Unit 8 Chemical Quantities Chemistry I Mr. 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 top Divide 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: Na 1+ ) – 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 (memorize this!) Conversion Factor 1: 1 mole = 6.02 x 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 X – You can substitute any item for the X

MOLES PARTICLES (atoms, molecules, ions, formula units) 6.02x mole

Ex: Convert 1 mole of Fe to number of Fe atoms. Use the factor-label method. mol Fe atoms Fe 1 mol Fe = 6.02 x atoms Fe Math: (1) x (6.02 x ) / (1) = 6.02 x x MOLES PARTICLES (atoms, molecules, ions, formula units ) 6.02x mole

Ex: Convert 7.8 mol of clipped fingernails to number of clipped fingernails (CF). Use the factor-label method. mol CF CF 7.8 mol CF = 4.7 x CF Math: (7.8) x (6.02 x ) / (1) = 4.7 x x MOLES PARTICLES (atoms, molecules, ions, formula units ) 6.02x mole

Ex: Convert 2.1 x 10 9 atoms of Li to moles of Li. Use the factor-label method. atoms Li mol Li 2.1 x 10 9 atom Li = 3.49 x mol Li Math: (2.1 x 10 9 ) x (1) / (6.02 x ) = 3.49 x x MOLES PARTICLES (atoms, molecules, ions, formula units ) 6.02x mole

Try the following conversions. 1)1.75 molecules CHCl 3 to mol CHCl 3 2)1.7 x mol of H + to ions H + 3)2.80 x atoms Si to mol Si 1)2.91 x mol CHCl 3 2)1.0 x 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 ElementMoles# of AtomsMassMolar Mass Al1 mol6.02 x g26.98 g/mol N1 mol6.02 x g14.01 g/mol Pb1 mol6.02 x g207.2 g/mol S1 mol6.02 x g32.07 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 CO 2 = 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? g/mol Fe (from Periodic Table) Ex: What is the molar mass of boron? g/mol B (from Periodic Table)

Ex: What is the molar mass of H 2 O? H: 2 x 1.01g = 2.02g O: 1 x 16.00g = 16.00g g/mol H 2 O Ex: What is the molar mass of C 6 H 12 O 6 ? C: 6 x 12.01g = 72.06g H: 12 x 1.01g = 12.12g O: 6 x 16.00g = 96.00g g/mol C 6 H 12 O 6

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. 6.02x mole

Ex: Convert 2.00 mol Carbon to grams C. Use the factor-label method. mol C mol C = g C Math: (2.0) x (12.01) / (1) = This is Molar Mass from periodic table 1 mol C = g C g C 1 GRAMS MOLES PARTICLES (atoms, molecules, ions, formula units ) MM=P.T. 6.02x mole

Ex: Convert 9.73 mol Fe to grams Fe. Use the factor-label method. mol Fe mol Fe = 543 g Fe Math: (9.73) x (55.85) / (1) = 543 This is Molar Mass from periodic table 1 mol Fe = g Fe g Fe 1 GRAMS MOLES PARTICLES (atoms, molecules, ions, formula units ) MM=P.T. 6.02x mole

Ex: Convert 122 g Al to moles Al. Use the factor-label method. g Al g Al = 4.52 mol Al Math: (122) x (1) / (26.98) = 4.52 This is Molar Mass from periodic table 1 mol Al = g Al mol Al GRAMS MOLES PARTICLES (atoms, molecules, ions, formula units ) MM=P.T. 6.02x mole

Ex: Convert 413 g C 6 H 12 O 6 to moles C 6 H 12 O 6. Use the factor-label method. g C 6 H 12 O g C 6 H 12 O 6 = 2.29 mol C 6 H 12 O 6 Math: (413) x (1) / (180.18) = 2.29 This is Molar Mass from periodic table 1 mol C 6 H 12 O 6 = g C 6 H 12 O 6 mol C 6 H 12 O GRAMS MOLES PARTICLES (atoms, molecules, ions, formula units ) MM=P.T. 6.02x mole

Ex: Convert 26 g He to atoms He. Use the factor-label method. g He 1 26 g He = 3.9 x atom He Math: (26) x (1) / (4.00) x (6.02 x ) / (1) = 3.9 x This is Molar Mass from periodic table 1 mol He = 4.00 g He mol He 4.00 GRAMS MOLES PARTICLES (atoms, molecules, ions, formula units ) MM=P.T. 6.02x mole mol He 6.02 x atom He 1 This is Avogadro’s Number 1 mol = 6.02 x atoms

Ex: Convert 345 g CO 2 to molecule CO 2. Use the factor-label method. g CO g CO 2 = 4.72 x molecules CO 2 Math: (345) x (1) / (44.01) x (6.02 x ) / (1) = 4.72 x This is Molar Mass from periodic table 1 mol CO 2 = g CO 2 mol CO GRAMS MOLES PARTICLES (atoms, molecules, ions, formula units ) MM=P.T. 6.02x mole mol CO x molec CO 2 1 This is Avogadro’s Number 1 mol = 6.02 x atoms

Try the following. 1)What is the Molar Mass of Platinum (Pt)? 2)Convert: g H 2 O to molecules H 2 O 1)195 g/mol 2)2.18 x molec. H 2 O GRAMS MOLES PARTICLES (atoms, molecules, ions, formula units ) MM=P.T. 6.02x 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) – 0 o C and 1 atm Conversion Factor 5: 1 mole = 22.4 L

LITERS GRAMS MOLESPARTICLES Avogadro Number 1 mole Molar Mass 1 mole Molar Volume (atoms, molecules, ions, formula units)

Ex: Convert 5 mol N 2 to liters of N 2. Use the factor-label method. mol N 2 L N 2 5 mol N 2 = 112 L N 2 Math: (5) x (22.4) / (1) =

Ex: Convert 12.5 mol Ar to liters of Ar. Use the factor-label method. mol Ar L Ar 12.5 mol Ar = 280 L Ar Math: (12.5) x (22.4) / (1) =

Ex: Convert 69.8 L Ne to mol of Ne. Use the factor-label method. L Ne mol Ne 69.8 L Ne = 3.17 mol Ne Math: (69.8) x (1) / (22.4) =

Ex: Convert g NH 3 to liters NH 3 at STP. Use the factor-label method. g NH g NH 3 = L NH 3 Math: (49.87) x (1) / (17.04) x (22.4) / (1) = This is Molar Mass from periodic table 1 mol NH 3 = g NH 3 mol NH mol NH L NH 3 1 This is Molar Volume at STP 1 mol = 22.4 L

Try the following. 1)What is the volume (L) of 589 g N 2 O? 2)Convert: 3.01 x molecules of SO 2 to liters. 1)300. L 2)11.2 L H 2 O

Chemical Formula The chemical formula can act as a conversion Example: Fe 2 O 3 – The subscripts tell us the number of atoms – 2 atoms of Fe and 3 atoms of O in one formula unit of Fe 2 O 3 – Assume we have 6.02 x formula units then… – Fe: 2 x (6.02 x atom Fe) = 2 mole Fe – O: 3 x (6.02 x atom O) = 3 mole O in 1 mol Fe 2 O 3

Chemical Formula The chemical formula is a mole ratio!!! If we have 1 mole C 6 H 12 O 6 then… 1 mol C 6 H 12 O 6 : 6 mol C : 12 mol H : 6 mol O Colon (:) 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 MOLESPARTICLES 6.02x mole Molar Mass Periodic Table 1 mole 22.4 L Chemical Formula

Ex: How many mol of N are in 1.00 mol NO 3 ? Use the factor-label method. mol NO mol NO 3 = 1.00 mol N Math: (1.00) x (1) / (1) = 2.00 This is Mole ratio from chemical formula 1 mol NO 3 = 1 mol N mol N 1

Ex: How many mol of P are in 1.00 mol P 2 O 5 ? Use the factor-label method. mol P 2 O mol P 2 O 5 = 2.00 mol P Math: (1.00) x (2) / (1) = 2.00 This is Mole Ratio from chemical formula 1 mol P 2 O 5 = 2 mol P mol P 1

Ex: How many mol of S are in 6.80 mol Pb 2 S 3 ? Use the factor-label method. mol Pb 2 S mol Pb 2 S 3 = 20.4 mol S Math: (1.00) x (2) / (1) = 2.00 This is Mole Ratio from chemical formula 1 mol Pb 2 S 3 = 3 mol S mol S 1

Ex: How many grams of Cl are in 8.00 mol CHCl 3 ? Use the factor-label method. mol CHCl mol CHCl 3 = 851 g Cl Math: (8.00) x (3) / (1) x (35.45) / (1) = 851 This is Mole Ratio from chemical formula 1 mol CHCl 3 = 3 mol Cl mol Cl g Cl 1 This is Molar Mass from periodic table 1 mol Cl = g Cl

Ex: How many grams of O are in 15 mol NO 2 ? Use the factor-label method. mol NO mol NO 2 = 480 g O Math: (15) x (2) / (1) x (16.00) / (1) = 480 This is Mole Ratio from chemical formula 1 mol NO 2 = 2 mol O mol O g O 1 This is Molar Mass from periodic table 1 mol O = g CO 2

Ex: How many grams of F are in 10.2 g XeF 6 ? Use the factor-label method. g XeF g XeF 6 = 4.74 g F Math: (10.2) x (1) / (245.29) x (6) / (1) x (19.00) / (1) = 4.74 This is Mole Ratio from chemical formula 1 mol XeF 6 = 6 mol F mol XeF mol XeF 6 6 mol F 1 This is Molar Mass from periodic table 1 mol F = g F g F mol F This is Molar Mass from periodic table 1 mol XeF 6 = g XeF 6

Try the following. 1)How many moles of acetate are in 2.00 mol Cr(C 2 H 3 O 2 ) 3 ? 2)Convert: 121 g NaOH to grams H. 1)6 mol C 2 H 3 O )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 X mass of sample x 100% (X represents some element found in the sample)

Ex: When 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 MgO x 100% = 8.20 g Mg g MgO x 100% % Mg = 60.3% Mg % O = mass of O mass of MgO x 100% = 5.40 g O g MgO x 100% % O = 39.7% O Note: All percents should add up to about 100%

Ex: When 89.1 g H 2 O decomposes, it produces 9.89 g H.What is the % composition? % H = mass of H mass of H 2 O x 100% = 9.89 g H 89.1 g H 2 O x 100% % H = 11.1% H % O = mass of O mass of H 2 O x 100% = (13.60 – 9.89) g O g H 2 O x 100% % O = 88.9% O Total mass must equal the sum of its parts: mass H 2 O = mass H + mass O

Ex: What is the % composition of C 3 H 8 ? % C = g C g C 3 H 8 x 100% = 81.68% C % H = 8.08 g H g C 3 H 8 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 C 3 H 8 : 3 mol g/mol 8 mol g/mol C 3 H g/molx x= g C = 8.08 g H

Ex: What is the % composition of (NH 4 ) 2 S? % N = g N g (NH 4 ) 2 S x 100% = 41.10% N % H = 8.08 g H g (NH 4 ) 2 S 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 (NH 4 ) 2 S: 2 mol g/mol 8 mol g/mol (NH 4 ) 2 S 1.01 g/molx x= g N = 8.08 g H % S = g S g (NH 4 ) 2 S x 100% = 47.04% S 1 mol32.07 g/molx= g S

Try the following. 1)What is the percent composition of NaOH? 2)What is the percent composition of CH 4 ? 1)57.5% Na 40.0% O 2.5% H 2)75.0% C 25.0% H

PART III: EMPIRICAL & MOLECULAR FORMULAS

Empirical and Molecular Formulas Each compound has a basic ratio of elements C 6 H 6, C 8 H 8, C 10 H 10  multiples of CH Empirical Formula (EF) – Lowest whole number ratio of elements – Ex: CH, CH 2 O Molecular Formula (MF) – Actual ratio of elements in a compound – Can be the same or whole # multiple of empirical – Ex: C 6 H 6, C 6 H 12 O 6

Empirical and Molecular Formulas To determine the empirical, you need % comp – Assume 100g of compound to make math easier To determine the molecular, you need 1.Molar Mass of Compound (Mass Spec) 2.Calculate the Ratio of MF to EF Ratio = Molecular Molar Mass Empirical Molar Mass Molecular Molar Mass is given in the problem.

Step to Solve EF/MF Problems

Ex: A molecule was determined to be 30.4% N and 69.6% O with a molar mass of g/mol. Determine the empirical & molecular formulas.

Ex: 40.0% C, 6.67% H, 53.3% O; MM=90.00 g/mol. Determine the empirical & molecular formulas.

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: C 4 H 5 N 2 O Molecular: C 8 H 10 N 4 O 2

Try the following. 1)Find the EF & MF for: % C, 8.80% H, 15.51% O with MM = 206 g/mol 1)EF: C 13 H 18 O 2 MF: C 13 H 18 O 2 (Ibuprofen)