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Chemical Quantities

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).

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Chemical Quantities

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  1. Chemical Quantities Math in Chemistry

  2. 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

  3. 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

  4. The # of Particles in a Mole • mole (mol) - the amount of a substance that contains 6.02 × 1023 representative particles of that substance • The number of representative particles in a mole, • 6.02 × 1023, 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.

  5. A mole of any substance contains Avogadro’s number of representative particles, or 6.02 × 1023 representative particles.

  6. 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 126C 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

  7. 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 SO3. • A molecule of SO3 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.

  8. SO3 • 1 Sulfur at 32.1 amu • 3 Oxygens at 16.0 amu • 32.1 + 3(16.0) =

  9. 1 molecule of SO3 = 80.1 amu 1 mole SO3 = 80.1 g

  10. The Mole “Road Map”

  11. 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.

  12. The Volume of a Mole of Gas • Standard Temperature and Pressure (STP) • means a temperature of 0°C and a pressure of 101.3 kPa, or 1 atmosphere (atm). • At STP; 1 mol or 6.02 × 1023 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.

  13. 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 • Formula on white board

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