Solutions & Hydrates

Lecture 4.1

Solutions = homogeneous mixture

Solute = substance that gets dissolved

Solvent = substance that does the dissolving

concentration is measured in ….

MOLARITY!!

Aqueous Solutions = dissolved in water

water is a great solvent …. why??

Solubility = how much of a substance will dissolve

- usually measured in grams per 100 mL

- general rule is “like dissolves like”

- polar solvents dissolve polar compounds

- non-polar solvents dissolve non-polar compounds

- general rule usually means that ionic compounds are soluble in water BUT some are not!

- solubility rules handout … memorize these rules!!

Electrolytes = solutions that conduct an electric current

3 Types:

1) Strong =

- strong acids and bases … on solubility sheet so know these too!!

- soluble ionic compounds

Ex: HCl + H₂O H₃O⁺ + Cl^-

100% !!

HCl is a STRONG acid!

Electrolytes = solutions that conduct an electric current

3 Types:

2) Weak =

- often not written as soluble

- Some ionic compounds (which we will try to explain) and weak acids and bases

Ex: HC₂H₃O₂ + H₂O H₃O⁺ + C₂H₃O₂^-

NOT 100% !!

HC₂H₃O₂ is a WEAK acid!

Electrolytes = solutions that conduct an electric current

3 Types:

3) Nonelectrolytes =

- Typically organic compounds

Ex: Ethanol

Preparing Solutions

2 ways:

a)

b) Weight out solid (mass required from moles needed)

c) Fill flask roughly ½ full with liquid (often water)

d)

e) Add water to filling mark on volumetric flask

Molarity!!

1) From Solids:

Preparing Solutions

2 ways:

Molarity!!

2) Dilutions = diluting a more concentrated solution

M₁ * V₁ = M₂ * V₂

★

★

Ex: What volume of a 1.70 M solution is needed to make 250 mL of a .500 M solution?

Hydrates =

Naming:

1. Name ionic compound

2) # of water molecules = covalent prefix + hydrate

Ex:

CuSO₄ • 5H₂O =

Percent Water & Hydrate Formulas

Mass of H₂O

% H₂O = x 100

Mass of Compound

★

★

Ex: An unknown hydrate with a mass of 104.5 g is heated until it loses its water of hydration. The anhydrous sample has a mass of 81.7 g. What is the percent water in the compound?

Percent Water & Hydrate Formulas

hydrate formulas are the same as empirical formulas of compounds, but just for H₂O and the ionic compound!

Ex: When 6.584 g of one of the hydrates of Na₂SO₄ was heated to drive off it water of hydration, the residue of anhydrous sodium sulfate had a mass of 2.889 g. What is the formula of the hydrate?