stoichiometry stoichiometry cdo high school. stoichiometry consider the chemical equation: 4nh 3 +...

StoichiometryStoichiometry

CDO High School


Consider the chemical equation:4NH4NH33 + 5O + 5O22 6H 6H22O + 4NOO + 4NO

There are several numbers involved. What do they all mean?

““stochio” = Greek for elementstochio” = Greek for element““metry” = measurementmetry” = measurement

Stoichiometry is about measuring the amounts of Stoichiometry is about measuring the amounts of elements and compounds involved in a reaction. elements and compounds involved in a reaction.


With Stoichiometry we find out that 4 : 5 : 6 : 4

do more than just multiply atoms.

4NH4NH33 + 5O + 5O22 6H 6H22O + 4NOO + 4NO

4 : 5 : 6 : 4Are what we call a mole ratio.

StoichiometryStoichiometry4NH4NH33 + 5O + 5O22 6H 6H22O + 4NOO + 4NO

4 : 5 : 6 : 4Can mean either:

4 molecules of NH3 react with 5 molecules of O2

to produce 6 molecules of H2O and 4 molecules of NO

OR

4 moles of NH3 react with 5 moles of O2

to produce 6 moles of H2O and 4 moles of NO

Stoichiometry EquationsStoichiometry Equations

Mole to MoleMole to Mole

Moles of Known

Coefficient Known

Coefficient Unknown

Stoichiometry Question (1)Stoichiometry Question (1)4NH3 + 5O2 6H2O + 4NO

How many moles of H2O are produced if 2.00 moles of O2 are used?

2.00 mol O2 2.40 mol H2O=

Notice that a correctly balanced equation is essential to get the right answer

6 mol H2O

5 mol O2

4 mol NO

6 mol H2O

Stoichiometry Question (2)Stoichiometry Question (2)

4 NH3 + 5 O2 6 H2O + 4 NO

How many moles of NO are produced in the reaction if 15 mol of H2O are also produced?

15 mol H2O10. mol NO=

Mole to MassMole to Mass

Mole of KnownCoefficient Unknown

Coefficient Known

Molar Mass Unknown

18.02 g H2O

1 mol H2O

6 mol H2O

4 mol NH3

Stoichiometry Question (3)Stoichiometry Question (3) 4 NH3 + 5 O2 6 H2O + 4NO

How many grams of H2O are produced if 2.2 mol of NH3 are combined with excess oxygen?

2.2 mol NH3 59 g H2O

=

Mass to MoleMass to Mole

Coefficient Unknown

Coefficient Known

Molar Mass Known

Mass Known

1 mol H2O5 mole O2

6 mol H2O

Stoichiometry Question (4)Stoichiometry Question (4) 4 NH3 + 5 O2 6 H2O + 4 NO

How many moles of O2 are required to produce 42.3g of H2O?

42.3 gH2O 1.96 mol O2=

18.02 g H2O

Mass to Mass ConversionsMass to Mass Conversions

Coefficient Unknown

Coefficient Known

Molar Mass Known

Mass Known

Molar Mass Unknown

Stoichiometry Question (5)Stoichiometry Question (5)4 NH3 + 5 O2 6 H2O + 4 NO

How many grams of NO is produced if 12 g of O2 is combined with excess ammonia?

4 mol NO

5 mol O2

12 g O2

9.0 g NO=

30.01 g NO

1 mol NO1 mol O2

32 g O2

3CuSO3CuSO44 + 2Al + 2Al Al Al22(SO(SO44))33 + + 3Cu3CuWhat is the mass of copper

formed when 15.8g of Aluminum is used?

3 mol Cu

2 mol Al

15.8g Al

55.8 g Cu=

63.55 g Cu

1 mol Cu1 mol Al

26.98 g Al

Have we learned it yet?Have we learned it yet?

4 NH3 + 5 O2 6 H2O + 4 NO

a) How many moles of H2O can be made using 1.6 mol NH3?

b) what mass of NH3 is needed to make 0.75 mol NO?

c) how many grams of NO can be made from 47 g of NH3?

AnswersAnswers4 NH3 + 5 O2 6 H2O + 4 NO

a)

b)

c)

6 mol H2O

4 mol NH3

x 1.6 mol NH3 2.4 mol H2O

=

4 mol NH3

4 mol NOx 0.75 mol NO 13 g

NH3

= 17.04 g NH3

1 mol NH3

x

4 mol NO

4 mol NH3

x 47 g NH3

83 g NO=

30.01 g NO

1 mol NOx 17.04 g/mol NH3÷

Reactions Involving aReactions Involving aLIMITING REACTANTLIMITING REACTANTReactions Involving aReactions Involving aLIMITING REACTANTLIMITING REACTANT

LIMITING REACTANTSLIMITING REACTANTS

Reactantseactants ProductsProducts

2 NO(g) + O2 (g) 2 NO2(g)

Limiting reactant = ___________Excess reactant = ____________

Limiting Reactants: An Limiting Reactants: An AnalogyAnalogy

If you were going to make pb and j sandwiches, and you had a new loaf of bread and a large jar of pb and a large jar of jelly, how many sandwiches can you make?

CDO IB Chemistry SL 20

Example: Limiting Example: Limiting ReactantsReactantsMix 5.40 g of Al with 8.10 g of Cl2. What

mass of AlCl3 can form?

Al(s) + Cl2(g) AlCl3 (s)


Cl2 was the limiting reactant.

Therefore, Al was present in excess.

But how much?

First find how much Al was

required.

Then find how much Al is in excess.

How much of which reactant will remain when reaction is complete?

How much of which reactant will remain when reaction is complete?

2 Al + 32 Al + 3 ClCl22 2 AlCl2 AlCl33

Calculating Excess AlCalculating Excess AlCalculating Excess AlCalculating Excess Al

White BoardsWhite BoardsIn the reaction BaCO3 + 2HNO3 Ba(NO3)2 + CO2

+ H2O,

what mass of Ba(NO3)2 can be formed by combining 55g BaCO3 and 26g HNO3

Percent YieldPercent Yield

2As2O3 + 3C 3CO2 + 4As◦If 8.87g of As2O3 is used in the

reaction and 5.33 g of As is produced, what is the percent yield?

Gas StoichiometryGas Stoichiometry

Many chemical reactions involve gases as a reactant or a product

Gas Stoichiometry – the procedure for calculating the volume of gases as products or reactants

Gases also have a molar volume (L/mol) rather than concentration.

This is the conversion factor used to convert (liters of gas) to (moles of gas)

Molar VolumeMolar VolumeMolar volume is the same for all gases at

the same temperature and pressure (remember, all gases have the same physical properties)

◦At STP, molar volume = 22.4 L/mol This can be used as a conversion factor just like molar

mass!

At STP, one mole of gas has a volume of 22.4 L, which is approximately the volume of 11 “empty” 2 L pop bottles.

STP = 22.4L/mol

Volume of Gas to Volume of GasVolume of Gas Known

Coefficient UnknownCoefficient Known

Volume of Gas to Mass

Volume of Gas Known

Volume of Gas Known

Coefficient Unknown

Coefficient Known

22.4 L

1 molMolar Mass Unknown

Mass to Volume of Gas Mass Known

Molar Mass Known

Coefficient Known

Coefficient Unknown 22.4 L

1 mol

Example #1Example #1If 300. 0g of propane burns, what

volume of oxygen measured at STP is required for the reaction?

C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(g)

300.0 g C3H8

44.11 g C3H8 1 mol C3H8

5 mol O2 22.4 L

1 mol

1 mol C3H8

= 761.7 L O2

Example #2Example #2

Hydrogen gas is produced when sodium metal is added to water. What mass of sodium is necessary to produce 20.0L of hydrogen at STP?

2Na(s) + 2H2O (l) 2NaOH(aq) + H2(g)

20.0 L H22 mol Na

22.4 L

1 mol22.99 g Na

1 mol H2 1 mol Na

= 41.1 g Na

SOLUTIONSSOLUTIONS

SolutionsSolutionsSolute – what is being dissolved, usually present in the smallest amount

Solvent – what is doing the dissolving, usually present in the largest amount

Solution – solute and solvent combined

Aqueous solutions – solutions in which water is the solvent

ConcentrationConcentrationConcentration – describes how

much solute is dissolved in solventSaturated solution – when the

solute can no longer dissolve in the given solvent

Concentration unit (mol/L) often referred to as Molarity (M)

[Concentration] = moles of solute volume of solution (L)


Example: ConcentrationExample: ConcentrationA solution contains 4.10 g of NaCl

in 1.00 L. What is the solutions concentration in mol/L.?


Standard SolutionStandard Solution


Example: Making a Standard Example: Making a Standard SolutionSolutionCalculate the mass of NaOH need

to make 250 mL of a 0.200 mol/L solution.


TITRATIONSTITRATIONS

TitrationsTitrationsLaboratory Technique – which uses a standard solution to find the concentration of another solution.

Titration CalculationTitration Calculation

n2M1V1 = n1M2V2

n= Coefficient of substanceM = molarity of substanceV = volume of substance

Example: TitrationExample: Titration

What volume of 0.100 mol/L NaOH is required to titrate 25 mL of 0.300 mol/L solution of HCl to produce a neutral solution?


HH22SOSO44 + 2NaOH + 2NaOH Na Na22SOSO44 + + 2H2H22OO

What is the concentration of 25.85 mL of H2SO4 that is reacted with 21.50 mL of 0.300 mol/L solution of NaOH to produce a neutral solution?

stoichiometry stoichiometry cdo high school. stoichiometry consider the chemical equation: 4nh 3 +...

Documents

g of o2

g of nh3

g of h2o

mol o2

mol of nh3

mol of h2o

mol nh3 mass

mass of nh3