CA_Lesson_5_Formulas_of_Hydrates_Powerpoint (1).pptx

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1. Formulas of Hydrates Lesson 5

2. Focus Question How can you determine the amount of water in a hydrate?

3. New Vocabulary hydrate

4. Review Vocabulary crystal lattice: a three-dimensional geometric arrangement of particles.

5. Naming Hydrates A hydrate is a compound that has a specific number of water molecules bound to its atoms. The bound water molecules are called waters of hydration. The number of water molecules associated with each formula unit of the compound is written following a dot. Sodium carbonate decahydrate = Na 2 CO 3 • 10H 2 O

6. Naming Hydrates In naming hydrates, prefixes are used to indicate the number of water molecules associated with each formula unit.

7. Analyzing a Hydrate When heated, water molecules are released from a hydrate, leaving an anhydrous compound. To determine the formula of a hydrate, find the number of moles of water associated with 1 mole of hydrate: Weigh hydrate. Heat to drive off the water. Weigh the anhydrous compound. Subtract and convert the difference to moles. The ratio of moles of water to moles of anhydrous compound is the coefficient for water in the hydrate.

8. Determining the Formula of a Hydrate Use with Example Problem 14. Problem A mass of 2.50 g of blue, hydrated copper sulfate (CuSO 4 • x H 2 O) is placed in a crucible and heated. After heating, 1.59 g of white anhydrous copper sulfate (CuSO 4 ) remains. What is the formula for the hydrate? Name the hydrate. Response ANALYZE THE PROBLEM You are given a mass of hydrated copper sulfate. The mass after heating is the mass of the anhydrous compound. You know the formula for the compound, except for x , the number of moles of water of hydration. KNOWN UNKNOWN mass of hydrated compound = 2.50 g CuSO 4 • x H 2 O formula of hydrate = ? mass of anhydrous compound = 1.59 g CuSO 4 name of hydrate = ? molar mass H 2 O = 18.02 g/mol H 2 O molar mass CuSO 4 = 159.6 g/mol CuSO 4 SOLVE FOR THE UNKNOWN Determine the mass of water lost. Subtract the mass of anhydrous CuSO 4 from the mass of CuSO 4 • x H 2 O. mass of hydrated copper sulfate 2.50 g mass of anhydrous copper sulfate −1.59 g mass of water lost 0.91 g

9. Determining the Formula of a Hydrate EVALUATE THE ANSWER Copper(II) sulfate pentahydrate is a common hydrate listed in Table 1 (from slide 6) . SOLVE FOR THE UNKNOWN Convert the known masses of H 2 O and anhydrous CuSO 4 to moles using a conversion factor—the inverse of molar mass—that relates moles and mass. Substitute mass CuSO 4 = 1.59 g, inverse molar mass CuSO 4 = 1 mol/159.6 g, and solve. Substitute mass H 2 O = 0.91 g, inverse molar mass H 2 O = 1 mol/18.02 g, and solve.   State the ratio of moles of H 2 O to moles of CuSO 4 . Substitute moles of H 2 O = 0.050 mol, moles of CuSO 4 = 0.00996 mol. Divide numbers, and cancel units to determine the simplest whole-number ratio. The ratio of H 2 O to CuSO 4 is 5:1, so the formula for the hydrate is CuSO 4 • 5H 2 O. The name of the hydrate is copper(II) sulfate pentahydrate.  

10. Uses of Hydrates Anhydrous forms of hydrates are often used to absorb water, particularly during shipment of electronic and optical equipment. Epsom salt (MgSO 4 • 7H 2 O) is used in bath salts to reduce inflammation and in gardening as a magnesium supplement. Hydrates such as Na 2 SO 4 ∙ 10H 2 O are used to store solar energy. When the Sun’s energy heats the hydrate, the Na 2 SO 4 dissolves in the water of hydration, and energy is absorbed. This energy is released when the temperature decreases and the hydrate crystallizes again.

11. waters of hydration D anhydrate C hydrate B crystal lattice A What term refers to a compound with a specific number of water molecules bound to its atoms? 1. CORRECT Quiz

12. one anhydrate C ten waters of hydration D ten hydrates B one crystal lattice A Each formula unit of the compound Na 2 CO 3 • 10H 2 O contains ______. 2. CORRECT Quiz

13. Quiz 2CaCl 2 • H 2 O D CaCl 2 • 2 H 2 O C (CaCl 2 ) 2 • H 2 O B CaCl 2 • H 2 O A Which of these is the formula for calcium chloride dihydrate? 3. CORRECT

14. bath salts D desiccants C sports drinks A solar energy storage B Which of the following is NOT a use of hydrates? 4. CORRECT Quiz