Unit 8Chemical Quantities
Chemistry IMr. Patel
SWHS
Topic Outline• MUST have a scientific calculator (not graphing)!!!• Review of Factor-label Method• The Mole: Particle to Mole Conversion (10.1)• Molar Mass: Gram to Mole Conversion (10.2)• Molar Volume: Volume to Mole Conversion (10.2)• Chemical Formula as a Conversion Factor (N/A)• Percent Composition (10.3)• Empirical and Molecular Formulas (10.3)• Solution Concentration (16.2)
PART I:CHEMICAL
CONVERSIONS
Conversion Factors
• Conversion factor – allows us to convert from one unit to another unit– Example: 1m = 1000mm, 1 dozen = 12 items
• We use the factor label method to convert
Old Unit
New UnitGiven
= Desired
Quantity
Remember:Multiply the topDivide the bottom
Measuring by Count
• A count refers to a grouping or a word representing a number– Pair (2), Dozen (12), Ream (500)
• A count is a conversion factor – can convert between a count unit and the number of items– Ex: 1 dozen egg is the same as 12 actual eggs
Ex: Convert 3 dozen apples to number of apples. Use the factor-label method.
1 dozen apples
12 apples3 dozen apples= 36 apples
Representative Particle
• Representative Particle – species present in a substance– Atoms (elements; ex: Fe atom)– Molecules (covalent compounds; ex: diatomics)– Ions (species with a charge; ex: Na1+)– Formula Units (ionic compounds; ex: NaCl)
The Mole
• The fundamental count in chemistry is the mole – SI unit for amount– Very similar to a dozen; represents a number– Abbreviation: mol– Contains an Avogadro’s Number of items– Avogadro’s Number = 6.02 x 1023 (memorize this!)
Conversion Factor 1: 1 mole = 6.02 x 1023 items
The Mole
• It is not appropriate to consider only one atom of an element or one formula unit of a compound– It is easier to group atoms using a large number– NOTE: 1 mole contains the same number of item…
but does not necessarily have the same mass!!!
The Mole
• Just like a dozen, the mole is a conversion factor!
• We can convert between the unit (mole) and the number of items
• Remember:– 1 mole X = 6.02 x 1023 X– You can substitute any item for the X
MOLES
PARTICLES(atoms, molecules,ions, formula units)
6.02x10231 mole
Ex: Convert 1 mole of Fe to number of Fe atoms. Use the factor-label method.
mol Fe
atoms Fe1 mol Fe = 6.02 x 1023 atoms Fe
Math: (1) x (6.02 x 1023) / (1) = 6.02 x 1023
6.02 x 1023
1
MOLES
PARTICLES(atoms, molecules, ions, formula units )
6.02x10231 mole
Ex: Convert 7.8 mol of clipped fingernails to number of clipped fingernails (CF).
Use the factor-label method.
mol CF
CF7.8 mol CF = 4.7 x 1024 CF
Math: (7.8) x (6.02 x 1023) / (1) = 4.7 x 1024
6.02 x 1023
1
MOLES
PARTICLES(atoms, molecules, ions, formula units )
6.02x10231 mole
Ex: Convert 2.1 x 109 atoms of Li to moles of Li. Use the factor-label method.
atoms Li
mol Li2.1 x 109 atom Li = 3.49 x 10-15 mol Li
Math: (2.1 x 109) x (1) / (6.02 x 1023) = 3.49 x 10-15
1
6.02 x 1023
MOLES
PARTICLES(atoms, molecules, ions, formula units )
6.02x10231 mole
Try the following conversions.
1) 1.75 molecules CHCl3 to mol CHCl3
2) 1.7 x 1015 mol of H+ to ions H+
3) 2.80 x 1024 atoms Si to mol Si
1) 2.91 x 10-24 mol CHCl3
2) 1.0 x 1039 ions H+
3) 4.65 mol Si
Mass of an Element
• On the periodic table, the mass of an element is given in units of atomic mass unit– 1/12 the mass of a carbon-12 atom
• In the laboratory, we do not use amu. We measure chemicals in grams.
• We can treat the amu as “grams per mole”.– Carbon: 12 amu 12 grams in 1 mole
Mole-Atom-Mass Relationship
Element Moles # of Atoms Mass Molar Mass
Al 1 mol 6.02 x 1023 26.98g 26.98 g/mol
N 1 mol 6.02 x 1023 14.01g 14.01 g/mol
Pb 1 mol 6.02 x 1023 207.2g 207.2 g/mol
S 1 mol 6.02 x 1023 32.07g 32.07 g/mol
Molar Mass (MM)
• The mass of one mole of an element of compound– Units: grams/mole (g/mol) – Can be called Molecular Weight (MW)– For element, MM comes directly from mass on PT– For compound, add the mass of each atom• CO2 = Add (mass of C) and 2 x (mass of O)
Conversion Factor 2: 1 mole = Mass in Grams (from PT)
Ex: What is the molar mass of iron?
55.85 g/mol Fe (from Periodic Table)
Ex: What is the molar mass of boron? 10.81 g/mol B (from Periodic Table)
Ex: What is the molar mass of H2O? H: 2 x 1.01g = 2.02g O: 1 x 16.00g = 16.00g 18.02 g/mol H2O
Ex: What is the molar mass of C6H12O6? C: 6 x 12.01g = 72.06g H: 12 x 1.01g = 12.12g O: 6 x 16.00g = 96.00g 180.18 g/mol C6H12O6
Molar Mass Conversions
• The molar mass is a conversion between the mole and grams.– Moles are used in theory– Grams are used in lab/practice
• Molar Mass allows: mole grams
• Using 2 conversion factors: particle grams– We must go through the mole!!!
GRAMS
MOLES
PARTICLES(atoms, molecules,ions, formula units )
MM=P.T.
6.02x10231 mole
1 mole
Ex: Convert 2.00 mol Carbon to grams C. Use the factor-label method.
mol C
12.012.0 mol C = 24.02 g C
Math: (2.0) x (12.01) / (1) = 24.02
This is Molar Massfrom periodic table1 mol C = 12.01 g C
g C
1
GRAMS
MOLES
PARTICLES(atoms, molecules, ions, formula units )
MM=P.T.
6.02x10231 mole
1 mole
Ex: Convert 9.73 mol Fe to grams Fe. Use the factor-label method.
mol Fe
55.859.73 mol Fe = 543 g Fe
Math: (9.73) x (55.85) / (1) = 543
This is Molar Massfrom periodic table
1 mol Fe = 55.85 g Fe
g Fe
1
GRAMS
MOLES
PARTICLES(atoms, molecules, ions, formula units )
MM=P.T.
6.02x10231 mole
1 mole
Ex: Convert 122 g Al to moles Al. Use the factor-label method.
g Al
1122 g Al = 4.52 mol Al
Math: (122) x (1) / (26.98) = 4.52
This is Molar Massfrom periodic table
1 mol Al = 26.98 g Al
mol Al
26.98
GRAMS
MOLES
PARTICLES(atoms, molecules, ions, formula units )
MM=P.T.
6.02x10231 mole
1 mole
Ex: Convert 413 g C6H12O6 to moles C6H12O6. Use the factor-label method.
g C6H12O6
1413 g C6H12O6 = 2.29 mol C6H12O6
Math: (413) x (1) / (180.18) = 2.29
This is Molar Massfrom periodic table
1 mol C6H12O6 = 180.18 g C6H12O6
mol C6H12O6
180.18
GRAMS
MOLES
PARTICLES(atoms, molecules, ions, formula units )
MM=P.T.
6.02x10231 mole
1 mole
Ex: Convert 26 g He to atoms He. Use the factor-label method.
g He
126 g He = 3.9 x 1024 atom He
Math: (26) x (1) / (4.00) x (6.02 x 1023) / (1) = 3.9 x 1024
This is Molar Massfrom periodic table
1 mol He = 4.00 g He
mol He
4.00
GRAMS
MOLES
PARTICLES(atoms, molecules, ions, formula units )
MM=P.T.
6.02x10231 mole
1 mole
mol He
6.02 x 1023 atom He
1
This is Avogadro’s Number 1 mol = 6.02 x 1023 atoms
Ex: Convert 345 g CO2 to molecule CO2. Use the factor-label method.
g CO2
1345 g CO2 = 4.72 x 1024 molecules CO2
Math: (345) x (1) / (44.01) x (6.02 x 1023) / (1) = 4.72 x 1024
This is Molar Massfrom periodic table
1 mol CO2 = 44.01 g CO2
mol CO2
44.01
GRAMS
MOLES
PARTICLES(atoms, molecules, ions, formula units )
MM=P.T.
6.02x10231 mole
1 mole
mol CO2
6.02 x 1023molec CO2
1
This is Avogadro’s Number 1 mol = 6.02 x 1023 atoms
Try the following.
1) What is the Molar Mass of Platinum (Pt)?
2) Convert: 652.7 g H2O to molecules H2O
1) 195 g/mol
2) 2.18 x 1025 molec. H2O
GRAMS
MOLES
PARTICLES(atoms, molecules, ions, formula units )
MM=P.T.
6.02x10231 mole
1 mole
Mole to Volume Conversion
• Gases are often measured in volume rather than grams
• A conversion is available between mole and volume only at specific conditions– Only for gases (ideal) – Standard Temperature and Pressure (STP)– 0oC and 1 atm
Conversion Factor 5: 1 mole = 22.4 L
LITERS
GRAMS
MOLES PARTICLESAvogadro Number
1 mole
1 mole Molar Mass
1 moleMolar
Volume (atoms, molecules, ions, formula units)
Ex: Convert 5 mol N2 to liters of N2. Use the factor-label method.
mol N2
L N25 mol N2 = 112 L N2
Math: (5) x (22.4) / (1) = 122
22.4
1
Ex: Convert 12.5 mol Ar to liters of Ar. Use the factor-label method.
mol Ar
L Ar12.5 mol Ar = 280 L Ar
Math: (12.5) x (22.4) / (1) = 280
22.4
1
Ex: Convert 69.8 L Ne to mol of Ne. Use the factor-label method.
L Ne
mol Ne69.8 L Ne= 3.17 mol Ne
Math: (69.8) x (1) / (22.4) = 3.17
1
22.4
Ex: Convert 49.87 g NH3 to liters NH3 at STP. Use the factor-label method.
g NH3
149.87 g NH3 = 65.56 L NH3
Math: (49.87) x (1) / (17.04) x (22.4) / (1) = 65.56
This is Molar Massfrom periodic table
1 mol NH3 = 17.04 g NH3
mol NH3
17.04 mol NH3
22.4 L NH3
1
This is Molar Volume at STP1 mol = 22.4 L
Try the following.
1) What is the volume (L) of 589 g N2O?
2) Convert: 3.01 x 1023 molecules of SO2 to liters.
1) 300. L
2) 11.2 L H2O
Chemical Formula
• The chemical formula can act as a conversion• Example: Fe2O3
– The subscripts tell us the number of atoms– 2 atoms of Fe and 3 atoms of O in one formula
unit of Fe2O3
– Assume we have 6.02 x 1023 formula units then…– Fe: 2 x (6.02 x 1023 atom Fe) = 2 mole Fe– O: 3 x (6.02 x 1023 atom O) = 3 mole O
in 1 mol Fe2O3
Chemical Formula
• The chemical formula is a mole ratio!!!• If we have 1 mole C6H12O6 then…
1 mol C6H12O6 : 6 mol C : 12 mol H : 6 mol OColon (:) means chemically equivalent
Conversion Factor 3: Chemical Formula (mole to mole)
Chemical Formula
• NOTE!!! When you are changing from one chemical to another, you must do this through the mole stage! – Mole X Mole Y
• This is strictly a mole to mole conversion.– NOT GRAMS!!!
Conversion Factor 3: Chemical Formula (mole to mole)
LITERS
GRAMS
MOLES PARTICLES6.02x1023
1 mole
1 mole Molar MassPeriodic Table
1 mole
22.4 L
ChemicalFormula
Ex: How many mol of N are in 1.00 mol NO3? Use the factor-label method.
mol NO3
11.00 mol NO3 = 1.00 mol N
Math: (1.00) x (1) / (1) = 2.00
This is Mole ratiofrom chemical formula
1 mol NO3 = 1 mol N
mol N
1
Ex: How many mol of P are in 1.00 mol P2O5? Use the factor-label method.
mol P2O5
21.00 mol P2O5 = 2.00 mol P
Math: (1.00) x (2) / (1) = 2.00
This is Mole Ratiofrom chemical formula
1 mol P2O5 = 2 mol P
mol P
1
Ex: How many mol of S are in 6.80 mol Pb2S3? Use the factor-label method.
mol Pb2S3
36.80 mol Pb2S3 = 20.4 mol S
Math: (1.00) x (2) / (1) = 2.00
This is Mole Ratiofrom chemical formula1 mol Pb2S3 = 3 mol S
mol S
1
Ex: How many grams of Cl are in 8.00 mol CHCl3? Use the factor-label method.
mol CHCl3
38.00 mol CHCl3 = 851 g Cl
Math: (8.00) x (3) / (1) x (35.45) / (1) = 851
This is Mole Ratiofrom chemical formula1 mol CHCl3 = 3 mol Cl
mol Cl
1 mol Cl
35.45 g Cl
1
This is Molar Massfrom periodic table1 mol Cl = 35.45 g Cl
Ex: How many grams of O are in 15 mol NO2? Use the factor-label method.
mol NO2
215 mol NO2 = 480 g O
Math: (15) x (2) / (1) x (16.00) / (1) = 480
This is Mole Ratiofrom chemical formula
1 mol NO2 = 2 mol O
mol O
1 mol O
16.00 g O
1
This is Molar Massfrom periodic table
1 mol O = 16.00 g CO2
Ex: How many grams of F are in 10.2 g XeF6? Use the factor-label method.
g XeF6
110.2 g XeF6 = 4.74 g F
Math: (10.2) x (1) / (245.29) x (6) / (1) x (19.00) / (1) = 4.74
This is Mole Ratiofrom chemical formula
1 mol XeF6 = 6 mol F
mol XeF6
245.29 mol XeF6
6 mol F
1
This is Molar Massfrom periodic table1 mol F = 19.00 g F
g F19.00
1 mol F
This is Molar Massfrom periodic table
1 mol XeF6 = 245.29 g XeF6
Try the following.
1) How many moles of acetate are in 2.00 mol Cr(C2H3O2)3?
2) Convert: 121 g NaOH to grams H.
1) 6 mol C2H3O21-
2) 3.03 g H
PART II:PERCENT
COMPOSITION
Percent Composition
• Describes the relative amounts of each element in a compound
• The percent composition is always the same - no matter the quantity of the sample
• Also called “Percent by Mass”
% X = mass of Xmass of sample x 100%
(X represents some element found in the sample)
Ex: When 13.60 g sample of MgO decomposes, it produces 8.20 g Mg and 5.40 g O.
What is the % composition?
% Mg = mass of Mg
mass of MgOx 100% = 8.20 g Mg
13.60 g MgOx 100%
% Mg = 60.3% Mg
% O = mass of O
mass of MgOx 100% = 5.40 g O
13.60 g MgOx 100%
% O = 39.7% O
Note: All percents should add up to about 100%
Ex: When 89.1 g H2O decomposes, it produces 9.89 g H.What is the % composition?
% H = mass of H
mass of H2Ox 100% = 9.89 g H
89.1 g H2Ox 100%
% H = 11.1% H
% O = mass of O
mass of H2Ox 100% = (13.60 – 9.89) g O
13.60 g H2Ox 100%
% O = 88.9% O
Total mass must equal the sum of its parts: mass H2O = mass H + mass O
Ex: What is the % composition of C3H8?
% C = 36.03 g C
44.11 g C3H8
x 100% = 81.68% C
% H = 8.08 g H
44.11 g C3H8
x 100% = 18.32% H
If we assume 1.00 mol of sample, then we can use periodic table for the mass!!!
• Mass of C:
• Mass of H:
• Mass of C3H8:
3 mol 12.01 g/mol
8 mol
44.11 g/mol C3H8
1.01 g/molx
x = 36.03 g C
= 8.08 g H
Ex: What is the % composition of (NH4)2S?
% N = 28.02 g N
68.17 g (NH4)2S x 100% = 41.10% N
% H = 8.08 g H
68.17 g (NH4)2S x 100% = 11.85% H
If we assume 1.00 mol of sample, then we can use periodic table for the mass!!!
• Mass of N:
• Mass of H:
• Mass of S:
• Mass of (NH4)2S:
2 mol 14.01 g/mol
8 mol
68.17 g/mol (NH4)2S
1.01 g/molx
x = 28.02 g N
= 8.08 g H
% S = 32.07 g S
68.17 g (NH4)2S x 100% = 47.04% S
1 mol 32.07 g/molx = 32.07 g S
Try the following.
1) What is the percent composition of NaOH?
2) What is the percent composition of CH4?
1) 57.5% Na40.0% O2.5% H
2) 75.0% C25.0% H
PART III:EMPIRICAL & MOLECULAR
FORMULAS
Empirical and Molecular Formulas
• Each compound has a basic ratio of elements• C6H6 , C8H8 , C10H10 multiples of CH• Empirical Formula (EF)– Lowest whole number ratio of elements– Ex: CH, CH2O
• Molecular Formula (MF)– Actual ratio of elements in a compound– Can be the same or whole # multiple of empirical– Ex: C6H6, C6H12O6
Empirical and Molecular Formulas
• To determine the empirical, you need % comp– Assume 100g of compound to make math easier
• To determine the molecular, you need1. Molar Mass of Compound (Mass Spec)2. Calculate the Ratio of MF to EF
Ratio = Molecular Molar MassEmpirical Molar Mass
Molecular Molar Mass is given in the problem.
Step to Solve EF/MF Problems
1. Convert: percent grams2. Convert: grams mole3. Divide all by the smallest amount of moles– If needed, multiply to get all whole numbers– Use ratios to determine Empirical Formula
4. Calculate the Ratio– Multiply: Ratio x Empirical Formula (Subscripts)– This will give the Molecular Formula
Ex: A molecule was determined to be 30.4% N and 69.6% O with a molar mass of 92.02 g/mol.
Determine the empirical & molecular formulas.
g N
130.4 g N= 2.17 mol N
mol N
14.01
g O
169.6 g O= 4.31 mol O
mol O
16.00
2.17
2.17
=
1 mol N
= 2 mol O
EmpiricalNO2
Ratio =92.02 g/mol46.01 g/mol 2= 2 x NO2
MolecularN2O4
Ex: 40.0% C, 6.67% H, 53.3% O; MM=90.00 g/mol. Determine the empirical & molecular formulas.
g C
140.0 g C= 3.33 mol C
mol C
12.01
g H
16.67 g H= 6.60 mol H
mol H
1.01
3.33
3.33
=
1 mol C
= 2 mol HEmpirical
CH2O
Ratio =90.00 g/mol30.03 g/mol 3= 3 x CH2O
MolecularC3H6O3
g O
153.3 g O= 3.33 mol O
mol O
16.003.33 = 1 mol O
Ex: A 150g sample consists of 74.25g C, 7.725g H, 43.35g N, and 24.75g O - molar mass of 195 g/mol. Determine the empirical and molecular formulas.
Answer:
Empirical: C4H5N2O
Molecular: C8H10N4O2
Try the following.
1) Find the EF & MF for:75.69 % C, 8.80% H, 15.51% O with MM = 206 g/mol
1) EF: C13H18O2
MF: C13H18O2
(Ibuprofen)
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