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Chemical Formula and Nomenclature
ENGR. YVONNE LIGAYA F. MUSICO
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Writing Chemical Formula
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Chemical Formula
A representation of the composition of compounds. It contains:
1. The symbol and formula of elements or radicals
2. The number of atoms of each element present written as numerical subscript to the right symbol.
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Things to know in writing a Chemical Formula
1. The symbols of elements and radicals
2. Corresponding valence or oxidation numbers
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Terminologies
Valence - denotes the number of electrons in the outermost energy level.
- It also describes the combining power of an atom in a compound.
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Predicting Ionic Charges
Group 1AGroup 1A::Lose 1 electron to form 1+ ionsLose 1 electron to form 1+ ions
HH++ LiLi++ NaNa++ KK++
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Predicting Ionic Charges
Group 2AGroup 2A::Loses 2 electrons to form 2+ ionsLoses 2 electrons to form 2+ ions
BeBe2+2+ MgMg2+2+ CaCa2+2+ SrSr2+2+ BaBa2+2+
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Predicting Ionic ChargesGroup 3AGroup 3A:: Loses 3 Loses 3 electrons to form electrons to form 3+ ions3+ ions
BB3+3+ AlAl3+3+ GaGa3+3+
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Predicting Ionic ChargesGroup 4AGroup 4A:: Lose 4 Lose 4 electrons or gain electrons or gain 4 electrons?4 electrons?
Neither! Group 3A Neither! Group 3A elements rarely elements rarely form ions.form ions.
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Predicting Ionic ChargesGroup 5AGroup 5A:: Gains 3 Gains 3 electrons to form electrons to form 3- ions3- ions
NN3-3-
PP3-3-
AsAs3-3-
Nitride
Phosphide
Arsenide
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Predicting Ionic Charges
Group 6AGroup 6A:: Gains 2 Gains 2 electrons to form electrons to form 2- ions2- ions
OO2-2-
SS2-2-
SeSe2-2-
Oxide
Sulfide
Selenide
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Predicting Ionic ChargesGroup 7AGroup 7A:: Gains 1 Gains 1 electron to form electron to form 1- ions1- ions
FF1-1-
ClCl1-1-
BrBr1-1-Fluoride
Chloride
Bromide
II1-1- Iodide
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Predicting Ionic Charges
Group 8AGroup 8A:: Stable Stable Noble gases Noble gases do do notnot form ions! form ions!
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Predicting Ionic ChargesGroups 3 - Groups 3 - 1212::
Many transition elements Many transition elements have more than one possible oxidation have more than one possible oxidation state.state.Iron(II) = Fe2+ Iron(III) = Fe3+
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Predicting Ionic ChargesGroups 3 - Groups 3 - 1212::
Some transition elements Some transition elements have only one possible oxidation state.have only one possible oxidation state.
Zinc = Zn2+ Silver = Ag+
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Terminologies
Radicals – group of elements which act as one or single atom in chemical reaction and show definite valence.
Example:
Sulfate ion (SO4-2)
Ammonium ion (NH4+1)
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Rules in Writing Chemical Formula
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Rules in Writing Chemical Formula
RULE 1 (CRISS-CROSS RULE) Chemical compounds are electrically charged, the
total number of positive charge is equal to the number of negative charges; hence, the valence of positive entity (ion or radical) equals subscript of negative entity.
The sum of the positive and the negative valence should add up to zero.
The positive ion is written first followed by the negative.
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Example: Aluminum sulfide
1. Write the formulas for the cation and anion, including CHARGES!
AlAl3+3+ SS2-2-2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.
Not balanced!
22 33
AlAl SS22 33
The Chemical Formula
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Rules in Writing Chemical Formula
RULE 2
When valence number is 1, subscript is not written
Example:
Sodium Chloride - Na+1Cl-1 → NaCl
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Rules in Writing Chemical Formula
RULE 3
When the oxidation numbers of both elements are numerically equal but greater than 1, the subscript are not also written.
Example:
Calcium Oxide - Ca+2O-2 → CaO
Exception: Benzene - C6H6
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Example: Magnesium carbonate
1. Write the formulas for the cation and anion, including CHARGES!
MgMg2+2+ COCO332-2-2. Check to see if
charges are balanced.
They are balanced!
MgMgCOCO33
Chemical Formula
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Example: Aluminum phosphate
1. Write the formulas for the cation and anion, including CHARGES!
AlAl3+3+ POPO443-3-2. Check to see if charges are
balanced.
They ARE balanced!AlAlPOPO44
Chemical Formula
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Rules in Writing Chemical Formula
RULE 4 All radicals take more than one (the subscript is 2 or more)
must be enclosed in parenthesis ().
Example:
Ammonium Sulfate - NH4+1SO4-2 → (NH4)2SO4
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Example: Barium nitrate
1. Write the formulas for the cation and anion, including CHARGES!
BaBa2+2+ NONO33--
2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.
Not balanced!
( )( )22
BaBa NONO33( )( )22
Chemical Formula
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Example: Zinc hydroxide
1. Write the formulas for the cation and anion, including CHARGES!
ZnZn2+2+ OHOH--2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.
Not balanced!
( )( )
22
ZnZn OHOH22
( )( )
Chemical Formula
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Rules in Writing Chemical Formula
RULE 5 All subscript must be reduced to lowest terms (except for
molecular or covalent compounds)
Example:
Tin (IV) Oxide - Sn+4O2-2 → Sn2O4
→ SnO2
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Rules in Writing Chemical Formula
RULE 5 All subscript must be reduced to lowest terms (except for
molecular or covalent compounds)
Example:
Tin (IV) Oxide - Sn+4O2-2 → Sn2O4
→ SnO2
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Formulas of Binary Ionic Compounds Containing
Metals with Variable Valence Oxidation Number or Valence
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A. Stock System
Roman numeral indicated after the name of the metal represents the oxidation number (valence) of metal.
Example:
Tin (IV) Chloride - Sn+4Cl-1 → SnCl4
Tin (II) Chloride - Sn+2Cl-1 → SnCl2
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Example: Iron(III) chloride
1. Write the formulas for the cation and anion, including CHARGES!
FeFe3+3+ClCl--2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.
Not balanced!
33
FeFeClCl33
The Chemical Formula
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Example: Iron(II) chloride
1. Write the formulas for the cation and anion, including CHARGES!
FeFe2+2+ClCl--2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.
Not balanced!
22
FeFeClCl22
The Chemical Formula
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B. Classical or Conventional System
The ic and ous ending are added to the line stem or root word of the Latin name of the metal
The ic ending indicates higher oxidation number or valence
The ous ending indicates lower oxidation number or valence
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B. Classical or Conventional System
Example:
Stannic Chloride - Sn+4Cl-1 → SnCl4
Stannous Chloride - Sn+2Cl-1 → SnCl2
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Example: Ferric chloride
1. Write the formulas for the cation and anion, including CHARGES!
FeFe3+3+ClCl--2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.
Not balanced!
33
FeFeClCl33
The Chemical Formula
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Example: Ferrous chloride
1. Write the formulas for the cation and anion, including CHARGES!
FeFe2+2+ClCl--2. Check to see if charges are balanced.
3. Balance charges , if necessary, using subscripts. Use parentheses if you need more than one of a polyatomic ion.
Not balanced!
22
FeFeClCl22
The Chemical Formula
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Formulas of Binary Molecular or Covalent
Compounds (Containing 2 Non-metals)
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Rule 1
The Greek prefix mentioned before the name of the non-metals are written as subscripts of the non-metals.
Example:
Dinitrogen Pentoxide → N2O5
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Rule 2
If prefix is mono, it is not mentioned at the start of the name, only the second portion.
Example:
Phosphorous Petachloride → PCl5
Carbon Monoxide → CO
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Greek Prefixes Used in Naming Binary Molecular Compounds
Number of Atoms
Prefix Number of Atoms
Prefix
1 mono 6 hexa
2 di 7 hepta
3 tri 8 octa
4 tetra 9 nona
5 penta 10 deca
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Try These
Write the chemical formula of the followingAluminum and carbonateCopper II and sulfateSilver phosphateLead II chlorideAmmonium acetate
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Answers
Al2(CO3)3
CuSO4
Ag3PO4
PbCl2NH4C2H3O2
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Formulas of Acids
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A. Binary Acids
Solutions of compounds consisting of hydrogen and non-metal.
The name starts with hydro and the ending ic attached to the acid forming element followed by the word acid.
The formula H followed by the other non-metal
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A. Binary Acids
Example:
Hydrochloric Acid - H+Cl-1 → HCl
Hydrosulfuric Acid - H+S-2 → H2S
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B. Ternary Acids or Oxyacids
Those containing, H, O, and acid forming element.
The names do not have prefix hydro in their name terminate in ous or ic.
IC – contains more oxygen → salt or radical ends in ate
OUS - contains less oxygen → salt or radical ends in ite
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B. Ternary Acids or Oxyacids
The formula starts with H+1 followed by the radical
H+1 (NMO-) polyatomic ion
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B. Ternary Acids or Oxyacids
Example:
Nitric Acid - H+1 NO3-1
→ HNO3
Nitrous Acid - H+1 NO2-1
→ HNO2
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Nomenclature (Naming Compounds)
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Rules in Naming Compounds
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I. Binary Ionic Compounds
Containing 2 different elements Metal and Non-metal
The name ends in ide
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I. Binary Ionic Compounds
Example:
NaF – Sodium Fluoride
KI – Potassium Iodide
Name of metal + stem name of non metal + ide
A. Binary Ionic Compounds containing a metal with fixed valence (IA and IIA metals and Al, Zn, Ag)
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I. Binary Ionic Compounds
Example:
SnF4 – Tin (IV) Flouride
SnF2 – Tin (II) Flouride
Name of metal (valence in Roman numeral) + stem name of non metal + ide
B. Binary Ionic Compounds containing a metal with variable valence
1. Stock System – Roman numeral enclosed in the parenthesis is written immediately following the name of the metal to indicate the valence of the metal.
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I. Binary Ionic Compounds
Example:
SnF4 – Stannic Flouride
SnF2 – Stannous Flouride
B. Binary Ionic Compounds containing a metal with variable valence
2. Classical (Old) Method – name of metal is modified with ending ic for higher valence and ous for lower valence.
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I. Binary Ionic Compounds
Example:
NH4I – Ammonium Iodide
KCN – Potassium Cyanide
Ca(OH)2 – Calcium hydroxide
Exception using ide endings – Hydroxides (OH), cyanide (CN) and ammonium (NH4) compounds are named with
ide ending although they are not.
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II. Binary Molecular Compounds
Example:
P2O4 – Diphosphorous pentaoxide or pentoxide
PCl3 – Phosphorous trichloride
Greek prefix + name of the first non-metal + Greek prefix + stem of name of second non-metal + ide
(Containing 2 non-metals) Greek prefixes are used to indicate the number of atoms.
The prefix mono is dropped at the start of the name.
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III. Binary Molecular Compounds Containing Hydrogen listed as the First Element
Example:
HF – Hydrogen Fluoride
HCl – Hydrogen Chloride
Hydrogen + stem of name of non-metal + ide
They are named without using Greek numerical prefixes
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IV. Binary Acids
Example:
HCl (in water solution) – Hydrochloric acid
HF (in water solution) – Hydroflouric acid
Hydro + stem of name of non-metal + ic ending + acid
Water solutions of molecular compounds composed of hydrogen and another non-metal except oxygen.
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V. Ternary Acids (OXY acids)
Example:
H3PO4 – Phosphoric acid
H2PO3 – Phosphorous acid
Stem of name of non-metal + ic or ous ending + acid
Name end in ous or ic OUS – less oxygen IC – more oxygen
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V. Ternary Acids (OXY acids)
Example:
HClO – Hypochlourous acid
HClO2 – Chlorous acid
HClO3 – Chloric acid
HClO4 – Perchloric acid
When there are more than two oxy acids of the same element, the acid wherein the non-metal exhibits a lower valence than the ous acid uses the prefix hypo and suffix ous + the word acid
The acid wherein the non-metal exhibits a higher valence than the ic acid uses the prefix per and the suffix ic + acid
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VI. Ternary Compounds
Example:
Al(NO3)3 – Aluminum Nitrate
NaNO2 – Sodium Nitrite
The name ends in ite for less oxygen, ate for more oxygen
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Try These
Name the following compoundsK2S
CaCO3
MnCl4HI
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ANSWERS
K2S potassium sulfide
CaCO3 calcium carbonate
MnCl4 manganese IV chloride
HI hydroiodic acid or hydrogen iodide
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Try These
Name the following compoundsPCl3CCl4COCO2
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ANSWERS
PCl3 phosphorus trichloride
CCl4 carbon tetrachloride
CO carbon monoxideCO2 carbon dioxide
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Empirical and Molecular Formula
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Calculating Formula Mass
Calculate the formula mass of magnesium Calculate the formula mass of magnesium carbonate, MgCOcarbonate, MgCO33..
24.31 g + 12.01 g + 3(16.00 g) 24.31 g + 12.01 g + 3(16.00 g) ==
84.32 g84.32 g
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Calculating Percentage Composition
Calculate the percentage composition of Calculate the percentage composition of magnesium carbonate, MgCOmagnesium carbonate, MgCO33..
From previous slide:From previous slide:24.31 g + 12.01 g + 3(16.00 g) = 24.31 g + 12.01 g + 3(16.00 g) = 84.32 g84.32 g 24.31
100 28.83%84.32
Mg 12.01
100 14.24%84.32
C
48.00100 56.93%
84.32O
100.00
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Formulas
molecular formula = (empirical formula)n [n = integer]
molecular formula = C6H6 = (CH)6
empirical formula = CH
Empirical formula: the lowest whole number ratio of atoms in a compound.
Molecular formula: the true number of atoms of each element in the formula of a compound.
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Formulas (continued)
Formulas for Formulas for ionic compoundsionic compounds are are ALWAYSALWAYS empirical (lowest whole empirical (lowest whole number ratio).number ratio).Examples:Examples:
NaCl MgCl2 Al2(SO4)3 K2CO3
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Formulas (continued)
Formulas for Formulas for molecular compoundsmolecular compounds MIGHTMIGHT be empirical (lowest whole be empirical (lowest whole number ratio).number ratio).
Molecular:Molecular:
H2O
C6H12O6 C12H22O11
Empirical:
H2O
CH2O C12H22O11
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Empirical Formula Determination
1. Base calculation on 100 grams of compound.
2. Determine moles of each element in 100 grams of compound.
3. Divide each value of moles by the smallest of the values.
4. Multiply each number by an integer to obtain all whole numbers.
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Empirical Formula Determination
Adipic acid contains 49.32% C, 43.84% O, and 6.85% H by mass. What is the empirical formula of adipic acid?
49.32 14.107
12.01
g C mol Cmol C
g C
6.85 16.78
1.01
g H mol Hmol H
g H
43.84 12.74
16.00
g O mol Omol O
g O
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Empirical Formula Determination(part 2)
4.1071.50
2.74
mol C
mol O
6.782.47
2.74
mol H
mol O
2.741.00
2.74
mol O
mol O
Divide each value of moles by the smallest Divide each value of moles by the smallest of the values.of the values.
Carbon:Carbon:
HydrogenHydrogen::
OxygenOxygen::
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Empirical Formula Determination(part 3)
Multiply each number by an integer to Multiply each number by an integer to obtain all whole numbers.obtain all whole numbers.
Carbon: 1.50Carbon: 1.50 Hydrogen: 2.50Hydrogen: 2.50 Oxygen: 1.00Oxygen: 1.00x 2 x 2 x 2
33 55 22
Empirical formula: C3H5O2
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Finding the Molecular Formula
The empirical formula for adipic acid The empirical formula for adipic acid is Cis C33HH55OO22. The molecular mass of . The molecular mass of adipic acid is 146 g/mol. What is the adipic acid is 146 g/mol. What is the molecular formula of adipic acid?molecular formula of adipic acid?
1. Find the formula mass of 1. Find the formula mass of CC33HH55OO22
3(12.01 g) + 5(1.01) + 2(16.00) = 3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g73.08 g
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Finding the Molecular Formula
The empirical formula for adipic acid The empirical formula for adipic acid is Cis C33HH55OO22. The molecular mass of . The molecular mass of adipic acid is 146 g/mol. What is the adipic acid is 146 g/mol. What is the molecular formula of adipic acid?molecular formula of adipic acid?
3(12.01 g) + 5(1.01) + 2(16.00) = 3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g73.08 g
2. Divide the molecular mass by 2. Divide the molecular mass by the mass given by the emipirical the mass given by the emipirical formula.formula.
1462
73
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Finding the Molecular Formula
The empirical formula for adipic acid The empirical formula for adipic acid is Cis C33HH55OO22. The molecular mass of . The molecular mass of adipic acid is 146 g/mol. What is the adipic acid is 146 g/mol. What is the molecular formula of adipic acid?molecular formula of adipic acid?
3(12.01 g) + 5(1.01) + 2(16.00) = 3(12.01 g) + 5(1.01) + 2(16.00) = 73.08 g73.08 g146
273
3. Multiply the empirical formula by 3. Multiply the empirical formula by this number to get the molecular this number to get the molecular formula.formula.
(C(C33HH55OO22) x 2 ) x 2 ==
CC66HH1010OO44
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Question or Comments?