Aqueous Reactions and Solution Stoichiometry

Aqueous Solutions

• Solutions in which water is the dissolving medium

Water Molecule

Hydrogen Bonds

Properties of Water Resulting from Hydrogen Bonding

• High surface tension• Low vapor pressure• High specific heat

capacity• High heat of vaporization• High boiling point

Solvents and Solutes

• Aqueous Solutions: Water samples containing dissolved substances

• Solute: the dissolved particles• Solvent: The medium the particles dissolve in• Solutions are homogeneous mixtures• Solutes can be solids, liquids or gases- ionic or

molecular

Like Dissolves Like

• Solvation: the process that occurs when a solute dissolves

• H2O and NaCl

• H2O and Oil

Solutions

• Homogeneous mixtures of solids, liquids, or gasses

Factors that affect Solubility

• Nature of the solvent and solute• Agitation (stirring)• Temperature• Surface Area

Agitation

• Affects only the rate of dissolution not the amount

Temperature• The higher the

temperature the higher the solubility

• Higher temperatures= greater kinetic energy = increased frequency of collisions between solute and solvent

Temperature vs. Solubility

Surface Area

• Fine powders will dissolve more rapidly than large crystals

• Dissolving is a surface phenomenon• More surface = faster dissolution

Solubility

• Is the amount of a substance that dissolves in a given quantity of a solvent at a given temperature

Saturated Solution

• A solution that contains the maximum amount of solute for a given amount of solvent at a constant temperature

Unsaturated

• Contains less solute than a saturated solution

Solubility of liquids

• Miscible: Two liquids that dissolve in each other (i.e. Ethanol and water)

• Immiscible: two liquids that are completely insoluble (i.e. Oil and water)

Solubility

http://phet.colorado.edu

Concentration

• Concentration of a solution is expressed as the amount of solute dissolved in an amount of solution

• Dilute solution: contains a low concentration of solute

• Concentrated Solution: contains a high concentration of solute

Concentration

Molarity

• Molarity (M) is the number of moles of solute dissolved per liter of solution

• Volume is the total volume of the solution, NOT the volume of the solvent alone

Molarity

• Molarity (M) = Moles of solute Liter of solution

Example

• A solution has a volume of 250 mL and contains 0.70 mol NaCl. What is the molarity of the solution?

• Molarity (M) = Moles of solute Liter of solution

Example

• A solution has a volume of 2.0 L and contains 36.0 g of glucose. If the molar mass of glucose is 180 g/mol what is the molarity of the solution?

Molarity (M) = Moles of solute Liter of solution

Making Dilutions

• You can make a solution less concentrated by diluting it with solvent

• The dilution reduces the moles of solute per unit volume

• Total moles of solute does not change• Moles of solute = moles of solute before dilution after dilution

Dilution

• M1V1=M2V2

• M= molarity• V= volume

Example

• How many milliliters of a stock solution of 4.00 M KI would you need to prepare 250.0 mL of 0.760 M KI?

• M1V1=M2V2

Electrolytes and Nonelctrolytes• Electrolytes:

compounds that conduct electricity in aqueous solution or molten state

• ALL Ionic compounds are electrolytes

• Not all conduct to the same degree

• Nonelectrolytes: don’t conduct

Acids

• Give food a sour flavor• Aqueous solutions of acids are electrolytes• React with compounds containing hydroxide

ions to form salt and water

Formulas of Acids

• An acid produces hydrogen ions- generic acid HX (X is an ion)

• IE– HCl– H2SO4

– HNO3

Common Monoprotic Acids

HCl Hydrochloric Acid

HF Hydrofluoric Acid

HNO3 Nitric Acid

CH3COOH Acetic Acid

Common Diprotic Acids

H2SO3 Sulfurous Acid

H2SO4 Sulfuric Acid

H2CO3 Carbonic Acid

Common Triprotic Acids

• H3PO4 Phosphoric Acid

Strong Acids

• Strong acids are completely ionized in an aqueous solution

• Hydrochloric Acid• Sulfuric Acid

• HCl (g) + H2O (l) H3O+ (aq) + Cl- (aq)

Weak Acids

• Weak acids ionize only slightly in aqueous solution, ionization is not complete

• CH3COOH (aq) + H2O H3O+(aq) + CH3COO- (aq)

• Ethanoic Acid Ethonate ion <1%

Bases

• Feel slippery• Taste bitter• Are electrolytes• React with acids to form water and salt

Strong Bases

• Strong bases dissociate completely into metal ions and hydroxide ions in aqueous solutions

• ALL bases containing OH- ions are strong bases

Weak Bases

• Weak bases react with water to form the hydroxide ion and the conjugate acid of the base

• NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq)

• <1%

Titration

• The concentration of an acid (or base) in a solution can be determined by performing a neutralization reaction

Steps for Titration

• A measured volume of an acidic solution is added to a flask

Steps for Titration

• Several drops of the indicator are added to the solution

Steps for Titration

• Measured volumes of a base of known concentration are mixed into the acid until the indicator barely changes color

Standard Solution

• The solution of known concentration Standard

Solution

End Point

• The point at which the indicator changes color

Equivalence Point

Equivalent

• Is the amount of acid (or base) that will give 1 mole of hydrogen (or hydroxide) ions

Equivalents

• Monoprotic Acids• HCl H+ + Cl-

• HNO3 H + + NO3-

• CH3COOH H+ + CH3COO-

Equivalents

• Diprotic Acids• H2SO4 2H+ + SO4

2-

• Triprotic Acids• H3PO4 3H+ + PO4

3-

Equivalents

• Bases• NaOH Na+ + OH-

• Ca(OH)2 Ca 2+ + 2OH-

• Al(OH)3 Al 3+ + 3OH-

Titration

• HCl (aq) + NaOH (aq) H2O (l) + NaCl (aq)

• 1 mol 1 mol 1 mol 1mol

• H2SO4 (aq) + 2KOH (aq) 2H2O (l) + K2SO4 (aq)

• 1 mol 2 mol 2 mol 1 mol

Example

• How many milliliters of 0.45 M hydrochloric acid must be added to 25.0 mL of 1.00 M potassium hydroxide to make a neutral solution?

Example

How many milliliters of 0.45 M hydrochloric acid must be added to 25.0 mL of 1.00 M potassium hydroxide to make a neutral solution?

HCL (aq) + KOH (aq) H2O (l) + KCl (aq)

25.0mLKOH =.0250 L KOH x1.00 mol =0.0250 mol KOH 1L0.025 mol KOH x 1 mol HCl x 1 L HCl = .0556 L HCl 1 mol KOH 0.45 mol HCl

Oxidation

• Originally meant: the combination of an element with oxygen to produce oxides

2Fe (s) + 3O2 (g) FeO2 (s)

Reduction

• The opposite of oxidation- originally meant the loss of oxygen

Redox Reactions

• Oxidation-reduction Reactions• Oxidation is loss of electrons or gain of oxygen• Reduction is gain of electrons or loss of

oxygen

Redox Reactions

• Mg + S Mg 2+ + S 2-

• Magnesium Sulfur Magnesium Sulfur

• Atom Atom Ion Ion

• Mg Mg 2+ + 2 e- (Loses 2 e-) oxidized• S S 2- (gains 2 e-) reduced

+

• Reducing Agent: the substance that loses electrons

• Oxidizing Agent: The substance that gains electrons

• Mg + S MgS

Oxidized

Reduced

Reducing Agent

Oxidizing Agent

Activity Series

Activity Series

• The activity series is used to predict the reactions between metals and either metal salts or acids

• Any metal on the list can be oxidized by the ions of elements below it