Unit V: THR MOLE COMCEPTV.1. Atomic Mass and Avogadro's Hypothesis

Equal volumes of different gases, at the same temperature and pressure, contain the same number of particles.

Back ground knowledge:
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Avogadro for short- he was born in Turin, Italy in 1776, into a family of church lawyers. He too studied ecclesiastical law, warning his Bachelor's degree at
the age of 16, and a Doctorate by 20. After three years he decided that a career in law was not ti his bent, and he began to study science and mathematics in earnest.
In 1809 he was appointed profressor of Natural Philosphy at Royal College of Vercelli in isolated Northern Italy.In 1811 he proposed his now famous hypothesis that
equal volumes of gases, at the same temperature and pressure, contain equal numbers of molecules.

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Gay-Lussac and others also believed such proportionality must exist, but what made Avogadro's hypothesis complete and correct was his new definition of a molecule as the smallest characteristic particle of a substance which may be a single elementary atom or a permanent union of several elementary atoms. He proposed that some gases, such as hydrogen and oxygen, consisted of diatomic molecules and a water molecule could consist of three elementary atoms, two of hydrogen and one of oxygen. Avogadro's concepts reconciled Daltin's atomic hypothesis with Gay-lussac's law of combining volumes.
For many reasons, Avogadro's hypothesis was ignored for about 50 years. For example, scientists such as Dalton(who was specifically mentioned in Avogadro's memoir) were threatened by the possibility that many of their atomic weights were incorrect. Avogadro's hypothesis was not accepted until Cannizzaro convincingly presented a system of atomic weights around 1858-1860 based on Avogadro's hypothesis.
However,Dalton's mass scale was just being introduced when the French Chemist Joseph Gay-Lussac began to study how gases reacted. Gay-Lussac reacted pairs of gases at the same temperature and pressure and found the following results.

Exerxise: IF 1,0L of unknown gas X contains 3.0×10^23 molecules at a certain temperature and pressure, how many molecules are present in 5.0L of oxygen gas at the same temperature and pressure?
key: Since the volume of oxygen is 5 times the volume of unknown gas X, there are 5 times as mny oxygen molecules as gas X molecules; that is, 5×3.0×10^23 = 10^24 molecules.