1. Chapter 12 Solutions and Their Behavior

2. Solutions The Solution Process Why do things dissolve? 1) The driving force towards a more random state (entropy) 2) The attractive forces between solute and solvent (enthalpy) Intermolecular Forces!!! Intermolecular Forces!!!

3. Solutions A solution is a particular type of mixture. Mixtures in chemistry are combinations of different substances where each substance retains its chemical properties. Generally, mixtures can be separated by non-chemical means such as filtration, heating, or centrifugation. A solution is a particular type of mixture. Mixtures in chemistry are combinations of different substances where each substance retains its chemical properties. Generally, mixtures can be separated by non-chemical means such as filtration, heating, or centrifugation. A solution is a homogeneous mixture, but that's not the full definition. Homogeneous means that the mixture is the same all the way through. You could take two same-sized samples: one from the bottom and one from the top and they would be identical. Homogeneous mixtures do not settle out if left to sit undisturbed, whereas a heterogeneous mixture would. Blood is a good example of a heterogeneous mixture. A solution is a homogeneous mixture, but that's not the full definition. Homogeneous means that the mixture is the same all the way through. You could take two same-sized samples: one from the bottom and one from the top and they would be identical. Homogeneous mixtures do not settle out if left to sit undisturbed, whereas a heterogeneous mixture would. Blood is a good example of a heterogeneous mixture. A solution is a homogeneous mixture where all particles exist as individual molecules or ions. This is the definition of a solution. A solution is a homogeneous mixture where all particles exist as individual molecules or ions. This is the definition of a solution.

4. Solutions A solution has two components: the solute and the solvent. A solution has two components: the solute and the solvent. The solvent is the substance in greater amount. The solvent is the substance in greater amount. It is usually a liquid, but could be a gas or even a solid. Water is defined as the universal solvent. It is usually a liquid, but could be a gas or even a solid. Water is defined as the universal solvent. The solute is the substance in lesser amount. The solute is the substance in lesser amount. The solute is usually a solid, but could be a liquid or gas. The solute is usually a solid, but could be a liquid or gas.

5. Dissolving Process- the Solvent rips the solute apart molecule by molecule or ion by ion. If a solute is soluble that means that a solvent is able to rip it apart. LIKE DISSOLVE LIKE Polar solvents can only dissolve. polar solutes and Non-Polar solvents can only dissolve non-polar solutes.

6. Like Dissolves Like Polar dissolves Polar Non-polar dissolves Non-Polar Polar to Polar Non-polar to Non-polar

7. Intermolecular Forces in Solutions (ionic and polar substances tend to be water-soluble)

8. Solubility Solubility Solubility is the amount of a substance that will dissolve in a given amount of solvent Recall dissociation equations Recall dissociation equations NaCl (s) ⇆ NaCl (aq) = Na + (aq) + Cl – (aq) solute (undissolved) ⇆ solute (dissolved) molecular form ionic form

9. Factors Affecting Solubility Most solids are more soluble at higher temp, most gases are less soluble at higher temp At Higher pressures there is no significant effect for solid or liquid solutes, but there is a major effect with gaseous solutes dissolved in liquid solvents Henry’s Law: gases are more soluble at higher pressure (e.g. Pepsi/Coke/Root Beer …) S g ∝ P g or S g = k H P g or S 1 /P 1 = S 2 /P 2 where S = solubility, P = pressure, k H = Henry’s law constant (depends on gas)

10. What happens when there is to much Solute to be dissolved? The Solute falls to the bottom unaffected. The Solute falls to the bottom unaffected. What if the solute is already dissolved? There are three types of solutions that pertain to this question. 1) Saturated 2) Unsaturated 3) Supersaturated.

11. Maximum vs Minimum Solubility A solution that contains the maximum amount of dissolved solute in a given amount of solvent is considered SATURATED. UNSATURATED means the solution can add more solvent at the existing conditions. SUPERSATURATED Solution – a solution that contains more than maximum solute at the given conditions a very unstable solution.

12. A Supersaturated Solution Videos Fun with Sodium Acetate Fun with Sodium Acetate Fun with Sodium Acetate Fun with Sodium Acetate

13. Solubility Solubility -The concentration of solute in solution when the solution is saturated. (Expressed as g/100 mL H 2 O) Solubility is measured and recorded with a solubility graph.

14. Solubility Graph The curve shows the # of grams of solute in a saturated solution containing 100 mL or 100 g of water at a certain temperature.The curve shows the # of grams of solute in a saturated solution containing 100 mL or 100 g of water at a certain temperature. Any amount of solute below the line indicates the solution is unsaturated at a certain temperatureAny amount of solute below the line indicates the solution is unsaturated at a certain temperature Any amount of solute above the line in which all of the solute has dissolved shows the solution is supersaturated.Any amount of solute above the line in which all of the solute has dissolved shows the solution is supersaturated.

15. Solution Concentration The word concentration refers to how much solute is dissolved. The word concentration refers to how much solute is dissolved. Dilute means that only a little solute is dissolved and concentrated means a lot is dissolved. Dilute means that only a little solute is dissolved and concentrated means a lot is dissolved. These are NOT numerical type numbers, but they are words you should be familiar with. These are NOT numerical type numbers, but they are words you should be familiar with. There are three concentration words that are numerical in nature: % by mass,molarity and molality. There are three concentration words that are numerical in nature: % by mass, molarity and molality.% by mass,molarity molality% by mass, molarity molality

16. Percentage by mass The % by mass is calculated by dividing the mass of solute dissolved by the mass of the total solution.

17. Percentage by mass Example problem: What is the percentage by mass of a 500.0 g salt solution that has 25.0 g of CaCl 2 in 475.0 g of water?

18. Molarity The molarity of a solution is calculated by taking the moles of solute and dividing by the liters of solution. The molarity of a solution is calculated by taking the moles of solute and dividing by the liters of solution.

19. Molarity (M) Example #1 - Suppose we had 1.00 mole of sucrose (it's about 342.3 grams) and proceeded to mix it into some water. It would dissolve and make sugar water. We keep adding water, dissolving and stirring until all the solid was gone. We then made sure that when everything was well- mixed, there was exactly 1.00 liter of solution. Example #1 - Suppose we had 1.00 mole of sucrose (it's about 342.3 grams) and proceeded to mix it into some water. It would dissolve and make sugar water. We keep adding water, dissolving and stirring until all the solid was gone. We then made sure that when everything was well- mixed, there was exactly 1.00 liter of solution. What would be the molarity of this solution? What would be the molarity of this solution? The answer is 1.00 mol/L. Notice that both the units of mol and L remain. Neither cancels. The answer is 1.00 mol/L. Notice that both the units of mol and L remain. Neither cancels. A replacement for mol/L is often used. It is a capital M. So if you write 1.00 M for the answer, then that is correct. A replacement for mol/L is often used. It is a capital M. So if you write 1.00 M for the answer, then that is correct.

20. Molarity Example #2 - Suppose you had 2.00 moles of solute dissolved into 1.00 L of solution. What's the molarity? Example #2 - Suppose you had 2.00 moles of solute dissolved into 1.00 L of solution. What's the molarity? The answer is 2.00 M. The answer is 2.00 M. Notice that no mention of a specific substance is mentioned at all. The molarity would be the same. It doesn't matter if it is sucrose, sodium chloride or any other substance. One mole of anything contains 6.02 x 10 23 units. Notice that no mention of a specific substance is mentioned at all. The molarity would be the same. It doesn't matter if it is sucrose, sodium chloride or any other substance. One mole of anything contains 6.02 x 10 23 units.

21. Molarity Now, let's change from using moles to grams. Now, let's change from using moles to grams. Example #4 - Suppose you had 100.0 grams of NaCl and you dissolved it in exactly 2.00 L of solution. What would be the molarity of the solution? Example #4 - Suppose you had 100.0 grams of NaCl and you dissolved it in exactly 2.00 L of solution. What would be the molarity of the solution? The answer is.855 mol/L (or 0.855 M). Sometimes, a book will write out the word "molar," as in 0.855- molar. The answer is.855 mol/L (or 0.855 M). Sometimes, a book will write out the word "molar," as in 0.855- molar. 100.0 g NaCl 1 mol NaCl 1 1 58.5 g NaCl 58.5 g NaCl 2.00 L

22. Molarity Try these examples problems : 5) Calculate the molarity of 25.0 grams of KBr dissolved in 750.0 mL. 5) Calculate the molarity of 25.0 grams of KBr dissolved in 750.0 mL. 6) 80.0 grams of glucose (C 6 H 12 O 6, mol. wt = 180. g/mol) is dissolved in enough water to make 1.00 L of solution. What is its molarity? 6) 80.0 grams of glucose (C 6 H 12 O 6, mol. wt = 180. g/mol) is dissolved in enough water to make 1.00 L of solution. What is its molarity?

23. Molality The molality of a solution is calculated by taking the moles of solute and dividing by the kilograms of solvent. This is a second method of calculating concentration one that becomes more useful for colligative properties.

24. Molality Example #1 - Suppose we had 1.00 mole of sucrose (it's about 342.3 grams) and proceeded to mix it into exactly 1.00 liter water. It would dissolve and make sugar water. We keep adding water, dissolving and stirring until all the solid was gone. We then made sure everything was well-mixed. Example #1 - Suppose we had 1.00 mole of sucrose (it's about 342.3 grams) and proceeded to mix it into exactly 1.00 liter water. It would dissolve and make sugar water. We keep adding water, dissolving and stirring until all the solid was gone. We then made sure everything was well-mixed. What would be the molality of this solution? Notice that my one liter of water weighs 1000 grams (density of water = 1.00 g / mL and 1000 mL of water in a liter). 1000 g is 1.00 kg, so: What would be the molality of this solution? Notice that my one liter of water weighs 1000 grams (density of water = 1.00 g / mL and 1000 mL of water in a liter). 1000 g is 1.00 kg, so:

25. Molality The answer is 1.00 mol/kg. Notice that both the units of mol and kg remain. Neither cancels. The answer is 1.00 mol/kg. Notice that both the units of mol and kg remain. Neither cancels. A replacement for mol/kg is often used. It is a lower- case m and is often in italics, m. Some textbooks also put in a dash, like this: 1.00-m. A replacement for mol/kg is often used. It is a lower- case m and is often in italics, m. Some textbooks also put in a dash, like this: 1.00-m.

26. Molality Example #2 - Suppose you had 2.00 moles of solute dissolved into 1.00 L of solvent. What's the molality? Example #2 - Suppose you had 2.00 moles of solute dissolved into 1.00 L of solvent. What's the molality? The answer is 2.00 m. The answer is 2.00 m. Notice that no mention of a specific substance is mentioned at all. The molarity would be the same. It doesn't matter if it is sucrose, sodium chloride or any other substance. One mole of anything contains 6.022 x 1023 units. Notice that no mention of a specific substance is mentioned at all. The molarity would be the same. It doesn't matter if it is sucrose, sodium chloride or any other substance. One mole of anything contains 6.022 x 1023 units.

27. Molality Now, let's change from using moles to grams. Now, let's change from using moles to grams. Example #4 - Suppose you had 100 grams of NaCl and you dissolved it in exactly 2.00 kg of pure water (the solvent). What would be the molality of the solution? Example #4 - Suppose you had 100 grams of NaCl and you dissolved it in exactly 2.00 kg of pure water (the solvent). What would be the molality of the solution? The Answer is 0.855 mol/kg (or 0.855 m). Sometimes, a book will write out the word "molal," as in 0.855- molal. The Answer is 0.855 mol/kg (or 0.855 m). Sometimes, a book will write out the word "molal," as in 0.855- molal. 100.0 g NaCl 1 mol NaCl 1 1 58.5 g NaCl 58.5 g NaCl 2.00 kg

28. Molality Try these examples problems: 5) Calculate the molality of 25.0 grams of KBr dissolved in 750.0 mL pure water. 5) Calculate the molality of 25.0 grams of KBr dissolved in 750.0 mL pure water. 6) 80.0 grams of glucose (C 6 H 12 O 6 mol. wt = 180. g/mol) is dissolved in1.00 kg of water. Calculate the molality. 6) 80.0 grams of glucose (C 6 H 12 O 6 mol. wt = 180. g/mol) is dissolved in1.00 kg of water. Calculate the molality.

29. Changing the Concentration Dilution To dilute a solution means to add more solvent without the addition of more solute. The resulting solution is thoroughly mixed and all parts of the solution are evenly distributed. To dilute a solution means to add more solvent without the addition of more solute. The resulting solution is thoroughly mixed and all parts of the solution are evenly distributed. The total number of solute particles stays constant, from this you can determine the Concentration. The total number of solute particles stays constant, from this you can determine the Concentration. moles before dilution = moles after dilution moles before dilution = moles after dilution

30. Dilution From the definition of molarity, we know that the moles of solute equals the molarity times the volume. From the definition of molarity, we know that the moles of solute equals the molarity times the volume. So we can substitute MV (molarity times volume) into the above equation, like this: So we can substitute MV (molarity times volume) into the above equation, like this: The "sub one" refers to the situation before dilution and the "sub two" refers to after dilution. The "sub one" refers to the situation before dilution and the "sub two" refers to after dilution. M 1 V 1 = M 2 V 2

31. Dilution Example #1 - 53.4 mL of a 1.50 M solution of NaCl is on hand, but you need some 0.800 M solution. How many mL of 0.800 M can you make? Example #1 - 53.4 mL of a 1.50 M solution of NaCl is on hand, but you need some 0.800 M solution. How many mL of 0.800 M can you make? Using the dilution equation, we write: M 1 V 1 = M 2 V 2 (1.50 mol/L) (53.4 mL) = (0.800 mol/L) (x) Solving the equation for x gives an answer of 100. mL. Notice that the volumes need not be converted to liters. Any old volume measurement is fine, just so long as the same one is used on each side. Notice that the volumes need not be converted to liters. Any old volume measurement is fine, just so long as the same one is used on each side.

32. Dilutions Example #2 - 100.0 mL of 2.500 M KBr solution is on hand. You need 0.5500 M. What is the final volume of solution which results? How do you make this solution? Example #2 - 100.0 mL of 2.500 M KBr solution is on hand. You need 0.5500 M. What is the final volume of solution which results? How do you make this solution? M 1 V 1 = M 2 V 2 (2.500 mol/L) (100.0 mL) = (0.5500 mol/L) (x) x = 454.5 mL Sometimes the problem might ask how much more water must be added. In this last case, the answer is 454.5 - 100.0 = 354.5 mL. x = 454.5 mL Sometimes the problem might ask how much more water must be added. In this last case, the answer is 454.5 - 100.0 = 354.5 mL.