.html
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