Chapter 3 Composition of Substances and Solutions Part A

Molecular mass of HCCl3 = 119.37 u Atoms Atomic Mass: Average mass of 1 atom Atomic Mass of Cl: Average mass of 1 atom Cl = 35.45 u Molecules Molecular Mass: Sum of atomic masses of all atoms in molecular formula. Molecular mass of HCCl3 ? Molecular mass of HCCl3 = 119.37 u

Formula Mass Ionic compounds Formula Mass: Sum of atomic masses of all atoms in ionic compound’s formula. formula mass of NaCl = 58.44 u

Mole: Unit for Amount 12g of 12C contains 6.022 × 1023 atoms 12C The mole is the amount of substance containing as many units as there are atoms in exactly 12 grams of 12C atoms 12g of 12C contains 6.022 × 1023 atoms 12C 1 mole of 12C contains 6.022 × 1023 atoms 12C 1 mole contains 6.022 × 1023 units (Always state explicitly the identity of the unit) 1 gram = 6.022 × 1023 u Avogadro’s number (NA) = number of units per mole NA = 6.022 × 1023 units.mole-1

Molar Mass Atoms Molar Mass of element: Mass per mole of atoms of the element (1 mole of atoms has 6.022 × 1023 atoms ) Atomic mass of Cl: Average mass of 1 atom Cl = 35.45 u Mass of 1 mole of atoms Cl = 35.45 g Molar mass of Cl =35.45 g /mol Molecules Molar Mass: Sum of molar masses of all atoms in the formula. Molecular mass of HCCl3 = 119.37 u 1 mole of HCCl3 has a mass of 119.37 g Molar mass of HCCl3 is 119.37 g/mol

Calculate Molar Mass What is the molar mass of C2H5COOH? 148 g/mol 6

Molar Mass Ionic compounds In General Molar Mass: Sum of molar masses of all atoms in ionic compound’s formula. Formula mass of NaCl = 58.44 u Molar mass NaCl = 58.44 g/mol In General Molar mass (MM) Mass of per mole of substance (atom of element, molecule, or ionic formula) in consideration. Unit for molar mass is g/mol MM of Cl= 35.45 g/mol, MM of NaCl= 58.44 g/mol

Calculate Molar Mass Formula is Mg3(PO4)2 What is the molar mass of magnesium phosphate? 262.9 g/mol 150.9 g/mol 333.6 g/mol 119.3 g/mol 166.9 g/mol Formula is Mg3(PO4)2 8

Molar mass of an element is the mass of the element per mole of its atoms. Atomic mass of O = 16.00 u molar mass of O = 16.00 g/mol Molar mass of a molecular substance is the mass of the compound per mole of its molecules. Molecular mass of O2=2 x 16.00 u=32.00 u Molar mass of O2 = 32.00 g/mol Molar mass of an ionic compound is the mass of the compound per mole of its formula units. Formula mass of NaCl = 58.44 u Molar mass of NaCl = 58.44 g/mol

Convert from grams to moles How many moles of potassium are in 4.70 g of potassium? 4.70 g K ( 1 mol K/39.10 g K) = 0.120 mol

Convert from moles to grams How many grams of argon are in 4.70 mol of Ar? 4.70 mol Ar (39.95 g Ar/1 mol Ar) = 188 g Ar

Convert from moles to grams Example: If we need 0.168 mole Ca3(PO4)2 for an experiment, how many grams do we need to weigh out? Calculate molar mass of Ca3(PO4)2 3mol Ca×molar mass Ca = 3 mol×40.078 g/mol = 120.23 g 2mol P× molar mass P = 2 mol × 30.97 g/mol = 61.94 g 8 mol O× molar mass O = 8 mol× 16.00 g/mol = 128.00 g 1 mole Ca3(PO4)2 = 310.17 g Ca3(PO4)2 Molar mass Ca3(PO4)2 = 310.17 g/mol Ca3(PO4)2

Convert from moles to grams Set up conversion factor so that what you want is on the top and what you start with is on the bottom = 52.11 g Ca3(PO4)2

Using Moles in Calculations Start with either Grams (Macroscopic) Elementary units (Microscopic) Use molar mass to convert from grams to mole Use Avogadro’s number to convert from moles to elementary units

Formula unit and Mole Conversions Calculate the number of formula units of Na2CO3 in 1.29 moles of Na2CO3. How many moles of Na2CO3 are there in 1.15 × 105 formula units of Na2CO3 ? = 7.77 × 1023 units of Na2CO3 = 1.91×10–19 mol Na2CO3

Deriving Number of Atoms from Mass for an Element How many silver atoms are in a 85.0 g silver bracelet? What do we want to determine? 85.0 g silver = ? atoms silver g Ag  mol Ag  atoms Ag = 4.75 × 1023 Ag atoms

Conversion from Number of atoms to Mass How much, in grams, do 8.85 × 1024 atoms of zinc weigh? = 961 g Zn 17

Conversion from formula unit to mass Calculate the mass in grams of FeCl3 in 1.53 × 1023 formula units. (molar mass = 162.204 g/mol) = 41.2 g FeCl3