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# Chapter 10 “Chemical Quantities”

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Chapter 10 “Chemical Quantities”
Yes, you will need a calculator for this chapter!

Section 10.1 Da Mole: A Measurement of Matter

How do we measure items? Measure mass in grams. Measure volume in liters. Measure amount in MOLES.

We’re not talking about this kind of mole!
What is the mole? We’re not talking about this kind of mole!

Moles (mol) It is an amount.
Defined as the number of carbon atoms in exactly 12 grams of carbon-12. 1 mole = 6.02 x of representative particles. 6.02 x 1023 is called: Avogadro’s number. 1 mole = 6.02 x 1023 = Avogadro’s number

Similar Words for amount
Dozen: Mole: 1 dozen muffins = 12 muffins 1 mol muffins = x 1023 muffins 2 dozen puppies = 24 puppies 2 mol puppies = 1.2 x 1024 puppies 36 m&m stuffed donuts = 3 dozen donuts 2.4 x 1024 m&m stuffed donuts = 4 mol donuts

What are Representative Particles?
The smallest pieces of a substance: Changes based on what we’re looking at For a molecular compound: it is the molecule. For an ionic compound: it is the formula unit (ex: NaCl, MgS). For an element: it is the atom. 1 mol of CO2 molecules, 1 mol of NaCl formula units, and 1 mol of H atoms all equal 6.02 x 1023 of that thing. Remember the 7 diatomic elements? (made of molecules)

Measuring Moles The atomic mass on the PT is also the molar mass (g/mol) – mass (in grams) of 1 mole of that atom = 16.0 g/mol Since the mole is the number of atoms in 12 grams of carbon-12, Gram atomic mass (GAM)- Equals the mass of 1 mole of an element in grams (from periodic table) 12.01 grams of C has the same number of pieces as 1.01 grams of H and grams of Fe. We can write this as: 12.01 g C = 1 mole C (this is also the molar mass) (**Remember we can count things by weighing them.)

Find the Molar Mass (g/mol) of the following:
Nitrogen Aluminum Zinc 14.01 g/mol 26.98 g/mol 65.39 g/mol

What about compound mass?
In 1 mole of H2O, there are 2 moles of H atoms and 1 mole of O atoms To find the mass of a compound: Determine number of each element present Multiply the number times their mass (from the periodic table) Add them up for the total mass

Calculating Compound Mass
Calculate the mass of magnesium carbonate, MgCO3. 24.31 g/mol g/mol x (16.00 g/mol) = 84.32 g/mol MgCO3

Practice Problem: What is the mass of one mole of CH4?
1 mole of C = g/mol 4 mole of H x 1.01 g = 4.04g/mol 1 mole CH4 = = g/mol 12

Mole Practice 1 mol = particles 2.5 mol MgCl2 = ? particles MgCl2 =
x 1024 Fe particles = ? mol Fe 2.5 mol 6.02 x 1023 particles 1.5 x 1024 particles of MgCl2 1 mol 7.2 x 1024 particles 1 mol 12 mol Fe 6.02 x particles

Molar Mass Practice 47 g/mol 180 g/mol 4. Molar mass of BeF2 =
5. Molar mass of C6H12O6 = Be = 9.0 g/mol (19.0) = 47 g/mol F = 19.0 g/mol C = 12.0 g/mol 6(12.0) + 12(1.0) + 6(16.0) = H = 1.0 g/mol 180 g/mol O= 16.0 g/mol

Section 10.2 Mole-Mass and Mole-Volume Relationships

Use to make conversion factors from these.
Since Molar Mass is… Number of grams in 1 mole. grams per mole (g/mol) Use to make conversion factors from these. - Use molar mass to convert to grams or mols of a substance.

For example How many moles is 5.69 g of NaOH? =
How many grams in .53 mol of NaOH? .142 mol NaOH 1 mol NaOH 5.69 g NaOH 40.0 g NaOH 40.0 g NaOH 21.2 g NaOH .53 mol NaOH 1 mol NaOH 17

28.1 grams C 1.000 mol Mg Practice Problems:
How much would 2.34 moles of carbon weigh? How many moles of magnesium is g of Mg? 28.1 grams C 1.000 mol Mg

The Mole-Volume Relationship
Under different circumstances, gases can change. Two things effect the volume of a gas: a) Temperature and b) Pressure **We need to compare all gases at the same temperature and pressure.

Standard Temperature and Pressure
abbreviated STP 0ºC (273K) and 1.0 atm pressure At STP 1 mole of gas occupies L= molar volume 22.4 L/mol of any gas at STP 20

Practice Problems: = 0.253 mol O2
What is the volume of 4.59 mole of CO2 gas at STP? How many moles is L of O2 at STP? 4.59 mol CO2 22.4 L CO2 = 103 L CO2 1 mol CO2 5.67 L O2 1 mol O2 = mol O2 22.4 L O2

12.3 L CH4 22.4 L CH4 8.8 g CH4 1 mol CH4 16.0 g CH4 1 mol CH4
What is the volume of 8.8 g of CH4 gas at STP? = 22.4 L CH4 8.8 g CH4 1 mol CH4 16.0 g CH4 1 mol CH4 12.3 L CH4

Summary: These four items are all equal: a) 1 mole
b) molar mass (in grams/mol) c) 6.02 x 1023 particles (atoms, molecules, or formula units) d) 22.4 L of a gas at STP **Thus, we can make conversion factors from them.

Avog. # Practice problems:
How many molecules of CO2 are in 4.6 moles of CO2? How many moles of water is in 5.87 x molecules? How many atoms of carbon are in moles of Carbon? How many moles is 7.78 x 1024 formula units of MgCl2? 2.8 x 1024 molecules of CO2 mol H2O (or 9.75 x 10-2) 7.405 x 1023 atoms C 12.9 moles MgCl2

Mixed Practice Problems:
How many atoms of lithium is 1.0 g of Li? How much would 3.45 x 1022 atoms of U weigh? What is the volume of 10.0 g of CH4 gas at STP? 8.7 x 1022 atoms Li 13.6 g U 14.0 L CH4

Section 10.3 Percent Composition and Chemical Formulas

Percentage Composition
Percentage by mass of each element in a compound

Calculating Percent Composition of a Compound
Like all percent problems: part whole Find mass of each element (from the periodic table) Next, divide by total mass of compound; then x 100 x 100 % = percent

Percentage Composition
Find the % composition of Cu2S. g Cu g Cu2S %Cu =  100 = 79.85% Cu 32.07 g S g Cu2S %S =  100 = 20.15% S

Percentage Composition
Find the mass percentage of water in calcium chloride dihydrate, CaCl2•2H2O? 36.04 g g %H2O =  100 = 24.51% H2O

Empirical Formula (EF)
Lowest whole number ratio of atoms in a compound C2H6 simplify subscripts CH3

Empirical Formula (EF)
Just find lowest whole number ratio C6H12O6 CH4N Formula is not just ratio of atoms, it is also ratio of moles. In 1 mole of CO2 there is 1 mole of carbon and 2 moles of oxygen. In one molecule of CO2 there is 1 atom of C and 2 atoms of O. = CH2O = this is already the lowest ratio.

Formulas (continued) Formulas for ionic compounds are ALWAYS empirical (the lowest whole number ratio = cannot be reduced). *Remember, we simplify beforehand Examples: NaCl MgCl2 Al2(SO4)3 K2CO3

Formulas (continued) Formulas for molecular compounds MIGHT be empirical (lowest whole number ratio). Molecular: H2O C6H12O6 C12H22O11 (Correct formula) Empirical: H2O CH2O C12H22O11 (Lowest whole number ratio)

Formulas Empirical Formula (EF) = lowest whole number ratio of elements in a compound. Molecular Formula (MF) = the actual ratio of elements in a compound. The two can be the same. CH2 = C2H4 = C3H6 = H2O = H2O is also MF EF MF MF EF 35

Last extra practice slide
How many O atoms are in 5 mol of Al2O3? How many Al atoms are in 5 mol of Al2O3? mol O 6.02e23 atoms O 5 mol Al2O3 3 1 mol Al2O3 1 mol O 9.03e24 atoms O 5 mol Al2O3 2 mol Al 6.02e23 atoms Al 1 mol Al2O3 1 mol Al 6.02e24 atoms Al

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