CHEM 1110 Lecture 7: Chapter7ChemicalFormulaRelationships

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pearmuskrat872

24 Mar 2017

School

Ohio State University

Department

Chemistry

Course

CHEM 1110

Professor

Ross Dalbey

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Document Summary

Molecular mass: the average mass of a molecule (based on the atomic masses of all atoms in the molecule) Formula mass: the average mass of a formula unit (based on atomic masses of all atoms in the formula unit) Avogadro"s number (na) = 6. 02 x 10^23. Mole (mol): the amount of any substance that contains the same number of units as the number of atoms in exactly 12g of c. The molar mass of any substance in grams per mole is numerically. Equal to the atomic, molecular, or formul mass of the substance in. Molar mass (for an element): the mass of one mole of the element. Molar mass (for a substance): the mass of one mole of the substance. Perception composition by mass: percent by mass of each element in a compound. Molecular formula: actual or true formula for a compound.

Related Questions

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 1110 Lecture 7: Chapter7ChemicalFormulaRelationships

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