 # 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

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

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

O atoms in 3.161X1021 molecules of CO2
Determine the number of moles of each specified atom or ion in the give samples of the following compounds. O atoms in 3.161X1021 molecules of CO2

Converting Number of Particles to Mass
Given the molar mass of NaCl (58.44 g/mol), find the mass in grams of 3.34X 1023 formula units of NaCl

7.990x1025 molecules of CH4 (molar mass of CH4=16.05 g/mol)
find the mass in grams.

Find the number of atoms in 237 g Cu (molar mass of Cu= 65.55 g/mol)

Average atomic mass Weighted average of masses of all naturally occurring isotopes of an element Calculate the average atomic mass of oxygen. Its compositions is 96.4% of atoms with a mass of amu, 1.4% with a mass of17.00 amu, and 2.2% with a mass amu.

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

Write the formula and then find the molar mass for calcium phosphate

Percent Composition The Percentage by mass of each element in a compound part/total x 100 Find the percentage of both elements in 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.