The mole
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What is the SI base unit for amount of substance?
The SI base unit for the amount of substance is the 'mole', symbol 'mol'. It quantifies the number of elementary entities (atoms, molecules, ions, etc.) of a substance.
Define one mole in terms of the number of particles.
One mole of any substance contains the same number of particles as there are atoms in 12 grams of carbon-12. This number is defined as the Avogadro constant (Nₐ).
What is the approximate value of the Avogadro constant, and what are its units?
The Avogadro constant (Nₐ) is approximately 6.022 × 10²³ mol⁻¹. It represents the number of particles (atoms, molecules, ions, etc.) per mole of a substance.
How do you calculate the number of moles (n) of a substance given the number of particles (N) and the Avogadro constant (Nₐ)?
The number of moles (n) can be calculated using the formula: n = N / Nₐ, where N is the number of particles and Nₐ is the Avogadro constant.
A sample contains 3.011 × 10²³ molecules of water (H₂O). How many moles of water are present?
n = N / Nₐ = (3.011 × 10²³) / (6.022 × 10²³) = 0.5 mol. Therefore, there are 0.5 moles of water.
Describe how the concept of the mole is important in stoichiometry.
The mole allows us to relate macroscopic measurements of mass to the number of atoms/molecules involved in a chemical reaction. Stoichiometric calculations rely on the mole ratio from balanced equations to predict quantities of reactants and products.
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