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steps to molecular/formula mass
- 1) dissect the compound into respective elements
- 2) look up each elements mass on periodic table
- 3) multiply each element's mass by the amount of that element in the compound
- 4) add
Becomes C 3(12.011)+ H 7(1.008) +Br (79.904)=122.993 formula/molecular mass
steps to convert Mass to Moles
- *convert mass (in g) by the molar/formula mass
- 1) convert mass to grams
- 2) find the molar mass of the element/compound
- 3) divide the given mass in grams by the molar mass (g/mol)
What is Avogadro's number used for?
to find the number of molecules in a mole of a substance, expressed in grams, is exactly equal to the substance's mean molecular weight.
steps to convert moles to atoms/molecules
- multiply the given moles by avogadro's number
- 1) convert the given to moles
- 2) multiply the amount of moles by avogadro's #
how many atoms of A and B in 2 molecules of A2B
4 molecules of A and 2 molecules of B
how do you find the percent composition of a compound?
Mass% of element X in Molecyel Y= (mass X in 1 mole of Y/Mollar Mass of Y)x 100
- 1) find the mass of the intended element in 1 mole of the molecule formula.
- 2) add up all the molar mass of each each element by their respective amount
- 3) find the mass percent of oxygen
formula for the mass percent of an element
Mass% of an element / the molar mass of the entire molecular formula
what types of digits are significant
- 1) all non-zero #'s
- 2) 0's at the end of a # & to the right of the decimal point are significant
- 3) 0's between significant digits are significant
- 4) exact conversions and counted # are exact & significant.
- 5) 0's to the right of a # & left of the implied decimal point are not significant, but are with a decimal point.
- 6) 0's to the left of a nonzero # are Not significant
- if the # to be dropped is 5, with no other numbers following it, the number to the left is changed as follows:
- odd= increased by 1
- even= decreased by 1
rule of significant digits during multiplication/dividion
the product must have no more significant digits than the figure than the value in the operation with the least significant figures
significant figures in addition and subtraction
the answer can only be as many decimal places as the with the least digits after the decimal place
rule for significant figures when combining multiplication and division
find the significant figures that must be in the numerator (number ater= top), and denominator (bottom).