Solutions

What on earth does this have to do with chemistry? Chemistry Joke What on earth does this have to do with chemistry? It’s a lit-moose test!

Solutions Homogeneous Mixtures Composed of a solute and a solvent Uniform throughout Composed of a solute and a solvent The solute is dissolved into the solvent The solute or the solvent can be a gas, a liquid, or a solid. Air: gas / gas solution Salt water: solid / liquid solution Carbonated water: gas / liquid solution Steel: solid / solid solution

“Like Dissolves Like” Polar solvents dissolve polar solutes Water is a polar molecule. It has an uneven distribution of charge. Water will easily dissolve polar solutes such NaCl.

“Like Dissolves Like” Nonpolar solvents dissolve nonpolar solutes Gasoline is a nonpolar molecule. It has an even distribution of charge. Gasoline is often used as a solvent to clean nonpolar grease from machine parts.

Making Solutions In order to dissolve, the solvent molecules must come in contact with the solute. Process is called solvation. 3 Factors that affect the rate Stirring (agitation) Particle size (surface area) Temperature

Stirring moves fresh solvent into contact with the solute. Making Solutions Stirring moves fresh solvent into contact with the solute. It’s why we stir iced tea when we add sugar. 2. Smaller pieces increase the amount of surface area of the solute. Think of how fast a breath mint dissolves when you chew it

Slowest Faster Fastest Making Solutions 3. Higher temperature makes the molecules of the solvent move around faster and contact the solute harder and more often. Slowest Faster Fastest

Making Solutions So, the rate of solubility is affected by: Stirring, Particle Size, & Temperature What determines the amount of solute that will dissolve? Temperature & Pressure

Making Solutions Temperature: Affects the solubility of solids, liquids, and gases. For most solids and liquids, the solubility increases with increasing temps. For most gases, the solubility decreases with increasing temps. As carbonated drinks get warm, they get “flat”

Effect of Temperature The mineral deposits around hot springs result from the cooling of the hot, saturated solution of minerals emerging from the spring.

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Affects only the solubility of gases. Effect of Pressure Pressure: Affects only the solubility of gases. Gas solubility increases as the partial pressure of the gas above the solution increases.

How Is Solubility Expressed? Max amount of a substance that will dissolve at a specific temp. Units are g solute/ 100 g solvent. Saturated Contains the max amount of solute that can dissolve Rate of particles dissolving equals rate of particles crystalizing.

How Is Solubility Expressed? Unsaturated Can still dissolve more solute Supersaturated Holds more than it can theoretically contain

How Is Solubility Expressed? Electrolytes Compounds that conduct electricity in aqueous solution or in a molten state All ionic compounds are electrolytes Some ionic compounds are strong electrolytes; others are weak electrolytes. Strong electrolytes dissociate (break apart) completely. Weak electrolytes only partially dissociate.

How Is Solubility Expressed? Most molecular compounds do not conduct electricity. Called nonelectrolytes Sugar and rubbing alcohol are nonelectrolytes

NaCl: Strong Electrolyte HgCl2: Weak Electrolyte Glucose: NonElectrolyte

Colligative Properties Properties that affect solutions. Depends only on the number of dissolved solute particles—not on what kind of particle they are Two important colligative properties are: Boiling point elevation As solute particles are added to a solution, the boiling point rises. Freezing point depression As solute particles are added to a solution, the freezing point lowers.

Ionic compounds work best because they dissociate in water into more particles. In water, NaCl becomes Na+ and Cl-.

Chemistry Joke Q: Why did the white bear dissolve in water? A: Because it was polar!!