Chemical Quantities Math in Chemistry

Measuring Matter measure the amount of something by one of three different methods— by count, by mass, and by volume. Apples are measured in three different ways: ◦ sold by the count (3 for $2.40). ◦ by weight ($1.29/pound) or mass ($2.79/kg). ◦ buy apples by volume ($12.00/bushel). Each of these different ways to measure apples can be equated to a dozen apples. By count: 1 dozen apples = 12 apples For average-sized apples the following approximations can be used. By mass: 1 dozen apples = 2.0 kg apples By volume: 1 dozen apples = 0.20 bushel apples

What is a mole? 1 dozen = 12 objects 1 baker’s dozen = 13 objects 1 gross = 144 objects ( 1 dozen dozen) A Mole is just a word that represents a quantity

The # of Particles in a Mole mole (mol) - the amount of a substance that contains 6.02 × representative particles of that substance The number of representative particles in a mole, 6.02 × 10 23, is called Avogadro’s number. It was named in honor of the Italian scientist Amedeo Avogadro di Quaregna (1776–1856) who helped clarify the difference between atoms and molecules. The term representative particle refers to the species present in a substance: usually atoms, molecules, or formula units.

A mole of any substance contains Avogadro’s number of representative particles, or 6.02 × representative particles.

The mass of a mole of an element atomic mass is expressed in atomic mass units (amu). atomic masses are relative values based on the mass of the most common isotope of carbon (carbon-12). 1 amu = 1/12 of a 12 6 C nucleus atomic mass of an element expressed in grams is the mass of one mole of the element. The mass of a mole of an element is its Gram Atomic Mass

The mass of a mole of a compound To find the mass of a mole of a compound, you must know the formula of the compound. formula of sulfur trioxide is SO 3. A molecule of SO 3 is composed of one atom of sulfur and three atoms of oxygen. To calculate the molar Gram Molecular Mass (Gram Formula Mass) of a compound, find the number of grams of each element in one mole of the compound. Then add the masses of the elements in the compound.

SO 3 1 Sulfur at 32.1 amu 3 Oxygens at 16.0 amu (16.0) =

1 molecule of SO 3 SO 3 1 molecule of SO 3 = 80.1 amu 1 mole SO 3 = 80.1 g

The Mole “Road Map”

The Molar Mass of a Substance is the mass (in grams) of one mole of the substance. It is based on how the substance exists in nature.

The Volume of a Mole of Gas Standard Temperature and Pressure (STP) means a temperature of 0°C (273 K) and a pressure of kPa, or 1 atmosphere (atm). At STP; 1 mol or 6.02 × representative particles, of any gas occupies a volume of 22.4 L. The quantity, 22.4 L, is called the molar volume of a gas.

Calculating Molar Mass from Density density of a gas at STP and the molar volume at STP (22.4 L/mol) can be used to calculate the molar mass of the gas. molar mass = density at STP × molar volume at STP

% Composition Relative amounts of each element in a compound reference tables Table T % composition by mass = mass of part/mass of whole x 100 We will revisit this later.