Solution Conductivity

Guiding Questions What is meant by dissociation? What is the molecular arrangement of water molecules?

A. Definitions Solution - homogeneous mixture Solute - substance being dissolved Solvent - present in greater amount

Arrhenius’s Theory of Electrolytic Dissociation Why do some solutions conduct electricity? An early hypothesis was that electricity produced ions in solution, and those ions allowed the electricity to flow. Arrhenius’s theory: Certain substances dissociate into cations and anions when dissolved in water. The ions already present in solution allow electricity to flow.

Dissociation http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf

Nonpolar vs. Polar When nonpolar substances dissolve in one another, they simply mix. When polar substances dissolve, electrical reactions pull apart the molecules.

IONIC COMPOUNDS Compounds in Aqueous Solution Many reactions involve ionic compounds, especially reactions in water — aqueous solutions. K+(aq) + MnO4-(aq) KMnO4 in water To play the movies and simulations included, view the presentation in Slide Show Mode.

ELECTROLYTES Are substances that form positive(+) and negative (-) ions in water Conduct an electric current

Types of Electrolytes A strong electrolyte dissociates completely. A strong electrolyte is present in solution almost exclusively as ions. Strong electrolyte solutions are good conductors. A weak electrolyte dissociates partially. Weak electrolyte solutions are poor conductors. Different weak electrolytes dissociate to different extents. A nonelectrolyte does not dissociate. A nonelectrolyte is present in solution almost exclusively as molecules. Nonelectrolyte solutions do not conduct electricity.

Electrolytic Properties of Aqueous Solutions Electrolytes dissociate to produce ions. The more the electrolyte dissociates, the more ions it produces.

Is it a strong electrolyte, a weak electrolyte, or a nonelectrolyte? Strong electrolytes include: Strong acids (HCl, HBr, HI, HNO3, H2SO4, HClO4) Strong bases (IA and IIA hydroxides) Most water-soluble ionic compounds Weak electrolytes include: Weak acids and weak bases A few ionic compounds Nonelectrolytes include: Most molecular compounds Most organic compounds (most of them are molecular) How do we tell whether an acid (or base) is weak?

B. Solvation Non- Electrolyte Weak Electrolyte Strong Electrolyte + sugar - + acetic acid - + salt Non- Electrolyte Weak Electrolyte Strong Electrolyte solute exists as molecules only solute exists as ions and molecules solute exists as ions only DISSOCIATION IONIZATION View animation online.

Electrolytes in the Body Make your own 50-70 g sugar One liter of warm water Pinch of salt 200ml of sugar free fruit squash Mix, cool and drink Carry messages to and from the brain as electrical signals Maintain cellular function with the correct concentrations electrolytes