Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia...
-
date post
22-Dec-2015 -
Category
Documents
-
view
218 -
download
0
Transcript of Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia...
![Page 1: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/1.jpg)
Quantitative Composition of Compounds
Preparation for College ChemistryLuis AvilaColumbia UniversityDepartment of Chemistry
![Page 2: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/2.jpg)
Depending upon Bonding type
Compounds
Ionic (Coulombic forces)
Molecular(Covalent bonds)
MoleculesCations Anions
![Page 3: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/3.jpg)
Careful experimentation lead Proust to demonstrate
H2(g) + Cl2(g)2HCl(g)
H2SO4(l) + 2NaCl(s) 2HCl(g) + Na2SO4(aq)
Proportions by mass of elementsin a compound VARY OVER A CERTAIN RANGE
Proportions by mass of elements in a compound ARE FIXED. VARIATIONS ARE DUE TO IMPURITIES.
Claude Berthollet:
Joseph Proust:
THE LAW OF DEFINITE PROPORTIONS (CONSTANT COMPOSITION):
“The proportions by mass of the elements in a compound ARE FIXED, and do not depend on its mode of preparation.”
![Page 4: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/4.jpg)
Wüstite, an iron oxide whose simplest formula is FeO,
with 77.73%Fe.
All gaseous compounds OBEY THE LAW OF DEFINITE PROPORTIONS.
Certain SOLIDS are exceptions of the Law of Constant Composition: NON STOICHIOMETRIC COMPOUNDS (BERTHOLLIDES)
Its composition truly ranges from Fe0.95O (76.8% Fe) to
Fe0.85O (74.8% Fe) depending of the method of preparation.
![Page 5: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/5.jpg)
The composition of a compound is shown by its CHEMICAL FORMULA.
C + O2 A
C + O2 B
CHEMICAL ANALYSIS:
If A is CO then B = CO2
For a FIXED mass of C the ratio of O in A and B is:
If A is CO2 then B is C2O4
Let’s take the elements C and O:
(1.000 g C and 1.333 g O)
(1.000 g C and 2.667 g O)
1.333 : 2.667 or 1: 2
We are unable to say which one is the right formula, but we know the ratio C : O
is the QUOTIENT OF INTEGERS.
![Page 6: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/6.jpg)
Molecules
Types of Formulas
Composition
![Page 7: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/7.jpg)
Composition
Usually made up of nonmetal atoms
Held together by covalent bonds
![Page 8: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/8.jpg)
Types of Formulas
Empirical
Molecular
Structural
CH3
C2H6
C
H
H
CH
H
H
H
![Page 9: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/9.jpg)
Atomic and Formula Masses
Meaning of Atomic Masses
Masses of Individual Atoms
Formula Mass
![Page 10: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/10.jpg)
Masses of Individual Atoms
The atomic masses of H, Cl, and Ni are
H = 1.008 amu
Cl = 35.45 amu
Ni = 58.69 amu
Therefore 1.008g H, 35.45g Cl, and 58.69g Ni all have the same number of atoms: NA
NA = Avogadro’s number = 6.022 x 1023
![Page 11: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/11.jpg)
Meaning of Atomic Masses
• Give relative masses of atoms based on C–12 scale • The Most common isotope of carbon is assigned an atomic mass of 12 amu.• The amu is defined as 1/12 of the mass of one neutral carbon atom
1amu =1dalton=112
12g612C
mol612C
×1mol6
12C6.0221×1023atoms6
12C
⎛
⎝ ⎜ ⎞
⎠ ⎟=1.66054 ×10−24 g/ atom6
12C
![Page 12: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/12.jpg)
Mass of H atom:
1 H atom x = 1.674 x 10–24g
Number of atoms in one gram of nickel:
1.00g Ni x = 1.026 x 1022 atoms
Masses of Individual Atoms
1.008g H6.022 x 1023 atoms
6.022 x 1023 atoms Ni58.69g Ni
![Page 13: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/13.jpg)
Formula Mass
The formula for water is H2O. What is its molar mass?
2H = 2(1.008g/mol) = 2.016 g/mol1O = 1(16.00 g/mol) = 16.00 g/mol
18.02 g/mol = molar mass of water
![Page 14: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/14.jpg)
The Mole
Meaning
Molar Mass
Mole - Mass Conversions
![Page 15: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/15.jpg)
Meaning 1 mol = 6.022 x 1023 items
Cl2 HCl H Cl
6.022 x 1023
molecules
6.022 x 1023
molecules
6.022 x 1023
atoms
6.022 x 1023
atoms
70.90 g Cl2 36.46g HCl 1.008g H 35.45g Cl
1 mol Cl2 1 mol HCl 1 at-gr H 1 at-gr Cl
1 molar mass Cl2 1 molar mass
HCl
1 molar mass
H
1 molar mass Cl
![Page 16: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/16.jpg)
Molar Mass
Generalizing from the previous examples, the molar mass, M, is numerically equal to the formula mass
formula mass molar massCaCl2 110.98 amu 110.98 g/mol
C6H12O6 180.18 amu 180.18 g/mol
![Page 17: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/17.jpg)
Mole-Mass Conversions
110.98g CaCl2
1 mol CaCl2
mass = 13.2 mol CaCl2 x = 1.47 x 103g
Calculate mass in grams of 13.2 mol CaCl2
Calculate number of moles in 16.4g C6H12O6
1 mol C6H12O6
180.18g C6H12O6moles = 16.4g C6H12O6 x = 9.10 x 10-2mol
![Page 18: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/18.jpg)
Calculating Composition
% Composition from Formula
Empirical Formula from % Composition
Molecular Formula from Empirical Formula
% Composition from Experimental Data
![Page 19: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/19.jpg)
Mass % from Formula
Percent composition of potassium dichromate, K2Cr2O7?
molar mass K2Cr2O7 = (78.20 + 104.00 + 112.00)g/mol = 294.20g/mol
78.20294.20
%K = x 100 = 26.58%
112.00294.20
%O = x 100 = 38.07%
Note that percents must add to 100
104.00294.20
%Cr = x 100 = 35.35%
![Page 20: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/20.jpg)
% Composition from Experimental Data
Calculate mass of compound formed
Divide mass of each element by total mass of compound and multiply by 100.
Aluminum chloride is formed by reacting 13.43 g aluminum with 53.18 g chlorine. What is the % composition of the compound?
13.43 gAl +53.18 gCl=66.61 gAlCl3
13.43 gAl
66.61 g AlCl 3
⎛
⎝ ⎜
⎞
⎠ ⎟×100 =20.16% Al
53.18 gCl66.61 g AlCl3
⎛
⎝ ⎜
⎞
⎠ ⎟×100 =79.84%Cl
![Page 21: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/21.jpg)
Empirical Formula from % Composition
Empirical formula of compound containing26.6% K, 35.4% Cr, 38.0% O
moles K = 26.6g x = 0.680 mol K1 mol39.10g
moles Cr = 35.4g x = 0.681 mol Cr1 mol52.00g
work with 100g sample:26.6 g K, 35.4 g Cr, 38.0 g O
![Page 22: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/22.jpg)
Empirical Formula from % Composition
moles O = 38.0g x = 2.38 mol O1 mol16.00g
Note that 2.38 / 0.680 = 3.50 = 7 / 2
Empirical formula: K2Cr2O7
Potassium Dichromate?
![Page 23: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/23.jpg)
Empirical Formula from Analytical Data
A sample of acetic acid (C, H, O atoms) weighing 1.000 g burns to give 1.446 g CO2 and 0.6001 g H2O. Empirical formula?
Solution:
find mass of C in sample (from CO2)
find mass of H in sample (from H2O)
find mass of O by difference
![Page 24: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/24.jpg)
Empirical Formula from Analytical Data
2.02g H18.02g H2O
mass H = 0.6001g H2O x = 0.0673g H
mass O = 1.00g – 0.394g – 0.067g = 0.539g O
mass C : 1.446 gCO2 ×1 mol CO244.01 g CO2
×1molC
1 mol CO2×12.01gC1molC
=0.394gC
![Page 25: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/25.jpg)
Simplest Formula from Analytical Data
1 mol C12.01g C
moles C = 0.394g C x = 0.0328 mol C
1 mol H1.008g H
moles H = 0.0673g H x = 0.0668 mol H
1 mol O16.00g O
moles O = 0.533g O x = 0.0333 mol O
Empirical formula is CH2O
![Page 26: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/26.jpg)
Molecular Formula from Empirical Formula
Must know molar mass
n = molar mass
mass of empirical formula= number of empirical formula units
Calculate empirical and molecular formulas of a compound that contains80%C, 20%H, and has a molar mass of 30.00 g/mol.
C : 80.0 gC×1 mol C atoms
12.01 g
⎛ ⎝ ⎜ ⎞
⎠ ⎟ =6.661 mol C
![Page 27: Quantitative Composition of Compounds Preparation for College Chemistry Luis Avila Columbia University Department of Chemistry.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649d805503460f94a65051/html5/thumbnails/27.jpg)
Molecular Formula from Empirical Formula
H : 20.0 gH×1 mol H atoms
1.008 g
⎛ ⎝ ⎜ ⎞
⎠ ⎟ =19.84 mol H
Divide each value by smaller number of moles
H : 19.84
6.661=2.97 ~3.00 C:
6.6616.661
=1.00
Empirical Formula: CH3
n = molar mass
mass of empirical formula=
30.0g15.01g
~2
Molecular Formula: (CH3)2 = C2 H 6