Solutions: Forming Solutions Unit 10

I. What is a solution? I. What is a solution? A. A. Solution – a homogeneous mixture in which the components are uniformly inter mingled. 1, 1, Solute – substance that is dissolved 2. Solvent – substance that does the dissolving 3. Aqueous solutions – water is the solvent!

B. Solubility – how things dissolve B. Solubility – how things dissolve 1. Solubility of Ionic Substances – when an ionic solid dissolves, it breaks apart into its ions which are dispersed throughout the solution 1. Solubility of Ionic Substances – when an ionic solid dissolves, it breaks apart into its ions which are dispersed throughout the solution

2. Solubility of Polar Substances – the polar parts of the molecule are attracted to the oppositely charged polar parts of the water molecule 2. Solubility of Polar Substances – the polar parts of the molecule are attracted to the oppositely charged polar parts of the water molecule

3. Substances Insoluble in Water – Nonpolar substances do NOT dissolve in water! 3. Substances Insoluble in Water – Nonpolar substances do NOT dissolve in water!

4. How Substances Dissolve 4. How Substances Dissolve A. Like Dissolves Like A. Like Dissolves Like 1.) Polar solvents dissolve polar solutes 1.) Polar solvents dissolve polar solutes 2.) Nonpolar solvents dissolve nonpolar solutes 2.) Nonpolar solvents dissolve nonpolar solutes

C. : An Introduction – there is a limit on how much solute can dissolve in a solvent C. Solution Composition: An Introduction – there is a limit on how much solute can dissolve in a solvent 1 1. saturated – when a solution contains as much solute as will dissolve at that temperature unsaturated – a solution that can dissolve more solute at that temperature 3. supersaturated – contains more solute than normal for that temperature, very unstable.

Unsaturated, Saturated, Supersaturated Solutions

4. 4. Concentrated – a solution in which a relatively large amount of solute is dissolved. 5. Dilute – a solution in which a relatively small amount of solute is dissolved. (Think strong vs. weak coffee) (Think strong vs. weak coffee)

D. D. Factors Affecting the Rate of Dissolving 1. Stirring – rate of dissolving increases when the solution is stirred! Temperature – a. Solids dissolve faster at higher temperatures B. Gases dissolve faster at colder temperatures 3. Surface Area – the more surface area there is, the faster something dissolves! (Think granulated sugar (large surface area) vs. sugar cubes (small surface area)

Measuring Concentration of a Solution Molarity (M) Moles (n) of solute dissolved per liter (V) of solution. M = n/V Molality (m) moles (n) of solute dissolved per kg of solvent m = n/kg solvent

Dilutions M 1 V 1 = M 2 V 2 M = molarity in mol/L M = molarity in mol/L V = volume in L V = volume in L When diluting a solution, the number of moles of solute never changes, just the volume. When diluting a solution, the number of moles of solute never changes, just the volume.

Colligative Properties are specific properties of solutions. They only depend upon the number of particles in solution NOT the particles composition! are specific properties of solutions. They only depend upon the number of particles in solution NOT the particles composition!

Boiling Point Elevation When a solute is added to pure water, it increases the boiling point of the solution. When a solute is added to pure water, it increases the boiling point of the solution. For example, adding NaCl increases the boiling point of water to 104°C. WHY? For example, adding NaCl increases the boiling point of water to 104°C. WHY? In order for water to boil, the vapor pressure (HUH?) of the water HAS TO EQUAL atmospheric pressure, BUT…the solute particles get in the way of the liquid water particles joining the gas particles in a bubble & escaping. Therefore, it requires more heat energy (higher temp.) in order to get the solution to boil. In order for water to boil, the vapor pressure (HUH?) of the water HAS TO EQUAL atmospheric pressure, BUT…the solute particles get in the way of the liquid water particles joining the gas particles in a bubble & escaping. Therefore, it requires more heat energy (higher temp.) in order to get the solution to boil.

Vapor Pressure In a container, vapor pressure is the pressure of the vapor particles above a liquid. In a container, vapor pressure is the pressure of the vapor particles above a liquid.

Boiling Point Elevation

ΔT b = k b im ΔT b = change in boiling point ΔT b = change in boiling point K b = boiling point elevation constant K b = boiling point elevation constant i = factor of particles in solution i = factor of particles in solution m = molality m = molality

Solvent K b (°C/m) Acetic acid 3.07 Benzene2.53 Carbon tetrachloride 4.95 Water.512

Freezing Point Depression Adding a solute also lowers the freezing point of a solution as well. Adding a solute also lowers the freezing point of a solution as well. For example, adding a solute (like salt) to water, interferes with the solution forming a regularly ordered solid. Therefore it takes even lower temperatures to force the solution to make a solid. For example, adding a solute (like salt) to water, interferes with the solution forming a regularly ordered solid. Therefore it takes even lower temperatures to force the solution to make a solid.

ΔT f = k fim ΔT f = change in freezing point ΔT f = change in freezing point K f = freezing point depression constant K f = freezing point depression constant i = factor of particles in solution i = factor of particles in solution m = molality m = molality gonstate.edu/cbqftr- std.jpg&imgrefurl= _gxBntImh87ZyAlQ1z-- 5YplQDng=&h=315&w=588&sz=24&hl=en&start=131&um=1 &tbnid=5fSA1ler_Q3OhM:&tbnh=72&tbnw=135&prev=/image s%3Fq%3Dfreezing%2Bpoint%2Bdepression%26ndsp%3D2 0%26hl%3Den%26sa%3DN%26start%3D120%26um%3D1 gonstate.edu/cbqftr- std.jpg&imgrefurl= _gxBntImh87ZyAlQ1z-- 5YplQDng=&h=315&w=588&sz=24&hl=en&start=131&um=1 &tbnid=5fSA1ler_Q3OhM:&tbnh=72&tbnw=135&prev=/image s%3Fq%3Dfreezing%2Bpoint%2Bdepression%26ndsp%3D2 0%26hl%3Den%26sa%3DN%26start%3D120%26um%3D1

Solvent K f (°C/m) Acetic acid 3.90 Benzene5.12 Carbon tetrachloride 30 Water1.86