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Ch. 10 Chemical Quantities

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Ch. 10 Chemical Quantities

- Counting
- Mass
- Volume

- If 0.20 bushel is 1 dozen apples, and a dozen apples has a mass of 2.0 kg, what is the mass of .050 bushel of apples?

- Count: 1 dozen apples = 12 apples
- Mass: 1 dozen apples = 2.0 kg apples
- Volume: 1 dozen apples = 0.20 bushels
apples

Conversion Factors:

- 1 dozen2.0 k.g1 dozen
12 apples 1 dozen 0.20 bushels

- 0.50 bushel x 1 dozen x 2.0 kg =
0.20 bushel 1 dozen

= 5.0 kg

- Named after the Italian scientist Amedo Avogadro di Quaregna
- 6.02 x 10 23

- 1 mol = 6.02 x 10 23 representative particles
- Representative particles: atoms, molecules ions, or formula units (ionic compound)

- Moles= representative x 1 mol
particles 6.02 x 10 23

- How many moles is 2.80 x 10 24 atoms of silicon?

- 2.80 x 10 24 atoms Si x 1 mol Si
6.02 x 10 23 atoms Si

= 4.65 mol Si

- How many molecules of water is 0.360 moles?

- 0.360 mol H2O x 6.02 x 10 23 molecules H2O1 mol H2O
=2.17 molecules H2O

- The atomic mass of an element expressed in grams = 1 mol of that element = molar mass

Molar mass S

Molar mass Hg

Molar mass C

Molar mass Fe

6.02 x 10 23 atoms S

6.02 x 10 23 atoms Hg

6.02 x 10 23 atoms C

6.02 x 10 23 atoms Fe

- If you have 4.5 mols of sodium, how much does it weigh?

- .45 mol Na x 23 g Na = 10.35 g Na = 1.0 x 10 2 g Na
1 mol Na

- If you have 34.3 g of Iron, how many atoms are present?

- 34.3 g Fe x 1 mol Fe x 6.02 x 10 23 atoms
55.8 g Fe 1 mol Fe

=3.70 x 10 23 atoms Fe

- To find the mass of a mole of a compound you must know the formula of the compound
- H2O H= 1 g x 2
O= 16 g

18 g = 1 mole = 6.02 x 10 23

molecules

- What is the mass of 1 mole of sodium hydrogen carbonate?

- Sodium Hydrogen Carbonate = NaHCO3
- Na=23 g
- H=1 g
- C=12 g
- O=16 g x3
- 84 g NaHCO3 = 1 mol NaHCO3

- Unlike liquids and solids the volumes of moles of gases at the same temperature and pressure will be identical

- States that equal volumes of gases at the same temperature and pressure contain the same number of particles
- Even though the particles of different gases are not the same size, since the gas particles are spread out so far the size difference is negligible

- Volume of a gas changes depending on temperature and pressure
- STP= 0oC (273 K)
101.3 kPa (1 atm)

- At STP, 1 mol = 6.02 X 1023 particles = 22.4 L of ANY gas= molar volume

- AT STP
- 1 mol gas22.4 L gas
22.4 L gas 1 mol gas

- At STP, what volume does 1.25 mol He occupy?

- 1.25 mol He x 22.4 L He = 28.0 L He
1 mol He

- If a tank contains 100. L of O2 gas, how many moles are present?

- 100. L O2 X 1 mol O2 = 4.46 mol O2
22.4 L O2

- The density of a gas at STP is measured in g/L
- This value can be sued to determine the molar mass of gas present

- A gaseous compound of sulfur and oxygen has a density of 3.58 g/L at STP. Calculate the molar mass.

- 1 mol gas x 22.4 L gas X 3.58 g gas =
1 mol gas 1 L gas

Molar Mass= 80.2 g

- The relative amounts of the elements in a compound
- These percentages must equal 100

- %element = mass of element x 100
mass of compound

- Find the percentage of each element present in Al2 (CO3)3

- Al2(CO3)3
- Al= 27 g x 2 = 54 g / 234 g x 100=23%
- C= 12 g x 3 = 36 g/ 234 g x 100= 15%
- O = 16 g x 9 = 144 g / 234 g x 100=62%
234 gAl2(CO3)3