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CHE 131 Chapter Notes - Chapter 3: Molar Mass, Organic Compound, Unified Atomic Mass Unit

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bluerat278
12 Sep 2016
School
Stony Brook University
Department
Chemistry
Course
CHE 131
Professor
Troy Wolfskill

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CHE 131 Full Course Notes
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CHE 131 Full Course Notes
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Document Summary

3. 2 - determining the formula of an unknown compound. The empirical formula is derived from mass analysis. It shows the lowest whole number of moles, and thus the relative number of atoms of each element in the compound. Hydrogen peroxide- 1 part mass hydrogen for every 16 parts mass of oxygen, Bc the atomic mass of hydrogen is 1. 008 amu and oxygen is 1 amu, there is 1 h for every o atom, so empirical formula is ho. Molecular formula- shows the actual number of atoms in each element in a molecule. Molecular formula h2o2, twice the empirical formula. Structural formula- shows the placement and connections of atoms in a molecule. There is a process to find the empirical formula of an unknown compound. Determine the mass (g) of each component element. Convert each mass (g) to amount (mol) and write a preliminary formula. Convert the amounts (mol) mathematically to whole number (integer) subscripts.

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Related Questions

1) How many atoms are there in 51.3 g of barium chloride (BaCl2)?
2) How many moles of carbon monoxide (CO) are in 29.3 g of the compound?

3) What is the formula for copper(II) phosphate? Capitalization and punctuation count?

4) How many atoms of phosphorus are in 2.90 mol of copper(II) phosphate?

5) How many moles of N are in 0.191 g of N2O?

6) A sample of C3H8 has 7.68 × 1024 H atoms. How many carbon atoms does the sample contain? What is the total mass of the sample?

7) Calculate the percent composition by mass of each element in Al(OH)3. Use at least three significant figures.

% Al= ?, % O=? , % H =?

8) What is the empirical formula of a compound composed of 3.25% hydrogen (H), 19.36% carbon (C), and 77.39% oxygen (O) by mass?

HCO (Insert subscripts as needed.)

9) A compound with the empirical formula CH2 has a molar mass of 98 g/mol. What is the molecular formula for this compound?


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.