The Mole Concept Chapter 9 CHM 130 GCC

9.1 Avogadro’s Number and The Mole Eggs come in dozens = convenient 12 = dozen Atoms come in moles 6.02 x 1023 = mole = NA NA is just a super large number

The Mole One mole of softballs would be the size of the Earth! But atoms are so tiny that one mole of atoms is about a handful. The mass of a mole of atoms = the atomic mass in grams in the Periodic Table 1 mole of C atoms is 12.01 grams 1 mole of Na atoms is 22.99 grams

Mole Examples sugar water lead mercury copper sulfur sodium chloride

9.2 Avogadro’s number : 6.02 x 1023 atoms or mlcls or 1 mol 1 mol 6.02 x 1023atoms or mlcls 1. How many calcium atoms are in 0.250 moles of calcium: 0.250 mol Ca (6.02 x 1023 atoms/mol) = 1.51 x 1023 Ca atoms 2. Calculate the moles of 3.75 x 1027 molecules of oxygen gas: 3.75 x 1027 mlcls O2 ( mol/6.02 x 1023 mlcls) = 6230 mol O2

9.3 Molar Mass: Periodic Table masses are in ( g /mol ) How many grams in one mole of carbon? gold? sodium? Note = these are all 6.02 x 1023 atoms! 12.01 g/mol 196.97 g/mol 22.99 g/mol

Molar Mass: 137.33 + 2 ( 16.00) + 2 ( 1.01 ) = 171.35 g / mol Calculate the molar mass of barium hydroxide. What is the formula? Add up the mass for every atom. Ba(OH)2 137.33 + 2 ( 16.00) + 2 ( 1.01 ) = 171.35 g / mol Very important – the units are grams per 1 mole, not just grams

9.4 Grams to Moles & Vice Versa Use Molar Mass as (g / mol) or (mol / g) How many grams is 1.667 moles of oxygen gas? How many moles is 45 grams of silver? How many grams is 0.0554 moles of water? 1.667 mol O2 ( 32.00 g/mol) = 53.34 g O2 45 g Ag ( mol/ 107.87 g) = 0.42 mol Ag 0.0554 mol H2O (18.02g /mol) = 0.998 g H2O

9.5 Molar Volume (V of 1 mole at STP)

STP is Standard Temperature and Pressure Volume of 1 mole of gas Gases are mostly empty space so they ALL have the same volume despite different mass 22.4 L per 1 mole of any gas at STP STP is Standard Temperature and Pressure 0°C and 1 atm

For Gases only at STP: 22.4 L / 1 mol or 1 mol / 22.4 L What is the volume of 1.25 moles of gas at STP? 1.25 mol ( 22.4 L / 1 mol) = 28.0 L gas What is the mass of 4.50 L of chlorine gas at STP? 4.50 L Cl2 (mol / 22.4L) (70.90 g/mol) = 14.2 g Cl2

d = = Density Calculate the density of ammonia gas, NH3, at STP. d = (17.04 g/mol ) / ( 22.4 L/mol ) = 0.761 g/L

9.6 Mole Calcs

Example How many grams does 17.35 liters of neon gas mass at STP? How many atoms is this? 17.35 L = 15.6 grams Ne 17.35 L = 4.66x1023 atoms Ne

Percent Composition = mass % of each element in a compound Water is basically 11% H and 89% O You divide the total element molar mass by the total compound molar mass. %H = (2.02 g H / 18.02 g H2O) x 100 = 11.2% H %O = (16.00 g O / 18.02 g H2O) x 100 = 88.79% O Note the %’s should add up to 100% total

Example Problem Find the percent composition for TNT, C7H5(NO2)3 Total molar mass is 227.15 grams per mole % C = (84.07g / 227.15g) x 100 = 37.01% C % H = (5.05g / 227.15g) x 100 = 2.22%H % N = (42.03g / 227.15g) x 100 = 18.50%N % O = (96.00g / 227.15g) x 100 = 42.26%O

Try at home How many liters will 3.425 grams of carbon dioxide gas occupy at STP? 1.74 L How many molecules are in 3.425 grams of carbon dioxide? 4.68 x 1022 molecules How many grams will 3.0 x 1015 molecules of carbon dioxide mass? 2.2 x 10-7 grams

Self Test Page 258 Try 1-7, 10-13 Answers in Appendix J