HW 3 15 Hydrates Notes IC Hydrates HW 4 Water in a Hydrate IC/HW Unit 8 Test Review HW 5 X Unit 8 Test In class on 2/13 and 2/14

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1 Name: Unit 8- The Mole Day Page # Description IC/HW Due Date Completed All 2 Warm-up IC Notes on the Mole IC The Mole IC Chemical Quantities HW 2 10 Percent Composition Notes IC X 2 Gum Lab IC/HW Percent Composition HW 2 Empirical and Molecular 13 Formula Notes IC 2 Empirical and Molecular 14 Formulas Practice HW 3 15 Hydrates Notes IC Hydrates HW 4 Water in a Hydrate IC/HW Unit 8 Test Review HW 5 X Unit 8 Test In class on 2/13 and 2/14 Unit 8: The Mole Page 1

2 Warm-up Day 1 1. If you are making 113 dozen mini cupcakes, and each batch makes 60 mini cupcakes, how many batches will you need to make? Day 2 1. How many atoms are in 2.5 moles of silver? 2. What is the molar mass of calcium phosphate? Day 3 1. What is the empirical formula for a compound which contains % aluminum, % sulfur, and % oxygen? Day 4 1. Magnesium chloride from a hydrated salt. When a sample of magnesium chloride is analyzed, it is found to contain % water. Determine the hydrate formed. Day 5 1. How many moles are in 1.20*10 25 atoms of iron? Unit 8: The Mole Page 2

3 Calculating the Molar Mass of a Compound The mass on the periodic table is known as the Molar Mass. It has units of g/mol. 1. Write the formula 2. Calculate the mass by adding up the masses of each element in the compound. 3. Make the unit g/mol. Example: Calculate the mass of one mole of calcium chloride. o Write the formula o Calculate the mass o Change the unit Barium nitrate Xenon tetrachloride Sodium Phosphate Carbon dioxide Potassium sulfide Unit 8: The Mole Page 3

4 Notes on the Mole A mole is a counting number. One mole is a specific number of atoms, molecules or formula units. Avogadro s number is. Now we can relate the atomic mass unit to the gram. 1 atom of carbon 12 has a mass of amu. 6.02*10 23 atoms of carbon-12 have a mass of g. 1 mole of carbon atoms have a mass of g. A formula unit is the lowest whole number ratio of atoms or ions in a compound. If you had 1.0 mol of quarters and stacked them up, how many times could you get to the moon and back? (1 quarter = 2.0 mm thick; the distance to the moon is km) Calculate the number of formula units present in 3.45 moles of barium nitrate. Calculate the number of molecules in 19.3 moles of ammonia (NH 3 ). Calculate the mass of 7.89*10-20 atoms of oxygen. Unit 8: The Mole Page 4

5 The Mole 1. A mole is defined as the amount of substance that contains as many particles as there are atoms in 2. Avogadro s number is equal to 3. The molar mass of a given substance is defined as 4. Recall that one atomic mass unit (amu) is defined as a relative unit used to express the masses of atoms (or molecules). 4. Perform the following conversions, using dimensional analysis. Mass Molar mass Moles 6.02 x Particles PT to find molar mass Avagadro s number (atoms, molecules) a) Calculate the mass of 1.73 mol of zirconium (Zr) mole Zr x g Zr = g Zr 1 mole Zr b) What is the mass in grams of 3.50 moles or the element copper? Unit 8: The Mole Page 5

6 c) Calculate the number of moles of zinc (Zn) in a sample that weighs 143 grams. d) A chemist produced 11.9 grams of AL. How many moles of aluminum were produced? e) Calculate the number of atoms of in a sample of calcium (Ca) with a mass of 6.14 grams g Ca x 1 mole Ca x atoms Ca = atoms Ca g Ca 1 mole Ca f) Determine the number of atoms in 1.50 grams of carbon. g) Calculate the mass of a sample of platinum (Pt) that contains 2.15 x atoms. Unit 8: The Mole Page 6

7 Chemical Quantities Show ALL work for the following problems!! g of Nitrogen is how many moles? 2. How many molecules are in 112.5g of dinitrogen tetroxide. 3. What is the mass of 6.70 x formula units of Lead (IV) Oxide? 4. How many molecules are in 56.2g of carbon dioxide? 5. How many molecules are in 36.5 g of water? Unit 8: The Mole Page 7

8 6. What is the mass of 4.67 x molecules of xenon pentafluoride? 7. How many atoms of chlorine are in a 56.2 g sample? 8. How many formula units are in 4.56 g of Zinc hydroxide? 9. How many atoms of fluorine are in a 56.8 g sample? 10. What is the mass of 8.96 x molecules of carbon tetrafluoride. Unit 8: The Mole Page 8

9 PERCENT COMPOSITION NOTES Percent composition refers to what percent of the compound is made up of each element. To calculate the percent composition, divide the mass of the element by the molar mass of the compound. If there is more than one atom of an element, you must multiply the molar mass by the number of moles. Let s calculate the percent composition of Oxygen and Hydrogen in water. Molar mass of oxygen: g Molar mass of hydrogen: g Molar mass of water: g The percent composition of oxygen is: If the two percents add up to 100 %, a good indication that you did the problem correctly Unit 8: The Mole Page 9

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12 Empirical and Molecular Formula Notes Empirical Formulas- Indicate the of atoms present in a compound. Molecular Formulas- Indicate the of atoms present in a compound. Ex: Glucose Steps to calculate an empirical formula: 1. Start with the mass of each element given in the problem. (If percents are given, assume the sample has 100 g, and change the percentage unit to grams.) 2. Convert to moles. 3. Divide each by the smallest number of moles to get the ratio. (If necessary, multiply to get whole numbers.) 4. Answers in #3 become subscripts. Ascorbic Acid (vitamin C) is 40.92% Carbon, 4.58% Hydrogen and 54.50% Oxygen by mass. Calculate the empirical formula for Ascorbic Acid. A g sample of methyl benzoate, a compound used in the manufacture of perfumes, is found to contain g of carbon, g of hydrogen and g of oxygen. What is the empirical formula of methyl benzoate. Steps to calculate a molecular formula: 1. Calculate the empirical formula. 2. Calculate the molar mass of the empirical formula. 3. Divide the mass of the molecular formula (given) by the mass of the empirical formula. 4. Multiply the subscripts in the empirical formula by the answer in step 3. Mesitylene, a hydrocarbon that occurs in crude oil, is 89.92% carbon. The molar mass of this compound is 121 g/mol. Calculate the empirical and molecular formulas of this substance. Unit 8: The Mole Page 12

13 Empirical and Molecular Formulas Practice 1. What is the empirical formula of a compound that is 25.9% nitrogen and 74.1% oxygen? 2. What is the empirical formula of a compound that is 79.9% carbon and 20.1% hydrogen? 3. What is the empirical formula of a compound that is 17.6% Na, 39.7% Cr and 42.7% O? 4. You find that 7.36g of a compound contains 6.93g of oxygen while the rest is hydrogen. If you know the molar mass of the compound is 34.0g/mol what is the molecular formula? 5. What is the molecular formula of a compound that is 54.5% carbon, 13.6% hydrogen and 31.8% nitrogen? Its molar mass is 88g/mol. 6. What is the molecular formula of a compound that is 40.0%C, 53.4%O and 6.6%H. Its molar mass is 120 g/mol. Unit 8: The Mole Page 13

14 Hydrates Notes A hydrate is with a specific number of molecules around it. o To name a hydrate, name the salt, then use the covalent pre-fixes to indicate the number of waters. Follow the pre-fix with the word hydrate. EX: MgSO 4 7H 2 O (Magnesium sulfate heptahydrate) o CuCl 2 6H 2 O An Anhydrous compound contains, but has the capability to water. Remember the formula for percent error! The percent of calcium in calcium chloride was experimentally determined to be 32.1%. Calculate the % error. Unit 8: The Mole Page 14

15 Hydrates 1. Name the following hydrates. a. NaC 2 H 3 O 2 3H 2 O b. Ba(OH) 2 8H 2 O c. CoCl 2 6H 2 O 2. Write the formula for the following hyrdrates. a. Calcium chloride dihyrdrate b. Ammonium oxalate monohydrate c. Iron (III) Phosphate hexahydrate 3. Calculate the % water in each of the following hydrates. a. Sodium carbonate decahydrate b. Barium hydroxide octahydrate. c. Strontium chloride hexahdrate. Unit 8: The Mole Page 15

16 4. A hydrated sodium tetraborate is commonly called Borax. Chemical analysis indicates that this hydrate is 52.8% sodium tetraborate [Na 2 B 4 O 7 ] and 47.2% water. Determine the formula and name the hydrate. 5. A g sample of a hydrate of magnesium iodide is heated until its mass is reduced to g and all water has been removed. What is the formula of the hydrate? 6. The data table below shows data from an experiment to determine the formulas of hydrated barium chloride. Determine the formula for the hydrate and the name of the hydrate. Mass of empty crucible Mass of hydrate and crucible Initial mass of hydrate Mass after heating Mass of anhydrate g g g Unit 8: The Mole Page 16

17 Unit 8 Test Review 1. The molecular formula of allicin, the compound responsible for the characteristic smell of garlic, is C 6 H 10 OS 2. (a) What is the molar mass of allicin? (b) How many moles of allicin are present in 5.00 mg of this substance? (c) How many molecules of allicin are present in 5.00 mg of this substance? (d) How many sulfur atoms are present in 5.00 mg of allicin? 2. A sample of glucose, C 6 H 12 O 6, contains 5.77 x atoms of carbon. (a) How many atoms of hydrogen does the sample contain? (b) How many molecules of glucose does the sample contain? (c) What is the mass of the sample? Unit 8: The Mole Page 17

18 3. Calculate the percent composition of Oxygen in the following compounds: calcium carbonate, lead (II) hydroxide, acetic acid, and magnesium phosphate. 4. Adrenaline, a hormone secreted into the bloodstream in times of danger or stress is 59.0% carbon, 7.1% Hydrogen, 26.2% oxygen and 7.7% nitrogen. The molar mass of adrenaline is 180 g/mol. Calculate the molecular formula of adrenaline. 5. The characteristic odor of pineapple is due to ethyl butyrate, a compound containing carbon, hydrogen and oxygen. Combustion of 2.78 mg of ethyl butyrate produces 6.32 mg of CO 2 and 2.58 mg of water. The molar mass of ethyl butyrate is g/mol. Determine the molecular formula of ethyl butyrate. 6. Epsom salts, a substance used as a strong laxative by veterinarians, is a hydrate of magnesium sulfate. When g of the hydrate is heated all the water of hydration is lost leaving g of the anhydrate. Determine the formula of this hydrate and name the hydrate. Unit 8: The Mole Page 18