7.05 Pogil Molfgarity Key 213s37
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Instructors Guide: Molarity Standards Connections Connections to NSTA Standards for Science Teacher Preparation ! ! ! ! !
C.1.1 – Multiple ways we organize our perceptions of the world and how systems organize the studies and knowledge of science. C.1.2 – Nature of scientific evidence and the use of models for explanation. C.1.3 – Measurement as a way of knowing and organizing observations of constancy and change. C.3.a.6 - Mole concept, stoichiometry, and laws of composition. C.3.b.20 - Solvent system concepts including non-aqueous solvents.
Connections to the National Science Education Standards: Properties and Changes of Properties in Matter:
!
A substance has characteristic properties, such as density, a boiling point, and solubility, all of which are independent of the amount of the sample. A mixture of substances often can be separated into the original substances using one or more of the characteristic properties.
Connections to New York Chemistry Core Curriculum: !
The concentration of a solution may be expressed as: molarity (M), percent by volume, percent by mass, or parts per million (ppm). (3.1pp)
Hints for Facilitation Suggestion #1 Make several glasses of iced tea or any powdered drink mix (with color) using different amounts of mix in each glass. Ask students which glass they would like to have and why? More concentrated drinks should be easily seen just by looking at its color. Ask students which solution is more/less concentrated. Suggestion #2 Model I: Make the CuSO4 concentrations in front of the students so they can see how they are made. Make a 1.0M CuSO4 solution by adding 160g of granular CuSO4 to a 1.0L volumetric flask then dissolve it in enough water to fill the flask to 1.0 L. Using a magnetic stirrer will make the dissolving occur more quickly.
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
1/8
Molarity
Suggestion #3 In order to make a 0.001M CuSO4 solution, take 10mL of the 1.0M CuSO4 solution and put it into another 1.0L volumetric flask then add 990mL of water. This will give the students the opportunity to see how a dilution is done. Suggestions for appropriate demonstrations, manipulatives, etc., that will enhance the activity. Demonstration: Part 1: Demonstrate how to make 6 M solution: Place 6 #10 stoppers into a 1000 mL graduated cylinder or calibrated beaker. Add enough water to fill up to the 1000 mL line. Part 2: Demonstrate how NOT to make a 6M solution: Fill the 1000 mL graduated cylinder or calibrated beaker to the 1000 mL line. Now add the 6 #10 rubber stoppers. These demonstrations should show that the second version has more than 1000 mL of solution and is less concentrated. It is not a 6 M solution (it is 6 m (molal) solution.) This demonstration can be used to save on chemicals in Model II.
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
2/8
Molarity
Molarity Why? When a substance (solute) is dissolved in a solvent, a solution is formed. A chemist often needs to know how much solute is present in a given volume of solution. In this activity you will learn how to determine the amount of solute that is dissolved in a given quantity of solvent by calculating the concentration of a solution.
Learning Objectives !
Solve problems involving the molarity of a solution.
Success Criteria !
Student can manipulate the relationship between moles of solute and volume of solution by using the definition of molarity.
Prerequisites ! ! ! ! ! ! !
Moles Solute Solution Solvent Volume Gram formula mass Stoichiometry
Vocabulary ! ! ! ! !
Concentration Concentrated Molarity Dilution Dilute
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
3/8
Molarity
Model I: What does concentration mean? Demo: You will observe two 1.0 liter volumetric flasks, each filled with a different concentration of CuSO4 (aq). With your class or group, discuss the concept of concentration using the dilute and concentrated as they relate to the two solutions.
Key Questions 1. Which solution has the darker color? The 1.0 molar (based on suggestion #2 in the instructors guide) or the one with the higher concentration 2. What might be responsible for the darker color in one of the solutions? More solute (CuSO4) dissolved in the water 3. Based on your observations of the solutions, which solution probably contains more solute per unit volume? Explain your answer. The darker one because it has more solute (CuSO4) dissolved; H20 is clear and colorless while the CuSO4 makes the solution blue. 4. What is meant by the term concentration? Amount of solute dissolved in a certain amount of solvent. 5. What factors should be considered when determining the concentration of a solution? The amount of solute and the amount of solvent 6. When a solution is diluted, additional solvent is added to the more concentrated solution. How does the amount of solute in the initial solution compare to the amount of solute in the final solution? The amount of solute remains the same but now there is more solvent so it is not as concentrated
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
4/8
Molarity
Information The most common measure of concentration used by chemists is molarity (M). Molarity is defined as the number of moles of solute (mol) divided by the total volume (V) of the solution in liters (L). Molarity = moles of solute per liter of solution (M = mol / L). Molarity also is called molar concentration. When the symbol M is accompanied by a numerical value, it is read as “molar.” For example, a solution labeled 3.0M NaCl is read as “three molar sodium chloride solution”.
Exercises 1. In a problem a student is given the amount of solute in grams and the volume of the solution in milliliters. What must be done with the information before the molarity can be calculated? Grams must be changed to moles (using the equation: Number of moles = given mass(g) / gram-formula mass) Volume must be changed to liters 2. Calculate the molarity of a solution in which 0.50 moles of MgCl2 are dissolved to produce 1.5 liters of solution. Molarity
= moles / liters = 0.50 moles / 1.5 liters = 0.33 M MgCl2
3. Intravenous (IV) saline solutions are often istered to patients in the hospital. Normal saline solution contains 0.90g NaCl in exactly 100. mL of solution. Calculate the molarity of this solution. NaCl gram formula mass = 58. grams / mole # moles = given mass / gram formula mass = 0.90 grams / 58 grams/mol = 0.016 moles Molarity
= moles / liters = 0.016 moles / 0.100 liters = 0.16 M NaCl
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
5/8
Molarity
4. Calculate the molarity of the following solutions. a. 1.0 mole of NaNO3 in 500. ml of H2O Molarity = moles / liters = 1.0 mole / 0.500 liters = 2.0 M NaNO3 b. 85.0 g of NaNO3 in 250. ml of H2O NaN03 gram formula mass = 85. grams/ mole Molarity = moles / liters = 1.0 mole / 0.250 liters = 4.0 M NaNO3 c. Which of the solutions, 4a or 4b, is more concentrated? Explain your answer. 4b because a 4.0 M solution has more moles of solute per liter of solution than a 2.0 M solution.
Model II Part I- Demonstration and discussion: When preparing one liter of a 1.0 molar solution one should pour some solvent (water) into a 1.0 liter volumetric flask. The measured amount of solute (1.0 mole) is added to the volumetric flask. The flask is stirred to dissolve the solute, and then additional solvent is added to bring the volume to the 1.0 liter mark. Part II – Demonstration and discussion: Fill a 1.0 liter volumetric flask with water up to the 1.0 liter mark and then add measured amount of solute (1.0 mole).
Key Questions 1. In demonstration 1, why is the solute added to some of the solvent and dissolved before more solvent is added to bring the volume to the 1.0 liter mark on the volumetric flask? Solute is added some solvent to dissolve the solute. The added solvent brings the total solution to volume of 1.0 liter.
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
6/8
Molarity
2. Which of the solutions prepared in Model II contains one liter of solvent? Explain. Part II because the flask was filled to the 1.0 liter mark before the solute was added. 3. Which of the solutions prepared in this demonstration contains a 1.0 M solution? Explain your answer. Part I because it contains 1.0 mole of solute in 1.0 liter of solution.
Problems 1. What volume of 0.25 M solution can be prepared using 0.50 mole of KCl? Molarity = moles / liters 0.25 M = 0.50 moles / X liters X = 2.0 L 2. What volume of 0.10 M solution can be prepared using 11.6 g of NaCl? Gram formula mass of NaCl = 58. grams / mole # moles = 11.6 grams / 58. grams / mole = 0.20 moles Molarity = moles / liters 0.10 M = 0.20 moles / X liters X = 2.0 L
Extension Activity Mini-lab: 1. Determine the mass of four 100 mL volumetric flasks. 2. In each flask prepare one of the following sucrose solutions: 0.0625 M, 0.125 M, 0.250 M, and 0.500 M. 3. Determine the mass of each solution then calculate the density of each solution. 4. Prepare a graph of density versus concentration of sucrose. Include the density of pure water on the graph, using the value 1.00 g/ml. © POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
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Molarity
Question: What is the relationship (direct, inverse, etc.) between concentration and density? Explain your answer. Direct, the more solute dissolved (greater concentration) the greater the density of the solution. Data for the extension activity will vary somewhat, depending on the accuracy of mass determination of each sample. The graph will show the trend of increasing density with increasing concentration.
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
8/8
C.1.1 – Multiple ways we organize our perceptions of the world and how systems organize the studies and knowledge of science. C.1.2 – Nature of scientific evidence and the use of models for explanation. C.1.3 – Measurement as a way of knowing and organizing observations of constancy and change. C.3.a.6 - Mole concept, stoichiometry, and laws of composition. C.3.b.20 - Solvent system concepts including non-aqueous solvents.
Connections to the National Science Education Standards: Properties and Changes of Properties in Matter:
!
A substance has characteristic properties, such as density, a boiling point, and solubility, all of which are independent of the amount of the sample. A mixture of substances often can be separated into the original substances using one or more of the characteristic properties.
Connections to New York Chemistry Core Curriculum: !
The concentration of a solution may be expressed as: molarity (M), percent by volume, percent by mass, or parts per million (ppm). (3.1pp)
Hints for Facilitation Suggestion #1 Make several glasses of iced tea or any powdered drink mix (with color) using different amounts of mix in each glass. Ask students which glass they would like to have and why? More concentrated drinks should be easily seen just by looking at its color. Ask students which solution is more/less concentrated. Suggestion #2 Model I: Make the CuSO4 concentrations in front of the students so they can see how they are made. Make a 1.0M CuSO4 solution by adding 160g of granular CuSO4 to a 1.0L volumetric flask then dissolve it in enough water to fill the flask to 1.0 L. Using a magnetic stirrer will make the dissolving occur more quickly.
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
1/8
Molarity
Suggestion #3 In order to make a 0.001M CuSO4 solution, take 10mL of the 1.0M CuSO4 solution and put it into another 1.0L volumetric flask then add 990mL of water. This will give the students the opportunity to see how a dilution is done. Suggestions for appropriate demonstrations, manipulatives, etc., that will enhance the activity. Demonstration: Part 1: Demonstrate how to make 6 M solution: Place 6 #10 stoppers into a 1000 mL graduated cylinder or calibrated beaker. Add enough water to fill up to the 1000 mL line. Part 2: Demonstrate how NOT to make a 6M solution: Fill the 1000 mL graduated cylinder or calibrated beaker to the 1000 mL line. Now add the 6 #10 rubber stoppers. These demonstrations should show that the second version has more than 1000 mL of solution and is less concentrated. It is not a 6 M solution (it is 6 m (molal) solution.) This demonstration can be used to save on chemicals in Model II.
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
2/8
Molarity
Molarity Why? When a substance (solute) is dissolved in a solvent, a solution is formed. A chemist often needs to know how much solute is present in a given volume of solution. In this activity you will learn how to determine the amount of solute that is dissolved in a given quantity of solvent by calculating the concentration of a solution.
Learning Objectives !
Solve problems involving the molarity of a solution.
Success Criteria !
Student can manipulate the relationship between moles of solute and volume of solution by using the definition of molarity.
Prerequisites ! ! ! ! ! ! !
Moles Solute Solution Solvent Volume Gram formula mass Stoichiometry
Vocabulary ! ! ! ! !
Concentration Concentrated Molarity Dilution Dilute
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
3/8
Molarity
Model I: What does concentration mean? Demo: You will observe two 1.0 liter volumetric flasks, each filled with a different concentration of CuSO4 (aq). With your class or group, discuss the concept of concentration using the dilute and concentrated as they relate to the two solutions.
Key Questions 1. Which solution has the darker color? The 1.0 molar (based on suggestion #2 in the instructors guide) or the one with the higher concentration 2. What might be responsible for the darker color in one of the solutions? More solute (CuSO4) dissolved in the water 3. Based on your observations of the solutions, which solution probably contains more solute per unit volume? Explain your answer. The darker one because it has more solute (CuSO4) dissolved; H20 is clear and colorless while the CuSO4 makes the solution blue. 4. What is meant by the term concentration? Amount of solute dissolved in a certain amount of solvent. 5. What factors should be considered when determining the concentration of a solution? The amount of solute and the amount of solvent 6. When a solution is diluted, additional solvent is added to the more concentrated solution. How does the amount of solute in the initial solution compare to the amount of solute in the final solution? The amount of solute remains the same but now there is more solvent so it is not as concentrated
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
4/8
Molarity
Information The most common measure of concentration used by chemists is molarity (M). Molarity is defined as the number of moles of solute (mol) divided by the total volume (V) of the solution in liters (L). Molarity = moles of solute per liter of solution (M = mol / L). Molarity also is called molar concentration. When the symbol M is accompanied by a numerical value, it is read as “molar.” For example, a solution labeled 3.0M NaCl is read as “three molar sodium chloride solution”.
Exercises 1. In a problem a student is given the amount of solute in grams and the volume of the solution in milliliters. What must be done with the information before the molarity can be calculated? Grams must be changed to moles (using the equation: Number of moles = given mass(g) / gram-formula mass) Volume must be changed to liters 2. Calculate the molarity of a solution in which 0.50 moles of MgCl2 are dissolved to produce 1.5 liters of solution. Molarity
= moles / liters = 0.50 moles / 1.5 liters = 0.33 M MgCl2
3. Intravenous (IV) saline solutions are often istered to patients in the hospital. Normal saline solution contains 0.90g NaCl in exactly 100. mL of solution. Calculate the molarity of this solution. NaCl gram formula mass = 58. grams / mole # moles = given mass / gram formula mass = 0.90 grams / 58 grams/mol = 0.016 moles Molarity
= moles / liters = 0.016 moles / 0.100 liters = 0.16 M NaCl
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
5/8
Molarity
4. Calculate the molarity of the following solutions. a. 1.0 mole of NaNO3 in 500. ml of H2O Molarity = moles / liters = 1.0 mole / 0.500 liters = 2.0 M NaNO3 b. 85.0 g of NaNO3 in 250. ml of H2O NaN03 gram formula mass = 85. grams/ mole Molarity = moles / liters = 1.0 mole / 0.250 liters = 4.0 M NaNO3 c. Which of the solutions, 4a or 4b, is more concentrated? Explain your answer. 4b because a 4.0 M solution has more moles of solute per liter of solution than a 2.0 M solution.
Model II Part I- Demonstration and discussion: When preparing one liter of a 1.0 molar solution one should pour some solvent (water) into a 1.0 liter volumetric flask. The measured amount of solute (1.0 mole) is added to the volumetric flask. The flask is stirred to dissolve the solute, and then additional solvent is added to bring the volume to the 1.0 liter mark. Part II – Demonstration and discussion: Fill a 1.0 liter volumetric flask with water up to the 1.0 liter mark and then add measured amount of solute (1.0 mole).
Key Questions 1. In demonstration 1, why is the solute added to some of the solvent and dissolved before more solvent is added to bring the volume to the 1.0 liter mark on the volumetric flask? Solute is added some solvent to dissolve the solute. The added solvent brings the total solution to volume of 1.0 liter.
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
6/8
Molarity
2. Which of the solutions prepared in Model II contains one liter of solvent? Explain. Part II because the flask was filled to the 1.0 liter mark before the solute was added. 3. Which of the solutions prepared in this demonstration contains a 1.0 M solution? Explain your answer. Part I because it contains 1.0 mole of solute in 1.0 liter of solution.
Problems 1. What volume of 0.25 M solution can be prepared using 0.50 mole of KCl? Molarity = moles / liters 0.25 M = 0.50 moles / X liters X = 2.0 L 2. What volume of 0.10 M solution can be prepared using 11.6 g of NaCl? Gram formula mass of NaCl = 58. grams / mole # moles = 11.6 grams / 58. grams / mole = 0.20 moles Molarity = moles / liters 0.10 M = 0.20 moles / X liters X = 2.0 L
Extension Activity Mini-lab: 1. Determine the mass of four 100 mL volumetric flasks. 2. In each flask prepare one of the following sucrose solutions: 0.0625 M, 0.125 M, 0.250 M, and 0.500 M. 3. Determine the mass of each solution then calculate the density of each solution. 4. Prepare a graph of density versus concentration of sucrose. Include the density of pure water on the graph, using the value 1.00 g/ml. © POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
7/8
Molarity
Question: What is the relationship (direct, inverse, etc.) between concentration and density? Explain your answer. Direct, the more solute dissolved (greater concentration) the greater the density of the solution. Data for the extension activity will vary somewhat, depending on the accuracy of mass determination of each sample. The graph will show the trend of increasing density with increasing concentration.
© POGIL 2005, 2006 Revised by: Lorraine Giloni, Kenneth Levy, and Kelly Levy Edited by Linda Padwa and David Hanson, Stony Brook University
8/8
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