1. Rice Lab Count out 1 dozen grains of rice and place in container.
Repeat until you have 3 containers each holding 12 grains of rice.
Mass each dozen and calculate the average mass of 1 dozen grains of rice. (Don’t forget to minus out the mass of container.)
Calculate the number of rice grains in 1.94 gram of rice.
Mass out rice grains until you reach a mass equal to the mass you calculated above.
Count the grains of rice in the sample.
Calculate the percent error between the calculated number of rice grains versus the actual number of rice grains.
Episode 701

2. Mole Avogadro’s number Molar Mass
the mole = x 1023
602,200,000,000,000,000,000,000
Molar Mass
The mass of one mole of any pure substance
Episode 701

3. Molar mass of an element (g/mol) Molar mass of a compound
Equals the atomic mass of the element in grams
Molar mass of a compound
Equals the sum of the molar masses of the elements making up the compound
Find the molar masses of-
Magnesium g/mol
Chlorine g/mol
Magnesium chloride
Write formula
Find the atomic mass of each element
Multiply atomic mass by the number of atoms for each element, then total the masses
MgCl2
24.3 g/mol + (2 x 35.5 g/mol) =
24.3
35.5
95.3 g/mol
Episode 701

4. Try it! (2x 27 g/mol) + (3 x16g/mol) 102 g/mol
Find the molar mass of aluminum oxide
(2x 27 g/mol) + (3 x16g/mol)
102 g/mol
Episode 701

5. Remember Rice Lab Calculations…
How many moles of atoms are there in 8.0 grams of Mg?
? moles = 8.0g Mg
How many atoms are in 0.7 grams of He?
? atoms = 0.7g He
1 mol Mg
24.3 g/mol
1 mol He
6.022 x 1023 atoms
4.0 g/mol
1 mol He
Episode 701

6. Formula Units… No Problem
What would the mass of 5.3 x 1022 formula units of calcium iodide?
Formula
Molar Mass
?g CaI2 = 5.3 x1022 fu
CaI2
40.1 g/mol + (2 x g/mol) = g/mol
1 mol CaI2
293.9 g CaI2
6.022 x 1023 fu
1 mol CaI2
26 g CaI2
Episode 701

7. Problem Set 1 How many atoms are in 3.5 grams of silicon?
How many formula units are in 32.6 grams of potassium oxide?
How many molecules are in 0.25 grams of dinitrogen pentoxide?
? atoms = 3.5g Si 1mol Si x 1023 atoms
= 7.5 x 1023 atoms Si
28.1g Si mol Si
? fu = 32.6 g K mol K2O x fu
= 2.1 x 1023 fu K2O
94.2g K2O mol K2O
? molec = 0.25 g N2O mol N2O x molec
= 1.4 x 1021 mole N2O5
108 g N2O mol N2O5
Episode 701