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24 terms

Chemistry chapter 3

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molecular mass
sum of the masses of the atoms making up the molecule (units amu) (molecular compounds only!)
Molecular mass H₂O
2+15.9994= 18
Molecular mass C₂H₄O₂
12*2+4+16*2= 24+4+32=60
formula mass
is the sum of atomic masses of all atoms in a formula unit of any compound, molecular or ionic (units amu)
Formula Mass NaCl
22.9+35.4=58.3
MgCO₃
24.3+12+16*3=84
Define mole
substance is the quantity of a given substance that contains as many molecules or formula units as the number of atoms in exactly 12g of C-12.
Like 12 eggs in a dozen
Avogadro's Number
6.022 x 1023 molecules) is the numerical value assigned to the unit, 1 mole
Calculate mass with moles
Formula mass/6.02 x 10²³
How many Li₂SO₄ units are in 3 moles of Li₂SO₄?
7+32+16*4= 103
3moles x 6.02 x 10²³ x 1/1= 1.81 x 10²⁴
How many Li atoms are in 3 moles of Li₂SO₄?
3 moles x 6.02 x 10²³ x 2/1= 3.61 x 10²⁴
How many S atoms in 3 moles of Li₂SO₄?
3 moles x 6.02 x 10²³ x 1/1= 1.81 x 10²⁴
How many O atoms in 3 moles of Li₂SO₄?
3 moles x 6.02 x 10²³ x 4/1= 7.22 x 10²⁴
Molar Mass
mass of one mole of that substance
mass/avogadros #
What is mass in grams of Ca?
40.1 g/mol CA divided by /6.02 x 10²³= 6.66 x 10⁻²³
moles to grams
mass/avogardo
Mole calculations: consider ethanol with a molar mass of 46.1g/mol. Prepare acetic acid from 10.0 g of ethanol
10.0g x 1/ 46.1 = .217g/mol
grams divided by mass
grams to moles
Analysis of a solution shows it contains 0.909 mol of H2O2 in 1.00L of solution. What is the mass of hydrogen peroxide in this volume of solution?
molar mass of H2O2 is 34.02 g/mol
.909 mol * 34.02 g H₂O₂/1 ml H₂O₂= 30.92g
mole multiplied by mass
moles to grams
HCN is a volatile colorless liquid. The compound is highly poisonous . How many molecules are there in 56mg HCN, the average toxic does?
Convert
56mg -->grams x 1000 56000
56000/mass-->56000/27.02
multiply by avogardo
56000/27.02 * 6.022 x 10²³
1.2 x 10²³
Percent Composition
Mass % A = mass A in the whole X 100%
whole mass
The molecular mass of NH4NO3 = 80.05; its molar mass = 80.05g/mol.
Hence
N= 28.02/ total
28.02/80.05= .35 x 100%= 35%
How many grams of nitrogen are there in a fertilizer containing 48.5g of NH4NO3?
NH4NO3 is 35.0% N
(Fraction N = 0.350
48.5 x .35= 16.975= 17.0 g
Empirical Formula
Determined from data about percent composition, tells only the smallest whole number ratio of atoms in a compound.
Molecular Formula
n= molecular mass/empirical formula mass
C₂H₄O= 44amu
divide by actual mass, 44 amu = 1