Today we disccussed the mol in more detail.

Today we discussed the mol in more detail. A mol has several definitions;

1 mol of an atom, molecule or formula unit contains 6.02 x 10²³ atoms, molecules or formula units
1 mol has a mass in grams equal to the atomic, formula or molar mass of a substance.

If we are given a mass, or amount of a substance we can determine the number of moles in the substance.

Sample #1:

Calculate the number of moles in 1.0 g of He. To solve this problem we must determine the mass, in grams, of 1 mol of helium. The mass of 1 mol of helium is the atomic mass of helium expressed in grams. We can use the identity

1 mol He = 4.0 g He

to setup a ratio which will allow us to convert between grams and moles for helium. That ratio is;

Now we can use the ratio to convert the mass of helium given...1.0 g to moles using the setup;

Sample #2:

Calculate the number of moles in 15 g of H₂SO₄. To solve this problem we must determine the mass, in grams, of 1 mol of sulfuric acid. The mass of 1 mol of H₂SO₄ is the formula mass of H₂SO₄ expressed in grams. The formula mass is obtained by summing the atomic masses of the elements in the formula;

2 H = 2 x 1.0 g = 2.0 g

1 S = 32.0 g = 32.0 g

4 O = 4 x 16.0 g = 64.0 g

Total formula mass = 98 g

We can use the identity

1 mol H₂SO₄ = 98 g H₂SO₄

to setup a ratio which will allow us to convert between grams and moles for sulfuric acid. That ratio is;

Now we can use the ratio to convert the mass of sulfuric acid given to moles using the setup;

Extra problems to try,

Calculate the number of moles in;

a) 0.457 grams Mo

b) 1.95 x 10² grams Na₂SO₄

c) 35 grams N₂O₄

We can also convert from moles back to grams of a substance.

Sample #3:

Calculate the number of grams in 1.95 moles of He. To solve this problem we must invert the factor we use for conversion. It is the same conversion factor as used in Sample 1 above, just inverted.

Sample #4:

Calculate the number of grams in 0.0492 moles of H₂SO₄. To solve this problem we must invert the factor we use for conversion. It is the same conversion factor as used in Sample 2 above, just inverted.

Extra problems to try,

Calculate the number of grams in;

a) 10.4 mol Mo

b) 4.69 x 10^-1 mol Na₂SO₄

c) 24.9 mol N₂O₄

We can also calculate moles from numbers of atoms, molecules or formula units. From above recall that 1 mol contains 6.02 x 10²³ atoms, molecules or formula units.

Sample #5:

Calculate the number of moles in 1.95 x 10²² atoms of Ne. To solve this problem we need to recall that 1 mol is equal to 6.02 x 10²³.

1 mol Ne = 6.02 x 10²³ Ne atoms

(Remember we know the formula for neon is Ne and it exists as atoms in its standard state.)

To solve this problem we use a ratio approach as we have on the other problem. The ratio is;

Now we can use the ratio to convert the atoms of neon to mol of atoms using the setup;

Sample #6:

Calculate the number of moles in 5.83 x 10²⁴ formula units of NaCl. To solve this problem we need to recall that 1 mol is equal to 6.02 x 10²³.

1 mol NaCl = 6.02 x 10²³ NaCl formula units

(NaCl is not an atom or a molecule, so we use the expression formula unit to describe NaCl.)

To solve this problem we use a ratio approach as we have on the other problem. The ratio is;

Now we can use the ratio to convert the formula units of NaCl given to number of mol using the setup;

Extra problems to try,

Calculate the number of mol in;

a) 7.25 x 10²⁴ molecules Cl₂

b) 8.71 x 10²¹ f.u. Na₂SO₄

c) 9.41 x 10²² atom C

After reviewing these calculations we looked at the chemical equation which describes the recycling of aluminum.

2Al₂O₃(s)+ 3C(s)------> 4Al(l)+ 3CO₂(g)

We can read this equation as 2 formula units of Al₂O₃plus 3 atoms of carbon react to form 4 atoms of aluminum and 3 molecules of carbon dioxide. We talked about aluminum cans for a few minutes and I indicated the mass of an aluminum 12 ounce can is approximately 16 grams. How many grams of Al₂O₃would be needed to make 16 grams of aluminum using this equation.

To solve this problem we must first realize how to read the chemical equation. We can read it in terms of numbers of atoms, molecules or formula units, but we can never read it in terms of grams.

If we read it in terms of atoms, molecules or formula units we can say (similar to the way it is read above) 2 mol of Al₂O₃plus 3 mol of C react to form 4 mol of Al and 3 mol of CO₂. We can say mol because a mol is equal to 6.02 x 10²³ atoms, molecules or formula units.

So what so we do with the 16 grams of Al? We must convert it to mol. To do that we use the conversion similar to example 1 and 2 above.

So 16 g Al is equivalent to 0.593 mol of Al. According to the equation everytime 4 mol Al are formed 2 mol of Al₂O₃must react. So we need to determine how many mol of Al₂O₃reacted. Again we can use a ratio. This ratio is called a stoichiometric ratio and is obtained from the equation, in this case it says,

We use this ratio to convert from mol of Al to mol of Al₂O₃.

This makes sense. The equation says half as much Al₂O₃is required to make Al. Now that we have mol of Al₂O₃we can determine the mass of Al₂O₃required.

We ended class and we had not completed this problem so we'll discuss it more on Tuesday.

Today we discussed the mol in more detail. A mol has several definitions;

1 mol of an atom, molecule or formula unit contains 6.02 x 1023 atoms, molecules or formula units

1 mol has a mass in grams equal to the atomic, formula or molar mass of a substance.

If we are given a mass, or amount of a substance we can determine the number of moles in the substance.

Sample #1:

Calculate the number of moles in 1.0 g of He. To solve this problem we must determine the mass, in grams, of 1 mol of helium. The mass of 1 mol of helium is the atomic mass of helium expressed in grams. We can use the identity

1 mol He = 4.0 g He

to setup a ratio which will allow us to convert between grams and moles for helium. That ratio is;

Now we can use the ratio to convert the mass of helium given...1.0 g to moles using the setup;

Sample #2:

2 H = 2 x 1.0 g = 2.0 g

1 S = 32.0 g = 32.0 g

4 O = 4 x 16.0 g = 64.0 g

Total formula mass = 98 g

We can use the identity

1 mol H2SO4 = 98 g H2SO4

to setup a ratio which will allow us to convert between grams and moles for sulfuric acid. That ratio is;

Now we can use the ratio to convert the mass of sulfuric acid given to moles using the setup;

Extra problems to try,

Calculate the number of moles in;

a) 0.457 grams Mo

b) 1.95 x 102 grams Na2SO4

c) 35 grams N2O4

We can also convert from moles back to grams of a substance.

Sample #3:

Calculate the number of grams in 1.95 moles of He. To solve this problem we must invert the factor we use for conversion. It is the same conversion factor as used in Sample 1 above, just inverted.

Sample #4:

Calculate the number of grams in 0.0492 moles of H2SO4. To solve this problem we must invert the factor we use for conversion. It is the same conversion factor as used in Sample 2 above, just inverted.

Extra problems to try,

Calculate the number of grams in;

a) 10.4 mol Mo

b) 4.69 x 10-1 mol Na2SO4

c) 24.9 mol N2O4

We can also calculate moles from numbers of atoms, molecules or formula units. From above recall that 1 mol contains 6.02 x 1023 atoms, molecules or formula units.

Sample #5:

Calculate the number of moles in 1.95 x 1022 atoms of Ne. To solve this problem we need to recall that 1 mol is equal to 6.02 x 1023.

1 mol Ne = 6.02 x 1023 Ne atoms

(Remember we know the formula for neon is Ne and it exists as atoms in its standard state.)

To solve this problem we use a ratio approach as we have on the other problem. The ratio is;

Now we can use the ratio to convert the atoms of neon to mol of atoms using the setup;

Sample #6:

Calculate the number of moles in 5.83 x 1024 formula units of NaCl. To solve this problem we need to recall that 1 mol is equal to 6.02 x 1023.

1 mol NaCl = 6.02 x 1023 NaCl formula units

(NaCl is not an atom or a molecule, so we use the expression formula unit to describe NaCl.)

To solve this problem we use a ratio approach as we have on the other problem. The ratio is;

Now we can use the ratio to convert the formula units of NaCl given to number of mol using the setup;

Extra problems to try,

Calculate the number of mol in;

a) 7.25 x 1024 molecules Cl2

b) 8.71 x 1021 f.u. Na2SO4

c) 9.41 x 1022 atom C

After reviewing these calculations we looked at the chemical equation which describes the recycling of aluminum.

2Al2O3(s) + 3C(s) ------> 4Al(l) + 3CO2(g)

To solve this problem we must first realize how to read the chemical equation. We can read it in terms of numbers of atoms, molecules or formula units, but we can never read it in terms of grams.

If we read it in terms of atoms, molecules or formula units we can say (similar to the way it is read above) 2 mol of Al2O3 plus 3 mol of C react to form 4 mol of Al and 3 mol of CO2. We can say mol because a mol is equal to 6.02 x 1023 atoms, molecules or formula units.

So what so we do with the 16 grams of Al? We must convert it to mol. To do that we use the conversion similar to example 1 and 2 above.

We use this ratio to convert from mol of Al to mol of Al2O3.

This makes sense. The equation says half as much Al2O3 is required to make Al. Now that we have mol of Al2O3 we can determine the mass of Al2O3 required.

We ended class and we had not completed this problem so we'll discuss it more on Tuesday.

1 mol of an atom, molecule or formula unit contains 6.02 x 10²³ atoms, molecules or formula units

1 mol H₂SO₄ = 98 g H₂SO₄

b) 1.95 x 10² grams Na₂SO₄

c) 35 grams N₂O₄

Calculate the number of grams in 0.0492 moles of H₂SO₄. To solve this problem we must invert the factor we use for conversion. It is the same conversion factor as used in Sample 2 above, just inverted.

b) 4.69 x 10^-1 mol Na₂SO₄

c) 24.9 mol N₂O₄

We can also calculate moles from numbers of atoms, molecules or formula units. From above recall that 1 mol contains 6.02 x 10²³ atoms, molecules or formula units.

Calculate the number of moles in 1.95 x 10²² atoms of Ne. To solve this problem we need to recall that 1 mol is equal to 6.02 x 10²³.

1 mol Ne = 6.02 x 10²³ Ne atoms

Calculate the number of moles in 5.83 x 10²⁴ formula units of NaCl. To solve this problem we need to recall that 1 mol is equal to 6.02 x 10²³.

1 mol NaCl = 6.02 x 10²³ NaCl formula units

a) 7.25 x 10²⁴ molecules Cl₂

b) 8.71 x 10²¹ f.u. Na₂SO₄

c) 9.41 x 10²² atom C

2Al₂O₃(s)+ 3C(s)------> 4Al(l)+ 3CO₂(g)

If we read it in terms of atoms, molecules or formula units we can say (similar to the way it is read above) 2 mol of Al₂O₃plus 3 mol of C react to form 4 mol of Al and 3 mol of CO₂. We can say mol because a mol is equal to 6.02 x 10²³ atoms, molecules or formula units.

We use this ratio to convert from mol of Al to mol of Al₂O₃.

This makes sense. The equation says half as much Al₂O₃is required to make Al. Now that we have mol of Al₂O₃we can determine the mass of Al₂O₃required.