Download Understanding the Mole Concept: From Dozens to Moles - Prof. Beverly A. Kelley and more Study notes Chemistry in PDF only on Docsity!
Chem 1075 Chapter 9 The Mole Concept Lecture Outline Slide 2 Dozen compared to Mole We use “dozen” to _________________________________; We know 1 dozen = _______________ We use “mole” to ___________________________________________________________________ Slide 3 The Mole The mole (mol) is a unit of measure for the ________________________________________in a chemical substance. A ____________ is _____________________________________(abbreviated “N”) of particles or _______________________________particles. 1 mol = Avogadro’s number = ___________________________ particles. We can use the __________relationship to convert between the number of __________________ and the _________________ of a substance. Slide 4 How Big is a Mole? The volume occupied by 1 mole of _________________________would be about the size of the _______________________. One mole of Olympic shotput balls has about the same _______________as the _________________. Slide 5 Mole Calculations I Use Avogadro’s number to convert between _________________________ and _______________: __________________________particles = _________ mole
Slide 6 Mole Calculations I How many sodium atoms are in 0.120 mol Na?
Slide 7 Mole Calculations I How many moles of potassium are in 1.25 x 10^21 atoms K?
Slide 8 Practice
- If you have 2.49 x 1024 molecules of CO2, then how many moles of carbon dioxide is that?
- How many atoms of Fe are in 4.75 moles of iron?
- How many moles would contain 3.56 x 1022 molecules of water?
Slide 9 Atomic Mass vs. Molar Mass
- Atomic mass mass of iron is 55.85 amu. is the mass of an _________________ expressed in __________. The atomic
- Molar mass is the mass of _______ ______________ of a substance expressed in ________. The molar mass of iron is 55.85 g.
- Why are the numbers the same? Slide 10 Molar Mass
- • Recall that 1 amu = ___________________g orCan show that 1mole Fe has a mass of 55.85g: ______________________amu = 1 g
- Molar mass for iron is 55.85g
- Can also think of as 55.85g = 1mole Fe or 55.85g/mole Slide 11 Calculating Molar Mass
- The molar mass of a substance is the sum of the molar masses of each element in the formula.
- What is the molar mass of magnesium nitrate, Mg(NO 3 ) 2? The sum of the molar masses is: 1 Mg x ___________ = ____________2 N x ____________ = ____________ 6 O x ____________ = ____________ Molar Mass = ___________ g / mole
Slide 18 Pressure and Units Pressure is defined as the ratio of ____________________per unit _________________ (i.e. psi)
Slide 19 Molar Volume of Gases ______mole gas = _____________________molecules gas = ___________L gas
Slide 20 Gas Density
- The density of gases is much ___________than that of liquids.
- • We can calculate the density of any gas _______________ easily.The formula for gas density at STP is:
Slide 21 Calculating Gas Density
- What is the density of ammonia gas, NH 3 , at STP?
- First we need the molar mass for ammonia;
- The molar volume NH 3 at STP is 22.4 L/mol.
- Density is mass/volume:
Slide 22 Molar Mass of a Gas
- We can also use ______________________________ to calculate the ___________________ of an unknown gas.
- • 1.96 g of an unknown gas occupies 1.00L at STP. What is the molar mass?We want g/mol, we have g/L.
Slide 23 Mole Unit Factors
- We now have three interpretations for the mole: _____________ = _____________________ particles _____________ = _____________________ (in grams)
- _____________ = _______________ at STP for a gasThis gives us 3 unit factors to use to convert between moles, particles, mass, and volume. Slide 24 Mole-Volume Calculation
Slide 25 Mole-Volume Calculation A sample of methane, CH 4 , occupies 4.50 L at STP. How many moles of methane are present?
Slide 26 Mass-Volume Calculation What is the mass of 3.36L of ozone gas, O 3 , at STP?
Slide 27 Molecule-Volume Calculation How many molecules of hydrogen gas, H 2 , occupy 0.500L at STP?
- The molecular formula of octane is __________
- The empirical formula of octane is ___________. Slide 34-35 Calculating Empirical Formulas (from experimental data) We can calculate the empirical formula of a compound from its experimental data. We can determine the mole ratio of each element from the mass to determine the formula of radium oxide, Ra?O?. A ________________ sample of radium metal was heated to produce ________________ of radium oxide. What is the empirical formula?
- Radium + oxygen à radium oxide
The ____________________ of radium is ____________ g/mol and the ______________________ of oxygen is ________________ g/mol. (Comes from periodic table)
- We get Ra______________ O _____________.
- Simplify the mole ratio by dividing by the smallest number.
- We get Ra ______________O______________ = RaO is the empirical formula. Slide 36-37 Empirical Formulas from % Composition We can also use percent composition data to calculate empirical formulas. Assume that you have ________________ of sample. Benzene is 92.2% carbon and 7.83% hydrogen, what is the empirical formula? If we assume ____________ of sample, we have _____________g C and __________g H. Calculate the moles of each element:
The ratio of elements in benzene is C_________H__________. Divide by the _________________________number to get the formula:
C ----------- H ------------- = C______ H _______ = _____________
Slide 38 Molecular Formulas The _____________________ formula for benzene is CH. This represents the __________________ ratio of C to H atoms of benzene. The actual molecular formula is some ___________________ of the empirical formula, ___________ Benzene has a molar mass of 78 g/mol. Find n to find the molecular formula.
Slide 39 Overview of Calculations
