Solutions and the Properties of Water

1. Solutions and the Properties of Water

2. Solutions • A solution is a homogeneous mixture; if something is soluble that means that it is capable of being dissolved • A solute is dissolved in a solvent. • solute is the substance being dissolved • solvent is the liquid in which the solute is dissolved • an aqueous solution has water as solvent

3. Solutions can happen in any state of matter

4. Suspension • Particles in a solvent are so large they settle out; unless the mixture is constantly stirred or agitated • Can be filtered • Example: Muddy water

5. Colloid • Particles are intermediate in size • Particles dispersed in water but not big enough to be filtered • Words like foam and emulsifying generally refer to colloids • Mayonnaise is a colloid

6. Tyndall Effect • Used to distinguish colloids from solutions • Light is scattered by colloidal molecules in a transparent medium

7. Dissolution of a solid state What are the driving forces which cause solutes to dissolve to form solutions? 1. Covalent solutes dissolve by H-bonding to water 2. Ionic solutes dissolve by dissociation into their ions.

8. Electrolytes vs. Nonelectrolytes • Electrolyte • Ionic compounds separate into positive and negative ions • Solution can conduct electricity due to charged particles • Salt water • Nonelectrolyte • Substance dissolves in water but does not conduct electricity • Sugar water

9. Factors affecting the rate of dissolution • Increasing surface area of the solute • Agitating the solution (stirring) • Adding heat to the solvent • Increases the kinetic energy of the molecules of the solvent

10. Solubility • There is a limit to the amount of solute that can be dissolved in a given solution • Solution equilibrium • Physical state in which dissolution and recrystallization of the solute are happening at equal rates

11. Saturated solution • A saturated solution is one where the concentration is at a maximum - no more solute is able to dissolve. • A saturated solution represents an equilibrium: the rate of dissolving is equal to the rate of crystallization. The salt continues to dissolve, but crystallizes at the same rate so that there “appears” to be nothing happening.

12. Saturated vs. unsaturated solution • A saturated solution contains the maximum quantity of solute that dissolves at that temperature. • An unsaturated solution contains less than the maximum amount of solute that can dissolve at a particular temperature

13. Supersaturated solution • SUPERSATURATED SOLUTIONS contain more solute than is possible to be dissolved • Supersaturated solutions are unstable. • The supersaturation is only temporary, and usually accomplished in one of two ways: • Warm the solvent so that it will dissolve more, then cool the solution • Evaporate some of the solvent carefully so that the solute does not solidify and come out of solution.

14. Water is a “Universal” Solvent • A liquid that is a completely homogeneous mixture of two or more substances is called a solution. • A sugar cube in a glass of water will eventually dissolve to form a uniform mixture of sugar and water. • The dissolving agent is the solvent and the substance that is dissolved is the solute. • In our example, water is the solvent and sugar the solute. • In an aqueous solution, water is the solvent. • Water is not really a universal solvent, but it is very versatile because of the polarity of water molecules.

15. Quick Review • Non-polar covalent compound: a compound in which e- shared equally. • Polar covalent compound: uneven distribution of e-, unequal sharing…electrons in the compound are more attracted to electronegative atom. In this case water is a POLAR MOLECULE! Polar molecule: one in which there are oppositely charged ends.

16. Water is a Polar Molecule -has oppositely charged ends • Water consists of an oxygen atom bound to two hydrogen atoms by two single covalent bonds. • Oxygen has unpaired & paired electrons which gives it a slightly negative charge while Hydrogen has no unpaired electrons and shares all others with Oxygen • Leaves molecule with positively and negative charged ends

17. Water molecules form Hydrogen bonds slightly positive charge hydrogen bond between (+) and (-) areas of different water molecules slightly negative charge

18. Water is an effective solvent as it can form hydrogen bonds. • Water clings to polar molecules causing them to be soluble in water. • Hydrophilic - attracted to water • Water tends to exclude nonpolar molecules. • Hydrophobic - repelled by water

19. ...when a solute dissolves in a solvent

20. General Rule: “Like dissolves like” • Means that a polar solute dissolves only in a polar solvent • Water is a solvent for many, but not all substances • Some substances will not dissolve in water, non polar

21. Hydrations and Hydrates • This process with water as the solvent is called hydration • Compounds that have water chemically attached are called hydrates • Like copper sulfate pentahydrate • CuSO4● 5H2O

22. Calculate the percent of water by mass 110 + 36 = 146 36/146 = .246 = 25 % 171 + 144 = 315 144/315 = .4571 = 46 % 106 + 180 = 286 180/286 = .6293 = 63% 202+ 180 = 382 180/382 = .4712 = 47 % • CaCl2●2H2O • Ba(OH)2 ●8H2O • Na2CO3 ●10H2O • Na2B4O7 ●10H2O