# Chap3 - Chem 200 Dr Saidane Lecture Notes Chapter 3...

This preview shows pages 1–3. Sign up to view the full content.

Chem 200 Dr. Saidane Lecture Notes Chapter 3 Stoichiometry Composition Stoichiometry is the quantitative analysis of substances. It deals with the mass relationships of elements in compounds. 1. A mole (mol) is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12. The mole is the SI unit for amount of substance. The number of particles in a mole has been experimentally determined as 6.022 x 10 23 , which is also known as Avogadro’s number. The mole is a counting unit, just as a dozen is. We all know that a dozen of pencils is the same as 12 pencils. Similarly, a chemist uses 1 mole of iron, which means 6.022 x 10 23 atoms of iron. 2. The molar mass is the mass of one mole of a pure substance. Molar mass is usually written in units of g/mol. The molar mass of an element is equal to the numerical atomic mass of the element in atomic mass unit, amu (which can be found in the periodic table). The molar mass of a compound is equal to the numerical sum of the average atomic masses of all the atoms present in the compound. 3. Converting moles to number of particles . To convert moles to particles or particles to moles, chemists use Avogadro’s number as follows: b) Number of moles = Number of particles / Avogadro’s number c) Number of particles = Number of moles x Avogadro’s number 4. Converting moles to mass . To convert moles to mass or mass to moles, chemists use the molar mass as a conversion factor. a) Mass of sample (grams) = number of moles x molar mass (in grams per mole) b) Number of moles = mass of sample / molar mass (grams per mole) 5. Determination of chemical formulas 1

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
b) Mass percentage composition . The percentage by mass of each element in a compound is known as the percentage composition of the compound. Mass  percentage of element  = (mass of element  in sample/total  mass of sample) x 100% c) Empirical formulas . An empirical formula consists of the symbols for the elements combined in a compound, with subscripts showing the smallest whole-
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 09/09/2011 for the course CHEM 200 taught by Professor Saidane during the Spring '11 term at Mesa CC.

### Page1 / 5

Chap3 - Chem 200 Dr Saidane Lecture Notes Chapter 3...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online