The mole and the Avogadro constant
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Define the term 'mole'.
A mole is the amount of substance containing the same number of particles (atoms, molecules, ions, etc.) as there are atoms in 12 grams of carbon-12. It's a counting unit for chemistry.
What is the Avogadro constant (NA), and what is its value?
The Avogadro constant (Nₐ) is the number of constituent particles (usually atoms or molecules) that are contained in the amount of substance given by one mole. Its value is approximately 6.022 x 10²³ mol⁻¹.
How do you calculate the number of moles in a given mass of a substance?
Number of moles (n) = mass (m) / molar mass (M).
What is the relationship between the number of particles, the number of moles, and the Avogadro constant?
Number of Particles = Number of Moles x Avogadro Constant (N = n x Nₐ). This equation allows conversion between the number of moles of a substance and the number of individual particles it contains.
A sample contains 3.011 x 10²³ molecules of a compound. How many moles of the compound are present?
Moles = Number of particles / Avogadro's constant. Therefore, moles = (3.011 x 10²³) / (6.022 x 10²³) = 0.5 moles.
Explain why the mole is a useful concept in chemistry.
The mole provides a convenient way to relate masses of substances to the number of atoms, molecules, or ions present. It bridges the macroscopic world (grams) to the microscopic world (atoms).
Define molar mass.
Molar mass (M) is the mass of one mole of a substance, usually expressed in grams per mole (g/mol). It is numerically equal to the substance's atomic or molecular weight in atomic mass units (amu).
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