Gravimetric Stoichiometry

Gravimetric Stoichiometry

LG: I can use mole ratios to predict masses of reactants and products in a chemical reaction.

Gravimetric Stoichiometry• The procedure for calculating masses of reactants

or products in a chemical reaction is called Gravimetric Stoichiometry

• All predictions are based on the number of moles and the mole ratio in the equation

Mass of Reactant

Mass of Product

Moles of Reactant

Moles of Product

Example 1• 1.00g of zinc reacts with sulfur to produce zinc sulfide. If

there is excess sulfur, what mass of zinc sulfide should be produced?

Zn(s) + S8(s) ZnS(s)

Steps:– Balance the equation to determine mole ratio– Convert mass of zinc to moles (using molar mass of Zn)– Use mole ratio to predict moles of ZnS produced– Convert moles of ZnS to mass (using molar mass of ZnS)

Mrs. Rickert’s Tip: Organize info in a table and show

all units!

Example 2• On space shuttles, exhaled carbon dioxide is removed

from the air by reacting it with solid lithium hydroxide:

CO2(g) + LiOH(s) Li2CO3(aq) + H2O(l)

• If a typical astronaut exhales880g of CO2 per day, what mass of lithium hydroxide would be required per astronaut, per day?

Stoichiometry Amounts• Refer to Example 2:– Notice that 40 moles of LiOH were needed to react with 20

moles of CO2. These values are multiples of the mole ratio indicated by the balanced equation.

• Stoichiometric Amount – is a quantity that is in the same proportion as the coefficients in the balanced equation.

• When Stoichiometric amounts of reactants are used, there should be no excess reagents at the end of a reaction – in other words “the reaction goes to completion”

Homework

• New Text: Pg. 325 # 5 – 10 • Old Text: Pg. 228 # 9 – 10; Pg. 229 # 2 – 4

• Note: If you are asked to make a prediction about products based on the mass of a single reactant, assume all other reactants are present in excess quantities