Module 7 Test Flashcards
What is Avogadro’s number equal to?
6.022 x 1023 units/mol
A mole is defined by?
The number of atoms in the exact amount of a unit
A unit can be what?
Atoms, molecules, ions
What do you use as a conversion factor when asked “how many molecules are in a ____ # of moles?
Avogadro’s number
Do you use Avogadro’s number directly to convert from grams?
No
What do you use to convert from grams if you don’t use Avogadro’s number?
The Mole Island chart
The molar mass of the compound is equal to what?
The molar mass of a compound is equal to the molar mass of the all the elements that it is composed of
What does the chemical formula tell you?
It tells you how many/much of each element is in the compound
What are the units for molar mass?
The units are g/mol
What is the formula unit?
The simplest ratio of cations to anions
What can molar mass be used for?
Can be used to convert the amount of a substance from moles to mass, or mass to moles
Why is percent composition useful for scientists?
Percent composition helps them determine the specific elements in a compound and the ratios of the elements in the compound
What is percent composition?
Percent composition is the percentage by mass of each element in a compound
If you know the composition of a compound, then what else can you do?
Then you can determine the percentage composition of the elements that make up the entire compound
What do you do first when finding percent composition?
You determine the mass of each element (by the amount of elements present x the atomic mass)
What is the second step for finding percent composition?
Calculate the molar mass of the compound (add all the masses of each element together)
What is the third step for finding percent composition?
Divide the mass of each element by the molar mass them multiply by 100 to get a percentage
What is the fourth and last step for finding percent composition?
Verify your answers and the percentages should add up to 100%
What is the empirical formula?
It is the simplest ratio of elements in a compound
It is okay if the empirical formula my not always be the right formula for the compound?
Yes
What is the empirical formula calculated from?
The percent composition
What is the first step in finding the empirical formula?
Convert the percent composition to mass in grams (assume in a 100 g sample)
What is the second step in finding the empirical formula?
You need to convert the mass to moles by using the atomic mass (divide each element by their own atomic mass)
What is the third step in finding the empirical formula?
Determine which element has the lowest number of moles
What is the fourth step in finding the empirical formula?
Set up ratios by dividing all each element by the least amount of moles
What do you need to do if each element does not have a full number after you divided by the least amount of moles?
You need to multiply all elements by a common number to get the smallest whole number ratio
If the number is/ends in .33 what do you multiply by?
Multiply by 3
If the number is/ends in .25 what do you multiply by?
Multiply by 4
If the number is/ends in .66 what do you multiply by?
Multiply by 3
If the number is/ends in .75 what do you multiply by?
Multiply by 4
If the number is/ends in.5 what do you multiply by?
Multiply by 2
What is the fifth step in finding the empirical formula?
Place the numbers from the ratios as the subscripts of that element in the empirical formula
What can empirical formulas be used to determine (in regards to the molecular formula)?
Can be used to determine the molecular formula if the molar mass of the compound is known
What is the first step in finding the molecular formula?
Make sure the empirical formula and the molar mass of the compound is given
What is the second step in finding the molecular formula?
Calculate the molar mass of the empirical formula
What is the third step in finding the molecular formula?
Divide the molar mass of the compound by the molar mass of the empirical formula
What is the fourth and final step in finding the molecular formula?
Multiply all of the subscripts by the ratio (answer) found in the previous step
