Unit 4, Lessons 9 and 10

Lesson 9:

Scientists use scientific notation to express numbers that are very big or very small. Correct scientific notation has only 1 digit before the decimal point! We've studied the use of scientific notation to express how many molecules are in a test sample. Once again, we looked at moles. One mole, 602 sextillion, is written in scientific notation as 6.022 x 10^23. The term "molar mass" refers to how much of a substance is needed to achieve 1 mole of molecules. The molar masses for all the known elements are the same as the atomic masses on the periodic table. Molar mass helps scientists convert between moles of atoms and grams of atoms. That's where the two tables I mentioned in lesson 7 come into play.

Problems:

4.) Give the molar mass for these elements:
A.) nitrogen, N - 14.0 g
B.) neon, Ne - 20.2 g
C.) chlorine, Cl -  35.5 g
D.) copper, Cu - 63.5 g

6.) Which contains more atoms?
A.) 12 g of hydrogen, H, or 12 g of carbon, C? 12 g of hydrogen. Hydrogen has the smaller molar mass.
B.) 27 g of aluminum, Al, or 27 g of iron, Fe? 27 g of aluminum. Aluminum has the smaller molar mass.
C.) 40 g of calcium, Ca, or 40 g of sodium, Na? 40 g of sodium. Sodium has the smaller molar mass.
D.) 40 g of calcium, Ca, or 40 g of zinc, Zn? 40 g of calcium. Calcium has the smaller molar mass.
E.) 10 g of lithium, Li, or 100 g of lead, Pb? 100 g of Pb, because it has the larger sample size.

Lesson 10:

Because individual atoms cannot be counted easily by themselves, scientists compare moles of substances rather than masses of substances. If one was given 50 moles of one element and 50 moles of another, their molar masses are significant, but only in telling which element would be lighter. Then, it's up to us to decide which sample is larger based off of how many more/less atoms it takes to make an equal sample. If given a compound, where the molar mass isn't clear but rather a bunch of molar masses thrown together, one must add the masses of each element in the compound, multiply by the subscripts (if there are any) and add all the masses together to find the compound's whole mass.

Problems:

5.) Which has more moles of metal atoms?
A.) 10.0 g of calcium, Ca, or 10.0 g of calcium chloride, CaCl2? Calcium chloride, CaCl2
B.) 5.0 g of sodium chloride, NaCl, or 5.0 g of sodium fluoride, NaF? Sodium fluoride, NaF
C.) 2.0 g of iron oxide, FeO, or 2.0 g of iron sulfide, FeS? Iron oxide, FeO

7.) What is the mass of 5 mol of iron (III) oxide, Fe2O3? 
Mass of iron: 55.8, x2 = 111.6 g
Mass of oxygen: 15.9, x3= 47.7 g
111.6 g + 47.7 g = 159.3 g <--- ONE MOLE
159.3 g x 5 moles = 796.5 g