Aqueous Solutions and Aqueous Solutions and ConcentrationConcentration

A. DefinitionsA. DefinitionsA. DefinitionsA. Definitions

Solution - Solution - homogeneous mixturehomogeneous mixture

Solvent Solvent - present in - present in greater amountgreater amount

Solute Solute - substance - substance being dissolvedbeing dissolved

A. DefinitionsA. DefinitionsA. DefinitionsA. Definitions

Solute Solute - KMnO- KMnO44 Solvent Solvent - H- H22OO

B. SolvationB. SolvationB. SolvationB. Solvation

Solvation – Solvation – the process of dissolvingthe process of dissolving

solute particles are separated solute particles are separated and pulled into solutionand pulled into solution

solute particles are surrounded solute particles are surrounded by solvent particlesby solvent particles

B. SolvationB. SolvationB. 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.

B. SolvationB. SolvationB. SolvationB. Solvation

DissociationDissociationseparation of an separation of an

ionic solidionic solid into into aqueous ionsaqueous ions

NaCl(s) Na+(aq) + Cl–(aq)

B. SolvationB. SolvationB. SolvationB. Solvation

IonizationIonizationbreaking apart of breaking apart of

some some polar polar moleculesmolecules into into aqueous ionsaqueous ions

HNO3(aq) + H2O(l) H3O+(aq) + NO3–(aq)

B. SolvationB. SolvationB. SolvationB. Solvation

Molecular Molecular SolvationSolvationmoleculesmolecules

stay intactstay intact

C6H12O6(s) C6H12O6(aq)

B. SolvationB. SolvationB. SolvationB. Solvation

NONPOLAR

NONPOLAR

POLAR

POLAR

““Like Dissolves Like”Like Dissolves Like”““Like Dissolves Like”Like Dissolves Like”

B. SolvationB. SolvationB. SolvationB. Solvation

Soap/DetergentSoap/Detergentpolar “head” with long nonpolar “tail”polar “head” with long nonpolar “tail”dissolves nonpolar grease in polar waterdissolves nonpolar grease in polar water

A. ConcentrationA. ConcentrationA. ConcentrationA. Concentration

The amount of solute in a solution.The amount of solute in a solution.

Describing ConcentrationDescribing Concentration% by mass% by mass - medicated creams - medicated creams% by volume% by volume - rubbing alcohol - rubbing alcoholppm, ppbppm, ppb - water contaminants - water contaminantsmolaritymolarity - used by chemists - used by chemistsmolality molality - used by chemists- used by chemists

B. MolalityB. MolalityB. MolalityB. Molality

solvent ofkg

solute of moles(m)molality =

mass of solvent onlymass of solvent only

1 kg water = 1 L water1 kg water = 1 L water

kg 1

mol0.25 0.25m =

B. MolalityB. MolalityB. MolalityB. Molality

How many grams of NaCl are req’d to make a How many grams of NaCl are req’d to make a 1.541.54mm solution using 0.500 kg of water? solution using 0.500 kg of water?

0.500 kg water0.500 kg water 1.54 mol NaCl1.54 mol NaCl

1 kg water1 kg water

= = 45.0 g NaCl45.0 g NaCl

58.44 g NaCl58.44 g NaCl

1 mol NaCl1 mol NaCl

kg

molm=

B. MolalityB. MolalityB. MolalityB. Molality

Find the molality of a solution containing Find the molality of a solution containing 75 g of MgCl75 g of MgCl22 in 250 mL of water. in 250 mL of water.

75 g MgCl75 g MgCl22 1 mol MgCl1 mol MgCl22

95.21 g MgCl95.21 g MgCl22

= = 3.23.2mm MgCl MgCl22

0.25 kg water0.25 kg water

kg

molm =

2211 VMVM =

C. DilutionC. DilutionC. DilutionC. Dilution

Preparation of a desired solution by Preparation of a desired solution by adding water to a concentrate.adding water to a concentrate.

Moles of solute remain the same.Moles of solute remain the same.

C. DilutionC. DilutionC. DilutionC. Dilution

What volume of 15.8What volume of 15.8MM HNO HNO33 is required to make is required to make 250 mL of a 6.0250 mL of a 6.0MM solution? solution?

GIVEN:

M1 = 15.8M

V1 = ?

M2 = 6.0M

V2 = 250 mL

WORK:

M1 V1 = M2 V2

(15.8M) V1 = (6.0M)(250mL)

V1 = 95 mL of 15.8M HNO3

D. MolarityD. Molarity

Molarity is the most important unit of Molarity is the most important unit of concentration.concentration.

Molarity = Molarity = moles of solutemoles of solute

liters of solutionliters of solution

Symbol for Molarity is Symbol for Molarity is MM..

Example: A solution contains 23 g of NHExample: A solution contains 23 g of NH44Cl per 145 Cl per 145

mL solution. What is its molarity?mL solution. What is its molarity?