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CP Sci 9- 1st Sem.

Gen Chem - 1st Sem.

Mole Conversions

Objectives:

1.    Explain how to convert between the number

2.    Define molar volume of a gas.

3.    Determine how to determine the number of particles in a given volume of gas at STP.

Key Terms:

    molar volume

Notes: (10-2)

The mole serves one very important function in scientific equations.  The mole is able the measure both mass and particles.  Because of this dual nature the mole is the central unit when converting from one type of measurement to the other.

Rules for converting moles to mass.

bulletFind the moles of the item you wish to convert.

example:          2.50 mol  NaCl

bulletDetermine the molar mass of the item you wish to convert. (set up the conversion factor - this time moles are on the bottom)

example:            58.5g NaCl / 1mole NaCl 

bulletSet up the equation and solve.

example:            2.50mol NaCl x (58.5g NaCl / 1mol NaCl) /  = 146g NaCl

 

Rules for converting mass to moles.
bulletFind the mass of the item you wish to convert.

example:          11.2g NaCl

bulletDetermine the molar mass of the item you wish to convert. (set up the conversion factor)

example:           1mole NaCl / 58.5g NaCl

bulletSet up the equation and solve.

example:            11.2g NaCl x (1mol NaCl / 58.5g NaCl) = 0.191 mol NaCl

 

Moles to particles: Going further

bulletDetermine the number of moles (as in the steps above)

example:            11.2g NaCl x 1mol NaCl / 58.5g NaCl = 0.191 mol NaCl

bulletWrite down the conversion factor remembering that Avogadro's number is equal to the particles in a mole of a substance.

example:            6.02 x 1023 /  1mol

bulletSet up the equation and solve

example:            0.191 mol NaCl  x  (6.02 x 1023 /  1mol) = 1.15 x 1023 NaCl ionic compounds  (or 1.15 x 1023 Na atoms and 1.15 x 1023 Cl atoms)

bulletSolved in one step

example:            11.2g NaCl x (1mol NaCl / 58.5g NaCl) x (6.02 x 1023 /  1mol) = 1.15 x 1023 NaCl ionic compounds

Box Method: (My way of keeping the units organized)

bulletThis is a good way of checking the setup before you solve the equation.

 

Molar equivalency of gases:

The mole pertains to all phases of matter.  The difference between the gas and other matter is that gas will expand until it fills a container.  Therefore, it is important to impose a few rules on gas in order to predict its molar mass and volume.

STP - Standard Temperature and Pressure 

bulletT = 0oC
bulletP = 1atm (760mmHg)

Under these conditions (STP) it has been experimentally proven that all gases occupy 22.4L (dm3) of space.  

Rules for converting volume of a gas to moles.
bulletFind the volume of the gas you wish to convert.

example:          1.0L CO2

bulletDetermine the number of liters in a mole. (set up the conversion factor)

example:           1mol CO2 / 22.4L CO2

bulletSet up the equation and solve.

example:            1.0L CO2 x (1mol CO2 / 22.4L CO2) = 0.045 mol CO2

 

Put it all together:

Solve for mass:

example:            1.0L CO2 x (1mol CO2 / 22.4L CO2) x (44g CO2 / 1mol CO2) = 1.96 g CO2

Solve for particles:

example:            1.0L CO2 x (1mol CO2 / 22.4L CO2) x (6.02 x 1023 /  1mol)  = 2.7 x 1022 molecules CO2

 

 

 

 

 

 

Last modified: September 05, 2004