Stoichiometry

6 Problem-Solving Strategies Calculating Molar Mass Calculating Molar Mass Grams  Moles and Mole  Grams Conversions Grams  Moles and Mole  Grams Conversions Particles  Moles and Moles  Particles Conversions Particles  Moles and Moles  Particles Conversions Percent Composition and Empirical Formula Percent Composition and Empirical Formula Writing Balanced Chemical Equations Writing Balanced Chemical Equations Writing Balanced Chemical Formulas Writing Balanced Chemical Formulas

Molar Mass Find the mass of each element and add them all up Find the mass of each element and add them all up Units: g/mol Units: g/mol Ex. FeSO 4 Ex. FeSO 4 Fe: 56 Fe: 56 S: 32 S: 32 O: 16 x 4 = 64 O: 16 x 4 = g/mol

Grams  Moles & Moles  Grams Grams  Moles Grams  Moles Divide by the molar mass of the compound Divide by the molar mass of the compound Ex. How many moles in 50 grams of H 2 O? Ex. How many moles in 50 grams of H 2 O? 50g H 2 O x 1 mol = 2.78 mol H 2 O 50g H 2 O x 1 mol = 2.78 mol H 2 O 18 g 18 g Moles  Grams Moles  Grams Multiply by the molar mass of the compound Multiply by the molar mass of the compound Ex. How many grams in 2 moles H 2 O? Ex. How many grams in 2 moles H 2 O? 2 mol H 2 O x 18 g = 36 g H 2 O 2 mol H 2 O x 18 g = 36 g H 2 O 1 mol 1 mol

Particles  Moles & Moles  Particles Particles = Molecules = Atoms Particles = Molecules = Atoms Particles  Moles Particles  Moles Divide by Avogadro’s number Divide by Avogadro’s number Ex. How many moles in 3.75 x particles of H 2 O? Ex. How many moles in 3.75 x particles of H 2 O? 3.75 x10 23 particles H 2 O x 1 mol = mol H 2 O 3.75 x10 23 particles H 2 O x 1 mol = mol H 2 O 6.02 x particles 6.02 x particles Moles  Particles Moles  Particles Multiply by Avogadro’s number Multiply by Avogadro’s number Ex. How many particles in 2 moles H 2 O? Ex. How many particles in 2 moles H 2 O? 2 mol H 2 O x 6.02 x particles = 1.2 x particles H 2 O 2 mol H 2 O x 6.02 x particles = 1.2 x particles H 2 O 1 mol 1 mol

Percent Composition and Empirical Formula Percent Composition Percent Composition Find the molar mass and percent by mass of each element Find the molar mass and percent by mass of each element Ex. HClO 3 Ex. HClO 3 H: 1 H: 1 Cl: 35.5 Cl: 35.5 O: 16 x 3 = 48 O: 16 x 3 = 48 Total = 84.5 Total = 84.5 H: 1/84.5 x 100 =1% H: 1/84.5 x 100 =1% Cl: 35.5/84.5 x 100 = 42% Cl: 35.5/84.5 x 100 = 42% O: 48/84.5 x 100 = 57% O: 48/84.5 x 100 = 57% 1% H, 42% Cl, & 57% O Empirical Formula Simplest form of molecular formula Divide each element by atomic mass, divide by smallest molar value, multiply by whole number Ex % N & 63.16% O 36.84/14 = /16 = /2.63 = /2.63 = 1.5 1x 2 = x 2= 3 N 2 O 3

Balanced Chemical Equations Rewrite the equation with blanks in front of each element Rewrite the equation with blanks in front of each element Determine the number of each atom on each side Determine the number of each atom on each side Alter coefficients until same amount of each element on each side of the equation Alter coefficients until same amount of each element on each side of the equation Ex. H 2 + O 2  H 2 O Ex. H 2 + O 2  H 2 O H: 2  2 H: 2  2 O: 2  1 O: 2  1 2H 2 + O 2  2H 2 O

Balanced Chemical Formulas 1 st : Determine the equation 1 st : Determine the equation 2 nd : Balance the equation 2 nd : Balance the equation Ex. Liquid butane burns in oxygen to produce carbon dioxide and water vapor Ex. Liquid butane burns in oxygen to produce carbon dioxide and water vapor C 2 H 6 (l) + O 2 (g)  CO 2 (g) + H 2 O (g) C 2 H 6 (l) + O 2 (g)  CO 2 (g) + H 2 O (g) 2C 2 H 6 (l) + 7O 2 (g)  4CO 2 (g) + 6H 2 O (g) 2C 2 H 6 (l) + 7O 2 (g)  4CO 2 (g) + 6H 2 O (g)

Problem-Solving Gallery Walk

Procedures Part I Part I Each individual will have a total of 5 minutes per station Each individual will have a total of 5 minutes per station Each person is to copy and solve the question on their own paper. They also need to identify which strategy is represented Each person is to copy and solve the question on their own paper. They also need to identify which strategy is represented Part II Part II The group is to identify which strategy is represented in the question and come to a consensus on the answer they would like to submit for grading The group is to identify which strategy is represented in the question and come to a consensus on the answer they would like to submit for grading Only write the group’s final answer and identification of strategy on the index card; NO WORK SHOULD BE SHOWN ON THE INDEX CARD Only write the group’s final answer and identification of strategy on the index card; NO WORK SHOULD BE SHOWN ON THE INDEX CARD Turn in 1 index card per group at the end of the activity Turn in 1 index card per group at the end of the activity The group with the most questions right will receive 5 additional points added to last Monday’s test The group with the most questions right will receive 5 additional points added to last Monday’s test

Review Problems

Problem #2 2. Which procedure represents the safest technique to use for diluting a concentrated acid? Add the acid to the water quickly Add the acid to the water quickly Add the acid slowly to the water with steady stirring Add the acid slowly to the water with steady stirring Add the water to the acid quickly. Add the water to the acid quickly. Add the water slowly to the acid with steady stirring Add the water slowly to the acid with steady stirring

Problem # 3 3. A biochemist is performing an experiment to determine the effects of Chemical X on the growth of bacteria. Which tube is the control? a. Test tube 1 b. Test tube 2 c. Test tube 3 d. Test tube 4

Day 2

Mole  Mole Stoichiometric Conversions

Balance the equation __N 2 H 4 + __H 2 O 2  __N 2 + __H 2 O

Molar Ratio

Ratio of coefficients of the different compounds in a reaction/equation Ratio of coefficients of the different compounds in a reaction/equation Coefficient of desired on top and coefficient of given on bottom they cancel out Coefficient of desired on top and coefficient of given on bottom they cancel out

Example 1N 2 H 4 + 2H 2 O 2  1N 2 + 4H 2 O What is the molar ratio of N 2 H 4 /H 2 O 2 ? What is the molar ratio of N 2 H 4 /H 2 O 2 ? 1 mol N 2 H 4 /2 mols H 2 O 2 1 mol N 2 H 4 /2 mols H 2 O 2 What is the molar ratio of H 2 O 2 /H 2 O? What is the molar ratio of H 2 O 2 /H 2 O? 2 mols H 2 O 2 /4 mols H 2 O 2 mols H 2 O 2 /4 mols H 2 O

Mole  Mole Conversions Step 1: Write a balanced equation Step 1: Write a balanced equation Step 2: Determine the molar ratio of given and desired Step 2: Determine the molar ratio of given and desired Step 3: Convert moles of given to moles of desired by multiplying moles of given by molar ratio Step 3: Convert moles of given to moles of desired by multiplying moles of given by molar ratio

Example How many moles of H 2 O will be produced from 6 moles of H 2 O 2 ? How many moles of H 2 O will be produced from 6 moles of H 2 O 2 ? Step 1: Write balanced equation Step 1: Write balanced equation 1N 2 H 4 + 2H 2 O 2  1N 2 + 4H 2 O Step 2: Determine the molar ratio Step 2: Determine the molar ratio 4 mols H 2 O 2 mols H 2 O 2 Step 3: Multiply moles of given by molar ratio Step 3: Multiply moles of given by molar ratio 6 moles H 2 O 2 X 4 mols H 2 O = 12 moles H 2 O 2 mols H 2 O 2 2 mols H 2 O 2

Example How many moles of N 2 H 4 are needed to produce 16 moles of H 2 O? How many moles of N 2 H 4 are needed to produce 16 moles of H 2 O? Step 1: Write balanced equation Step 1: Write balanced equation 1N 2 H 4 + 2H 2 O 2  1N 2 + 4H 2 O Step 2: Determine the molar ratio Step 2: Determine the molar ratio 1 mols N 2 H 4 4 mols H 2 O Step 3: Multiply moles of given by molar ratio Step 3: Multiply moles of given by molar ratio 16 moles H 2 O X 1 mols N 2 H 4 = 4 moles N 2 H 4 4 mols H 2 O 4 mols H 2 O

Practice Problems

Determine the equation below How many moles of hydrogen are produced from the reaction of three moles of zinc (II) with an excess of hydrochloric acid? Zn + HCl  ZnCl 2 + H 2

How many moles of hydrogen are produced from the reaction of three moles of zinc with an excess of hydrochloric acid? Step 1: Write a balanced equation Step 1: Write a balanced equation Step 2: determine molar ratio Step 2: determine molar ratio Step 3: multiply given by molar ratio Step 3: multiply given by molar ratio

How many moles of oxygen are necessary to react with four moles of propane (C 2 H 6 )?

How many moles of potassium nitrate are produced when two moles of potassium phosphate react with two moles of aluminum nitrate?

Day 3

Mass  Mole ; Mole  Mass

When given the mass of one reactant or product, we can find the number of moles of a particular product or reactant When given the mass of one reactant or product, we can find the number of moles of a particular product or reactant And vice versa, when given the moles of one product or reactant, we can find the mass of a particular product or reactant And vice versa, when given the moles of one product or reactant, we can find the mass of a particular product or reactant

Mass  Mole; Mole  Mass Conversions Step 1: Write the balanced equation. Step 1: Write the balanced equation. Step 2: Determine the molar ratio. Step 2: Determine the molar ratio. Step 3: Convert grams of given to moles of desired. Step 3: Convert grams of given to moles of desired. ONLY WHEN GIVEN MASS IN THE ORIGINAL PROBLEM (ie- MASS  MOLE CONVERSION) ONLY WHEN GIVEN MASS IN THE ORIGINAL PROBLEM (ie- MASS  MOLE CONVERSION) Step 4: Convert moles of given to grams of desired Step 4: Convert moles of given to grams of desired ONLY WHEN GIVEN MOLES IN THE ORIGINAL PROBLEM (ie- MOLE  MASS CONVERSION) ONLY WHEN GIVEN MOLES IN THE ORIGINAL PROBLEM (ie- MOLE  MASS CONVERSION)

Example- Mass  Mole How many moles of H 2 O are produced when 64 g of O 2 react in the synthesis of water? Step 1: write a balanced equation Step 1: write a balanced equation 2H 2 + O 2  2H 2 O Step 2: determine molar ratio Step 2: determine molar ratio 2 mol H 2 O 1 mol O 2 Step 3: convert mass of given to moles of desired Step 3: convert mass of given to moles of desired 64 g O 2 x 1 mol O 2 x 2 mol H 2 O = 4 mol H 2 O 32 g O 2 1 mol O 2 Step 4: not needed only trying to get to moles not mass Step 4: not needed only trying to get to moles not mass

Example- Mole  Mass How many grams of KClO 3 are created when 1.02 moles KCl react in the decomposition reaction of KClO 3 ? Step 1: Write a balanced equation Step 1: Write a balanced equation 2KClO 3  2KCl + 3O 2 Step 2: determine molar ratio Step 2: determine molar ratio 2 mol KClO 3 2 mol KCl Step 3: not needed given moles Step 3: not needed given moles Step 4: convert moles of given to grams of desired Step 4: convert moles of given to grams of desired 1.02 mol KCl x 2 mol KClO 3 x g KClO 3 = 125 g KClO 3 2 mol KCl1 mol KClO 3 2 mol KCl1 mol KClO 3

Day 4

Catalyst 1) Given this equation: N 2 + 3H 2  2NH 3, write the following molar ratios: a) N 2 / H 2 a) N 2 / H 2 b) N 2 / NH 3 b) N 2 / NH 3 c) H 2 / NH 3 c) H 2 / NH 3 2) Answer the following questions for this equation: 2H 2 + O 2  2H 2 O a) What is the H 2 / H 2 O molar ratio? a) What is the H 2 / H 2 O molar ratio? b) Suppose you had 20 moles of H 2 on hand and plenty of O 2, how many moles of H 2 O could you make? b) Suppose you had 20 moles of H 2 on hand and plenty of O 2, how many moles of H 2 O could you make? c) What is the O 2 / H 2 O molar ratio? c) What is the O 2 / H 2 O molar ratio? d) Suppose you had 20 moles of O 2 and enough H 2, how many moles of H 2 O could you make? d) Suppose you had 20 moles of O 2 and enough H 2, how many moles of H 2 O could you make?

Mass  Mass Stoichiometric Conversions

Review

Moles  Moles Stoichiometry Step 1: Write a balanced equation Step 1: Write a balanced equation Step 2: Determine the molar ratio of given and desired Step 2: Determine the molar ratio of given and desired Step 3: Convert moles of given to moles of desired by multiplying moles of given by molar ratio Step 3: Convert moles of given to moles of desired by multiplying moles of given by molar ratio

Mass  Mole; Mole  Mass Conversions Step 1: Write the balanced equation. Step 1: Write the balanced equation. Step 2: Determine the molar ratio. Step 2: Determine the molar ratio. Step 3: Convert grams of given to moles of desired. Step 3: Convert grams of given to moles of desired. ONLY WHEN GIVEN MASS IN THE ORIGINAL PROBLEM (ie- MASS  MOLE CONVERSION) ONLY WHEN GIVEN MASS IN THE ORIGINAL PROBLEM (ie- MASS  MOLE CONVERSION) Step 4: Convert moles of given to grams of desired Step 4: Convert moles of given to grams of desired ONLY WHEN GIVEN MOLES IN THE ORIGINAL PROBLEM (ie- MOLE  MASS CONVERSION) ONLY WHEN GIVEN MOLES IN THE ORIGINAL PROBLEM (ie- MOLE  MASS CONVERSION)

Mass  Mass Stoichiometry Step 1: Write the balanced equation. Step 1: Write the balanced equation. Step 2: Determine the molar ratio. Step 2: Determine the molar ratio. Step 3: Convert grams of given to grams of desired. Step 3: Convert grams of given to grams of desired. 3-step conversion 3-step conversion

Example- Mass  Mass How many grams of H 2 O are produced when 64 g of O 2 react in the synthesis of water? Step 1: write a balanced equation Step 1: write a balanced equation 2H 2 + O 2  2H 2 O Step 3: determine molar ratio Step 3: determine molar ratio 2 mol H 2 O 1 mol O 2 Step 4: convert grams of given to grams of desired Step 4: convert grams of given to grams of desired 64 g O 2 x 1 mol O 2 x 2 mol H 2 O x 18 g H 2 O = 72 g H 2 O 32 g O 2 1 mol O 2 1 mol H 2 O

Practice Problems Refer to problems 12 & 13 from earlier handout

Problem 12 If 40.0 g of sulfur dioxide are formed in the reaction between sulfur and oxygen, what is the mass of oxygen used?

Problem 13 In the equation 2NaCl + H 2 SO 4  2HCl + Na 2 SO 4, what is the mass of sodium chloride that reacts with g of sulfuric acid?

Review Questions

Problem 6 The diagram below shows the results of Rutherford’s experiment in which he used a radioactive source to “shoot” alpha particles at a thin sheet of gold foil. Based on these results, what were Rutherford’s conclusions? Atoms are solid matter with positive and negative charges scattered throughout. Atoms are solid matter with positive and negative charges scattered throughout. Atoms are solid, positively charged matter with negatively charged electrons scattered throughout. Atoms are solid, positively charged matter with negatively charged electrons scattered throughout. Atoms are mostly empty space with small, dense, positively charged centers. Atoms are mostly empty space with small, dense, positively charged centers. Atoms are mostly empty space with small, dense, negatively charged centers. Atoms are mostly empty space with small, dense, negatively charged centers.

Day 5

Catalyst ***use molar mass or molar ratios to get to your answer*** Consider the reaction below which begins with 2.50 moles of Calcium Hydroxide and excess water. Consider the reaction below which begins with 2.50 moles of Calcium Hydroxide and excess water. CaH 2 + 2H 2 O  Ca(OH) 2 + 2H 2 How many moles of hydrogen will be produced? How many moles of hydrogen will be produced? What mass (grams) of water is needed? What mass (grams) of water is needed? How many moles of copper oxide would be needed to make 19.2 g of copper? How many moles of copper oxide would be needed to make 19.2 g of copper? 4CuO + CH 4 → 4Cu + CO 2 + 2H 2 O How much calcium oxide is produced by heating 25g of calcium carbonate? How much calcium oxide is produced by heating 25g of calcium carbonate? CaCO 3 → CaO + CO 2

Homework Answers A : g H 2 A : g H 2 B: g NH 3 B: g NH 3 C: g H 2 C: g H 2 1 A: 4.22 g AgCl A: 4.22 g AgCl 1B: 3.06 g BaCl 1B: 3.06 g BaCl 1C: g Ba(NO 3 ) 2 1C: g Ba(NO 3 ) 2 1D: g AgNO 3 1D: g AgNO g NaNO g CaC g O g Ag g H 2 O

Test Content Mole  Mole Conversions Mole  Mole Conversions Mass  Mole & Mole  Mass Conversions Mass  Mole & Mole  Mass Conversions Mass  Mass Conversions Mass  Mass Conversions Naming Compounds (Ionic and Covalent) Naming Compounds (Ionic and Covalent) Balancing Equations Balancing Equations Unit 2 Molar Conversions Unit 2 Molar Conversions

Naming Compounds Ionic Compounds Ionic Compounds Bond between metal and nonmetal Bond between metal and nonmetal Name the cation the element’s name and the anion with the ending ide Name the cation the element’s name and the anion with the ending ide Ex. NaCl – Sodium Chloride Ex. NaCl – Sodium Chloride Transition Metals: name using the same rule but use roman numerals to represent the charge of the transition metal Transition Metals: name using the same rule but use roman numerals to represent the charge of the transition metal Ex. Fe 2 O 3 - Iron (III) Oxide Ex. Fe 2 O 3 - Iron (III) Oxide Polyatomic ions: name the cation and the name of the anion is just the name of the polyatomic ion Polyatomic ions: name the cation and the name of the anion is just the name of the polyatomic ion Ex. CaSO 4 - Calcium Sulfate Ex. CaSO 4 - Calcium Sulfate Covalent Compounds 2 or more nonmetals Name the same as ionic compounds but with Prefixes Ex. N 2 O 5 – Dinitrogen Pentaoxide

Stoichiometry Practice Test 25 minutes

Test Questions