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Stoichiometry
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Molecular Mass
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Mole Conversion
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Perecent Composition
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Molarity
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Empirical Formulas
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Hydrates |
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Molecular Formulas
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Molecular
Mass
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| 1) Multiply the
mass of each element by the number of atoms |
| 2) Add |
| Examples: Li2F Li = 7 x 2 = 14 F = 19 x 1 = 19 33 amu |
Ga2Se3 Ga = 70 x 2 = 140 Se = 79 x 3 = 237 377 amu |
Ca3
(PO 4 )2 Ca = 40 x 3 = 120 P = 31 x 2 = 62 O = 16 x 8 = 128 310 amu |
| 1) ZnCl
2 |
2) Tin
Nitrate
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| Answers: |
Sn(NO3
) 4 |
| Zn = 65
x 1 = 65 Cl = 35.5 x 2 = 71 136 AMU |
Sn = 119 x 1
= 119 N = 14 x 4 = 56 O = 16 x 12 = 192 367 AMU |
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Mole Conversion
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| 1 mole = 6 .02 x 10 23 particles | 6.02 x 1023
particles is Avogadro's Number |
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1 mole of any substance
= The molecular mass in grams
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| Convert grams
to moles: |
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| Convert moles
to grams: |
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| Convert moles
to molecules: |
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Percent Composition
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| % = Part/Total
x 100 |
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Determine the % Composition
of each element in the following:
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| Examples: 1) Zn3P2 2) A 4.162 g sample of an iron & sulfur compound contains 2.236 g of iron. Answers: 1) Zn = 65 x 3 = 195 % = 195/257 x 100 = 75.9% P = 31 x 2 = 62 % = 62/257 x 100 = 24.1% 257 2) Fe = 2.236/4.162 x 100 = 53.7% [g of Sulfur = 4.162 - 2.236 = 1.926] S = 1.926/4.162 x 100 = 46.3% |
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Molarity
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| Molarity = moles
of solute/liters of solution
M = mol l Examples: |
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Empirical
Formulas
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| 1) Empirical
Formula also means the Simplest Formula. 2) The Empirical Formula may or may not be the molecular formula. Examples:
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Molecular Formula
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Empirical Formula
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H2O2
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HO
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H2O
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H2O
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Na2SO4
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Na2SO4
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N2H4
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NH2
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| To Solve Empirical
Formula Problems: 1) Change grams to moles 2) Divide by the smallest molar ratio 3) If the ratios are not close to whole # ratios, then multiply by a number that will make it a whole #. You must multiply all by # so you don't change the ratio. [Close means within about .15 of the whole #] |
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Hydrates
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| To Solve a Hydate Problem
it is worked like an Empirical Formula Problem Difference: 1) It is compounds and not elements 2) The ratio will always be 1 compound and a # of water molecules. [Example: How many ticks are on 1 dog] |
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Molecular
Formulas
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| To Solve Molecular
Formula Problems: 1) Determine the mass of the empirical formula 2) Divide the molecular mass/empirical formula mass = RATIO 3) Multiply the RATIO by the empirical formula to get the molecular formula |
| Example: Caffeine has an empirical formula of C 4H5N2O and a molecular mass of 194 amu. Find the molecular formula. Answer: 1) C = 12 x 4 = 48 2) 194/97 = 2 3) C4H5N 2O x 2 = C 8H10N 4O2 H = 1 x 5 = 5 N = 14 x 2 = 28 O = 16 x 1 = 16 97 |