Relative Mass:
Expressed by company it mathematically to the mass of another object.
Avogardo's Law:
Equal volume of all gases under same conditions of temperature and pressure contain equal no of molecules.
Things to understand about Avogadro's number:
• It is a number, just as is "dozen", and thus is dimensionless; you can think of Avogadro's number as the "chemist's dozen".
• It is a huge number, far greater in magnitude than we can visualize;
• Its practical use is limited to counting tiny things like atoms, molecules, "formula units", electrons, or photons.
• Its value can be known only to the precision that the number of atoms in a measurable weight of a substance can be estimated. Because large numbers of atoms cannot be counted directly, a variety of ingenious indirect measurements have been made involving such things as brownian motion and X-ray scattering.
Several related terms are used to express the mass of one mole of a substance.
- Molecular weight This is analogous to atomic weight: it is the relative weight of one formula unit of the compound, based on the carbon-12 scale. The molecular weight is found by adding atomic weights of all the atoms present in the formula unit. Molecular weights, like atomic weights, are dimensionless}; i.e., they have no units.
- Formula weight The same thing as molecular weight. This term is sometimes used in connection with ionic solids and other substances in which discrete molecules do not exist.
- Molar mass The mass (in grams, kilograms, or any other unit) of one mole of particles or formula units. When expressed in grams, the molar mass is numerically the same as the molecular weight, but it must be accompanied by the mass unit.
What is the formula weight of copper(II) chloride, CuCl2?
Answer: the atomic weights of Cu and Cl are, respectively 63.55 and 35.45;
63.55 + 2(25.35) = 134.45.
Answer: the atomic weights of Cu and Cl are, respectively 63.55 and 35.45;
63.55 + 2(25.35) = 134.45.
What is the molar mass of copper(II) chloride, CuCl2?
Answer: the masses of Cu and Cl are, respectively, 63.55 g and 35.45 g;
(63.55 g) + 2(25.35 g) = 134.45 g.
Answer: the masses of Cu and Cl are, respectively, 63.55 g and 35.45 g;
(63.55 g) + 2(25.35 g) = 134.45 g.
