Unit II

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Unit II Quantities in Chemical Reactions
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Question 1

• What is a dozen ?

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Question 2

• How do you know?

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Question 3

• What is a mole?

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Is it this?
Or this?
Or this?
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The Mole (for chemists)

• The mole is a unit of measurement used by
  chemists. It provides a method to level the
  playing field and treat all matter equally
• One mole of a substance (an element, a molecule,
  an ion or anything else) is made from Avogadros
  number of particles

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Rules Utilized With The Mole

• I. The chemical formula represents a mole of that
  substance. ( HCl would mean 1 mole of HCl)

II. The formula mass, expressed in grams,
represents the mass of one mole of that substance.
III. One mole of any substance contains 6.02 x 10
23 particles.

• IV. One mole of any gas, at STP conditions,
  occupies 22.4 liters of volume.

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History of the Mole

• The number of objects in one mole, that is, 6.02
  x 1023 , is commonly referred to as Avogadro's
  number. Amadeo Avogadro was an Italian physics
  professor who proposed in 1811 that equal volumes
  of different gases at the same temperature
  contain equal numbers of molecules. About fifty
  years later, an Italian scientist named Stanislao
  Cannizzaro used Avogadro's hypothesis to develop
  a set of atomic weights for the known elements by
  comparing the masses of equal volumes of gas.
  Building on this work, an Austrian high school
  teacher named Josef Loschmidt calculated the size
  of a molecule of air in 1865, and thus developed
  an estimate for the number of molecules in a
  given volume of air. While these early estimates
  have since been refined, they led to the concept
  of the mole - that is, the theory that in a
  defined mass of an element (its atomic weight)
  there is a precise number of atoms Avogadro's
  number.

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How do we use the Mole?

• Here s a problem that well work on solving.

When you add 10.0 grams of hydrogen gas to 10.0
grams of oxygen gas, how many grams of water will
be made?
The answer
11.25 grams