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Chapter 4 101Lesson 19 – Chapter 4 Formula Calculations – The Mole Goal • To begin to understand the process of quantifying matter on microscopic and macroscopic scales Why? When matter reacts, we represent these reactions by single or multiple formula units. However, when we quantify matter in the laboratory, we use measurable quantities like mass and volume. We will need a means to express very small things like molecules in a quantity large enough to useful and measurable. We would also like to be able to represent these quantities in easy to understand values. Additional Resources A Conceptual Introduction to Chemistry, Chapter 4, p. 116-128 Prerequisites • Be able to read a formula • Understand average atomic masses for the elements Terms mole Homework Problems: Online homework portions of Chapter 4 Textbook Chapter 4: 1-44, 95-101 Atomic Masses and Formulas 1. What is the average atomic mass of the elements listed? a. Silicon ________________ b. Zinc ________________ c. Carbon ________________ d. Nitrogen ________________ e. Potassium ________________ f. Hydrogen ________________ g. Oxygen ________________ h. Chlorine ________________ i. Fluorine ________________ j. Calcium ________________ k. Sulfur ________________ l. Aluminum ________________ m. Sodium ________________ n. Phosphorus ________________Lesson 19 1022. How many atoms of which elements are in each compound? a. Ca3(PO3)2 b. CH3(CH2)5OH c. (NH4)2CO3 d. H3PO4 Atomic Mass Units and Mass in Grams 3. If one gram of carbon-12 contains 5.02 × 1022 atoms, what is the mass equivalent of atomic mass units to grams? (units of g·amu–1)? 4. For the elements, convert the masses to grams. a. Carbon b. Oxygen c. Nitrogen d. Hydrogen 5. Above, for each element, show the equality of one atom and its mass in grams and amu. (ie 1 atom of hydrogen = 1.008 amu, etc)Chapter 4 103The Mole 6. With regards to carbon, show what the mole is. 7. How many chocolate candies are in 0.050 mol of chocolate candies? 8. If each candy has a mass of 1.0 oz (they are small candies), what is the total mass (in tons) of candy? (16 oz = 1 pound and 2000 pounds = 1 ton). Use dimensional analysis or the factor label method (remember Chapter 1) 9. If every student at UWM (28 000 students) were to help each the candies and were able each able to consume 500 candies per day, how long would it take to eat 0.050 mol of candy? (How sick of chocolate would we all be?) 10. How many oxygen atoms in 1 mole of oxygen atoms? What is the mass of 1 mole of oxygen atoms? 11. How many nitrogen atoms in 1 mole of nitrogen atoms? What is the mass of 1 mole of nitrogen atoms? 12. How many hydrogen atoms in 1 mole of hydrogen atoms? What is the mass of 1 mole of hydrogen atoms?Lesson 19 10413. How many hydrogen atoms are in 1.008 g of hydrogen? 14. How many oxygen atoms are in 2.5 mol of oxygen atoms? a. What is the mass of 2.5 mol of oxygen atoms? Molar Masses 15. Determine the molar masses. a. Magnesium phosphate Step 1: The formula – give the formula for the substance Æ Mg3(PO4)2 Step 2: The elements – read the formula 3 Mg atoms, 2 phosphorus atoms, 8 oxygen atoms in one formula unit 3 moles of Mg atoms, 2 moles of phosphorus atoms, 8 moles of oxygen atoms in one mole of magnesium phosphate formula units. Step 3: Their masses – what is the mass of 1 mole of each of the elements in the compound? Mg: 3 moles × 24.31 g⋅mol−1 = 72.93 g P: 2 moles × 30.97 g⋅mol−1 = 61.94 g O: 8 moles × 16.00 g⋅mol−1 = 128.00 g Step 4: The sum of its parts – one mole of the substance has a mass in grams (its molar mass) equal to the mass of each element which comprises the compound. 72.93 + 61.94 + 128.00 = 262.87 g⋅mol−1 b. Sulfur


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UW-Milwaukee CHEM 100 - Lecture Notes

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