Atomic Mass and Carbon-12 Standard Quiz

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What is atomic mass?

Atomic mass is the mass of an atom.

How is the mass of an atom determined in the present system?

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

What is the definition of one atomic mass unit (amu)?

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

Why is the average atomic mass of an element calculated?

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. Signup and view all the answers

What is the significance of the agreement made by IU PAC in 1961 regarding atomic mass?

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. Signup and view all the answers

Explain the concept of atomic mass in relation to the isotopes of an element.

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. Signup and view all the answers

According to Avogadro's law, if 1 volume contains n molecules, how many molecules of hydrogen and oxygen combine to form water vapor?

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

What are the four key features of Dalton's atomic theory?

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. Signup and view all the answers

What is the order of magnitude of the mass of a single atom?

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

What are isotopes, and how do they differ from one another?

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. Signup and view all the answers

Explain the difference between molality (m) and molarity (M) as units of concentration.

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. Signup and view all the answers

How does the structure of an atom, as described by Dalton's atomic theory, explain the laws of chemical combination?

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. Signup and view all the answers

What is the relationship between the unified mass unit (u or Da) and grams?

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

How is the average atomic mass of an element calculated from its isotopic abundances?

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

Why are atomic masses in the periodic table rounded off to the nearest whole number?

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

Calculate the atomic mass of oxygen in unified mass units (u), given that the mass of an oxygen atom is 26.56896 × 10^-24 g.

The atomic mass of oxygen is 16.0 u. Signup and view all the answers

What is the significance of the term 'average' when referring to atomic masses listed in the periodic table?

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

Why was the unified atomic mass unit (u or Da) introduced, replacing the older amu (atomic mass unit)?

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