CH 1000 MOD 2 DB

CH1000 Fundament als of Chemistry Module 2 – Chapter 7

The Mole (or mol)

• In chemistry, a mole (mol) is a standard scientific unit for measuring large quantities of very small entities such as atoms, molecules, or other specified particles.

• The number represented by 1 mole above is also called Avogadro’s number.

• 1 mol of any element contains the same number of atoms, but can vary greatly in the overall mass. (Atoms of different elements have different masses)

Molar Mass

•Molar Mass is the atomic mass of an element or compound in grams which contains Avogadro’s number of particles • Molar masses are expressed

to 4 significant figures in the text

•Convert atomic mass units on the periodic table to grams and sum the masses of the total atoms present

Mole Map ** Not found in the textbook,

save for easy access

Molar Mass of Compounds

•Much like an element, molar mass can be defined for a compound •Molar Mass is the mass of one mole of the formula unit of a compound • The molar mass of a

compound is equal to the sum of the molar masses of all the atoms in the molecule

Percent Composition of Compounds

Percent composition is the mass percent of each element in a compound. • Percent = parts per 100 parts • Molar mass is the total mass (100%) of the compound

% Composition is independent of sample size

% Composition can be determined by:

• 1. Knowing the compound’s formula • 2. Using experimental data

Percent Composition from the Compound’s Formula

Percent Composition from Experimental Data

Empirical and Molecular Formula

Empirical Formula Smallest whole number ratio of atoms in a compound

Molecular Formula Actual formula of a compound. Represents the total number of atoms in one formula unit of the compound

Calculating Empirical Formulas •Special Case: • If fractions are

encountered, multiply by a common factor to provide whole numbers for each subscript.

Calculating the Molecular Formula from the Empirical Formula

•If molar mass is known, the molecular formula can be calculated from the empirical formula •Molecular formula is a multiple of the empirical formula.

Reading Review

What is Avagadro’s number?

How would you convert from grams

to atoms of an element?

What is a mole?

What is the difference between

empirical and molecular formulas?

What is the special case when

calculating empirical formulas?