MOLE CALCULATIONS : MASS , MOLES , MOLAR MASS

Mass of 1 Carbon-12 atom= 12 amu

12g Carbon-12 isotope = 1 mole CARBON-12   atoms

6.023 x 10²³ particles = 1 mole

6.023 x 10²³ CARBON-12 atoms = 1 mole CARBON-12 Atoms

Mass of 1 mole = Molar mass [on periodic table]

22.4L = 6.023 x 10²³ particles = Molar volume

Mole = amount of substance compared to 1/12^th mass of one atom of CARBON-12 isotope.

MOLES

Mass of element on periodic table.

Mass of element compared to 12g of Carbon-12.

Carbon-12 scale:

12g of Carbon-12 isotope/12 = 1.0g

SIMPLE EXPERIMENT FOR CALCULATING MOLAR MASS OF ELEMENTS:

Use the box container shown below .

The container should be very rigid and should not allow any expansion.

Fill the container with finely powdered carbon. Ensure stiff packing with no air spaces.

Mark the level when the mass of the carbon powder in the container is 12.00g

This carbon will contain all the carbon isotopes -12 , C-13 and C-14. [Best result if you have only 12g of carbon-12 isotope].

Find Molar mass of every element:

Clean and dry container.

Fill container with any element up to the level previously marked for the 12.00g of carbon and weigh it.

The mass of element = total mass – mass of container = Mass of 1.0 mole of the element. = MOLAR MASS of element. [approximately]

This simple experiment should be very easy with powdered iron, or zinc or copper metals or even gold. However, for diatomic elements such as Nitrogen gas N₂, or Chlorine gas Cl₂, Hydrogen gas H₂, Oxygen gas O₂ and liquid bromine, Br₂ . you have to divide the mass by 2 to get the approximate molar mass.

You can use the raw values from this weighing without the percent abundance as Approximate Average Molar Mass of the element.

Actual Molar mass of element = Value of the sum of [ mass of all isotopes of elements X percentage abundance of occurrence in nature] = mass of element on periodic table (a.k.a. MOLAR MASS or average atomic mass unit of element).

Approximate values for elements on periodic table; H=1g, Na = 23g  , O=16g , N=14g , Cl=35.5g

AVOGADRO’s LAW =  Mass of 1.0mole of substance contains 6.023 x 10²³ particles.

MOLE FORMULA

Molar mass = mass/moles

Mass = moles x molar mass

Moles= mass / Molar mass

CALCULATION OF MOLES AND MASS OF COMPOUNDS

1. Calculate the percent by mass of Sn and Oxygen in SnO₂

 % element = Total Mass of element in compound x 100

                                MASS OF COMPOUND

                     =     Molar mass of Sn   x   100

                               Molar mass SnO₂

2.   How many moles are there in 47.4g Ca

LOOK on periodic table for conversions; 1 mole Ca = 40.08g Ca,               

 

Make a Conversion ratio = needed unit up/other unit down.

Needed unit is MOLES; therefore,

Conversion ratio = Mole      up

                                    Grams down   

Answer =Given amount [47.4g] x Conversion ratio

               =47.4g Ca x [1 mole Ca/40.0gCa]

3 .

How many grams of gold are in 11.5 moles of Gold Au.

 

Look on periodic table ; 1 mole Au = 197g Au , needed unit is grams

Conversion ratio = grams upwards / other unit down

                                = 197g Au/1 mole Au

Given amount = 11.5 moles Au

Answer = given amount x CR = 11.5 mole Au x [197g Au/1 mole Au]

4.

How many atoms in 20.3 moles sulfur(S).

 

1 mole = 6.023 x 1023 particles, we need particle [atoms] up in Conversion ratio (CR);

CR = 6.023 x 1023 S atoms

             1 mole S

Given amount = 20.3 moles

Answer = given amount x CR = 20.3 moles x [6.023 x 1023 S atoms]

                                                                                         1 mole S