Solutions

Chapter 14 Solutes and Solvents A solution is a homogeneous mixture of two or more substances. The relative abundance of the substances in a solution determines which is the solute and which is the solvent. For each of the following solutions, identify which substance is the solute and which is the solvent. 1. 20 g NaCl and 100g of H2O solvent _____ solute ______

2. 50 g of benzene and 1.0 g aspirin solvent _____ solute ______

3. 100g of He and 50 g O2 solvent _____ solute ______

4. 25 g CH3COCH3 and 100 g H2O solvent _____ solute ______

5. Solvents and solutes may be classified as polar or nonpolar. What are the four possible

solution situations? a.

b.

c.

d.

6. What is the most common unit of concentration in chemistry?

7. What is the difference between molarity and molality

8. In terms of polarity, which solvent-solute combinations are most likely to form

solutions?

9. What is the process by which solvent molecules surround solute particles?

10. Define the following terms: a. solution b. solvent c. solute d. miscible

11. What is the universal solvent?

H. Cannon, C. Clapper and T. Guillot

Klein High School

Solutions

Properties of Solutions

1. Underline the condition that causes sugar to dissolve faster in water. a. as a whole cube or in granulated form b. when allowed to stand or when stirred c. at a higher temperature or a lower temperature

2. Name three factors that influence the rate at which a solute dissolves in a solvent.

a.

b.

c.

3. True or False: Finely ground particles dissolve more rapidly than larger particles because finer particles expose a greater surface area to the colliding solvent molecules.

4. By what term do we refer to the amount of a substance that dissolves in a given quantity of solvent at a constant temperature?

5. What type of solution contains the maximum amount of a solute for a given quantity of solvent at a constant temperature?

6. How does the solubility of a gas change with an increase in temperature?

7. What is the trend for the solubility of most solids as the temperature of the solvent increases?

8. How does a solution become supersaturated?

9. What term refers to a measure of the amount of solute dissolved in a given quantity of solvent?

10. What is the term that describes the attachment of water molecules to dissolving molecules?

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Solubility Use the solubility curve to answer the following questions.

1. How much NaCl will dissolve in 100.0g of water at 50.0°C?

2. How much potassium nitrate will dissolve in 100.0g of water at 70.0°C? 3. How much sodium chlorate will dissolve in 100.0g of water at 20.0°C?

4. At what temperature will 80.0g of KBr dissolve in 100.0g of water?

5. At what temperature will 120.0g of sodium chlorate dissolve in 100.0g of water?

6. If 170.0g of sodium chlorate dissolve in 100.0g of water at 70.0°C, is the solution

unsaturated, saturated or super saturated?

7. If 50.0g of sodium chloride dissolve in 100.0g of water at 50.0°C, is the solution unsaturated, saturated or super saturated?

8. If 90.0g of potassium bromide dissolve in 100.0g of water at 70.0°C, is the solution unsaturated, saturated or super saturated?

9. If 85.0 of sodium chlorate dissolve in 100.0g of water at 15.0°C, is the solution unsaturated, saturated or super saturated?

10. If 80.0g of potassium nitrate dissolve in 100.0g of water at 70.0°C, is the solution unsaturated, saturated or super saturated?

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Molarity Problems ________ 1. Calculate the molarity of a 4.00L solution that contains 1.80

moles of solute.

________ 2. If 1.70 moles of salt are dissolved in water to make 6.00L of solution, what is the molarity of the solution?

________ 3. If 35.0g of NaCl are dissolved in water to 2.50L of solution, what is the molarity of the solution?

________ 4. If 4.00g of antifreeze (ethylene glycol C2H4(OH)2) are dissolved in your 9.00L capacity radiator, what is the molarity of the solution?

________ 5. Calculate the molarity of a 1.25L solution that contains 0.750moles of solute.

________ 6. If 0.580 moles of sugar are dissolved in water to make 4.60L of solution, what is the molarity of the solution?

________ 7. If 50.0g of glucose (C6H12O6) are dissolved in water to make 1.50L of solution, what is the molarity of the solution?

________ 8. If 80.5g of sodium bicarbonate are dissolved in water to make 5.00L of solution, what is the molarity of the solution?

________ 9. If 15.8g of magnesium phosphate are dissolved in water to make 3.00L of solution, what is the molarity of the solution?

________ 10. If the molarity of 7.50L of a solution is 1.20M, how many moles of solute are contained in the solution?

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Molarity Problems #2 ________ 1. Seawater contains roughly 28.0g of NaCl per liter. What is the

salt concentration of seawater? ________ 2. What is the molarity of 1.00 L of a solution containing

245.0g of sulfuric acid? ________ 3. How many moles of sodium carbonate are there in 10.0L of a

2.00M solution? ________ 4. How many moles of sodium carbonate are there in 10.0ml of a

2.00M solution? ________ 5. What mass of (Na)2CO3 is in the solution in problem 3? ________ 6. What mass of sulfuric acid would need to be dissolved in water

to make 750.0ml of 2.00M solution?

________ 7. What would be the volume of 18.0M sulfuric acid that contains 2.45g of sulfuric acid?

________ 8. What volume of 12.0ml HCl solution is needed to contain 3.00 moles of HCl?

________ 9. What mass of calcium hydroxide would be needed to make 100.0ml of 0.250M solution?

________ 10. What is the molarity of 50.0 ml of solution containing 20.0g of phosphoric acid?

________ 11. What mass of KCl would be found in 2.50L of 0.500M KCl solution?

________ 12. What is the molarity of a solution made by dissolving 12.0g of NaOH in water to make 250ml of solution?

________ 13. What mass of copper (II) nitrate would be needed to make 0.289L of a 0.003000M solution?

________ 14. What would be the final volume of the solution if 8.97g of ammonium carbonate were dissolved to form a 0.250M solution?

________ 15. What is the molarity of 45.0ml of plumbous chloride solution containing 0.0348g of plumbous chloride?

________ 16. How many grams of sodium fluoride would be needed to make 508ml of a 2.75M solution?

________ 17. What would be the final volume of the solution if you dissolved 0.783g of sodium carbonate in water to form a 0.348M solution?

________ 18. If 6.20L of a solution containing sodium oxide was found to have a molarity of 3.76M, how many grams of sodium oxide must have been dissolved in the solvent to form that solution?

________ 19. What would be the molarity of 250.0ml of a solution if it were determined to contain 0.897g of ammonium carbonate?

________ 20. What would be the final volume of a 3.89M solution if it were determined to contain 4.67 moles of lithium sulfite?

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Molality Problems ________ 1. What is the molality of a solution containing 15.0g of ethanol

(C2H5OH) in 17.0g of water? ________ 2. What’s the molality of a solution with 1.50 moles of solute

dissolved in 0.750Kg of a solvent? ________ 3. What is the molality of a solution containing 26.0g of I2

dissolved in 650.0g of CCl4 ________ 4. How many Kg of solvent are required to prepare a 1.25 molal

solution containing 61.0g of dimethyl ether (C2H6O) ________ 5. How many grams of NaCl should be added to 250 ml of water to

make a 1.80m solution? ________ 6. How many grams of glucose (C6H12O6) are contained in 0.500

Kg of water in a 1.70m solution? ________ 7. How much water is needed to prepare a 2.30m solution with

18.6g of NaOH in it? ________ 8. Determine the molality of a solution which contains 54.0g of

cane sugar (C12H22O11) dissolved in 225g of water. ________ 9. A solution contains 23.0g of NaCl dissolved in 82.0g of water.

What is the mole fraction of each component? ________ 10. What is the formula weight of a solute if 2.15g of a solute are

dissolved in 28.0g of water to make a 0.500m solution? ________ 11. If you used 75.0g of solute dissolved in 1250 ml of water to

make a 2.75m solution what is the formula weight? ________ 12. What is mole fraction of each component if the solution contains

44.0g of CH3OH dissolved in 120.0g of water? ________ 13. How many grams of water must be added to 65.0g of glucose to

prepare a 2.00m solution?

________ 14. What is the molality of a solution containing 650.0g of water and 170.0g of ethanol?

________ 15. What would be the mass of vinegar (acetic acid HC2H3O2) needed to dissolve 95.0g of sugar (C12H22O11) if you want an 8.99m solution?

________ 16. Calculate the molality of a solution containing3.50g of sulfuric acid in 12.0g of water.

________ 17. Calculate the grams of water necessary to make a 12.0m solution containing 4.10 moles of sulfuric acid.

________ 18. What would be the molality of a solution if it contained 620.0g of water and 28.0g of calcium chloride?

________ 19. Calculate the molality of a solution with 2.60g of glucose dissolved in 110.0g of water.

________ 20. How many grams of silver nitrate are needed to dissolve in 1200ml of water if you want a 0.500m solution?

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Molality Problems (2)

1. What is the molality of a solution containing 16.0 g of methyl alcohol (CH3OH) in 200.0 ml of water?

2. What is the molality of a solution containing 7.62 g of I2 dissolved in 450.0g of carbon tetrachloride?

3. How many grams of ethyl alcohol (C2H5OH) are required to make a 1.54 molal solution in 2500.0g of water?

4. How many grams of solute are contained in 0.500kg of a 0.500m solution of glucose in water (C6H12O6)

5. How many kilograms of solvent are required to prepare a 0.200 m solution containing 57.0g of dimethyl ether (C2H6O)?

6. How many grams of water must be added to 110.0g of NaOH to make a 5.20m solution?

7. How many grams of calcium chloride should be added to 300.0ml of water to make up a 2.46m solution?

8. What is the molality of a solution that contains 20.0g of sucrose (C12H22O11) dissolved in 125.0g of water?

9. How many grams of hydrochloric acid are required to prepare a 0.750m solution in 1500.0 g of water?

10. The molality of a solution of ethyl alcohol in water is 1.54m. How many grams of alcohol are in 25.0kg of water?

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Dilutions Use the following stock solutions to solve the problems below. 12.5M HCl 8.0M HNO3 10.0 M H2SO4 9.0 M NaOH

_____ _____

1. How much water and stock solution must be used to make 2.20L of a 1.50 M HNO3 solution?

_____ 2. How much stock solution of HCl is needed to make 750.0 ml of a solution with a concentration of 1.2M?

_____ _____

3. How much water and stock solution must be used to make 5.00L of a 1.50M H2SO4 solution?

_____ 4. How much stock solution of HCl is needed to make 750.0ml with a concentration of 0.75M?

_____ 5. How much water is needed to make 1.25L of a 1.50M NaOH solution?

_____ 6. What is the molarity of a solution when 75.0ml of a 7.50M stock solution was used to make 125ml of the diluted solution?

_____ 7. What is the molarity of a stock solution when 58.0ml of the stock solution was used to make 150.0ml of a 1.25M solution?

_____ 8. How much stock solution of NaOH is needed to make 500.0ml with a concentration of 0.100M?

_____ 9. What is the molarity of a solution when 25.0ml of a 7.50M stock solution was used to make 250.0ml of the diluted solution?

_____ 10. What is the molarity of a stock solution when 110.0ml of the stock solution was used to make 175.0ml of a 4.20M solution?

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Molarity/Molality Problems

1. Determine the number of moles of solute in each of the following: a. 2.50 liters of 2.00M H2SO4 b. 5.00 liters of 0.525M Ba(OH)2

2. Determine the molarity of the following solutions:

a. 41.65g of magnesium chloride in 3.50 L of solution b. 4.90g of chromium (III) sulfate in 25.0 ml of solution

3. Calculate the molarity of a solution, 2.00 liters of which contain 2.60 moles of

solute.

4. How many grams of sulfuric acid are contained in 0.800L of 0.050M sulfuric acid?

5. What volume of 0.20M potassium sulfate would contain 57.0g of the salt.

6. What is the formula weight of a solute, if 168g of it, dissolved in water will give 1550ml of a 1.11M solution?

7. A solution has a molarity of 0.030M and contains 55.0g of solute in 20.0L of solution, what is the formula weight of the solute?

8. What is the molarity of a solution of 22.0g of cane sugar (C12H22O11) dissolved in 125 ml of water?

9. How many grams of solute would be needed to make 1.00 L of 2.00M potassium iodide solution?

10. How many grams of solute are required to prepare 1.00L of 1.00M lead (II) nitrate? what is the molar concentration of the solution with respect to each of the ions?

11. What is the molality of a solution containing 10.0g of sodium sulfate dissolved in 1000.0ml of water?

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12. What is the molality of a solution containing 30.0g of naphthalene (C10H8) dissolved in 500.0g of toluene?

13. What mass of sodium chloride must be dissolved in 100.0ml of water to produce a 2.68m solution?

14. How much water must be used to dissolve 3.76g of sodium hydroxide if you wish to make a 0.110 m solution?

15. What would be the molality of a solution formed by dissolving 20.0g of calcium chloride in 700.0g of water?

16. What mass of water would be necessary to form a 0.125m solution containing 3.25g of nickel (II) chloride?

17. How many grams of potassium nitrate would be found in 5.00 x 102ml of a 2.00M solution?

18. What volume of a 0.250M solution could you make with 32.0g of sodium nitrate?

19. The molality of an aqueous solution of cane sugar is 1.62m. Calculate the mole fractions of sugar and water.

20. Calculate the molarity, molality and mole fractions in a solution that is made of 25.0g of ethanol and 40.0g of water.

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Solutions

Effect of Temperature on Solubility of a Salt In this experiment, you will study the effect of changing temperature on the amount of solute that will dissolve in a given amount of water. Water solubility is an important physical property in chemistry, and is often expressed as the mass of solute that dissolves in 100g of water at a certain temperature. In this experiment, you will completely dissolve different quantities of potassium nitrate in the same volume of water at a high temperature. As each solution cools, you will monitor temperature using a temperature probe and observe that precise instant that solid crystals start to form. At this moment, the solution is saturated and contains the maximum amount of solute at that temperature. Thus each data pair consists of a solubility value (g of solute per 100g of water) and a corresponding temperature. A graph of the temperature-solubility data, known as a solubility curve, will be plotted using the TI-83 type calculator.

1. Prepare four test tubes, each with 5ml of water and precisely measured amounts of potassium nitrate according to the chart.

Test Tube # g KNO3/ 5 ml H2O (measured)

g KNO3/100g H2O (calculated)

1 2.0g 2 4.0g 3 6.0g 4 8.0g

2. Prepare the temperature probe for data collection a. Plug the temperature prove into the adapter cable in Channel 1 of the

CBL. b. Connect the CBL System to the calculator with the link cable using the

port on the bottom edge of each unit. Firmly press in the cable ends.

3. Turn on the CL unit and the calculator. Press PRGM and select CHEM. Press ENTER, then press ENTER again to go to the CHEM MAIN MENU

4. Set up the calculator and CBL for a temperature probe and calibration (in °C). a. Select 1:SET UP PROBES from the CHEM MAIN MENU b. Enter “1” as the number of probes c. Select 1:TMEPERATURE from the SELECT PROBE menu d. Enter “1” as the channel number e. Select 3:USE STORED from the CALIBRATION menu

5. Set up the calculator and CBL for data collection.

a. Select 2: COLLECT DATA from the CHEM MAIN MENU b. Select 3: TRIGGER/PROMPT from the DATA COLLECTION menu.

6. Heat a water bath to 90°C. Place the temperature probe in the water bath to monitor the temperature and to warm the probe. CAUTION: To keep from damaging the temperature probe wire, hang it over another utility clamp pointing away from the hot plate, as shown in Figure 1.

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7. Fasten the first test tube to the ring stand and lower it into the water. Heat and stir until the KNO3 is completely dissolved. Do not leave the test tube in the water any longer than is necessary to dissolve the solid.

8. Remove the probe from the water, dry it and place it in the solution in the tube. Unfasten the clamp and tube from the ring stand. Use the clamp to hold the tube up to the light to look for the first sign of crystal formation. At the same time, stir the solution with a slight up and down motion of the probe. At the moment crystallization starts to occur, press “trigger” on the CBL. Enter the mass in f in the calculator (from column 3 of the table). After you have saved the temperature-mass data pair, return the test tube to the rack and place the temperature probe in the water bath for the next trial.

9. Select 1:MORE DATA on the calculator to do another trial. Repeat steps 7 and 8 for each of the other three test tubes. Here are some suggestions to save time:

a. One lab partner can be stirring the next KNO3-water mixture until it dissolves while the other partner watches for crystallization and enters data pairs using the calculator.

b. Test tubes 1 and 2 may be cooled to lower temperatures using cool tap water. This drops the temperature much greater than air. If the crystals form too quickly, briefly warm the test tube in the hot water and redissolve the solid. Then repeat the cooling and collect the data pair.

10. Once data on all four tubes has been collected, select 2:STOP.

11. View the data collected by going to stat. Record the data in your data table.

12. Prepare a graph of solubility vs. temperature. Before you print the graph, set up the style and scaling.

a. Press “enter” and select NO when asked if you want to repeat. Select 6: QUIT to quit the data collection program.

b. Press “2nd” (STAT PLOT), then select 1:PLOT 1. Determine the settings appropriate for graphing your data and enter them as requested.

13. Draw a best-fit curve for your data points. According to your data, how is solubility of KNO3 affected by an increase in temperature of the solvent?

14. Is your graph what you expected from a solubility curve? If it is not, what point or points might be in error? Repeat you laboratory process as necessary (if time allows) to achieve better data.

Follow-Up

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Using your graph tell if each of the following solutions would be saturated or unsaturated. 110g of KNO3 in 100g of water at 40°C 60g of KNO3 in 100g of water at 70°C 140g of KNO3 in 200g of water at 60°C According to your graph, will 50g of KNO3 completely dissolve in 100g of water at 50 degrees C? Will 120g of KNO3 dissolve in 100g of water at 40 degrees C? How any grams of KNO3 will dissolve in 100g of water at 30 degrees C? Calculate the molality of the solution at each of your measured points. Assuming that the density of the 4th solution at the measured temperature is 1.13 g/ml, calculate the molarity of the solution. How many grams of KNO3 can dissolve In 2.0L of water at 50 degrees?

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Freezing Point Depression/Boiling Point Elevation Problems

1. What is the freezing point of a solution of 92.0g of ethyl alcohol (C2H5OH) and 500.0g of water?

2. By how much will 50.0g of water have its freezing point lowered if 3.00g of sodium chloride are added to it?

3. The antifreeze commonly used in car radiators is ethylene glycol, C2H4(OH)2. How many grams of ethylene glycol must be added to 100.0ml of water to make a solution that will freeze at -150°C?

4. At what temperature will a solution boil if 3.55g of calcium chloride are dissolved in 250.0g of water?

5. If 1.00g of an unknown compound that dissociates into two ions is dissolved in 10.0g of water, the solution freezes at –1.22°C. What is the molecular weight of the unknown compound?

6. When 0.512g of a substance is dissolved in 7.03g of naphthalene, the solution freezes at 75.2°C. What is the molecular weight of the substance? (Naphthalene f.p. = 80.2°C, Kf = 6.9 °C/mole)

7. A solution containing 7.24 g of C2H4Cl2 in 115.3g of carbon tetrachloride freezes at –24.89°C. What is the molal freezing point constant of carbon tetrachloride? (f.p. = -22.96°C)

8. A solution of 22.0g of nonionic ascorbic acid in 100.0g of water freezes at –2.33°C. What is the formula weight of the acid?

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Freezing Point/Boiling Point Problems

1. What would be the freezing and boiling points of a solution of 5.00g of sodium

chloride dissolved in 25.0g of water?

2. What would be the freezing and boiling points of a solution prepared by dissolving 1.00g of benzoic acid (C6H5CO2H) in 10.0g of benzene?

3. What mass of ethylene glycol (C2H6O2) must be added to 10.0L of water to produce a solution for use in a car’s radiator that freezes –23.3°C?

4. Thyroxine is a hormone that controls metabolism. If 0.546g of thyroxine was dissolved in 15.0g of benzene, and the freezing pint of the solution was 0.240°C, what is the molecular weight of thyroxine?

5. How much calcium chloride would you add to 2.00L of water to produce a solution that freezes at –10.0°C?

6. Calculate the molecular mass of a nonionic solute when 7.60g are dissolved in 475g of water, resulting in a solution with a freezing point of 0.735°C?

7. Suppose 1500g of a compound are dissolved in 35.00g of camphor. The freezing point of pure camphor is 178.75°C, the freezing point of the solution is 164.4°C and the freezing pint constant for camphor is 37.7°C/mol. Assuming no ionization, what is the formula weight of the compound?

8. If 20.8g of a compond with a formula mass of 200.0 g/mol is dissolved in 126g of acetic acid, what would be the new freezing and boiling points?

9. If 8.02g of sodium sulfate is dissolved in 861g of water, what are the new freezing and boiling points?

10. How many grams of a solute with a molecular mass of 116 g/mol would be necessary to lower the freezing point of 63.5g of nitrobenzene to 3.40°C? (FP nitrobenzene = 5.76°C, Kfp nitrobenzene = 6.852 /mol)

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Freezing Point Depression Lab

Introduction: Any pure liquid has a specific freezing point temperature. Adding a solute will interfere with the formation of crystals of the solute, requiring a lower temperature for impure crystals to form. The amount that the freezing point temperature is lowered can be calculated using the concentration of the solution and the freezing point standards of the solvent. Problem: In this lab we will demonstrate the colligative property of a solution by showing how the addition of salt affects the freezing point of water. We will use the salt water solution to freeze ice cream. Procedure: Prepare the ice cream mixture. Pour approximately ½ can of sweetened condensed milk into the small can. Add 1 tablespoon of vanilla pudding mix and 1 teaspoon of vanilla. Fill the can to the first ridge from the top with milk. Place the lid on the can, secure with tape and shake well to mix. Freeze the ice cream. Place the small can inside the large can. Fill the space around and above the small can with ice and salt, approximately one handful of salt for every three handfuls of ice, spread as evenly as possible. Place the lid on the large can. Turn the can on its side and roll back and forth between partners (if the lid is secure, it should not leak). Every few minutes check to see if the ice cream is freezing and record the temperature. You need 4-6 readings. You will know that the ice cream has frozen when you see the ice cream sticking to the lid of the inner can. Questions: 1. Were you surprised to see that water remained liquid below 0°C?

2. What temperature did it take to freeze your ice cream?

3. What concentration of salt solution did it take to freeze your ice cream?

4. If 333.0g of CaCl2 were mixed with 1200.0g of warm water, at what temperature

would the mixture freeze?

5. How many grams of Al(NO3)3 would you need to mix with 500.0ml of water to make a solution that freezes at -10°C?

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