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**The Mole and Chemical Composition**

Chapter 7 The Mole and Chemical Composition

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**Avogadro’s Number Mole 6.022x10 23 /mole**

Can be: ions, molecules, atoms, formula units

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**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+

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**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

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**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

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**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

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**7.990x1025 molecules of CH4 (molar mass of CH4=16.05 g/mol)**

find the mass in grams.

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

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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.

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**Chemical Formulas and mole composition**

Find the molar mass for the compound CaHPO4

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

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Percent Composition The Percentage by mass of each element in a compound part/total x 100 Find the percentage of both elements in H2O

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**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

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

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**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

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**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.

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Molecular Formula Whole-number multiples of empirical formulas.

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**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

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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.

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