Chapter 3 Stoichiometry
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Transcript of Chapter 3 Stoichiometry
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Chapter 3
Stoichiometry
http://www.shodor.org/UNChem/basic/stoic/
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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
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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
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Calculating the Mass of a Compound
Compound Formula Formula Mass
Table salt
Potassium Bromide
Aluminum Hydroxide
Magnesium Iodide
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Calculating the Mass of a Molecule
Molecule Formula MolecularMass
Water
Dinitrogen Pentoxide
Simple Sugar
Sulfur Dioxide
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THINK
What is the difference between a compound and a molecule?
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A.M.U?!?!?!
Define:
Units:
Examples and Calculations:
http://en.wikipedia.org/wiki/Atomic_mass_unit
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What is Stoichiometry?
Define:
http://www.chem4kids.com/files/react_stoichio.html
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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
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Conversions
1 mole= atomic mass of substance
1 mole= 6.022 X 1023 atoms
1 mole= 22.4L
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1 mole of Ag= 1 mole of H2O= 1 mole of CO2
How many grams, liters and atoms are in the following?
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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
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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?
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How many atoms are in 16.2 grams of N2?
How much volume of ammonia will be present in 45.2 grams?
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If there are 44.5L of Hydrogen gas, how many grams are present?
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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
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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?
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How to Solve % of element = ____________________ x 100
Element Number of Moles
Atomic Mass Molar Mass
Compound mass =
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Use these numbers to determine the percent of each component:
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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?
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Simplest Formula from Chemical Analysis
Simplest formula: Gives the simplest _____________________ ___________ of the atoms present.
http://www.carlton.srsd119.ca/chemical/Molemass/empirical_formula.htm
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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.
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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!
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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)
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Molecular formula from Simplest Formula
The molecular formula is a _______________________ ________________ of the simplest formula.
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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?
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How To Solve It Find the simplest formula Figure out what to multiply by determining the ration
of the simplest to the molecular masses.
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Writing and Balancing Equations
word:
formula:
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Balancing Equations
Ca + O2 CaO
Mg + N2 Mg3N2
AgNO3 + Cu Cu(NO3)2 + Ag
http://richardbowles.tripod.com/chemistry/balance.htm
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Mass Relations from Equations
The coefficients of a balanced equation represent the number of _______________ of reactant and products
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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?
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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.
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Limiting Reactant Limiting reactant: The reactant that
_________________ the amount of _____________.
http://www.chem.tamu.edu/class/majors/tutorialnotefiles/limiting.htm
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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
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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
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Example 2Identify the limiting reactant when 1.7 grams of
sodium reacts with 2.6 L of chlorine to produce salt.
Na + Cl2 NaCl
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Experimental Yield; Percent Yield
Percent Yield:
Actual Yield:
Expected Yield:
http://www.800mainstreet.com/6/0006-007-percent-yield.html
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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
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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