Reactions in Aqueous Solution

Chapter 4 – Part 1

Solutions

A

solution

is a homogenous mixture The

solute

is present in the smaller amount The

solvent

is present in the larger amount Solution Soft drink (

l

) Air (

g

) Soft Solder (

s

) Solvent H 2 O N 2 Pb Solute Sugar, CO 2 O 2 , Ar, CH 4 Sn 4.1

An

electrolyte

is a substance that, when dissolved in water, results in a solution that can conduct electricity.

A

nonelectrolyte

is a substance that, when dissolved, results in a solution that does not conduct electricity.

nonelectrolyte weak electrolyte strong electrolyte 4.1

Conduct electricity in solution?

Cations (+) and Anions (-) Strong Electrolyte – 100% dissociation NaCl (

s

) H 2 O Na + (

aq

) + Cl (

aq

) Weak Electrolyte – not completely dissociated CH 3 COOH CH 3 COO (

aq

) + H + (

aq

) 4.1

Hydration

is the process in which an ion is surrounded by water molecules arranged in a specific manner.

d d + H 2 O

Electrolytes   Substances that dissociate into ions when dissolved in water allow water to conduct electricity.

A dissolve in water, but it does not dissociate into ions when it does so.

nonelectrolyte may

Electrolytes and Nonelectrolytes Soluble ionic compounds tend to be electrolytes.

Electrolytes and Nonelectrolytes Molecular compounds tend to be nonelectrolytes, except for acids and bases.

 Strong Electrolytes Are… Strong acids

  Strong Electrolytes Are… Strong acids Strong bases

   Strong Electrolytes Are… Strong acids Strong bases Soluble ionic salts

Precipitation Reactions When one mixes ions that form compounds that are insoluble (as could be predicted by the solubility guidelines), a precipitate is formed.

Acids:   Substances that increase the concentration of H + when dissolved in water (Arrhenius).

Proton donors (Brønsted–Lowry).

Bases:   Substances that increase the concentration of OH − when dissolved in water (Arrhenius).

Proton acceptors (Brønsted–Lowry).

Neutralization Reactions Generally, when solutions of an acid and a base are combined, the products are a salt and water.

HCl ( aq ) + NaOH ( aq )  NaCl ( aq ) + H 2 O ( l )

Gas-Forming Reactions  The expected product decomposes to give a gaseous product (CO 2 or SO 2 ).

CaCO 3 ( s ) + HCl ( aq )  CaCl 2 ( aq ) NaHCO 3 ( aq ) + HBr ( aq )  NaBr ( aq + CO ) 2 + CO ( 2 g ( ) g ) + H 2 O ( l ) + H 2 O ( l ) SrSO 3 ( s ) + 2 HI ( aq )  SrI 2 ( aq ) + SO 2 ( g ) + H 2 O ( l )

Oxidation-Reduction Reactions   An oxidation occurs when an atom or ion loses electrons.

A reduction occurs when an atom or ion gains electrons.

Displacement Reactions   In displacement reactions, ions oxidize or reduce an element.

The ions, then, are reduced or oxidized.