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Solution ConductivitySolution Conductivity

Guiding QuestionsGuiding Questions

What is meant by dissociation?What is meant by dissociation?

What is the molecular arrangement of What is the molecular arrangement of water molecules?water molecules?

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A. DefinitionsA. Definitions

Solution - Solution - homogeneous mixturehomogeneous mixture

Solvent Solvent - present in - present in greater amountgreater amount

Solute Solute - substance - substance being dissolvedbeing dissolved

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Why do some solutions conduct electricity?Why do some solutions conduct electricity?

An early hypothesis was that electricity An early hypothesis was that electricity producedproduced ions in solution, and those ions ions in solution, and those ions allowed the electricity to flow.allowed the electricity to flow.

ArrheniusArrhenius’’s theory:s theory: Certain substances Certain substances dissociatedissociate into ca into cattions and ions and

anions when dissolved in water.anions when dissolved in water. The ions The ions already present in solutionalready present in solution allow allow

electricity to flow.electricity to flow.

Arrhenius’s Theory ofArrhenius’s Theory ofElectrolytic DissociationElectrolytic Dissociation

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DissociationDissociation

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

Nonpolar vs. PolarNonpolar vs. Polar

When nonpolar substances dissolve in When nonpolar substances dissolve in one another, they simply mix.one another, they simply mix.

When polar substances dissolve, electrical When polar substances dissolve, electrical reactions pull apart the molecules.reactions pull apart the molecules.

IONIC COMPOUNDSIONIC COMPOUNDSCompounds in Aqueous SolutionCompounds in Aqueous Solution

Many reactions involve ionic Many reactions involve ionic compounds, especially reactions in compounds, especially reactions in water — water — aqueous solutions.aqueous solutions.

KMnOKMnO44 in water in water KK++(aq) + MnO(aq) + MnO44--(aq)(aq)

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ELECTROLYTESELECTROLYTES

Are substances that form positive(+) Are substances that form positive(+)

and negative (-) ions in waterand negative (-) ions in water

Conduct an electric current Conduct an electric current

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A A strong electrolytestrong electrolyte dissociates completely. dissociates completely. A strong electrolyte is present in solution almost A strong electrolyte is present in solution almost

exclusively as exclusively as ionsions.. Strong electrolyte solutions are good conductors.Strong electrolyte solutions are good conductors.

A A weak electrolyteweak electrolyte dissociates partially. dissociates partially. Weak electrolyte solutions are poor conductors.Weak electrolyte solutions are poor conductors. Different weak electrolytes dissociate to different Different weak electrolytes dissociate to different

extents.extents.

A A nonelectrolytenonelectrolyte does not dissociate. does not dissociate. A nonelectrolyte is present in solution almost A nonelectrolyte is present in solution almost

exclusively as exclusively as moleculesmolecules.. Nonelectrolyte solutions do not conduct electricity.Nonelectrolyte solutions do not conduct electricity.

Types of ElectrolytesTypes of Electrolytes

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• Electrolytes dissociate to produce ions.

Electrolytic Electrolytic Properties Properties of Aqueous of Aqueous SolutionsSolutions

The more the electrolyte dissociates, the more ions it produces.

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Strong electrolytes include:Strong electrolytes include: Strong acids (HCl, HBr, HI, HNOStrong acids (HCl, HBr, HI, HNO33, H, H22SOSO44, HClO, HClO44)) Strong bases (IA and IIA hydroxides)Strong bases (IA and IIA hydroxides) Most water-soluble ionic compoundsMost water-soluble ionic compounds

Weak electrolytes include:Weak electrolytes include: Weak acids and weak basesWeak acids and weak bases A few ionic compoundsA few ionic compounds

Nonelectrolytes include: Most molecular compounds Most organic compounds (most of them are molecular)

Is it a strong electrolyte, a weak Is it a strong electrolyte, a weak electrolyte, or a nonelectrolyte?electrolyte, or a nonelectrolyte?

How do we tell whether an acid

(or base) is weak?

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B. SolvationB. Solvation

StrongElectrolyte

Non-Electrolyte

solute exists asions only

- +

salt

- +

sugar

solute exists asmolecules

only

- +

acetic acid

WeakElectrolyte

solute exists asions and

molecules DISSOCIATION IONIZATION

View animation online.

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Electrolytes in the BodyElectrolytes in the Body

Carry messages Carry messages to and from the to and from the brain as brain as electrical signalselectrical signals

Maintain cellular Maintain cellular function with the function with the correct correct concentrations concentrations electrolyteselectrolytes

Make your ownMake your own50-70 g sugar50-70 g sugarOne liter of warm One liter of warm

waterwaterPinch of saltPinch of salt200ml of sugar 200ml of sugar

free fruit squashfree fruit squashMix, cool and drinkMix, cool and drink