Solutions

1. Solutions

2. Remember mixtures? A combination of two or more substances that are not chemically combined and can be separated by physical means. Mixture Heterogeneous Homogeneous

3. So, what does this have to do with solutions? A solution is a homogeneous mixture of two or more substances in a single phase. Thoroughly mixed SameComposition Throughout SameProperties Throughout

4. solution solute(s) solvent Ocean water Coca-cola Humid air What makes up a solution? • Solute: the substance being dissolved • Solvent: the substance doing the dissolving Name the solute and solvent: salt water Sugar, carbon dioxide water Water vapor air

5. Examples of solutions Solvent Gas Liquid Solid Gas Oxygen and other gases in nitrogen (air) Carbon dioxide in water (carbonated water) Hydrogen dissolves rather well in metals; platinum has been studied as a storage medium Liquid Water vapor in air (humidity) Ethanol (common alcohol) in water; various hydrocarbons in each other (petroleum) Water in activated charcoal; moisture in wood Solid The odor of a solid results from molecules of that solid being dissolved in the air Sucrose (table sugar) in water; sodium chloride (table salt) in water Steel, brass, other metal alloys Solute Adapted from http://en.wikipedia.org/wiki/Solution

6. What types of solutions are there? • Aqueous solutions (aq): solutions in which water is the solvent. • Electrolytes: specific aqueous solutions in which the solute dissolves to form ions. • Tinctures: solutions in which alcohol is the solvent. • Alloys: solid solution of two or more metals. • Amalgams: specific alloys in which one of the metals is mercury.

7. If the particles in a solvent are so large that they settle out unless the mixture is constantly stirred or agitated, the mixture is called a suspension. Suspensions Example: Muddy Water

8. Particles that are intermediate in size between those in solutions and suspensions form mixtures known as colloidal dispersions, or colloids. Colloids Examples: paints, mud, gelatin, milk, mayonnaise, shaving cream, smoke, fog, butter

9. Tyndall Effect • A beam of light • distinguishes a colloid • from a solution. • The particles in a • colloid will scatter light, • making the beam • visible. NaCl Solution Gelatin and Water

10. Solutes: Electrolytes vs. Nonelectrolytes Dissolves in water to give a solution that conducts an electric current. Electrolyte Ionic Compounds (NaCl) Highly Polar Molecular Compounds (HCl)

11. Nonelectrolyte Dissolves in water to give a solution that does not conduct electrical current. Neutral solute molecules (not charged particles). Sugar is a nonelectrolyte.

14. Questions: What does soluble mean? Is sugar more soluble in hot tea or iced tea?

15. Soluble By experience you know that sugar will dissolve in tea. Sugar is described as being “soluble” in tea. Soluble – capable of dissolving in a particular solvent.

16. Back to tea. Why does sugar dissolve faster in hot tea versus iced tea? • Temperature • Heating a solvent • allows solvent • molecules to move • faster and their kinetic • energy increases. Factors Affecting the Rate of Dissolution • At higher temperatures, collisions between • solvent molecules and the solute are more • frequent and are of higher energy. • Helps to separate solute particles from each other and • have better dispersion among the solvent molecules.

17. Increasing the Surface Area of the Solute • Dissolution can be sped • up if surface area of solute is • increased. • Crushing sugar cubes • increases its surface area. • The more finely divided a substance is, the greater • the surface area and more quickly it dissolves.

18. Agitating a Solution • Stirring or shaking helps to • disperse the solute particles • and bring fresh solvent into • contact with the solute surface. • Contact between the solute • and solvent is increased.

19. Is there a limit to the amount of salt that will dissolve in a glass of water? Yes!! Why????????

20. Suppose you spoon copper sulfate into water until no more will dissolve. There is a little copper sulfate in the bottom. This means that copper sulfate is dissolving into the water as fast as copper sulfate is crystallizing out onto the bottom. That is dynamic equilibrium. Solution Equilibrium Solution equilibrium is the physical state in which the opposing processes of dissolution and crystallization of a solute occur at equal rates.

21. Saturated vs. Unsaturated Solutions A solution that contains the maximum amount of dissolved solute is described as a saturated solution. A solution that contains less solute than a saturated solution under the existing conditions is an unsaturated solution.

23. Supersaturated Solutions A supersaturated solution is a solution that contains more dissolved solute than a saturated solution contains under the same conditions. How does a supersaturated solution form? Heat saturated solution Let cool slowly – unstable If disturbed – will rapidly crystallize

24. Solubility The solubility of a substance is the amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature.

25. Question: Why does vinegar dissolve in water but not in vegetable oil? Type of bonding, polarity or nonpolarity of molecules, and the intermolecular forces between the solute and the solvent.

26. “Like Dissolves Like” Polar Solvents Ionic Compounds Nonpolar Compounds Nonpolar Solvents

27. Double, Double, Toil and Trouble… • What can happen when we mix two liquids together? Either they mix, or they don’t! • If two liquids mix well together, and one dissolves in the other, we call them miscible(think “mixable”) • If two liquids do not mix well together, and they separate, we call them immiscible (think “unmixable”)

28. Like Oil & Water… • How do we know that two liquids will be miscible or immiscible? • Rule of thumb: “Like dissolves Like” • Polar solutes will dissolve in polar solvents. • Nonpolar solutes will dissolve in nonpolar solvents. • Water is the “universal solvent”.

29. …And never the two shall meet? • How can we mix polar and nonpolar molecules into solutions? Can it be done? • We use emulsifiers – agents that have both polar and nonpolar ends to join the two unlike molecules together. • Creates an emulsion: A suspension of small globules of one liquid in a second liquid with which the first will not mix.

31. Concentration of Solutions The concentration of a solution is a measure of the amount of solute in a given amount of solvent or solution.

32. Concentration Units

33. Molarity Molarity is the number of moles of solute in one liter of solution. The symbol for molarity is M. For example, a “one molar” solution of sodium hydroxide, NaOH, contains one mole of NaOH in every liter of solution. The concentration of this solution would be written as 1 M NaOH.

34. Molarity Note that a 1 M solution is not made by adding 1 mol of solute to 1 L of solvent.

35. Molality Molality is the concentration of a solution expressed in moles of solute per kilogram of solvent. The symbol for molality is m. For example, a “one molal” solution of sodium hydroxide, NaOH, contains one mole of NaOH dissolved in exactly 1 kg of solvent. The concentration of this solution would be written 1 m NaOH.

36. Molality