 # The Mole and Chemical Composition

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The Mole and Chemical Composition
Chapter 7 The Mole and Chemical Composition

Avogadro’s Number Mole 6.022x10 23 /mole
Can be: ions, molecules, atoms, formula units

Examples: Converting Amount of Moles to Number particles
Practice Page 228 1. How many ions are there in mol of Na+ ions? 0.187 mol Na+ (6.022*10^23 ions Na+/ 1 mol)= 1.13x10^23 ions Na+

Practice page 228 4. How many formula units are there in 5
Practice page How many formula units are there in 5.9 mol of NaOH? 5.9 mol NaOH (6.022x10^23 formula units/1 mol)= 3.55X10^24 formula units NaOH

a. O atoms in 3.161X1021molecules of CO2
Page 229: Determine the number of moles of each specified atom or ion in the give samples of the following compounds. a. O atoms in 3.161X1021molecules of CO2

Molar Mass The mass in grams of one mole of substance
Example page 231 practice 2) 3.01X 1023 formula units of NaCl (molar mass of NaCl=58.44 g/mol) Na molar mass: Cl molar mass:

3) 3.990x1025 molecules of CH4 (molar mss of CH4=16.05 g/mol)

1. Find the number of atoms in 237 g Cu (molar mass of Cu= 65
1. Find the number of atoms in 237 g Cu (molar mass of Cu= g/mol)

Average atomic mass Weighted average of masses of all naturally occurring isotopes of an element Example page 236 practice 2 Calculate the average atomic mass of oxygen. Its compositions is 99.76% of atoms with a mass of amu, 0.038% with a mass of amu, and 0.20% with a mass amu.

Chemical Formulas and mole composition
Find the molar mass for the compound B) CaHPO4

Write the formula and then find the molar mass F) tin (II) chloride

Percent Composition The Percentage by mass of each element in a compound Example: H2O

Find the % composition of a compound which contains 16. 56g C, 26
Find the % composition of a compound which contains 16.56g C, 26.22g F, and 4.14 g H

Empirical Formula Lowest whole number ratio of elements in a compound.

Steps for determining an Empirical Formula
Percent to mass Mass to moles Divide each mole value by the smallest number of moles calculated Multiply (or round) till whole

Example: A chemical analysis of a liquid shows that there is 60
Example: A chemical analysis of a liquid shows that there is 60.0% C, 13.4% H, and 26.6% O by mass. Calculate the empirical formula of the substance.

Molecular Formula Whole-number multiples of empirical formulas.

Calculate the molecular formula of the compound whose molar mass is 60
Calculate the molecular formula of the compound whose molar mass is 60.0 g/mol and empirical formula is CH4N

Determine the molecular formula for a compound for a compound that has a molar mass of 34g and is 94.1% oxygen and 5.9% hydrogen.