CHEM 0110 Chapter Notes - Chapter 3: Formula Unit, Ionic Compound, Reagent

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Molecular mass (mm) - the sum of the atomic masses of all the atoms in a molecule of the substance; average mass of a molecule of a substance expressed in atomic mass units. Formula mass (fm) - sum of the atomic masses of all atoms in a formula unit of the compound, whether molecular or not. Identify number and type of atoms in chemical formula. Use periodic table to obtain the atomic mass of each of the elements present in the compounds. **take into account the number of each atom in formula** Sum the masses of the atoms (subscript * amu) Can be used to describe mass of 1 atom/molecule in amu or 1 mole in moles. Mole (mol) - defined as the quantity of a given substance that contains as many molecules or formula units as the number of atoms in exactly 12 g of carbon-12. Avogadro"s number - number of atoms in a 12-g sample of carbon-12.

Related Questions

There are two different isotopes of bromine atoms. Under normal conditions, elemental bromine consists of Br2 molecules, and the mass of a Br2 molecule is the sum of the masses of the two atoms in the molecule. The mass spectrum of Br2 consists of three peaks. Mass (amu) Relative Size157.836 0.2569159.834 0.4999161.832 0.2432(a) What is the origin of each peak (of what isotopes does each consist)? (Enter all particles in the form AX.)mass 157.836 amu 159.834 amu 161.832 amu molecule (b) What is the mass of each isotope? (Calculate using the given masses.)lighter isotope amuheavier isotope amu(c) Determine the average molecular mass of a Br2 molecule. amu(d) Determine the average atomic mass of a bromine atom. amu(e) Calculate the abundances of the two isotopes.

Determine the empirical and molecular formulas of each of the following substances:

(a) Styrene, a compound substance used to make Styrofoam^® cups and insulation, contains 92.3% C and 7.7% H by mass and has a molar mass of 104 g/mol.

(b) Caffeine, a stimulant found in coffee, contains 49.5% C, 5.15% H, 28.9% N, and 16.5% O by mass and has a molar mass of 195 g/mol.

(c) Monosodium glutamate (MSG), a flavor enhancer in certain foods, contains 35.51% C, 4.77% H, 37.85% O, 8.29% N, and 13.60% Na, and has a molar mass of 169 g/mol.

Empirical formula of this compound is CH.

To determine the molecular formula, we need to find out how many times is molar mass higher than the mass of empirical formula:

Molecular formula is C₈H₈.

b) Empirical formula of caffeine:

Empirical formula of caffeine is C₄H₅N₂O. The sum of atomic masses from empirical formula is 97 g/mol.

Molecular formula of caffeine is 2 × empirical formula = C₈H₁₀N₄O₂

c) Empirical formula of MSG:

Empirical formula of MSG is C₅H₈NO₄Na. The sum of atomic masses of empirical formula is 169 g/mol, the same as molar mass. Empirical and molecular formula are identical.

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CHEM 0110 Chapter Notes - Chapter 3: Formula Unit, Ionic Compound, Reagent

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