Atomic Mass and Carbon-12 Standard Quiz

Atomic mass is the mass of an atom.

The mass of an atom is determined relative to the mass of a carbon-12 atom as the standard.

One amu is defined as a mass exactly equal to one twelfth of the mass of one carbon-12 atom.

<p>The average atomic mass of an element is calculated because many naturally occurring elements exist as a mixture of more than one isotope with different atomic masses.</p> Signup and view all the answers

<p>In 1961, IU PAC agreed to assign an atomic mass of exactly 12.00000 amu to a carbon-12 atom, establishing it as the standard reference for atomic masses.</p> Signup and view all the answers

<p>The atomic mass of an element is the weighted average of atomic masses of its isotopes, considering both the atomic masses and relative abundances of the isotopes.</p> Signup and view all the answers

<p>According to Avogadro's law, 2n molecules of hydrogen combine with n molecules of oxygen to give 2n molecules of water vapor.</p> Signup and view all the answers

<p>The four key features of Dalton's atomic theory are: 1) Matter consists of tiny, indivisible particles called atoms. 2) All the atoms of a given element have identical properties including mass. Atoms of different elements differ in mass. 3) Compounds are formed when atoms of different elements combine in a fixed ratio. 4) Chemical reactions involve only the reorganization of atoms, and atoms are neither created nor destroyed in a chemical reaction.</p> Signup and view all the answers

<p>The mass of a single atom is on the order of $10^{-23}$ grams.</p> Signup and view all the answers

<p>Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. As a result, isotopes of an element have the same atomic number but different mass numbers.</p> Signup and view all the answers

<p>Molality (m) is the number of moles of solute per kilogram of solvent, whereas molarity (M) is the number of moles of solute per liter of solution. Molality is independent of temperature, while molarity can change with temperature due to volume changes.</p> Signup and view all the answers

<p>Dalton's atomic theory, with its key features of atoms being the fundamental building blocks of matter, atoms of the same element having identical properties, and atoms combining in fixed ratios to form compounds, can explain the laws of chemical combination, such as the law of constant composition and the law of multiple proportions.</p> Signup and view all the answers

<p>1 u = 1.66056 × 10^-24 g</p> Signup and view all the answers

<p>The average atomic mass is calculated as the sum of the products of each isotope's mass and its fractional abundance.</p> Signup and view all the answers

<p>For practical purposes, atomic masses are rounded off when they differ from the nearest whole number by a very small fraction.</p> Signup and view all the answers

<p>The atomic mass of oxygen is 16.0 u.</p> Signup and view all the answers

<p>The atomic masses listed are the weighted averages of the masses of the naturally occurring isotopes of each element.</p> Signup and view all the answers

<p>The unified atomic mass unit was introduced to provide a more consistent and standardized unit for expressing atomic and molecular masses.</p> Signup and view all the answers