1. Ch 7 Mole & chemical composition

2. Avogadro’s number & mole conversion
Size of atoms, ions, and molecules very small
Use the mole to convert a large # of these particles.
Mole: SI base unit used to measure the amount of a substance whose # of particles is the same as the # of atoms in 12.0 g of C-12.
Avogadro’s number: x 1023, which is the # of particles in 1.000mol
Used to count any kind of particle.
1.0 mol = x 1023

3. Mole conversion Mol <--> # particles
Avogadro's number
Molar/formula mass (relate moles to mass)
The mass in grams of one mole of a substance
Equal to the sum of all the atomic weights in cpd. Units g/mol.
Mass < > moles <-----> # particles
Molar mass Avogadro’s number
Convert the following: x 1014 formula units ReO2 to mass.
9925g NO2- to # of ions.

4. Relative atomic mass & chemical formulas.
Average atomic mass
Weighted average of the masses of all naturally occurring isotopes of an element.
Know mass of each isotope and % occurrence
= (mass istopeA x %) + (mass isotopeB x %) + …
% in decimal form
Determine the average atomic mass of chlorine with the following data: Cl-35 mass = amu & 75.8%, and the rest Cl-37 mass = amu.
The relative average atomic can also predict which isotope has the higher relative %. Example: Carbons has 3 isotopes, C-12, C-13 & C-14, with an average atomic mass of amu. Which isotope is in highest %?

5. Chemical formula
Gives what element and ratio of elements in a cpd or polyatomic ions
From formula can calculate the molar mass of cpd. Units g/mol
Determine the number of atoms of each element in the cpd Al2(SO4)3
Determine the molar mass of the following: Na2SO4, Ca3(PO4)2

6. Formula and % composition.
The % by mass of each element in a cpd.
Used % composition to determine chemical formula.
Determine the % by mass of each element in Mg(NO3)2.
Determining empirical formula:
Empirical formula: lowest (simplest) ratio of atoms in a cpd.
1. Convert % to mass each element (direct)
2. Convert mass to moles of each (atomic wt.)
3. Divide smallest into all mole amount -> lowest whole #
4. If end in .2 then x5, .25 then x 4, .33 then x 3, .5 then x2
All values.

7. Determine formula cont.
Determine the empirical formula for the following
63.52% Fe, 36.48% S
26.58% K, 35.35% Cr, 38.07% O
29.15% N, 8.333% H, 12.50% C, 50.00% O

8. Molecular formula Whole # multiple (n) of the empirical formula.
Not necessarily the smallest whole number.
n determine by dividing formula mass into the molar mass of cpd.
Determine molecular formula from each:
Molar mass g/mol and empirical formula OCNCl
Molar mass g/mol and empirical formula CH2O