6.02 X Memorize this Number

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1 Honors Chemistry - Unit 6 Chapters 3 & 7 The Mole Math with Chemical Formulas Voc. Assignment Due: Quiz Date(s): TBA Problem Set (UT Quest) Due: Test Date: Unit 6 Packet - Page 1 of 14 **VOCABULARY Assignment** (Use the Study Skills Section of your textbook (in the appendix) to assist you in making a Concept Map from these vocabulary items/concepts): 1) molecular mass 2) formula mass 3) hydrate 4) mole 5) percent composition 6) empirical formula 7) molecular formula 8) formula unit 9) ionic compound 10) molecular compound 11) Avogadro s number (constant) 12) molarity FORMULA/CONSTANTS to be memorized Molar mass conversion; *Avogadro s number; *Molarity; Steps for empirical formula/ molecular formula problems OBJECTIVES: Be able to perform math functions with and without your calculator using correct scientific notation. Be able to find molecular/formula mass using the periodic table. Be able to calculate Molarity. Be able to calculate percent composition. Be able to determine empirical and molecular formulas using lab data. Percent to mass; mass to mole; divide by small; multiply to whole! Understand the mole and Avogadro s number. Be able to convert to/from atoms, ions, molecules, moles and grams. Guided Note-Taking for THE MOLE! What is a mole? l Official Definition l the amount of a substance that contains as many particles as there are atoms in exactly 12g of carbon-12 l A mole is a counting unit l just like a dozen l other examples.. Avogadro s Number l Constant l the number of particles in exactly one mole of a pure substance 6.02 X Memorize this Number 1 mol = 6.02 X10 23 of anything But most often the mole is used with atoms, ions, formula units or molecules

2 Examples of Conversion Factors: Unit 6 Packet - Page 2 of 14 1 mol 6.02 X atoms 1 mol 6.02 X ions or formula units 1 mol 6.02 X molecules Molar Mass l Mass in g of 1 mole of anything l For, the is equal to the. l 1 mol atomic wt. (g) Molar Mass Examples: 1 mol C and 12.0 g C

3 You try: 1 mol Ca 1 mol Fe g Ca g Fe Unit 6 Packet - Page 3 of 14 Now, you have Two conversion Factors for a mole.. Avogadro s number Molar mass 1 mol and 1 mol 6.02 X atoms, ions, formula units, or molecules? g Example 1 How many g in 2.0 mol of He? Example 2 How many moles in 3.01 X atoms Ag? Example 3 What is the mass of 1.20 X 10 8 atoms of Cu?? You try: Convert 11.5 g B to moles B Convert 8.0 X atoms of Ag to g Formula Mass/Molecular Mass/Molar Mass l Sum of masses in a compound Example: Molar Mass of sodium chloride NaCl Example: Molar Mass of Ca(NO3)2 You try: Calculate the molar mass of sodium phosphate Na3PO4

4 Calculate the molar mass for the following: Unit 6 Packet - Page 4 of 14 Molar mass can be used as conversion factors! 1 mol NaCl 1 mol MgCl2 1 mol Ca(NO3) g NaCl 95.21g MgCl g Ca(NO3)2 Example: How many mol in 127g barium chloride?

5 Unit 6 Packet - Page 5 of 14

6 Guided Note-Taking on Percent Composition Unit 6 Packet - Page 6 of 14 l Percent composition is the percent by mass of each element in a compound. l Percent composition is the same, regardless of the size of the sample. Percent Composition Calculations % comp = mass of element X 100% = % element in the compound molar mass of cpd Example: Find the % composition of Cu2S l First, find the molar mass: l Next, find the % of each element l Next, check your work do the %s add up to 100? You try: 1) barium chloride 2) sodium phosphate Answer: barium 65.90%; chloride 34.10% Answer: sodium 42.07%; phosphorus 18.89%; oxygen 39.04%

7 Unit 6 Packet - Page 7 of 14 Guided Note-Taking on Empirical Formulas l Empirical Formula = Simplest Formula To find the empirical formula from data: 1. Assume 100% sample; change % to grams for each element (% to mass) 2. Find moles from the grams of each element (mass to moles) 3. Find the smallest whole # ratio by dividing by the smallest number of moles (divide by small) 4. If necessary, multiply to get rid of fractions. (multiply to whole!)

8 Unit 6 Packet - Page 8 of 14 Example 1: A compound is 78% B and 22% H. What is the empirical formula? First, change % to grams and find moles: Next, divide all mole numbers by the smallest number of moles: Finally, use these whole numbers as the number of each individual element. They are the subscripts. Example 2: l Analysis shows a compound to contain 26.56% K, 35.41% Cr, and 38.03% O. Find the empirical formula of this compound: l First (always!) assume 100g sample, convert % to g and then find moles of each element. Next, Conversion to moles: Next, divide all numbers by the smallest whole number to find the smallest whole number ratios: l So, if you have: multiply all by:.25 or or l For our example:

9 You Try: Unit 6 Packet - Page 9 of 14 What is the empirical formula if we have a sample containing 66.0% Ca and 34.0% P? Answer: Ca3P2 You Try: Find the empirical formula of a compound with 32.38% Na; 22.65% S; and 44.99% O. Answer: Na2SO4

10 Molecular Formula Unit 6 Packet - Page 10 of 14 Molecular Formula = Actual Formula Example: C2H6 molecular CH3 empirical MF = (EF)x where X = Molecular mass Empirical mass Example: The empirical formula of a compound was found to be P2O5. Experimentation shows that the molar mass of this compound is g/mol. What is the compound s molecular formula?

11 Guided Note-Taking on Moles in Solution (Molarity) Unit 6 Packet - Page 11 of 14 l Molarity is the term used for moles dissolved in solution l Symbol for Molarity = M l Definition moles of solute per liter of solution l Formula M = moles solute (mol) liter solution (L) Example 1: What is the molarity of a 0.5L solution containing 2 moles of NaCl? Example 2: What is the molarity of a 250 ml solution containing 12.7 g of lithium bromide? Example 3: How would you make 500mL of a 0.32M solution of LiBr and water? You try: 1) Calculate the M of a 700. ml solution of 23.2g calcium chloride 2) How would you make a 0.2 L solution of 0.50 M CaCl2 solution?

12 CONVERSION WORKSHEET Unit 6 Packet - Page 12 of 14 NAME: A. Convert the following: x atoms of N to moles g of carbon to moles x atoms of Tl to grams moles of Cd(IO3)2 to formula units g of Ca to moles g of potassium nitride to formula units x formula units of CsBr to grams moles of Cl to grams moles of carbon dioxide to molecules x formula units of copper (II) sulfate to grams g of trisulfur dioxide to moles x atoms of Mg to moles g of Ni to atoms B. Molarity Practice 14. What is the molarity of the following? a g Fe(NO3)2 in 100 ml of solution. b g of ammonium iodide in 0.5 L of solution. c. 3.2 kg of cobalt (II) sulfate in 4.3 L of solution. 15. Describe the preparation of the following: a. 200 ml of 3.0 M NiCl2 b. 1 L of 1.5 M AgF

13 Chapter Seven Practice Sheet Unit 6 Packet - Page 13 of 14 CONVERSIONS 1. How many moles is 23.8 g of dinitrogen pentoxide? 2. How many formula units in 27 moles of iron (II) acetate? 3. How many g in 2.5 x formula units of Calcium chloride? 4. How many molecules in 32.5 g of water? PERCENT COMPOSITION Find the percent composition of the following: 5. KNO3 6. Mg(NO3)2 7. The % of O in CuSO4 Empirical, Molecular, and Molarity 8. Analysis of a sample of sulfuric acid shows it to contain 0.17 g of hydrogen, 2.82 g of sulfur, and 5.67 g of oxygen. What is the empirical formula for this compound? 9. Analysis of a salt results in the following composition: 3.47 g of Na, 2.12 g of N and 7.27 g of oxygen. What is the simplest formula of this salt? 10. A barium salt is found to contain g of barium, 5.12 g of sulfur and g of O. What is the empirical formula? 11. A compound contains: 26.7 % C, 2.2 % H and 71.1 % O. The molecular weight of the compound is 90. What is the compound s molecular formula? 12. A certain compound contains only C, H, and O. If 54.6 % is C and 9.0 % is H and the molecular weight is 176, what are the compounds empirical and molecular formulas? 13. The percentage composition of ethane gas is 80.0 % C and 20.0 % H. The molecular weight for ethane is 30. What is the molecular formula for this compound? 14. What is the M of 32.3 g of calcium chloride in 750 ml of solution? 15. How do you prepare 600 ml of 1.25 M CuO?

14 REVIEW Chemistry Unit Six Unit 6 Packet - Page 14 of How many moles are present in g of nitrogen dioxide? 2. How many moles of nitrate are present in one mole of magnesium nitrate? 3. How many formula units in 64.3 g of lithium sulfate? 4. What is the molarity of 9.94 g of cobalt (II) sulfate in 250. ml of solution? 5. How would you prepare 250. ml of a M solution of Cd(IO3)2? 6. What is the percentage of nitrogen in urea, CO(NH2)2? 7. A compound contains 27.3 g of C and 72.7 g of O. What is the empirical formula for this compound? 8. Benzoic acid is a compound used as a food preservative. The compound contains 68.8 % C, 4.95 % H and 26.2 % O by mass. What is the compound s empirical formula? 9. Ascorbic acid, also known as Vitamin C, has a percentage composition of 40.9 % carbon, 4.58 % hydrogen, and 54.5 % oxygen. Its molecular mass is u. What is its molecular formula? ANSWERS: mol NO moles x formula units Li2SO M CoSO4 5. Add g of Cd(IO3)2to enough water to make 250. ml of solution % N 7. CO2 8. C7H6O2 9. C6H8O6