laws of chemical combination + stoichiometry
DESCRIPTION
TRANSCRIPT
![Page 1: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/1.jpg)
Laws of Chemical Combination
Chem1 SY 10-11
-kaaferrer
![Page 2: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/2.jpg)
What makes compounds different?
![Page 3: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/3.jpg)
Law of Constant Composition 1799 Joseph Proust
a chemical compound contains the same elements in exactly the same proportions (ratios) by mass regardless of the size of the sample or source of the compound
![Page 4: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/4.jpg)
For example, water always consists of oxygen and hydrogen atoms, and it is always 89 percent oxygen by mass and 11 percent hydrogen by mass
![Page 5: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/5.jpg)
Does mass change during a chemical reaction?
![Page 6: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/6.jpg)
Law of Conservation of Mass Lavoisier heated a measured amount of
mercury to form the red oxide of mercury. He measured the amount of oxygen removed from the jar and the amount of red oxide formed. When the reaction was reversed, he found the original amounts of mercury and oxygen.
![Page 7: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/7.jpg)
Law of Conservation of Mass 1744 Antoine Lavoisier matter can not be created or destroyed in
ordinary chemical or physical changes. the mass of the reactants (starting materials)
equals the mass of the products
2Mg (s) + O2 (g) → 2MgO (s)
48.6 g 32.0 g 80.6 g
![Page 8: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/8.jpg)
Example
10 grams of CaCO3 on heating gave 4.4g of CO2 and 5.6 of CaO. Show that these observations are in agreement with the law of conservation
![Page 9: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/9.jpg)
Law of Multiple Proportions 1803 John Dalton
States that when two elements combine to form more than one compound, the masses of one element which combine with a fixed mass of the other element are in ratios of small whole numbers
![Page 10: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/10.jpg)
Example: Carbon monoxide (CO): 12 parts by mass of
carbon combines with 16 parts by mass of oxygen.
Carbon dioxide (CO2): 12 parts by mass of carbon combines with 32 parts by mass of oxygen.
Ratio of the masses of oxygen that combines with a fixed mass of carbon (12 parts) 16: 32 or 1: 2
![Page 11: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/11.jpg)
Water has an oxygen-to-hydrogen mass ratio of 7.9:1.
Hydrogen peroxide, another compound consisting of oxygen and hydrogen, has an oxygen-to-hydrogen mass ratio of 15.8:1.
Ratio of the masses of oxygen that combines with a fixed mass of hydrogen is 7.9: 15.8 or 1: 2
![Page 12: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/12.jpg)
Chemical Formula Relationships
![Page 13: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/13.jpg)
How many number of ATOMS? Ca(NO)3
NaNO3
Ba(IO3 )2
![Page 14: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/14.jpg)
Molecular and Formula Weights The sum of all the atomic weights of each
atom in its chemical formula.
Formula mass = ∑ atomic masses in the formula unit
![Page 15: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/15.jpg)
SEATWORK!
![Page 16: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/16.jpg)
Percentage Composition from Formulas Percentage by mass contributed by each
element in the substance.
%element= (# of atoms of that element)(atomic mass of that element)
------------------------------------------------------------------------
formula mass of the compound
![Page 17: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/17.jpg)
Stoichiometry
The quantitative relationships between the substances involved in a chemical reaction, established by the equation for the reaction
![Page 18: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/18.jpg)
Terminologies
ATOM◦ Smallest particle of an element
MOLECULE◦ Smallest unit particle of a pure substance
ION◦ An atom or group of bonded atoms with electrical charge
because of an excess or deficiency of electrons
ELEMENT◦ Pure substance; CANNOT be broken down into 2 or more
pure substances by chemical means
COMPOUND◦ Pure substance; CAN be broken down into 2 or more pure
substances by chemical means
![Page 19: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/19.jpg)
Atomic Mass
Atomic Mass = used to numerically indicate the mass of an atom in its ground state, it is expressed in the non SI unit of u
u = refers to unified atomic mass unit (formerly known as atomic mass unit or amu)
1 amu = 1/12 the mass of carbon-12 atom, therefore the mass of C-12 atom is made EQUAL to 12
amu Carbon-12 atom is an isotope of carbon
1 amu = 1.66 x 10-24 g
![Page 20: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/20.jpg)
Atomic Mass
Mass of e = 1/1800 of mass of p and n so it is negligible making the equation
Atomic mass of 12C = mass of p + mass of n
subatomic particle
charge Mass (amu)
Neutron None 1.0087 ≈ 1
Proton Positive 1.0073 ≈ 1
Electron Negative 5.486 x 10-4 ≈ 0
![Page 21: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/21.jpg)
Atomic Mass vs. Average Atomic Mass
Atomic Mass Average Atomic Mass
For carbon it is 12 u not 12.01 u
*Used to relate the fact that the numerical value assigned to each element in the periodic table reflects the average abundances of the atoms that compose a naturally occurring element
*Related to isotopes
*For carbon it is 12.01 u
*Chemists often will use the term “atomic mass” when they are actually referring to average atomic mass of an atom.
![Page 22: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/22.jpg)
Average Atomic Mass (calculation)
Solve for the Average Atomic Mass of the element Boron
Average atomic mass = ∑ (mass x percent abundance)
Where ∑ means “sum”
Isotope Mass (u) Percent Abundance
11B 11.009305 80.110B 10.012937 19.9
![Page 23: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/23.jpg)
Relative Atomic Mass & Atomic Weight
Have different meaning from atomic mass but synonymous with each other, although of different historical origins
Relative Atomic Mass “Ratio” of the average mass of the atom to the
unified atomic mass; dimensionless
Atomic Weight The name Dalton used in the early 19th century to
numerically describe the weight of atoms relative to each other
![Page 24: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/24.jpg)
The average mass of the molecules of a binary compound (non metal-non metal)
Unit: u
Ex.: The molecular mass of carbon dioxide gas, CO2 is 28.01 u.
Molecular Mass
![Page 25: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/25.jpg)
The average mass of the molecules of an ionic compound (metal-non metal)
Unit: u
Ex.: The formula mass of barium chloride, BaCl2 is 208.2 u.
Formula Mass
![Page 26: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/26.jpg)
The Mole Concept
Used to describe the number of particles (atoms, molecules, etc.) that make up sample of matter
“One mole is the amount of any substance that contains the same number of units as the number of atoms in exactly 12 grams of carbon-12.”
1 mol of any substance = 6.02 x 1023 units of that substance,
where 6.02 x 1023 Avogadro’s Number, N
![Page 27: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/27.jpg)
Molar Mass
Mass of 1 mole of substance SI unit: g/mol Provides a bridge between mass and amount
![Page 28: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/28.jpg)
Conversion
GRAMS MOLESFORMULA
UNITS
Use molar mass
Use N
![Page 29: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/29.jpg)
Atomic mass Molar mass
Unit: g/mol
Unit:amu; u
Atomic level
Macroscopic level
Numerically
equivalent
Comparison of Atomic and Molar Mass
Total massof p+ and no
Mass of 1 mole
![Page 30: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/30.jpg)
Empirical Formula and Molecular Formula
![Page 31: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/31.jpg)
Shows the relative number of atom of each element in the compound
EMPIRICAL FORMULA
![Page 32: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/32.jpg)
A compound is found out to contain 20.0% carbon, 2.2% hydrogen, and 77.8% chlorine. Determine EF of the compound.
Problem 1
![Page 33: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/33.jpg)
Shows the actual number of atom of each element in the compound
MOLECULAR FORMULA
![Page 34: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/34.jpg)
MF = (EF)nwhere n is an integer
therefore,
n = MMF
MEFwhere M is molar mass
Relationship between EF & MF
![Page 35: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/35.jpg)
A compound with the empirical formula C2H5 has a molar mass of 58.12 g/mol. Find the molecular formula of the compound.
Problem 2
![Page 36: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/36.jpg)
The molar mass of a compound that is 54.6% carbon, 9.0% hydrogen and 36.4% oxygen is 88 g/mol. Find MF of the compound.
Problem 3
![Page 37: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/37.jpg)
The Mole
One mole is the amount of any substance that contains the same number of units as the number of atoms in exactly 12 grams of carbon-12.
6.02 x 1023 Avogadro’s Number
![Page 38: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/38.jpg)
MOLAR Mass The mass in grams of one (1) mole of a
substance. g/mol, grams per mole
The molar mass of any substance in grams per mole is always numerically equal to the atomic, formula, or molecular mass of the substance in amu.
![Page 39: Laws of Chemical Combination + Stoichiometry](https://reader035.vdocuments.us/reader035/viewer/2022081412/5452cbc2af7959904c8b48f3/html5/thumbnails/39.jpg)
moleatom
s gramFormula weight
Avogadro’s
number