Multiple Choice
Which of the following is the atomic mass of cobalt (Co)?
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2. Atoms & Elements
Atomic Mass
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Which element was originally used as the standard for determining atomic weights?
A
Hydrogen
B
Oxygen
C
Carbon-12
D
Nitrogen
Verified step by step guidance1
Understand that atomic weights (now called relative atomic masses) are determined by comparing the mass of atoms to a standard reference.
Historically, the first element used as the standard for atomic weights was hydrogen because it is the lightest element and simplest atom.
Later, oxygen was used as a standard because it was easier to work with experimentally and was abundant in compounds.
In modern times, carbon-12 isotope is used as the standard for atomic masses, defined exactly as 12 atomic mass units.
Therefore, the element originally used as the standard for determining atomic weights was hydrogen.
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