Stoichiometry …like a beautiful sunset on a serene lake – NOT!

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Stoichiometry …like a beautiful sunset on a serene lake – NOT!

What the heck is Stoichiometry Stoichiometry is the study of quantities of materials produced and consumed in chemical reactions. Or, in a way normal people (not honors students) could understand… … solving problems using relationships found in balanced, chemical equations! Stoichiometry is the study of quantities of materials produced and consumed in chemical reactions. Or, in a way normal people (not honors students) could understand… … solving problems using relationships found in balanced, chemical equations!

A mole is a counting number used by chemists …Kind of like 1 dozen eggs – 12 eggs Avogadro defined the mole as the number of Carbon atoms in exactly 12 grams of pure Carbon – 12 (think the graphite in a pencil!) It was determined that 1 mole = 6.02 x 10 23 units The units are usually atoms or molecules This number is called AVOGADRO’S NUMBER! MOLE (a mole is a unit or have you heard containing 6 x 10 to the 23 rd )

Just How Big is This Number? (not as big as your hips or mouth!!) How big is 6.02 x 10 23 ? A huge number! 1 mole of marbles would cover the entire earth a depth of 50 miles! 1 mole sheets of paper would go to the moon and back 80 billion times. 1 mole of pennies- each of us on earth could spend 1 million dollars each hour (day and night) and have ½ of it left if we died at age 70! (Much too big a number to comprehend) How big is 6.02 x 10 23 ? A huge number! 1 mole of marbles would cover the entire earth a depth of 50 miles! 1 mole sheets of paper would go to the moon and back 80 billion times. 1 mole of pennies- each of us on earth could spend 1 million dollars each hour (day and night) and have ½ of it left if we died at age 70! (Much too big a number to comprehend)

Comparisons of 1 mole of different elements Aluminum6.02 x 10 23 atoms26.98 grams Gold6.02 x 10 23 atoms196.97 grams Boron6.02 x 10 23 atoms10.81 grams

So… what is the connection between moles and atomic weights? The atomic weights (or the mass numbers or the atomic masses) of the elements on the periodic table are equal to 1 mole of that substance. That’s why we LOVE the periodic table!

You have 10 g of Al. Calculate the number of moles AND the number of atoms. Remember: the mass of 1 mole of Al equals 26.98 or 27 grams (the at. wt.)

Mole Map

A silicon chip used in your cell phone has a mass of 5.68 mg (which is 0.00568g). How many Si atoms are present in this chip?

Co is a metal added to steel (a mixture) to help the steel resist corrosion. You have 5.00 x 10 20 atoms of Co. Calculate: a.The number of moles: b.The mass of Cobalt:

Molecular or Formula Weights A formula weight gives the mass of 1 mole of a molecule. Find the formula weight of CH 4 (a byproduct of Chipotle)

Calculate the formula weight of NaCl

Calculate the formula weight of C 10 H 6 O 3, a natural herbicide (weed killer) and dye in Rit Dye.

Now, nerds of the world…calculate the number of moles of C 10 H 6 O 3 in 0.0156 g

Isopentyl acetate (C 7 H 14 O 2 ) is the compound responsible for the scent of bananas. Bee’s also release this same compound when they sting in order to attract other bees (to the buffet) and join in the attack. (smell you bee sting next time!) They release 1 microgram in each bee sting. 1.How many molecules of C 7 H 14 O 2 are released in one bee sting?

How many atoms of C are present in one bee sting? (a fact you have always wanted to know)

Percent Composition Ethanol, an additive to gas (and alcoholic drinks) has the formula C 2 H 5 OH. Find the % of each element in ethanol. STEP 1: STEP 2:

Find the mass % of each element in C 10 H 14 O

Penicillin, an antibiotic, has the formula C 14 H 20 N 2 SO 4. 1.Find the % of Nitrogen in penicillin. 2.Find the number of moles of penicillin if you give a patient a 250 mg tablet.

A empirical formula is the simplest, whole number ratio of atoms. Most formulas are empirical. What is the key? If it CAN’T be reduced, it is empirical. If it CAN be reduced, it is a molecular formula. What are these? Na 2 SO 4 C 12 H 22 O 11 C 6 H 12 O 6 N 4 O 12

To find the Empirical Formula (from %) 1.Convert % data to grams (% means “parts per hundred”). 2.Convert the grams to moles (÷ by the atomic weight) 3.Divide by the smallest to the get the simplest, whole-number ratio. 1.Convert % data to grams (% means “parts per hundred”). 2.Convert the grams to moles (÷ by the atomic weight) 3.Divide by the smallest to the get the simplest, whole-number ratio.

The junior scientist was given 38.67% C, 16.23% H and 45.1% N. Find the empirical formula.

A white powder was found near where mole died and was found to contain 43.64% P and 56.36% O. Find the empirical formula and name this molecule.

How many grams of potassium can be produced when 150.6 g of potassium sulfate is completely decomposed? First, find the % of K in K 2 SO 4 Next, multiply the % (decimal) by the mass given.

How many grams of Cu are needed to make 16.6 g of copper II phosphate? First, find the % of Cu: Second, multiply the % by the mass given: First, find the % of Cu: Second, multiply the % by the mass given:

Molecular Formulas A molecular formula is NOT the simplest formula (it can be reduced…but don’t do it!) Formula: – W – Where X is an integer A molecular formula is NOT the simplest formula (it can be reduced…but don’t do it!) Formula: – W – Where X is an integer

A compound with an empirical formula of CH 5 N has a molecular weight of 93 g/mole. Find the molecular formula.

Find the empirical and molecular formulas (normal kids don’t get to do this….you’re lucky!) for a compound that is 71.65% Cl, 24.27% C, and 4.07% H. The molecular formula weight is 98.96 g/mol. Four Steps to find the Molecular Formula: 1.Find the empirical formula: 2.Find the empirical formula weight: Four Steps to find the Molecular Formula: 1.Find the empirical formula: 2.Find the empirical formula weight:

3. Find X (X = Molec.fwt/Emp. Fwt) 4. Multiply X by the empirical formula to get the molecular formula. 3. Find X (X = Molec.fwt/Emp. Fwt) 4. Multiply X by the empirical formula to get the molecular formula.

CH 4 + O 2 → CO 2 + H 2 O In a chemical reaction, atoms have been rearranged but have NOT been created or destroyed. This is why we have to balance every chemical reaction/equation. Balance CH 4 + O 2 → CO 2 + H 2 O Balance HCl + NaHCO 3 → CO 2 + H 2 O + NaCl When balancing equations, the formulas must NEVER be changed. We may just add coefficients. CH 4 + O 2 → CO 2 + H 2 O In a chemical reaction, atoms have been rearranged but have NOT been created or destroyed. This is why we have to balance every chemical reaction/equation. Balance CH 4 + O 2 → CO 2 + H 2 O Balance HCl + NaHCO 3 → CO 2 + H 2 O + NaCl When balancing equations, the formulas must NEVER be changed. We may just add coefficients.

Balance the following reactions: C 2 H 5 OH + O 2 → CO 2 + H 2 O (NH 4 ) 2 Cr 2 O 7 → Cr 2 O 3 + N 2 + H 2 O C 3 H 8 + O 2 → CO 2 + H 2 O NH 3 + O 2 → NO + H 2 O

Diatomic Elements N 2, Cl 2, O 2, H 2, I 2, Br 2, F 2 Memory aid: I Bring Clay For Our New House Or Never Collect Our House Insurance Before Friday (this one is ghetto!) Diatomic elements always combine with a like atom when they are a free element. An arrow pointing up (↑) indicates a gas. The abbreviation ppt. or a down arrow (↓) indicates a precipitate. N 2, Cl 2, O 2, H 2, I 2, Br 2, F 2 Memory aid: I Bring Clay For Our New House Or Never Collect Our House Insurance Before Friday (this one is ghetto!) Diatomic elements always combine with a like atom when they are a free element. An arrow pointing up (↑) indicates a gas. The abbreviation ppt. or a down arrow (↓) indicates a precipitate.

Chemical equations indicate a… Chemical change. Remember, they must obey the Law of Conservation of Mass – the number of atoms of the reactants MUST equal the number of atoms of products. The coefficients from the balanced equation tell us the mole ratios of reacting substances (this will be important later!!!) 2K + S → K 2 S 2FeCl 3 + 3Ca(OH) 2 → 2Fe(OH) 3 + 3CaCl 2

Five Types of Chemical Reactions 1. Composition (or Combination) Reactions A + B → AB Sodium and sulfur yields _____________ 1. complete the word equation 2. write the correct formulas 3. Balance that bad boy! 1. Composition (or Combination) Reactions A + B → AB Sodium and sulfur yields _____________ 1. complete the word equation 2. write the correct formulas 3. Balance that bad boy!

Aluminum and iodine yields ??

2. Decomposition Reactions (6 types) Generic equation AB → A + B These are the opposite of Composition Reactions. Here, one thing is HEATED and it breaks down into two things. The best way to learn these six types of equations is to MEMORIZE them!!! Generic equation AB → A + B These are the opposite of Composition Reactions. Here, one thing is HEATED and it breaks down into two things. The best way to learn these six types of equations is to MEMORIZE them!!!

1. Binary Compound into Elements Arsenic III oxide yields when heated ______________ + ________________ Water yields with electricity _____________ + ____________. Arsenic III oxide yields when heated ______________ + ________________ Water yields with electricity _____________ + ____________.

2. Metal Carbonates form metal oxides and carbon dioxide Magnesium carbonate yield when heated _________________+ _________________ Sodium carbonate yields when heated _________________ + _________________ Magnesium carbonate yield when heated _________________+ _________________ Sodium carbonate yields when heated _________________ + _________________

3. Metal hydroxides yield metal oxides and water Potassium hydroxide yields when heated __________________ +________________ Calcium hydroxide yields when heated _________________ + _________________ Potassium hydroxide yields when heated __________________ +________________ Calcium hydroxide yields when heated _________________ + _________________

4. Metal chlorates yield metal chlorides and oxygen Potassium chlorate yields when heated _________________ + ___________________

Calcium bromate yields when heated _________________ + _________________ Iron II bromate yields when heated _________________ + _________________ Calcium bromate yields when heated _________________ + _________________ Iron II bromate yields when heated _________________ + _________________

6. Acids when heated form nonmetal oxides and water Carbonic acid when heated yields _________________ + __________________

3. Single Replacement Reactions (two types) A. Positive Replacement (3 types) AX + B → BX + A The single element will replace the positive element in the compound A. Positive Replacement (3 types) AX + B → BX + A The single element will replace the positive element in the compound

1. Replacement of a Metal by a more active metal Magnesium and calcium nitrate yields

2. Replacement of hydrogen in water by a metal (to form a metallic hydroxide and hydrogen gas) Aluminum and water yields

3. Replacement of H in an acid by a metal Aluminum and hydrochloric acid yields

B. Negative Replacement - Replacement of Halogens (1 type) A + MB → MA + B The halogens are Br -1, Cl -1, F -1, and I -1 and they are all diatomic when they stand alone (Br 2, Cl 2, F 2, and I 2 )

Hydrochloric acid and bromine yields…

4. Ionic/Exchange/Double Replacement Reactions AB + CD → AD + CB The product MAY produce a solid or a precipitate PRECIPITATE: an insoluble substance formed in solution. a liquid + liquid → solid but only one of the products may be a precipitate AB + CD → AD + CB The product MAY produce a solid or a precipitate PRECIPITATE: an insoluble substance formed in solution. a liquid + liquid → solid but only one of the products may be a precipitate

Solubility Rules See chart in your book, the chart in your handouts section or on the back of your Chem Helper.

Sodium hydroxide + iron III chloride →

Lead II nitrate + potassium iodide →

Sodium sulfate + lead II nitrate →

Combustion reactions are the burning of a fuel (usually a hydrocarbon like CH 4 ) with oxygen (O 2 ) to form CO 2 and H 2 O. Methane gas (CH 4 ) is burned in a furnace Combustion reactions are the burning of a fuel (usually a hydrocarbon like CH 4 ) with oxygen (O 2 ) to form CO 2 and H 2 O. Methane gas (CH 4 ) is burned in a furnace

Propane gas (C 3 H 8 ) is used to cook in most campers.

First 10 Hydrocarbons Methane CH 4 Octane C 8 H 18 Ethane C 2 H 6 Nonane C 9 H 20 Propane C 3 H 8 Decane C 10 H 22 Butane C 4 H 10 Pentane C 5 H 12 Hexane C 6 H 14 Heptane C 7 H 16 Methane CH 4 Octane C 8 H 18 Ethane C 2 H 6 Nonane C 9 H 20 Propane C 3 H 8 Decane C 10 H 22 Butane C 4 H 10 Pentane C 5 H 12 Hexane C 6 H 14 Heptane C 7 H 16

MASS/MASS Problems Five Steps: 1.Balance the equation 2.Find the formula weights of given and wanted 3.Convert the known mass to moles 4.Use the mole ratio to get from the given to the wanted 5.Convert the moles to grams of the wanted Five Steps: 1.Balance the equation 2.Find the formula weights of given and wanted 3.Convert the known mass to moles 4.Use the mole ratio to get from the given to the wanted 5.Convert the moles to grams of the wanted

Lithium hydroxide is used in the space shuttle to remove exhaled carbon dioxide from the living environment to form lithium carbonate and water. What mass of CO 2 can be absorbed by one Kg of lithium hydroxide?

Sodium bicarbonate is often used as an antacid because it neutralizes HCl secreted by the stomach to form sodium chloride, water and carbon dioxide. How much baking soda is required to neutralize 6.8 g of HCl?

Summer Job: Preparing lunch at Boy Scout camp 400 hungry boy scouts need lunch. You have 35 loaves of bread, 17 jars of jelly and 2 jars of peanut butter. During the sandwich-making process (the “reaction”) which “reactant” will you run out of first (bread, jelly, or pb?) The “reactant” that you run out of 1 st will stop the sandwich-making process. And, 300 boy scouts are going to tie you up in the knots they just learned to tie and hang you in an oak tree (they just learned to identify trees) 400 hungry boy scouts need lunch. You have 35 loaves of bread, 17 jars of jelly and 2 jars of peanut butter. During the sandwich-making process (the “reaction”) which “reactant” will you run out of first (bread, jelly, or pb?) The “reactant” that you run out of 1 st will stop the sandwich-making process. And, 300 boy scouts are going to tie you up in the knots they just learned to tie and hang you in an oak tree (they just learned to identify trees)

Limiting Reagent Problems X + Y → XY 3g + 4g → both are used up completely What would happen if we reacted 3g of X with 5 grams of Y? X + Y → XY 3g + 4g → both are used up completely What would happen if we reacted 3g of X with 5 grams of Y?

Ammonia is an important fertilizer used by farmers. It is produced by a famous reaction called the Haber process. Suppose 25,000 grams of N 2 and 5000 grams of H 2 are mixed to form NH 3. Find the limiting reactant and calculate the amount of ammonia produced. First, write the balanced equation: Next, find the moles of each reactant:

Next, use the mole bridge to find the moles NEEDED.

Now that you know the limiting reactant, use it to work a mass/mass problem to find grams of ammonia

Ammonia and copper II oxide yields nitrogen gas, copper, and water vapor. If 18.1 g of ammonia is reacted with 90.4 g of copper II oxide, which is the limiting reagent? How many g of nitrogen will be formed?

Wood alcohol is methanol (CH 3 OH). If hydrogen + carbon monoxide yields methanol, write the balanced equation.

If 68.5 Kg of CO is reacted with 8.60 Kg of hydrogen, find the limiting reagent:

Now, calculate the mass of methanol produced.

If the actual yield is 35,700 g, calculate the % yield of CH 3 OH.

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