AQUEOUS SOLUTIONS

Section 17.3

After reading Section 17.3, you should know: The meaning of “likes dissolve likes” and

how to determine which compounds will dissolve into each other

The difference between strong, weak and non-electrolytes

The difference between hygroscopic and deliquescent substances

Solvent vs Solute

Aqueous Solutions – water samples containing dissolved substances

Solvent – the substance doing the dissolving

Solute – the substance being dissolved

Example of an aqueous solution = salt water Solvent = water Solute = salt

Review: Ionic and Covalent

Ionic comounds = metal + nonmetal Held together by ionic charges

Polar Covalent molecules = 2 or more nonmetals Have a slight charge due to electronegativity

differences

Nonpolar Covalent molecules = 2 or more nonmetals Do not have a charge because the shape of the

molecule cancels the electronegativity differences out

“Likes Dissolve Likes” Ionic compounds and polar compounds will

dissolve in other ionic and polar compounds Ionic compounds have a full charge and polar

compounds have a slight charge, so the charges are attracted to each other.

Nonpolar compounds will only dissolve in other nonpolar compounds

Salt will dissolve in water Salt is ionic, water is polar

Oil and water do not mix Oil is nonpolar and water is polar

Solutions

Solutions are homogenous mixtures

Solvation – the process that occurs when a solute dissolves

Example: salt dissolving in water Salt is an ionic compound, water is a polar

molecule Animation of salt water and the interactions

between the molecules

Electrolytes and Nonelectrolytes Electrolytes – compounds that conduct

an electric current in aqueous solution or the molten state All ionic compounds are electrolytes

Nonelectrolytes - compounds that do not conduct an electric current in aqueous solution or the molten state

Strong electrolyte – when a substance is dissolved and almost all of the solute molecules separate into ions

Weak electrolytes – when a substance is dissolved and only a fraction of the dissolved solute separate into ions

Table 17.3 on page 485

Water of Hydration

Water of hydration is the water contained in a crystal

Hydrate – a compound containing water Example: copper (II) sulfate pentahydrate

CuSO4*5H2O

Table 17.4 on page 486

Effloresce – process that occurs when a hydrate has a vapor pressure higher than that of water vapor in the air

Hygroscopic – substances that remove water from the air Have low vapor pressure Used as desiccants or drying agents

Deliquescent – compounds that remove a sufficient water from the air to dissolve completely and form solutions When a substance has a lower vapor

pressure that that of the water in the air Example: solid NaOH pellets – react with

moisture from the air and will “melt” over time

After reading Section 17.3, you should know:

The meaning of “likes dissolve likes” and how to determine which compounds will dissolve into each other

The difference between strong, weak and non-electrolytes

The difference between hygroscopic and deliquescent substances