C H E M I S T R YM S . M A T T S O N

STOICHIOMETRY

STOICHIOMETRY

• Stoichiometry• the mole-mass relationship between reactants

and products.

• Molecular Mass • measured in atomic mass units (a.m.u.)

• Review: Calculate the molecular mass of chloroethane C2H5Cl.• 64.5 a.m.u.

STOICHIOMETRY

• Mole • A unit that refers to the number of molecules or

ions that take part in a chemical reaction.• Molar Mass• One mole is equal to the molecular mass in

grams.• Ex: C2H5Cl = 64.5 a.m.u. = 1 mole = 64.5 grams• Potassium (K) has molecular mass 39.1 a.m.u.• What is 1 mole of potassium in grams?• 39.1 grams

STOICHIOMETRY

• Molecular Mass (a.m.u.) = Molar Mass (g) = 1 mole

• Activity 1• Given molecule A in grams show the equation

that would convert grams of A to moles of A.

• Given the moles of molecule B show the equation that would convert moles of B to grams of B.

STOICHIOMETRY

• Problem 1• Convert 15.0 grams of C2H4 to moles of C2H4.• 0.536 moles

• Convert 0.536 moles of HCl to grams of HCl.• 19.6 grams

STOICHIOMETRY

• Molecular Mass (a.m.u.) = Molar Mass (g) = 1 mole

• Activity 2 • Given the reaction 2A + 3B A2B + B2

show the equation that would convert the grams of A into the grams of B that are required to fulfill the reaction.

• Grams to moles to moles to grams!

• Problem 2 • Sodium hypochlorite (NaOCl) is best known as

household bleach. It is prepared by reacting sodium hydroxide (NaOH) with chlorine Cl2:

2NaOH + Cl2 NaOCl + NaCl + H2O

• How many grams of NaOH are needed to react with 25.0 g of Cl2?

• 28.2 g NaOH

STOICHIOMETRY

• Problem 3• Aspirin is prepared by a reaction of salicylic acid

(C7H6O3) with acetic anhydride (C4H6O3) according to the following equation: C7H6O3 + C4H6O3 C9H8O4 + CH3COOH

Salicylic acid Acetic anhydride Aspirin

138.1 g 102.1 g 180.2 g• How many grams of acetic anhydride are needed to

react with 4.50 g of salicylic acid?• 3.33 g C7H6O3

• How many grams of aspirin will result?• 5.87 g C9H8O4

STOICHIOMETRY

STOICHIOMETRY

• Problem 4• In preparation of iron from hematite Fe2O3 reacts

with carbon:

Fe2O3 + C Fe + CO2

How many grams of carbon are needed to react with 525 g of hematite?

59.2 g C

STOICHIOMETRY

• Problem 5Magnesium metal burns in oxygen to form magnesium oxide, MgO2. Write and balance an equation for this reaction.

2Mg + O2 2MgO2

How many grams of Mg(MM 24.3g) are needed to react with 25.0 g of O2 (MM 32.0g)?

38.0g MgHow many grams of MgO2 (MM 40.3) will result?

63.0 g MgO2

How many grams of O2 are needed to react with 25.0 g of Mg?16.5 g O2

How many grams of MgO2 will result?41.5 g MgO2