Water & Solutions Chapter 17 & 18 Assignment & Problem Set

Transcription

1 Water & Solutions Chapter 17 & 18 Assignment & Problem Set Name Warm-Ups (Show your work for credit) Date 1. Date 2. Date 3. Date 4. Date 5. Date 6. Date 7. Date 8.

2 Water & Solutions 2 Vocabulary (know the definition and what it means): electron dot structure (Lewis structure) polar and nonpolar molecule molecular attractions (intermolecular forces) dispersion force dipole force hydrogen bond force surface tension surfactant vapor pressure specific heat capacity heat of vaporization strong electrolyte weak electrolyte non-electrolyte ionize water of hydration Study Guide: Things You Must Know hydrate hygroscopic desiccant solution solvent solute solubility hydration rate of dissolution saturated, unsaturated and supersaturated dilute vs. concentrated solution concentration terms (percent, ppm, molarity) colligative property: o freezing point depression o boiling point elevation Learning Objectives: the dot structure of water. the geometric shape of the water molecule and that water is polar. the types of molecular attractions that hold water molecules together in the liquid and solid states. the hydrogen bond force is the strongest molecular attraction holding water molecules together. how to explain each of the properties of water that depend on the strength of molecular attractions: surface tension, vapor pressure, specific heat, heat of vaporization, boiling point. why ice floats. what substances are strong-, weak-, and non-electrolytes. how to write formulas and name hydrated compounds. how to calculate the percent water in a hydrated compound. solution and homogeneous mixture are synonyms. how to determine which ionic substances (Table F) and molecular substances (polar) dissolve in water. why certain ionic compounds do not dissolve in water. what like dissolves like means. factors that affect the rate of dissolution. how to test a solution to determine if it is unsaturated, saturated, or supersaturated. how to read and interpret solubility curves (Table G). the effect of temperature on the solubility of solids and liquids. the effect of temperature on the solubility of gases. the effect of pressure on the solubility of gases. pressure has no effect on the solubility of solids and liquids. how to solve quantitative problems with concentration units (percent, ppm, molarity). how to solve dilution problems starting with a stock solution, using the dilution equation. the two colligative properties. the effect of adding a solute to a solvent on the boiling point and freezing point. ionic compounds have a greater affect on colligative properties than molecular compounds because ionic compounds break into ions when dissolved. practical applications of colligative properties, especially freezing point depression. Key Reference Tables Table B: Physical Constants for Water Table F: Solubility Guidelines for Aqueous Solutions Table G: Solubility Curves Table H: Vapor Pressure of Four Liquids Table T: Important Formulas and Formulas

3 Water & Solutions 3 Read Chapter 17: Water and Aqueous Solutions Read Chapter 18: Solutions. Skip Section 18.4 on pp Lab 16: Solvent Properties of Water Lab 17: Electrolytes and Nonelectrolytes Lab 18: Water of Hydration Lab 19: Freezing Point Depression Warm-ups and problems will be collected before you take the test. Answer all problems in the space provided. For problems involving an equation, carry out the following steps: 1. Write the equation. 2. Substitute numbers and units. 3. Show the final answer with units. There is no credit without showing work. The Water Molecule and It s Properties 1. Explain, using a Lewis structure, why water molecules are polar. 2. Draw a diagram of two water molecules that are hydrogen bonding. 3. Hydrogen bonding, a strong attractive force between water molecules, is responsible for many of the unusual properties of water. State whether the following properties for water are unusually high (H) or unusually low (L) compared to other molecules of similar molar mass: a. surface tension b. vapor pressure c. boiling point d. heat of vaporization e. specific heat capacity 4. Why do the particles at the surface of a liquid behave differently from those in the bulk of a liquid? 5. From your knowledge of intermolecular forces, which liquid, water (H 2O) or hexane (C 6H 14), has greater surface tension? Explain. 6. Define specific heat capacity. What is the value for water? 7. Explain, in terms of intermolecular forces, why water has a relatively high boiling point. 8. How many joules are required to heat 256 g of water from 20 o C to 99 o C? How many joules are required to heat the same mass of iron through the same range of temperature? (Specific heat of iron is 0.46 J/g o C)

4 Water & Solutions 4 9. How many joules are required to vaporize 5.0 mg of water at its boiling point? 10. How many kilojoules are required to melt 24 g of ice at 0 o C? 11. If 5.00g of steam at o C condenses to liquid water and is then cooled to 50.0 o C, how much heat is liberated in kilojoules? (Hint: this is a two step process.) 12. What is the difference between the structure of liquid water and the structure of ice? How does this explain why ice floats in liquid water. 13. Explain which properties of water are responsible for these occurrences. a. Water in tiny cracks in rocks helps break up the rocks when it freezes. b. Water beads up on a newly waxed car. c. As you exercise and your body temperature increases, our body cools itself by producing sweat. d. Temperatures below 28 o F damage grapevines. When severe frost is predicted, grape growers spray a mist of water on their vines. e. An efficient way of heating a large building is to generate steam in a boiler and circulate it through pipes to radiators throughout the building. 14. Distinguish between an electrolyte and a nonelectrolyte. Distinguish between a weak electrolyte and a strong electrolyte. Give an example of all three. 15. Why does molten sodium chloride conduct electricity?

5 Water & Solutions 5 Water of Hydration 16. What is water of hydration? 17. Name these hydrates and determine the percent by mass of water in each. a. SnCl 4 5H 2O b. BaBr 2 4H 2O c. FeSO 4 7H 2O d. Na 2CO 3 H 2O e. MgSO 4 7H 2O Solubility 18. What is the significance of the statement "like dissolves like"? What does "like" refer to? 19. Why is water an excellent solvent for most ionic compounds and polar covalent molecules but not for nonpolar compounds? 20. Describe how an ionic compound dissolves in water. As an example, write an equation for dissolving calcium chloride in water. 21. Write an equation showing aluminum iodide dissociating in water. 22. Which of the following substances dissolve to a significant extent in water? Explain your answer in terms of each substance being ionic, covalent nonpolar or covalent polar. a. CH 4 b. He c. sucrose d. KCl e. MgSO 4 f. NaHCO 3 g. HCl h. CaCO 3 i. NH 3

6 Water & Solutions Honors Explain why propanol (C 3H 7OH) will dissolve in both gasoline and water. 24. Suppose an aqueous solution contains both sugar and salt. Can you separate either of these solutes from the water by filtration? Explain. Solubility in Water 25. Define: a. solvent b. solute c. solution d. solubility e. saturated solution f. unsaturated solution 26. For a given solvent and solute, name the three factors that influence the rate at which a solute dissolves in a solvent. 27. What could you do to change: a. a saturated solution to an unsaturated solution? b. an unsaturated solution to a saturated solution? 28. Can a solution with undissolved solute be supersaturated? Explain. 29. What is the solubility of potassium nitrate in water at 55 o C? 30. What mass of sodium chloride can be dissolved in 7.5 x 10 2 g of water at 25 o C? 31. What mass of KNO 3 can be dissolved in 250 g of water at 40 o C?

7 Water & Solutions Will 100. g of ammonium chloride dissolve in 0.22 L of water at 80 o C? 33. Honors How many grams of NaNO 3 will precipitate if a saturated solution of NaNO 3 in 200 g H 2O at 50 o C is cooled to 20 o C? Effect of Temperature and Pressure on Solubility 34. For dissolving most solids in a liquid, what effect does raising temperature have on solubility of that solid? 35. For dissolving gases in a liquid, what effect does raising temperature have on solubility of that gas? 36. What is the effect of raising pressure on the solubility of gases in a liquid? 37. Is the solubility of nitrogen gas in water greater at 40 o C or at 80 o C? Explain. Solution Concentration 38. How many grams of salt are needed to prepare 500. g of a 37 % (m/m) aqueous solution? 39. How many grams of ammonium chloride are in 0.80 kg of 4.5 % (m/m) aqueous solution of ammonium chloride? 40. What is the ppm concentration of a solution of 27 mg glucose dissolved in 20. kg water? 41. Calculate the molarity of 0.50 mol MgCl 2 in 1.5L of solution. 42. How many moles of sodium chloride do you need to make 150 ml of a 0.80 M solution?

8 Water & Solutions How many moles of ammonium nitrate are in 335 ml of M solution? 44. How many grams of sodium sulfate are in 250 ml of a 1.2 M solution? 45. Calculate the molarity of 400.g CuSO 4 in 4.00 L of solution. 46. A solution has a volume of 2.0 L and contains 36.0 g of glucose. If the molar mass of glucose is 180 g/mol, what is the molarity of the solution? Dilutions 47. How would you prepare 200. ml of a 1.4 M solution of HCl starting with a 3.0 M stock solution of HCl? 48. You have the following stock solutions available: 2.00M NaCl, 4.0M KNO 3, and 0.50M MgSO 4. Calculate the volumes you must dilute to make the following solutions. a mL of M NaCl b. 2.0 L of 0.20M MgSO 4 c ml of 0.20M KNO 3 Colligative Properties 49. How many moles of particles are present when 1.0 mol of each compound is dissolved in water? a. NaCl b. K 2SO 4 c. Fe(NO 3) 3 d. sucrose 50. How does increasing the pressure on the surface of water affect the water s boiling point? Explain.

9 Water & Solutions You have to predict the properties of four liquids: water, 1.0M KI, 1.0M MgF 2, and 1.0M sucrose. Rank these four liquid from lowest to highest for: a. boiling point b. freezing point Review 52. The decomposition of hydrogen peroxide is given by this equation. 2H 2O 2(l) 2H 2O(l) + O 2(g) Calculate the volume of oxygen at STP formed when 2.00 x 10-3 mol of hydrogen peroxide is decomposed. 53. Calculate the mass of water produced in the complete combustion of 8.00L of propane (C 3H 8) at STP given the following unbalanced equation: C 3H 8 + O 2 CO 2 + H 2O 54. Honors Write a balanced equation for the reaction of Na 2SO 4(aq) with BaCl 2(aq). If a 250 ml sample of Na 2SO 4 is reacted with excess BaCl 2 and 5.28 g BaSO 4 is precipitated, what is the molarity of the Na 2SO 4 solution? 55. A gas occupies 750 cm 3 at 27 o C and 1.6 kpa. Find its volume at STP.