STOICHIOMETRY

Mass-Mass Problems

Mass-Mass Problems

STEP 1STEP 1

Write a Balanced Write a Balanced EquationEquation

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Mass-Mass Problems

STEP 2STEP 2

Determine the Given Determine the Given and the Unknownand the Unknown

Convert Given to Convert Given to MolesMoles

Mass-Mass Problems

STEP 3 STEP 3

Determine the Mole Determine the Mole Ratio using the Ratio using the

EquationEquation

Mass-Mass Problems

STEP 3STEP 3

Determine the Mole Determine the Mole Ratio using the Ratio using the

EquationEquation

Mass-Mass Problems

STEP 4STEP 4

Using Molar mass Using Molar mass convert Unknown convert Unknown

moles back to moles back to GramsGrams

Mass-Mass Problems

Given in grams

1 Mole of Given

(Coefficient) Moles

Unknown

Molar Mass of Unknown

1Molar mass

of Given

(Coefficient) Moles Given

1 Mole of

Unknown

The Steps to solve mass –mass The Steps to solve mass –mass problems will always follow this problems will always follow this factor-label guideline.factor-label guideline.

Limiting ReactantYou work in a bakery and your boss says that she

wants you to bake as many cakes as you can. You have a 100 pound bag of sugar and a 100 pound bag of flour. Which ingredient will you run out of first?

What if you knew that one cake requires 245 g of sugar and 283 g of flour. Which

ingredient will you run out of first?

Flour. That is going to limit the number of cakes you can make. Will you have sugar left over? it will be the excess reactant

Limiting Reactant You have a brand new jar of

peanut butter and a new jar of grape jelly and 9 slices of bread. How many of my son’s favorite sandwiches can you make?

4.5

What limits the number of sandwiches? The slices of bread

Bread is the limiting reactant. Peanut butter and jelly are both in excess.

A limiting reactant is the reactant that limits the amount of the other reactants that can combine, and the amount of products formed in a chemical reaction.

The excess reactant is the substance that is not used up completely in a reaction.

Limiting Reactant

Other examples:

Four hundred people want to take a flight. The plane has only 350 seats available. Only 350 people can go on the flight.

The number of seats on the airplane limits the number of people that can travel.

There are 50 people in excess.

Limiting Reactant

Its February, Alex is going to pass out Valentine cards. He goes through his valentines and discards the ones that don’t have Sponge Bob or ____________ on them. He now has only 12 acceptable valentines. He knows he’ll get a kiss from each girl that receives an acceptable valentine. But there are 15 girls in his class.

Limiting reactant: acceptable valentines Excess reactant: girls

The product: The KISSES are limited to 12

Limiting ReactantHow about the game of musical Chairs??

:

the limiting reactant is the chairs

the players are in excess.

Limiting Reactant

Real Life How many times do you breathe in one minute? Let’s count.

Did you know that the average person exhales 20 moles of carbon dioxide in a day. How many grams is this?

20 moles CO2 | 44.01 g CO2 = 880 g CO2

1 | 1 mol CO2

Limiting ReactantDo we ever need to worry about the amount

of CO2 that we exhale? Why not?

What if we were in a contained atmosphere? Prolonged exposure of humans to concentrations of 5 % CO2 may cause unconsciousness and death.

How do we remove CO2 from the air?

React it with lithium hydroxide.

2 LiOH + CO2 Li2CO3 + H2O

How much LiOH is needed to remove the CO2 from the atmosphere for one

person for one day?Given: 20 moles CO2 Unknown: grams of LiOH

20 moles CO2 | 2 mole LiOH | 23.949 g LiOH = 960 grams LiOH

1 | 1 mole CO2 | 1 mole LiOH

Who might need this information?

CO2 Launch

Apollo 13 space flight there were two compartments to capsule, the service station compartment blew

up and the 3 astronauts had to remain in the Lunar Module. Carbon dioxide levels were rising. Did

they have enough LiOH to absorb the carbon dioxide produced by 3 people?

On the Lunar Module there was:“5 filters to last 2 people for 1.5 days”

How much LiOH does 1 filter contain?

1 filter | 2 people | 960 g LiOH | 1.5 days = 576 grams LiOH 1 | 5 filters | 1 person

So LiOH would have been the limiting reactant and CO2 would have been the excess reactant.

Stoichiometry Overview

Click on the following page and then go to section 4.8 Limiting Reactants.

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