Chemical Reactions:Chemical Reactions:Aqueous SolutionsAqueous Solutions

Mr. BennettMr. Bennett

November, 2009November, 2009Adapted from J. Speck (2008) and A. Allen,

2008

SolutionSolution

Solution- A homogeneous mixture of Solution- A homogeneous mixture of two or more substances, in which two or more substances, in which one is generally considered the one is generally considered the solvent and the other the solute.solvent and the other the solute.

Solvent- Medium in which another Solvent- Medium in which another substance is dissolved.substance is dissolved.

Solute- the substance which is Solute- the substance which is dissolved.dissolved.

Classification Classification of Matterof Matter

Solutions are homogeneous mixtures

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Aqueous solutionAqueous solution

Aqueous Solution- a solution that is Aqueous Solution- a solution that is made using water as the solvent.made using water as the solvent.

The water you drink every day The water you drink every day contains small concentrations of contains small concentrations of many ions, which result from the many ions, which result from the dissolving of solid materials in the dissolving of solid materials in the environment. Many of these are environment. Many of these are necessary ingredients in our diet.necessary ingredients in our diet.

Aqueous SolutionsAqueous Solutions

Dissolving an ionic solid involves Dissolving an ionic solid involves separating each ion from the separating each ion from the oppositely charged ions that oppositely charged ions that surround it in the solid state.surround it in the solid state.

Water is very good at this because Water is very good at this because each water molecule has a positively each water molecule has a positively and negatively charged end.and negatively charged end.

Structure of waterStructure of water

ElectrolytesElectrolytes

Electrolytes- compounds whose Electrolytes- compounds whose aqueous solutions conduct aqueous solutions conduct electricity.electricity.

When we dissolve compounds in When we dissolve compounds in water we can test to see if they water we can test to see if they break down into ion or not by seeing break down into ion or not by seeing if a charge will pass through it. if a charge will pass through it.

Types of ElectrolytesTypes of Electrolytes

Electrolytes can be classified as Electrolytes can be classified as strong or weak.strong or weak.

A strong electrolyte will dissolve A strong electrolyte will dissolve completely like NaCl. completely like NaCl.

NaCl (aq) NaCl (aq) ≡ Na≡ Na++ (aq) + Cl (aq) + Cl-- (aq) (aq) 100% Dissociation = strong electrolyte100% Dissociation = strong electrolyteBecause ions are highly concentrated in the Because ions are highly concentrated in the

solution, the solution is a good conductor solution, the solution is a good conductor of electricity and is a strong electrolyteof electricity and is a strong electrolyte

Types of ElectrolytesTypes of Electrolytes

Other substances produce only a small Other substances produce only a small concentration of ions when they dissolve, concentration of ions when they dissolve, and so they are poor conductors of and so they are poor conductors of electricity. These are called electricity. These are called weak weak electrolytes.electrolytes.

Ex: acetic acid dissolves in water, only a Ex: acetic acid dissolves in water, only a small percent of the molecules are ionized small percent of the molecules are ionized to produce cations and anions. Thus it to produce cations and anions. Thus it does not conduct electricity very well and does not conduct electricity very well and is a weak electrolyte.is a weak electrolyte.

Types of ElectrolytesTypes of Electrolytes

Nonelectrolytes- substances that Nonelectrolytes- substances that dissolve in water but do not ionize. dissolve in water but do not ionize. Thus they do not conduct electricity.Thus they do not conduct electricity.

These consist of molecular or These consist of molecular or covalent compounds like sugar, covalent compounds like sugar, ethanol, and antifreeze.ethanol, and antifreeze.

Solubility of Ionic Solubility of Ionic CompoundsCompounds

Not all ionic compounds dissolve in Not all ionic compounds dissolve in water. Many dissolve only to a small water. Many dissolve only to a small extent and other are insoluble. extent and other are insoluble.

There are rules about which types of There are rules about which types of ionic compounds are water soluble.ionic compounds are water soluble.

You will receive a hand out You will receive a hand out explaining the rules.explaining the rules.