THE MOLE (a counting unit).again!

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1 Name: Period: Date: THE MOLE (a counting unit).again! A mole represents a, much in the same way that a dozen represents a set of twelve. 1 dozen eggs = 12 eggs; 1 mol eggs = eggs 1 dozen carbon atoms = 12 carbon atoms; 1 mol carbon atoms = carbon atoms The number is known as. If you write out Avogadro s number, it looks like this: 602,200,000,000,000,000,000,000 Remember: 1 mole of atoms = atoms 1 mole of molecules = molecules 1 mole of formula units = formula units 1 mole of ions = ions Atomic Mass vs. Molar Mass: = the mass of ONE ATOM expressed in atomic mass units (amu) o Ex: Oxygen s atomic mass = amu; this is the average mass of oxygen atom = the mass of ONE MOLE of atoms, molecules, or formula units expressed in grams o Ex: Oxygen s molar mass = g; this is the mass of oxygen atoms Atomic Mass vs. Molar Mass Element & Symbol Atomic Mass Average mass of 1 Atom Molar Mass Mass of 1 mole of atoms (6.02 X atoms) Carbon (C) Helium (He) 12.0 amu 4.00 amu 1

2 ACIDS: You need to know these! Hydrochloric Acid = Nitric Acid = Sulfuric Acid = Carbonic Acid = Phosphoric Acid = Acetic Acid = I. CALCULATING MOLAR MASS: Find the molar mass of each of the following compounds: 1. Phosphoric Acid 2. Calcium Nitrate 3. Iron (III) Carbonate 2

3 Molar Mass Homework #1-9 Below Find the molar mass for the following compounds: 1) sulfuric acid 2) iron (II) bromide 3) manganese(ii) phosphate 4) diphosphorous pentoxide Answer the following questions based on your notes. 5) is the mass of ONE MOLE of atoms, molecules, or formula units expressed in 6) is the mass of ONE ATOM expressed in 7) What is the numeric value of the mole? 8) What does the mole measure? 9) The mole is also referred to as number. 3

4 II. FINDING PERCENT COMPOSITION: = is the percent by mass of each element in the compound. The percent composition is the same regardless of the size of the sample. Ex: H 2 0 is ALWAYS 11.2 % hydrogen and 88.8% oxygen (by mass) The percent composition of the elements in a compound adds up to. Formula Used: Molar Mass of the element in a compound Total Molar Mass of the compound X 100 Or think of it as: Part _ Whole X 100 Steps: 1. Find molar mass of each element (parts) 2. Find the total molar mass of the compound (whole) 3. Part Whole X Evaluate your answer (percentages should add to approximately 100%) Ex: Find the percent composition of aluminum sulfate. NOTE: Therefore, a 100g sample of Al 2 (SO4) 3 would contain g Al, g S, and g O 4

5 % Composition Homework: # 1-4 Below 1. Find the percent composition of magnesium hydroxide. 2. Find the percent composition of calcium cyanide. 3. Find the percent composition of nickel (II) iodide. 4. Find the percent composition of copper (I) sulfide. 5

6 III. CONVERSIONS BETWEEN GRAMS & MOLES o KEY IDEA: It is important to know the following conversion: The molar mass of a compound or the mass an element is equal to 1 mole of that compound or element. Ex: 1 mole of carbon is equal to 12 grams of carbon! Ex: of water is equal to (molar mass) of water o Use a T-chart to convert from what you know to what you do not know. Use your conversion factors so cancel out! Ex #1: How many moles are represented by 11.5 g of magnesium hydroxide? Ex #2: How many grams of aluminum sulfide are present in 0.44 moles of aluminum sulfide? 6

7 Grams & Moles Conversion Homework = #1-4 Below 1. How many grams of barium cyanide are present in moles of barium cyanide? 2. How many moles of calcium bromide are present in 50.4 grams of calcium bromide? 3. How many grams of calcium hydroxide are present in 1.26 moles of calcium hydroxide? 4. How many moles of acetic acid are present in 86.2 grams of acetic acid? 7

8 IV. CALCULATION of FORMULAS: 2 types of formulas: 1. (M.F.) = shows the types and numbers of atoms combined in a single molecule. o Ex: C 6 H 12 O 6 (glucose) Actually has 24 atoms! 2. (E.F.) = a chemical formula showing the simplest whole number ratio of atoms in a compound. o Ex: Reduce glucose C 6 H 12 O 6 by dividing all the subscripts by 6 the empirical formula would be o In the chart below, fill in the empirical formula given the molecular formula: Molecular Formula Empirical Formula H 2 O 2 H 2 O C 8 H 16 C 2 H 4 o Notice 2 things: 1. Some molecular formulas be reduced (H 2 O) 2. Several compounds can the same E.F., but each compound has its own molecular formula WHY DO WE USE THE EMPIRICAL FORMULA IF IT CONTAINS LESS INFORMATION? It is easier to experimentally determine the empirical formula of a compound than the molecular formula. So the E.F. is usually found 1 st as a step towards finding the molecular formula. 8

9 Steps to finding an EMPIRICAL FORMULA: 1. The amount of each element should be listed in grams. If analysis of the compound is in percent, convert to grams: assume a 100 g sample of the compound. 2. Convert grams of EACH element to moles (T-chart). 3. Divide moles of each element by the smallest number of moles. 4. Round each answer from 3 to the nearest whole number and write the empirical formula using these numbers as subscripts. * NOTE: ROUND ALL NUMBERS to Ex #1: What is the empirical formula for a compound if a sample contains 0.9g of calcium and 1.6g of chlorine? Ex # 2: What is the empirical formula for a compound that is 40% C, 6.71% H, and 53.3% O? 9

10 Empirical Formula Homework: #1-4 Below 1. Calculate the empirical formula of a compound that contains 1.67g of cerium, Ce, and 4.54g of iodine, I Methylpropene is a compound used to make synthetic rubber. A sample of 2-methylpropene contains 0.566g C and g H. Determine its empirical formula. 3. Determine the empirical formula of a compound containing 63.50% silver, 8.25% nitrogen, and 28.25% oxygen. 4. Freons are gaseous compounds used in refrigeration. A particular freon contains 9.93% C, 58.6% Cl, and 31.4% F by mass. What is the empirical formula of this freon? 10

11 Steps to finding a MOLECULAR FORMULA 1. If it is not given, determine the empirical formula of the compound. (Follow all steps necessary to determine an empirical formula) 2. Calculate molar mass of the empirical formula. 3. Divide the molar mass of the by the molar mass determined from the. 4. Round the answer to 3 to the nearest whole number and multiply all subscripts in the empirical formula by this number. Ex #1: What is the molecular formula of a substance that has an empirical formula of AgCO 2 and a molar mass of 304g/mol? Ex #2: An unknown compound contains 85.64% carbon and 14.36% hydrogen. It has a molar mass of g/mol. Find its molecular formula. 11

12 Molecular Formula Homework: #1-7 Below 1. The molar mass of benzene, an important industrial solvent, is 78.0g/mol and its empirical formula is CH. What is the molecular formula for benzene? 2. What is the molecular formula of dichloroacetic acid, if the empirical formula is CHOCl and the molar mass of the acid is 129g/mol? 3. A compound used as an additive for gasoline to help prevent engine knock, shows the following percentage composition: 24.27% C, 4.07% H, and 71.65% Cl. The molar mass is known to be g/mol. Determine the empirical formula and the molecular formula for this compound. 12

13 4. Suppose a sample of cyclohexane contains g of carbon and g of hydrogen. The molar mass of cyclohexane is 84.2 g/mol. Determine the molecular formula. Answer the following questions based on your notes. 5. The specifies the actual number of atoms of each element in one molecule or formula unit of the substance. 6. The for a compound is the formula with the smallest wholenumber ratio between elements. 7. What is the empirical formula for C 10 H 8? 13

V. HYDRATES: copper II sulfate pentahydrate CuSO 4 5H 2 O Suppose an ionic substance is dissolved in water. The water can be evaporated to leave the solid ionic compound.

= an ionic compound containing water molecules incorporated into its solid crystal structure o In other words, a hydrate is a collection of (negative ions), (positive ions), and = the ionic compound

produce an anhydrous salt can be illustrated as follows: hydrate + heat anhydrous salt + water Naming Hydrates & Writing Hydrate Formulas: o Prefixes are used as coefficients in the following manner

14 V. HYDRATES: copper II sulfate pentahydrate CuSO 4 5H 2 O Suppose an ionic substance is dissolved in water. The water can be evaporated to leave the solid ionic compound. SOME ionic compounds, however, will form solid crystals that incorporate (where the water molecules are weakly attracted to the ions in the crystal structure). = an ionic compound containing water molecules incorporated into its solid crystal structure o In other words, a hydrate is a collection of (negative ions), (positive ions), and = the ionic compound that remains after the water has been removed (usually by heating) from the hydrate o Note: salt = ionic compound (usually an ionic compound that does not contain OH ions) The heating of a hydrate to produce an anhydrous salt can be illustrated as follows: hydrate + heat anhydrous salt + water Naming Hydrates & Writing Hydrate Formulas: o Prefixes are used as coefficients in the following manner in the chemical formulas for hydrates. o The chemical formula for magnesium sulfate heptahydrate is 7 moles of H 2 O are associated with every 1 mole of MgSO 4. o The chemical formula for zinc sulfate dihydrate is 2 moles of H 2 O are associated with every 1 mole of ZnSO 4. o What is the name of the following hydrate, FePO 4 4H 2 O? MOLAR MASS OF HYDRATES: When determining the molar mass of a hydrate, the molar mass of the associated water must be included. EX #1: Calculate the molar mass of calcium sulfate dihydrate. 14

15 PERCENT COMPOSITION of HYDRATES: Steps: 1. Find molar mass of water. 2. Find the molar mass of the salt. 3. Add the mass of the water and the salt in order to get the total mass of the hydrate. 4. Mass of Water (part) X 100 Mass of Hydrate (whole) Ex: What percentage of water is found in sodium sulfide nonahydrate? EMPIRICAL FORMULA of a HYDRATE: Steps: 1. Identify what you know and what you do not know. 2. All amounts should be listed in grams. If analysis is in percent, convert to grams: assume a 100 g sample. 3. Convert grams of anhydrous salt to moles. 4. Convert grams of water to moles. 5. Divide moles by the smallest number of moles. 6. Round each answer from 5 to the nearest whole number and these numbers become the COEFFICIENTS for the salt and water. Ex: Suppose a hydrate contains g barium iodide and 0.887g water. Determine the formula of the hydrate. 15

16 Hydrate Homework: # Determine the percentage of water in copper (II) sulfate pentahydrate. 2. Suppose a hydrate contains 0.391g Li 2 SiF 6 and g H 2 0. Determine the formula of the hydrate. 3. Determine the percentage of water in sodium carbonate monohydrate. 16

17 4. Suppose a hydrate contains 0.737g magnesium sulfate and 0.736g water. Determine the formula of the hydrate. 5. Suppose a hydrate contains 76.9% calcium sulfite and 23.1% water. Determine the formula of the hydrate. 6. Suppose a hydrate contains 89.2% barium bromide and 10.8% water. Determine the formula of the hydrate. 17

18 7. The salt is the ionic compound that remains after the water has been removed from the hydrate. 8. A is an ionic compound containing water molecules incorporated into its solid crystal structure. 9. How can water molecules be removed from a hydrate? 10. What is the formula for nickel II chloride hexahydrate? 11. How many water molecules are present in the following hydrate: nickel II chloride hexahydrate? 12. Write the name of the following compound: MgCO 3 5H

19 THE MOLE & MATH REVIEW WORKSHEET 1) Calculate the molar mass for the following: a) Aluminum sulfate b) Ammonium phosphate 2) Convert: a) 6.38 moles of iron (II) phosphate to g b) 5.49 moles of potassium iodide to g c) 188 g calcium hydroxide to moles d) 84.2 g potassium phosphate to moles 19

20 3) Find the percent composition of zinc hydroxide. 4) Determine the percent of water in sodium sulfate decahydrate. 5) Determine the empirical formulas for the following two compounds that were analyzed and found to contain the following: a) 3.30 g magnesium, 21.7 g bromine b) 40.23% potassium, 26.95% chromium, 32.81% oxygen 20

21 6) A compound of aluminum and chlorine is composed of 9.00 g of aluminum for every 35.5 g of chlorine. The molar mass of this compound is 267 g/mol. Determine the empirical formula and the molecular formula. 7) A compound with a molar mass of g/mol is found to be 40.00% carbon, 6.71% H, and 53.28% oxygen. Determine the empirical formula and the molecular formula of the compound. 8) What is the formula for a hydrate that is 90.7% strontium oxalate and 9.30% water? 21

22 9) What is the formula for a hydrate that is grams of Mo 2 S 5 and 66.5 grams of H 2 O? 10) The is the mass of one mole of atoms, molecules, or formula units and is expressed in. 11) The specifies the actual number of atoms of each element in one molecule or formula unit of the substance. 12) is the numeric value of the mole. 13) The salt is the ionic compound that remains after the water has been removed from the hydrate. 14) The is the mass of one atom and is expressed in. 15) The for a compound is the formula with the smallest whole-number ratio between elements. 16) What does the mole measure? 17) A is an ionic solid with trapped water molecules. 18) What is the empirical formula for C 6 H 8 O 6? 19) The mole is also referred to as number. 20) How many water molecules are present in the following hydrate: barium hydroxide octahydrate? 21) Write the formulas for the following acids: a) Carbonic acid b) Sulfuric acid c) Phosphoric acid d) Nitric acid e) Acetic acid f) Hydrochloric acid 22) What is the formula for sodium acetate trihydrate? 23) Write the name of the following compound: CoCl 2 6H

23 Unit Learning Map (11 days): Mole & Math Mrs. Hostetter Class: Academic Chemistry A - Grade 11 Unit Essential Question(s): How do you analyze and solve chemistry math problems? Optional Instructional Tools: Guided Notes Lab Materials: Chalk Lab MgO Lab Hydrate Lab Concept Concept Concept Concept Molar mass Percent composition Conversions Empirical and molecular formulas Lesson Essential Questions: Lesson Essential Questions: Lesson Essential Questions: Lesson Essential Questions: How is molar mass determined? How is percent composition determined? How are molar mass and Avogadro s number used in conversion? How are empirical and molecular formulas determined? Vocabulary: Vocabulary: Vocabulary: Vocabulary: Percent composition Molar mass Avogadro s number Mole Atomic mass Formula mass Molar mass Empirical formula Molecular formula Hydrate Anhydrous 23

24 Math & Moles Vocabulary: 1) Mole = unit of measurement for an amount of a something; a counting unit 2) Atomic mass = the mass of one atom expressed in atomic mass units 3) Molar mass = the mass of one mole of atoms, molecules, or formula units expressed in grams 4) Percent Composition = is the percent by mass of each element in the compound Steps: 1. Find molar mass of each element (parts) 2. Find the total molar mass of the compound (whole) 3. Part X 100 Whole 4. Evaluate your answer (percentages should add to approximately 100%) 5) Avagadro s number = x ) Molecular formula (M.F.) = shows the types and numbers of atoms combined in a single molecule Steps to finding a MOLECULAR FORMULA 1. If it is not given, determine the empirical formula of the compound. (Follow all steps necessary to determine an empirical formula) 2. Calculate molar mass of the empirical formula. 3. Divide the molar mass of the compound by the molar mass determined from the empirical formula. 4. Round the answer to 3 to the nearest whole number and multiply all subscripts in the empirical formula by this number. 7) Empirical formula (E.F.) = a chemical formula showing the simplest whole number ratio of atoms in a compound Steps to finding an EMPIRICAL FORMULA: 1. The amount of each element should be listed in grams. If analysis of the compound is in percent, convert to grams: assume a 100 g sample of the compound. 2. Convert grams of EACH element to moles (T-chart). 3. Divide moles of each element by the smallest number of moles. 4. Round each answer from 3 to the nearest whole number and write the empirical formula using these numbers as subscripts. 8) Hydrate = an ionic compound containing water molecules incorporated into its solid crystal structure 9) Anhydrous salt = the ionic compound that remains after the water has been removed (usually by heating) from the hydrate ACIDS: You need to know these! Hydrochloric Acid = HCl Nitric Acid = HNO 3 Phosphoric Acid = H 3 PO 4 Sulfuric Acid = H 2 SO 4 Carbonic Acid = H 2 CO 3 Acetic Acid = CH 3 COOH 24

23 carbon atoms The number is known as Avogadro s d Number.

23 carbon atoms The number is known as Avogadro s d Number. THE MOLE (a counting unit).again! i A mole represents a set or group, much in the same way that a dozen represents a set of twelve. 1 dozen eggs = 12 eggs; 1 mol eggs = 6.022 10 23 eggs 1 dozen carbon