The Mole
The mole is a fundamental concept in chemistry that is used to measure the amount of a substance. It is defined as the amount of a substance that contains the same number of entities (such as atoms, molecules, ions, or other particles) as there are atoms in exactly 12 grams of carbon-12. This number is known as Avogadro's number and is approximately 6.022 x 10^23 entities per mole.
Molar Mass
The molar mass of a substance is the mass in grams of one mole of that substance. It is numerically equal to the atomic or molecular mass of the substance, but it is expressed in grams. The units for molar mass are g/mol.
To calculate the molar mass of a compound, you add up the atomic masses of all the atoms in the compound. For example, the molar mass of water (H2O) is calculated as 2(1.01 g/mol) + 16.00 g/mol = 18.02 g/mol.
Avogadro's Number
Avogadro's number, denoted as NA, is the number of atoms, ions, or molecules in one mole of a substance. It is a fundamental constant in chemistry and is approximately 6.022 x 10^23 entities per mole. This number allows chemists to relate the mass of a substance to the number of atoms or molecules it contains.
Practice Problems
- Calculate the molar mass of calcium carbonate, CaCO3.
- How many atoms are present in 2 moles of carbon dioxide (CO2)?
- What is the mass of 3 moles of sulfur (S8)?
Answers
- The molar mass of calcium carbonate, CaCO3, is calculated as 40.08 g/mol (Ca) + 12.01 g/mol (C) + 3(16.00 g/mol) = 100.09 g/mol.
- 2 moles of carbon dioxide (CO2) contain 2 x NA molecules, where NA is Avogadro's number. Therefore, the number of molecules is 2 x 6.022 x 10^23 = 1.2044 x 10^24 molecules.
- The mass of 3 moles of sulfur (S8) is calculated as 3 moles x 8 atoms/mole x 32.07 g/mole = 770.16 g.
Studying the mole concept and practicing problems related to molar mass and Avogadro's number is crucial for understanding the quantitative aspects of chemistry. The mole is an essential concept in stoichiometry, which involves the calculation of quantities of reactants and products in chemical reactions.
Remember to always work with units and pay attention to significant figures when performing calculations involving the mole.
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