Chapter 3

Stoichiometry

http://www.shodor.org/UNChem/basic/stoic/

THINK

Why do the masses on the periodic table have decimals if we can’t have part of a proton or a neutron?

http://richardbowles.tripod.com/chemistry/structure/structure.htm

1961: Scientists decided to have a standard of masses, they chose Carbon. They decided it has a mass of 12 atomic mass units (amu) and base all other elements on this.

Example: He is 1/3 the mass of Carbon. What is Heliums atomic mass?

http://richardbowles.tripod.com/chemistry/structure/structure.htm

Calculating the Mass of a Compound

Compound Formula Formula Mass

Table salt

Potassium Bromide

Aluminum Hydroxide

Magnesium Iodide

Calculating the Mass of a Molecule

Molecule Formula MolecularMass

Water

Dinitrogen Pentoxide

Simple Sugar

Sulfur Dioxide

THINK

What is the difference between a compound and a molecule?

A.M.U?!?!?!

Define:

Units:

Examples and Calculations:

http://en.wikipedia.org/wiki/Atomic_mass_unit

What is Stoichiometry?

Define:

http://www.chem4kids.com/files/react_stoichio.html

What is a mole?

Definition: (and citation) Value: Another name for this value: What does it mean? (in your own words!)

http://www.youtube.com/watch?v=1R7NiIum2TI

Conversions

1 mole= atomic mass of substance

1 mole= 6.022 X 1023 atoms

1 mole= 22.4L

1 mole of Ag= 1 mole of H2O= 1 mole of CO2

How many grams, liters and atoms are in the following?

Mole-Gram Conversions

Use Dimensional Analysis to calculate the answer to the following:

How many moles are in 11.5 grams of C2H5OH?

http://dbhs.wvusd.k12.ca.us/webdocs/Mole/Moles-to-Grams.html

How many moles of water are in 1.20X1025 atoms?

If the volume of Nitrogen gas is 75.0 L, how many grams are present?

How many atoms are in 16.2 grams of N2?

How much volume of ammonia will be present in 45.2 grams?

If there are 44.5L of Hydrogen gas, how many grams are present?

Percent composition from Formula

The subscripts in a formula represent not only the atom ration in which the different elements are combined, but also the ______________ ____________.

Formula Atom Ratio

Mole Ratio

H2O

KNO3

C12H22O11

http://www.chemcool.com/regents/molesstoichiometry/aim4.htm

Examples

Sodium hydrogen carbonate, commonly called “bicarbonate of soda”, is used in many commercial products to relieve an upset stomach. It has the formula NaHCO3. What are the mass percents of Na, H, C, and O in sodium hydrogen carbonate?

How to Solve % of element = ____________________ x 100

Element Number of Moles

Atomic Mass Molar Mass

Compound mass =

Use these numbers to determine the percent of each component:

Example 2 An iron containing mineral responsible

for the red color of soil in many parts of the country is limonite, which has a formula Fe2O3 • 3/2 H2O. What mass of iron in grams can be obtained from a metric ton (103 kg = 106 g) of limonite?

Simplest Formula from Chemical Analysis

Simplest formula: Gives the simplest _____________________ ___________ of the atoms present.

http://www.carlton.srsd119.ca/chemical/Molemass/empirical_formula.htm

Example

A 25.0 g sample of an orange compound contains 6.64 g of potassium, 8.84 g of chromium, and 9.52 g of oxygen. Find the simplest formula.

How To Solve Change all grams to moles for comparisons. Calculate the mole ratio. Make them all whole numbers. Because the mole ratio is the same as the atom

ratio, you are done!! Just write the final answer and box it!

Example 2

When a sample of ethyl alcohol is burned in air it is found that 5.00 grams of ethyl alcohol convert to 9.55 grams of carbon dioxide, and 5.87 grams of water. What is the simplest formula of ethyl alcohol? (Hint: Find the mass of each ELEMENT first!! Then continue the problem)

Molecular formula from Simplest Formula

The molecular formula is a _______________________ ________________ of the simplest formula.

Example

Vitamin C’s formula is found to be C3H4O3. From an experiment the molecular mass is found to be 180 g/mol. What is the molecular formula of vitamin C?

How To Solve It Find the simplest formula Figure out what to multiply by determining the ration

of the simplest to the molecular masses.

Writing and Balancing Equations

word:

formula:

Balancing Equations

Ca + O2 CaO

Mg + N2 Mg3N2

AgNO3 + Cu Cu(NO3)2 + Ag

http://richardbowles.tripod.com/chemistry/balance.htm

Mass Relations from Equations

The coefficients of a balanced equation represent the number of _______________ of reactant and products

Example

Ammonia is used in fertilizer and is made by reacting nitrogen of the air with hydrogen. (a) How much ammonia (in grams) is formed from 1.34 mol of nitrogen? (b) how much nitrogen (in grams) is required to form 1.00 kg of ammonia? (c) How much hydrogen (in grams) is needed to react with 6.00 grams of nitrogen?

How To Solve It Write a balanced equation for this reaction Use the mole rations (coefficients of the reaction) to

relate moles of one substance to moles of another. Change from moles to grams.

Limiting Reactant Limiting reactant: The reactant that

_________________ the amount of _____________.

http://www.chem.tamu.edu/class/majors/tutorialnotefiles/limiting.htm

Example

If 3.5 grams of copper is added to 6.0 grams of AgNO3, which one is the limiting reactant?

Cu + AgNO3 Cu(NO3)2 + Ag

How To Solve ItTake grams of reactant #1 and find the mass of the

product.Take grams of reactant #2 and find the mass of the

product.The reactant that produces less product is the limiting reactant

Example 2Identify the limiting reactant when 1.7 grams of

sodium reacts with 2.6 L of chlorine to produce salt.

Na + Cl2 NaCl

Experimental Yield; Percent Yield

Percent Yield:

Actual Yield:

Expected Yield:

http://www.800mainstreet.com/6/0006-007-percent-yield.html

ExampleA piece of copper with a mass of 5.00 grams is placed in a solution of silver nitrate. The silver

metal that is produced has a mass of 15.2 grams. What is the percent yield?

[Hint: 5.00 g Cu -> ? g Ag (theoretical yield)]Cu + AgNO3 Cu(NO3)2 + Ag

Example 2Determine the percent yield for the reaction between 2.80 grams of Al(NO3)3 and excess NaOH if 0.966

grams of Al(OH)3 is recovered. Al(NO3)3 + NaOH NaNO3 + Al(OH)3