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by: Freya Kniaz

10

1

1

# CHM1040 Week 7 CHM1040

Freya Kniaz
WSU

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These notes cover chapter eight.
COURSE
Chemistry Skills and Reasoning
PROF.
Dr. Andrea Matti
TYPE
Class Notes
PAGES
1
WORDS
CONCEPTS
chemical, composition, CHM1040, Matti, WSU
KARMA
25 ?

## Popular in Chemistry

This 1 page Class Notes was uploaded by Freya Kniaz on Friday October 7, 2016. The Class Notes belongs to CHM1040 at Wayne State University taught by Dr. Andrea Matti in Fall 2016. Since its upload, it has received 10 views. For similar materials see Chemistry Skills and Reasoning in Chemistry at Wayne State University.

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Date Created: 10/07/16
Chemistry Skills and Reasoning 1 Week Seven Notes Chapter Eight: Chemical Composition - Objects do not need to have identical masses to be counted by weighing, all we need to know is the average mass of the objects - To count the atoms in a sample of a given element by weighing we must know the mass of the sample and the average mass for that element - Atoms have very tiny masses so scientists created a unit to avoid using very small numbers - The average atomic mass for an element is the weighted average of the masses of all the isotopes of an element - Average Atomic Mass for Carbon: even though natural carbon does not contain a single atom with mass 12.01, for our purposes, we can treat carbon as though it is composed of only one type of atom with a mass of 12.01 - This enables us to count atoms of natural carbon by weighing a sample of carbon - The mole: the number equal to the number of carbon atoms in 12.01 grams of carbon - 1 mole of anything = 6.022e23 - grams —> moles: divide by molar mass; moles —> atoms: multiply by 6.022e23 - and vice versa (except switch multiply and divide) - Moles of a compound = mass of sample (g)/molar mass of compound (g/mol) - Mass of a sample (g) = (moles of sample)(molar mass of compound) - Mass percent of an element = mass of the element present in one mole of compound/mass of one mole of compound - Empirical formulas: formula of a compound that is the simplest whole number ration of the atoms present in the compound, it can be found from the percent composition of the compound. - Steps for determine the Empirical Formula of a Compound: - Obtain the mass of each element present (in grams) - Determine the number of moles of each type of atom present - Divide the number of moles of each element by the smallest number of moles to convert the smallest number to one. - If all the numbers so obtained are whole numbers, these are the subscripts in the empirical formula - If one or more of these numbers are not whole numbers, go to the next step - Multiply the numbers you derived in step three by the smallest integer that will convert all of them to whole numbers - This set of whole numbers represents the subscripts in the empirical formula - The molecular formula is the exact formula of the molecules present in a substance, it is always an integer multiple of the empirical formula This is a lot of math, make sure to do the practice problems in the lecture slides.

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