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

Hygroscopic – substances that remove water from the air 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