Percent Composition Empirical Formulas Moles Stoichiometry 1

Formula Mass The formula mass of a molecule, formula unit, or ion is the sum of the average atomic masses of all the atoms represented in the formula. The formula mass of KClO 3 : K= Cl= O= 2

For each of the following calculate the mass, show all work and include all units. 1.BaCO 3 Ba= C= O= 2. Sr(NO 3 ) 2 Sr= N= O= 3

3.Fe 2 O 3 Fe= O= 4.Ca(HCO 3 ) 2 Ca= H= O= 4

3. Aluminum Oxide 4. Strontium Hydroxide 5

Molar Mass or Gram Formula Mass This value is numerically equal to the formula mass but it is in grams. It is the mass of one mole of a substance. g mole 6 The molar mass of Lithium is __________. The molar mass of copper is _________.

1. Molar mass of KClO 3 is: K= Cl= O= 2.The molar mass of carbon dioxide (CO 2 ) is: C= O= 34

3.The molar mass of glucose (C 6 H 12 O 6 ) is: C= H= O=

What is the molar mass of barium nitrate? 7

PERCENT COMPOSITION The percent by mass of each element in a compound. Round to tenth place! Percent composition of element in compound should equal 100%. 8

Find the percent composition (percent by mass) of copper in copper (I) sulfide, Cu 2 S. Find the percent composition of both element in lead (II) chloride. 9

HYDRATES In the process of crystallization, the water molecules bind to the salt to form hydrates. Hydrates are represented as follows: Na 2 CO 3 10H 2 O (sodium carbonate decahydrate) 10

Anhydrate (Anhydrous Salt) No water is attached to the salt. The water has been evaporated off by adding heat. Na 2 CO 3 Classify as a hydrate or anhydrate: 1. CuSO 4 5H 2 O 2. CuSO 4 3. CuCl 2 2H 2 O

Na 2 CO 3 10H 2 O (sodium carbonate decahydrate) 1.Calculate the molar mass. Na= C= O= H 2 O =

2. Calculate the percent composition of water in Na 2 CO 3 10H 2 O. 11

Calculate the formula mass first and then the % composition of each element in the compound. 1. CuSO 4 5H 2 O Formulas mass: 12

2. CuSO 4 5H 2 O % Cu % H 2 O % S % O % H 13

3. CuCl 2 2H 2 O Formula Mass: 14

CuCl 2 2H 2 O % Cu % Cl % H %O %H 2 O 15

If an unknown substance is made of 5 grams of potassium and 7 grams of sulfur and 10 grams of oxygen. What is the percent composition of each element? 16

A student has an 8.2 gram piece of bubble gum. After chewing the gum, it has a mass of 3.7 grams. What is the percent composition of sugar in the gum? 17

EMPIRICAL FORMULAS The chemical formula that represents the simplest (lowest) atomic ratio in which elements can combine. Formulas for ____________ are the empirical formula because they are ALWAYS expressed as the lowest possible ratios. Ex: Formulas for molecular compounds are NOT necessarily the empirical formula. 18

Molecular Formula The actual chemical formula for a molecule. It may contain atoms in multiples of their simplest ratio. Molecular : C 6 H 12 O 6, S 2 O 4, H 2 O 2 Empirical: ________, ______, ______ 19

Determining Empirical Formulas from Percent Composition: EXAMPLE: What is the empirical formula of a compound that is 78.6% Boron and 21.4% Hydrogen? STEP 1: Convert to percent to mass. (Assume you have 100 g. of the given substance) 78.6% B → 21.4% H → STEP 2: Determine how many moles of each element you have by dividing by the molar mass of that element. STEP 3: Reduce the molar ratio by dividing by the smaller number. 7.1 moles B is lowest number STEP 4: Round to the whole numbers and insert the numbers as subscripts. 20

1. What is the empirical formula of a compound containing 32.38% Na, 22.65% S and 44.99% O? 21

2. What is the empirical formula of a compound containing 26.56% potassium, 35.41% chromium, and the remainder is oxygen? 22

Sometimes you are not given the information in percents, but you are given the information in grams. In this case, skip step one and go directly to step 2 (calculate the number of moles you have). 3. In a g. sample, g. are phosphorous and the rest is oxygen. What is the empirical formula for this compound? 23

4. Analysis of a compound indicates that it contains 0.606grams of nitrogen and grams oxygen. What is the empirical formula for the compound? 24

DETERMINING MOLECULAR FORMULAS Empirical Formula= Molecular formula= In order to determine the molecular formula, you must know the molecular mass! 25

What is the molecular formula of a compound with empirical formula BH 3 and molecular mass 28 g? 1.Add up the empirical mass. g B + g H = grams empirical mass 2. Divide molecular mass by empirical mass. Molecular mass : g = Empirical mass : g 3. Multiple the subscripts in the empirical form by your answer. X BH 3 = B H 26

1.What is the molecular formula of a compound with a molecular mass of 34 g. that consists of 0.44 g. H and 6.92 g. O? 27

2. What is the empirical formula of a compound that contains 65.5% carbon, 5.5% hydrogen, and 29.9% oxygen? What is the molecular formula if the molecular mass is 110g.? 28

bowe/sections/projectfolder/flashfiles/stoic hiometry/empirical.htmlhttp:// bowe/sections/projectfolder/flashfiles/stoic hiometry/empirical.html Composition of hydrate simulation

THE MOLE 29

What is a mole? A. A small furry animal B. Clusters of pigmented cells that often appear as small, dark brown spots C. The SI base unit that measures an amount of substance/ a number 6.02 x 10 23

The Mole 1 dozen = 1 gross = 1 ream = 1 mole = x There are exactly 12 grams of carbon-12 in one mole of carbon

Avogadro’s Number 6.02 x is called “Avogadro’s Number” in honor of the Italian chemist Amadeo Avogadro ( ). Amadeo Avogadro I didn’t discover it. Its just named after me! 31

1 mole of books= books 1 mole of socks = socks 1 mole atoms = atoms 32

Remember Molar Mass (Gram Formula Mass) the UNIT is Mole= 33

Conversion Factors involving the mole: These are used to convert from mass to moles and from moles to mass: Grams of Element or Moles of Element Moles of Element Grams of Element 35

use molar mass Grams Moles Calculations with Moles: Converting mass to moles 36

MASS TO MOLE CONVERSIONS If you are dealing with compounds, you must first find the molar mass of the compound before you use the conversion factors!!! 37

Converting moles to mass How many grams of lithium are in 3.50 moles of lithium? 3.50 mol Li = 1 X 38

Converting moles to mass 1.What is the mass in grams of 3.50 mol of the element copper, Cu? 39

Converting moles to mass 2. What is the mass in grams of 2.25 mol of the element iron? 40

Converting moles to mass 3. What is the mass in grams of mol of the element potassium, K? 41

Converting moles to mass 4. What is the mass in grams of 2.5 mol of sodium chloride, NaCl? 42

Converting moles to grams 5. What is the mass in grams of 5 mol of water, H 2 O?

use molar mass Grams Moles Calculations with Moles: Converting mass to moles

Converting mass to moles How many moles of lithium are in 18.2 grams of lithium? 18.2 g Li = X 1

Mass to mole conversions 1. A chemist produces 11.9 g of aluminum. How many moles is this?

Mass to mole conversions 2. How many moles of calcium, Ca, are in 5.00g of calcium?

Mass to mole conversions 3. How many moles of gold, Au, are in g of gold?

Mass to mole conversions 4. How many moles of water, H 2 O are in 50 g of water?

Mass to mole conversions 5. How many moles of magnesium oxide (MgO) are in 20g of MgO?

Moles to Particles/ Particles to Moles Conversions Particles include: 1 mole of atoms = 6.02 x atoms 1 mole of ions = 6.02 x ions 1 mole of molecules = 6.02 x molecules ________________ = _______________

use Avogadro’s number Moles particles Calculations

Calculations with Moles: How many atoms of lithium are in 3.50 moles of lithium? 3.50 mol Li = atoms Li X 1

Particles to Moles Conversions 1. How many moles of silver are in 3.01x10 23 atoms of silver?

Particles to Moles Conversions 2. How many moles of fluorine are in 1.50x10 23 atoms of fluorine?

Moles to Particles 3. How many atoms of carbon are in 5 moles of carbon?

Moles to Particles 4. How many atoms of silicon are in 0.75 moles of silicon?

Moles to Particles 5. How many molecules of water are in 4.25 moles of water?

Particles to Moles 6. How many moles of carbon dioxide are in x10 23 molecules of CO 2 ?

Stoichiometry

Chocolate Chip Cookies!! 1 cup butter 1/2 cup white sugar 1 cup packed brown sugar 1 teaspoon vanilla extract 2 eggs 2 1/2 cups all-purpose flour 1 teaspoon baking soda 1 teaspoon salt 2 cups semisweet chocolate chips Makes 3 dozen How many eggs are needed to make 3 dozen cookies? How much butter is needed for the amount of chocolate chips used? How many eggs would we need to make 9 dozen cookies? How much brown sugar would I need if I had 1 ½ cups white sugar?

Cookies and Chemistry…Huh!?!? Just like chocolate chip cookies have recipes, chemists have recipes as well Instead of calling them recipes, we call them reaction equations Furthermore, instead of using cups and teaspoons, we use moles Lastly, instead of eggs, butter, sugar, etc. we use chemical compounds as ingredients

STOICHIOMETRY Mathematics which predicts that amount of a substance involved in a chemical reaction. REACTION STOICHIOMETRY:

In order to correctly solve stoichiometry problems, you MUST be able to correctly balance equations!! Stoichiometry problems are solved by using RATIOS from the balanced equation.

Chemistry Recipes Looking at a reaction tells us how much of something you need to react with something else to get a product (like the cookie recipe) Be sure you have a balanced reaction before you start! Example: Na + Cl 2  NaCl This reaction tells us that by mixing __ moles of sodium with 1 mole of chlorine we will get 2 moles of sodium chloride What if we wanted 4 moles of NaCl? 10 moles?

4Fe+ 3O 2 → 2 Fe 2 O 3 How many moles of iron? How many moles of oxygen? How many moles of iron (III) oxide? 2Al + 3CuSO 4 → Al 2 (SO 4 ) 3 + 3Cu How many moles aluminum? How many moles of copper (II) sulfate? How many moles of aluminum sulfate? How many moles of copper?

Practice Write the balanced reaction for hydrogen gas reacting with oxygen gas. –How many moles of reactants are needed? –What if we wanted 4 moles of water? –What if we had 3 moles of oxygen, how much hydrogen would we need to react and how much water would we get? –What if we had 50 moles of hydrogen, how much oxygen would we need and how much water produced?

MOLE RATIOS A conversion factor that relates the amount of moles of any 2 substances involved in a chemical reaction. Al 2 O 3 (l) → Al (s) + O 2 (g)

MOLE RATIOS 1. 4Fe+ 3O 2 → 2 Fe 2 O Al + 3CuSO 4 → Al 2 (SO 4 ) 3 + 3Cu

3. 2Al 2 O 3 → 4Al + 3O 2 4. N 2 + 3H 2 → 2NH 3 5. H 2 O (l) → H 2 (g) + O 2 (g) 6.5C (s) + 2SO 2 (g) → CS 2 (l) + 4CO (g)

Mole Ratios These mole ratios can be used to calculate the moles of one chemical from the given amount of a different chemical Example: How many moles of chlorine is needed to react with 5 moles of sodium (without any sodium left over)? 2 Na + Cl 2  2 NaCl 5 moles Na = 1 X

Mole-Mole Problems: You are given the amount of one substance in moles and asked to solve for the amount of another substance. How many MOLES of Al (s) will be produced from the decomposition of 13.0 mol of Al 2 O 3 (l) ? 2Al 2 O 3 (l) → 4Al (s) + 3O 2 (g)

1. How many moles of O 2 (g) will be produced when 36 mol Al (s) are produced from the decomposition of Al 2 O 3 (l) ? 2Al 2 O 3 (l) → 4Al (s) + 3O 2 (g)

2. How many moles of O 2 (g) are produced when 15 mol of Al 2 O 3 (l) react? 2Al 2 O 3 (l) → 4Al (s) + 3O 2 (g)

3. How many moles of NH 3 are produced when 0.60 mol of nitrogen react with hydrogen? Balance the equation. N 2 (g) + H 2 (g) → NH 3 (g)

4. How many moles of H 2 are needed to react with the 0.60 mol of N 2 ? N 2 (g) + 3H 2 (g) → 2NH 3 (g)

5. How many moles of O 2 are produced when 1.5 mol H 2 O are decomposed by electrolysis into H 2 and O 2 ? Balance the equation. H 2 O (l) → H 2 (g) + O 2 (g)

6. Given the balanced equation for the burning of isopropyl alcohol in air how many moles of O 2 are needed to react with 3.40 mol of C 3 H 7 OH? 2C 3 H 7 OH (l) + 9O 2 (g) → 6CO 2 (g) + 8H 2 O (g)

7. How many moles of CO 2 are formed when 3.4 mol of C 3 H 7 OH (l) react? 2C 3 H 7 OH (l) + 9O 2 (g) → 6CO 2 (g) + 8H 2 O (g)

8. How many moles of H 2 O are formed when 3.40 mol. of C 3 H 7 OH (l) react? 2C 3 H 7 OH (l) + 9O 2 (g) → 6CO 2 (g) + 8H 2 O (g)

9. How many moles CS 2 form when 2.70 mol of carbon react? Balance the reaction. C (s) + SO 2 (g) → CS 2 (l) + CO (g)

10. How many moles of C are needed to react with 5.44 mol of SO 2 ? 5C (s) + 2SO 2 (g) → CS 2 (l) + 4CO (g)

11. How many moles of CO form at the same time that mol of CS 2 form? 5C (s) + 2SO 2 (g) → CS 2 (l) + 4CO (g)

12. How many moles of SO 2 are required to make 118 mol of CS 2 ? 5C (s) + 2SO 2 (g) → CS 2 (l) + 4CO (g)

Conversions liters to moles 22.4 Liters of gas = 1 mole of gas 22.4 Liters gas = 1 mole of gas 1 mole of gas 22.4 Liters gas

↔ 1 mole 22.4 Liters of gas 6.022x10 23 atoms (Ne) or molecules (CO 2 ) or formula units (NaCl) Grams compound or element (Found on Periodic Table) ↔↔ How many liters of O 2 are present if you have 15 moles O 2 ?

↔ 1 mole 22.4 Liters of gas 6.022x10 23 atoms (Ne) or molecules (CO 2 ) or formula units (NaCl) Grams compound or element (Found on Periodic Table) ↔↔ How many moles are there in 30 liters of O 2 gas?

↔ 1 mole 22.4 Liters of gas 6.022x10 23 atoms (Ne) or molecules (CO 2 ) or formula units (NaCl) Grams compound or element (Found on Periodic Table) ↔↔ How many liters of H 2 O are present in 1.5 moles of H 2 O?