Ch. 10.2 Mole-Mass and Mole-Volume Relationship

The Mole-Mass Relationship Molar mass of any substance is the mass in grams of one mole of that substance. Applies to atoms, molecules, formula units, etc. With gases, you must be clear as to whether the gas is atomic or molecular ( O vs. O2). Use the molar mass of a substance to convert between the mass of a substance and the moles of a substance (molar mass = one mole).

mass(grams) = # of moles x mass(grams)/moles Ex: molar mass of NaCl is 58.5 g/moles. What is the mass of 3.00 moles of NaCl? 3.00 mol x 58.5g/mol = 176 grams

Practice—moles to mass What is mass of 9.45 moles of aluminum oxide? What is the mass of 4.52x10-3 moles C20H42? What is the mass of 2.50 moles of iron(II) hydroxide?

Practice—mass to moles Moles = mass(grams) x 1 mole/mass(grams) How many moles in 92.2 grams of iron(III) oxide? How many moles in 3.70x10-1g of boron? How many moles in 75.0g of dinitrogen trioxide?

The mole-volume relationship One mole of any gas, at standard temperature and pressure, will always occupy the same volume. Reason is that, in a gas, the atoms or molecules are so far apart, that the size of the individual atoms or molecules is insignificant compared to the distances between the atoms or molecules.

Standard Temperature Pressure STP Temperature: 0oCelcius Pressure: 1 atmosphere (atm) or 101.3 kilo Pascal (kPa) One mole of any gas (6.02 x 1023 RP) at standard temperature and pressure (STP) will always occupy 22.4 liters.

Practice How much volume does 0.5 moles of oxygen take up? Multiply: 0.5 moles x 22.4 l/mole = 11.2 l How many moles N2 are found in 50.00 l of gas? Calculate: 50.00 l x 1 mole / 22.4 l = 2.2 moles

Go To Mole Island!!! Volume of Gas multiply moles by divide volume 22.4 l/moles by 22.4 l/mole Divide mass by Mole multiply mole with Molar mass 6.02 x 1023 multiply moles with molar mass divide RPs Representative Mass 6.02 x 1023 Particles RP

Practice Problem 1 Find the number of molecules in 50.8 liters of O2 First write pathway Volume → moles → RP 50.8 l x 1 mole/22.4l = 2.27 moles 2.27 moles x 6.02 x 1023 RP/mole= 1.36 x 1024 O2 How many atoms? 2 atoms/RP x 1.36 x 1024 RP = 2.42 x 1024 Atoms Oxygen

Practice Problem 2 Find the volume of 500 g of PO2 Mass → moles → volume Molar mass of PO2 30.97 + (2x16.00) = 62.97 g/mol moles: 500g x 1 mole/62.97g = 7.94 moles Volume: 22.4moles/liter x 7.94 moles= 177.8 liters

Practice Problem 3 How many atoms are in 400 g of C2(OH2)4 Mass → moles → RP → Atoms Molar mass: 2x 12.01 + 4 x (16.00 + 2 x 1.01) =96.10 g/mol # of atoms: 14 400 g x 1 mole/96.10 g = 4.16 moles 4.16 moles x 6.02 x 1023 RP= 25.04 x 1023 = 2.50 x 1024 RP 2.50 x 1024 RP x 14 atoms/RP= 35.00 x 1024 =3.50 x 1025 atoms