Chapter 3Chapter 3

Formulas, Equations,and Moles

3.1 Balancing Equation3.1 Balancing Equation

Balancing EquationsBalancing Equations

Chemical ReactionChemical Reaction

Reactants Reactants Products Products Steps:Steps:

Write the unbalance equationWrite the unbalance equation Find an appropriate coefficient and place in Find an appropriate coefficient and place in

front of the formula unit to balance the front of the formula unit to balance the equationequation

Reduce the coefficients to the smallest ratioReduce the coefficients to the smallest ratio Check your answerCheck your answer

Balancing EquationBalancing Equation

Propane, CPropane, C33HH88 is a colorless gas often used is a colorless gas often used as a heating and cooking fuel in campers as a heating and cooking fuel in campers and rural homes. Write a balance equation and rural homes. Write a balance equation for the combustion reaction of propane with for the combustion reaction of propane with oxygen to yield carbon dioxide and water.oxygen to yield carbon dioxide and water. Step 1: Write out the unbalanced equationStep 1: Write out the unbalanced equation Step 2: Balance C atomsStep 2: Balance C atoms Step 3: Balance C and HStep 3: Balance C and H Step 4: Balance C, H and OStep 4: Balance C, H and O Reduce coefficients to the smallest ratioReduce coefficients to the smallest ratio Check answerCheck answer

ExamplesExamples When solid potassium reacts with liquid water, When solid potassium reacts with liquid water,

the products are hydrogen gas and potassium the products are hydrogen gas and potassium hydroxide, the later remains dissolved in the hydroxide, the later remains dissolved in the water. From these information, write the water. From these information, write the balanced equation for the reactionbalanced equation for the reaction

Write the balanced equation for the following Write the balanced equation for the following reactionreaction Solid carbon reacts with gaseous oxygen to form Solid carbon reacts with gaseous oxygen to form

gaseous carbon dioxidegaseous carbon dioxide

Glass is sometimes decorated by etching patterns on Glass is sometimes decorated by etching patterns on its surface. Etching occurs when hydrofluoric acid its surface. Etching occurs when hydrofluoric acid (in a aqueous solution of HF) reacts with the silicon (in a aqueous solution of HF) reacts with the silicon dioxide in the glass to form gaseous silicon dioxide in the glass to form gaseous silicon tetrafluoride and the liquid water.tetrafluoride and the liquid water.

Chemical symbols on Different Chemical symbols on Different LevelsLevels

Chemical symbols represent both a microscopic and a Chemical symbols represent both a microscopic and a macroscopic levelmacroscopic level

Microscopic levelMicroscopic level – chemical symbols represent the – chemical symbols represent the behavior of individual atoms and moleculesbehavior of individual atoms and molecules

E.gE.g Atoms and molecules are much too small to be Atoms and molecules are much too small to be seen seen use microscopic behavior to describe use microscopic behavior to describe

2 H2 H2 2 + O + O22 2 H 2 H22OO Two molecules of hydrogen react with one Two molecules of hydrogen react with one

molecule of oxygen to yield two molecule of water.molecule of oxygen to yield two molecule of water. Help to understand how reaction occurHelp to understand how reaction occur

Chemical symbols on Different Chemical symbols on Different LevelsLevels

Macroscopic levelMacroscopic level – – formula and equations formula and equations represent the large-represent the large-scale behavior of atoms scale behavior of atoms and molecules that give and molecules that give rise to observable rise to observable propertiesproperties

Deal with macroscopic Deal with macroscopic behavior in the laboratorybehavior in the laboratory

E.gE.g Weighing amount Weighing amount of reactants, place them of reactants, place them in a flask and observe in a flask and observe visible changes.visible changes.

3.3 Avogadro Number and 3.3 Avogadro Number and The MoleThe Mole

Described the number of objects Described the number of objects present in a dozenpresent in a dozen Based on C-12Based on C-12

1 mol of anything = 6.02 x 101 mol of anything = 6.02 x 102323 units units of that substance (atoms, molecules, of that substance (atoms, molecules, particles, dollars etc..)particles, dollars etc..) Avogadro’s number or nAvogadro’s number or nAA

Avogadro’s numberAvogadro’s number

MolesMoles

or Formula unitor Formula unit

MassMass Molecular mass (molecular weight)Molecular mass (molecular weight) – sum of – sum of

the atomic masses of all atoms in a molecule the atomic masses of all atoms in a molecule (covalent molecule)(covalent molecule)

Formula massFormula mass – sum of atomic masses all atoms – sum of atomic masses all atoms in a formula unit of any substances (ionic salts)in a formula unit of any substances (ionic salts)

Units = amuUnits = amu

Formula Mass =Number of atoms of 1st element inChemical compound

x Atomic mass of1st element

+Number of atoms of 2nd element inChemical compound

x Atomic mass of2nd element

Molecular WeightMolecular Weight

What is the molecular weight of CHWhat is the molecular weight of CH44?? Calculate molecular weight of sulfur Calculate molecular weight of sulfur

dioxide, a gas produced when sulfur dioxide, a gas produced when sulfur containing fuels are burned.containing fuels are burned.

Calculate the formula weight of the Calculate the formula weight of the substance below (record to two substance below (record to two decimal places)decimal places) BaBa33(PO(PO44))22

Molar MassMolar Mass

Like density, it’s a ratio of two numbers.Like density, it’s a ratio of two numbers. Mass per one mole of substanceMass per one mole of substance

Unit => g/molUnit => g/mol Replaced with molecular weight Replaced with molecular weight

because molar mass described the because molar mass described the concept more accuratelyconcept more accurately E.gE.g Molecular weightMolecular weight Molar MassMolar Mass

18.02 amu18.02 amu 18.02 g/mol18.02 g/mol

Molar MassMolar Mass

Calculate the molar mass for each of Calculate the molar mass for each of the substance below (record to two the substance below (record to two decimal places)decimal places) CC22HH44

NHNH33

CC22HH55ClCl

3.4 Stoichiometry Chemical 3.4 Stoichiometry Chemical ArithmeticArithmetic

RecallRecall Molar mass is the mass per one mole of a Molar mass is the mass per one mole of a

substancesubstance 1 mol of substance = # g1 mol of substance = # g Use as a conversion factorUse as a conversion factor

E.gE.g if the molar mass of NaCl = 58.44 if the molar mass of NaCl = 58.44 g/molg/mol

Moles Moles Grams Grams or or Grams Grams Moles Moles

StoichiometryStoichiometry

Calcium carbonate (also called as Calcium carbonate (also called as calcite, CaCOcalcite, CaCO33), is the principal mineral ), is the principal mineral found in limestone, marble, chalk, found in limestone, marble, chalk, pearls and the shells of marine animals pearls and the shells of marine animals such as clamssuch as clams Calculate the molar mass of calcium Calculate the molar mass of calcium

carbonatecarbonate A certain sample of calcium carbonate A certain sample of calcium carbonate

contains 4.86 mol. What is the mass in contains 4.86 mol. What is the mass in grams of this sample?grams of this sample?

StoichiometryStoichiometry

How many moles of sucrose are in a table How many moles of sucrose are in a table spoon of sugar that contains 2.85 g? The spoon of sugar that contains 2.85 g? The molar mass of sucrose is 342.0 g/molmolar mass of sucrose is 342.0 g/mol

Calculate the mass of 4.85 mol of acetic Calculate the mass of 4.85 mol of acetic acid, HCacid, HC22HH33OO22. Vinegar is a dilute solution . Vinegar is a dilute solution of acetic acidof acetic acid

How many water molecules are in a 10.0g How many water molecules are in a 10.0g sample of water?sample of water?

Mass CalculationMass Calculation

Steps for Calculating the Masses of Steps for Calculating the Masses of Reactants and Product in Chemical ReactionsReactants and Product in Chemical Reactions Step 1: Balance the equation for the reactionStep 1: Balance the equation for the reaction Step 2: convert the masses of reactants or Step 2: convert the masses of reactants or

product to molesproduct to moles Step 3: use the balanced equation to set up the Step 3: use the balanced equation to set up the

appropriate mole ratio(s)appropriate mole ratio(s) Step 4: Use the mole ratio(s) to calculate the Step 4: Use the mole ratio(s) to calculate the

number of moles of the desired reactant or number of moles of the desired reactant or productproduct

Step 5: Convert from moles back to masses (of the Step 5: Convert from moles back to masses (of the desired reactant or product)desired reactant or product)

ExampleExample Aqueous solution of sodium Aqueous solution of sodium

hypochlorite (NaOCl), best known as hypochlorite (NaOCl), best known as household bleach, are prepared by household bleach, are prepared by reaction of sodium hydroxide with reaction of sodium hydroxide with chlorine:chlorine:

… …..NaOH(aq) + ….Cl..NaOH(aq) + ….Cl22(g) (g) … …NaOCl(aq) + NaCl(aq) + ….HNaOCl(aq) + NaCl(aq) + ….H22O(l)O(l)

How many gram of NaOH are needed to How many gram of NaOH are needed to react with 2.5g Clreact with 2.5g Cl22??

Limiting ReactantLimiting Reactant

Limiting Reactant (limiting Limiting Reactant (limiting reagent)reagent):: is the reactant that is is the reactant that is completely consumed in a chemical completely consumed in a chemical reaction and limits the amount of reaction and limits the amount of product.product.

Excess ReactantExcess Reactant:: Any of the other Any of the other reactants still present after reactants still present after determination of the limiting reactant.determination of the limiting reactant.

Steps in Determination Steps in Determination Limiting ReagentLimiting Reagent

i.i. Check to be sure you have a balanced Check to be sure you have a balanced equation equation

aA + bB aA + bB c C c C

ii.ii. Convert the amount of reagent oneConvert the amount of reagent one that that was given into was given into the number molesthe number moles productproduct that you that you could form if that reagent could form if that reagent was completely was completely consumed.consumed.

gA gA moles A moles A moles C moles C

iii.iii. Convert the amount of reagent twoConvert the amount of reagent two that that was given into was given into the number molesthe number moles of of productproduct that that you could form if that reagent was completely you could form if that reagent was completely consumed. consumed.

gB gB moles B moles B moles C moles C

Steps in Determination Steps in Determination Limiting ReagentLimiting Reagent

iv.iv. The reactant that produced the The reactant that produced the LEAST LEAST amount of productamount of product in step 2 or 3 will the in step 2 or 3 will the limiting reagent. limiting reagent.

v.v. Convert the Convert the LEAST molesLEAST moles into the into the number grams productnumber grams product and that will be and that will be your your theoretical yieldtheoretical yield.. Theoretical yieldTheoretical yield is the amount of product is the amount of product

that can be made in a chemical reaction that can be made in a chemical reaction based on the amount of limiting reagentbased on the amount of limiting reagent

Excess ReactantExcess Reactant

To determine how much of reactants To determine how much of reactants are left over from the reaction:are left over from the reaction: Larger moles of product – smaller moles Larger moles of product – smaller moles

of productof product Convert this moles of product to the g Convert this moles of product to the g

of the excess reactantof the excess reactant

ExampleExample

If we have 42.5 g Mg and 33.8 g OIf we have 42.5 g Mg and 33.8 g O22, , what is the limiting reactant?what is the limiting reactant?

2 Mg(s) + O2 Mg(s) + O22(g) (g) 2 MgO(s) 2 MgO(s)

ExampleExample

Ammonia, NHAmmonia, NH33, can be synthesis by the , can be synthesis by the following reaction:following reaction:

2 NO(g) + 5 H2 NO(g) + 5 H22(g) (g) 2 NH 2 NH33(g) + 2H(g) + 2H22O(g)O(g)

Starting with 86.8 g NO and 25.6 g HStarting with 86.8 g NO and 25.6 g H22, , find the theoretical yield of ammonia in find the theoretical yield of ammonia in gramsgrams

Calculate the number grams of excess Calculate the number grams of excess reactant that are unused from the reactionreactant that are unused from the reaction

3.5 Percent Yield3.5 Percent Yield

RecallRecall Theoretical yieldTheoretical yield is the amount is the amount

of product that can be made in a of product that can be made in a chemical reaction based on the chemical reaction based on the amount of limiting reagentamount of limiting reagent

actual yieldactual yield Percent yield = --------------------- x 100Percent yield = --------------------- x 100

theoretical yieldtheoretical yield

ExamplesExamples

Ethyl alcohol is prepared industrially Ethyl alcohol is prepared industrially by the reaction of ethylene, Cby the reaction of ethylene, C22HH44 with water. What is the percent with water. What is the percent yield of the reaction if 4.6 g of yield of the reaction if 4.6 g of ethylene gives 4.7g of ethyl alcohol?ethylene gives 4.7g of ethyl alcohol? CC22HH44(g) + H(g) + H22O(l) O(l) C C22HH66(l)(l)

ExamplesExamples Titanium (IV) oxide is a white compound Titanium (IV) oxide is a white compound

used as a coloring pigment. Solid used as a coloring pigment. Solid titanium (IV) oxide can be prepared by titanium (IV) oxide can be prepared by reacting gaseous titanium (IV) chloride reacting gaseous titanium (IV) chloride with oxygen gas. A second product of with oxygen gas. A second product of this reaction is chlorine gas. this reaction is chlorine gas. Suppose 6.71 x 10Suppose 6.71 x 1033 g of titanium (IV) chloride g of titanium (IV) chloride

is reacted with 2.45 x10is reacted with 2.45 x1033 g of oxygen. g of oxygen. Calculate the mass of titanium (IV) oxide that Calculate the mass of titanium (IV) oxide that can formcan form

If the percent yield of TiOIf the percent yield of TiO22 is 75%, what mass is 75%, what mass is actually formed?is actually formed?

3.11 Percent Composition 3.11 Percent Composition and Empirical Formulaand Empirical Formula

Formula of a compound represents Formula of a compound represents the relative numbers of various the relative numbers of various types of atoms present.types of atoms present. E.g COE.g CO22, H, H22O etc..O etc..

Empirical formula: simplest formulaEmpirical formula: simplest formula Molecular formula: the actual Molecular formula: the actual

formula of a compoundformula of a compound

ExamplesExamples In each case below, the molecular formula for In each case below, the molecular formula for

a compound is given. Determine the a compound is given. Determine the empirical formula for each compoundempirical formula for each compound CC66HH66. This is the molecular for benzene; a liquid . This is the molecular for benzene; a liquid

commonly used in industry as a starting material commonly used in industry as a starting material for many important productsfor many important products

HH22OO22. This is hydrogen peroxide, a substance . This is hydrogen peroxide, a substance commonly diluted with water and used as a commonly diluted with water and used as a disinfectantdisinfectant

CClCCl44. This is carbon tetrachloride, an organic . This is carbon tetrachloride, an organic solventsolvent

Percent CompositionPercent Composition

Percent compositionPercent composition – the mass – the mass present of each element present in a present of each element present in a compoundcompound

Atomic mass of an Atomic mass of an elementelement

% composition % composition =……………………………….. X 100=……………………………….. X 100

Molar mass of the Molar mass of the compound compound

Percent CompositionPercent Composition

To calculate the percent composition To calculate the percent composition (percentage composition) of a compound (percentage composition) of a compound Calculate the Calculate the molar massmolar mass of the compound of the compound Calculate the total mass of each element Calculate the total mass of each element

present in the formula of the compound present in the formula of the compound Calculate the percent composition (percentage Calculate the percent composition (percentage

composition):composition):% by weight (mass) of element = (total mass % by weight (mass) of element = (total mass of element present ÷ molecular mass) x 100 of element present ÷ molecular mass) x 100

ExamplesExamples

Glucose or blood sugar, has the Glucose or blood sugar, has the molecular formula Cmolecular formula C66HH1212OO66. What is . What is the empirical formula, and what is the empirical formula, and what is the percent composition?the percent composition?

Determination of an Determination of an empirical formulaempirical formula

Step 1: Obtain the mass of each element Step 1: Obtain the mass of each element present (in grams)present (in grams)

Step 2: Determine the number of moles of Step 2: Determine the number of moles of each type of atom presenteach type of atom present

Step 3: Divide the number of mole of Step 3: Divide the number of mole of each element by the smallest number of each element by the smallest number of moles to convert the smallest number to moles to convert the smallest number to 1. If all of the numbers so obtained are 1. If all of the numbers so obtained are integers, these are the subscripts in the integers, these are the subscripts in the empirical formula. If one or more of these empirical formula. If one or more of these number are not integers, go on to step 4number are not integers, go on to step 4

Determination of an Determination of an empirical formulaempirical formula

Step 4: Multiply the numbers you Step 4: Multiply the numbers you derived in step 3 by the smallest derived in step 3 by the smallest integer that will convert all of them integer that will convert all of them to whole numbers. This set of whole to whole numbers. This set of whole numbers represents the subscripts numbers represents the subscripts in the empirical formulain the empirical formula

ExampleExample

In a lab experiment it was observed that In a lab experiment it was observed that 0.6884 g of lead combines with 0.2356 g of 0.6884 g of lead combines with 0.2356 g of chlorine to form a binary compound. chlorine to form a binary compound. Calculate the empirical formula of this Calculate the empirical formula of this compoundcompound

When a 2.00 g sample of iron metal is heated When a 2.00 g sample of iron metal is heated in air, it reacts with oxygen to achieve a final in air, it reacts with oxygen to achieve a final mass of 2.573 g. Determine the empirical mass of 2.573 g. Determine the empirical formula for this iron oxideformula for this iron oxide

ExamplesExamples

What is the empirical formula for What is the empirical formula for sodium thiosulfate with the percent sodium thiosulfate with the percent composition of 30.36% O, 29.08% composition of 30.36% O, 29.08% Na and 40.56%SNa and 40.56%S

ExampleExample

Cisplatin, the common name for a Cisplatin, the common name for a platinum compound that is used to platinum compound that is used to treat cancerous tumors, has the treat cancerous tumors, has the composition (mass percent) 65.02% composition (mass percent) 65.02% platinum, 9.34 % nitrogen, 2.02% platinum, 9.34 % nitrogen, 2.02% hydrogen, and 23.63% chlorine. hydrogen, and 23.63% chlorine. Calculate the empirical formula for Calculate the empirical formula for csiplatincsiplatin

Molecular FormulaMolecular Formula

Molecular formulaMolecular formula – gives the – gives the actual numbers of atoms in a actual numbers of atoms in a moleculemolecule

Molecular formulaMolecular formula = = nn x empirical x empirical formulaformula may be the same as the empirical formulamay be the same as the empirical formula

Molecular FormulaMolecular Formula

a multiple of the empirical formula (or a multiple of the empirical formula (or # of empirical unit) is defined:# of empirical unit) is defined:

Emperical massEmperical mass MultipleMultiple or or nn = -------------------------- = --------------------------

( # of empirical unit)( # of empirical unit) Molecular mass Molecular mass

ExamplesExamples

Ribose, a sugar present in the cells Ribose, a sugar present in the cells of all living organism, has a of all living organism, has a molecular mass of 150 amu and the molecular mass of 150 amu and the empirical formula CHempirical formula CH22O. What is the O. What is the molecular formula?molecular formula?

ExamplesExamples

A compound used as an additive for A compound used as an additive for gasoline to help prevent engine knock gasoline to help prevent engine knock shows the following percent compositionshows the following percent composition

71.65 % Cl71.65 % Cl 24.27 % C24.27 % C4.07 % H4.07 % H

The molar mass is known to be 98.96 The molar mass is known to be 98.96 g/mol. Determine the empirical formula g/mol. Determine the empirical formula and the molecular formula for this and the molecular formula for this compoundcompound

Combustion AnalysisCombustion Analysis

CxHyOz (O can be replaced with any CxHyOz (O can be replaced with any other element)other element)

gCOgCO22 moles CO moles CO22 moles C moles C

gHgH22O O moles H moles H22O O moles H moles H g of O or unknown element = grams g of O or unknown element = grams

of sample – (g of H + g of C)of sample – (g of H + g of C) Follow the steps in determination of Follow the steps in determination of

an empirical formulaan empirical formula

Combustion AnalysisCombustion Analysis

Caproic acid, the substance responsible for Caproic acid, the substance responsible for the aroma of dirty gym socks and running the aroma of dirty gym socks and running shoes, contains carbon, hydrogen and shoes, contains carbon, hydrogen and oxygen. On combustion analysis, a 0.450 g oxygen. On combustion analysis, a 0.450 g sample of caproic acid gives 0.418 g of Hsample of caproic acid gives 0.418 g of H22O O and 1.023 g of COand 1.023 g of CO22. what is the empirical . what is the empirical formula of caproic acid? If the molecular formula of caproic acid? If the molecular mass of caproic acid is 116.2 amu, what is mass of caproic acid is 116.2 amu, what is the molecular formula?the molecular formula? Determine the percent composition of caproic Determine the percent composition of caproic

acid?acid?

ExamplesExamples Coniine, a toxic substance isolated from Coniine, a toxic substance isolated from

poison hemlock, contains only carbon, poison hemlock, contains only carbon, hydrogen and nitrogen. Combustion hydrogen and nitrogen. Combustion analysis of a 5.024 mg sample yields analysis of a 5.024 mg sample yields 13.90 mg of CO13.90 mg of CO22 and 6.048 mg of H and 6.048 mg of H22O. O. What is the empirical formula of coniine?What is the empirical formula of coniine?

EXAM 1 EXAM 1 (Chapter 1-3, except 3.7-3.10)(Chapter 1-3, except 3.7-3.10)