a cenote

INTRODUCTIONWATER IN LIFE ON EARTH

Water covers almost two thirds of our planet

Water has been the key to much of Earth’s evolutionary

history

Life itself is almost certainly originated from water

Our body is about 60% water by mass

Water possesses many unusual properties essential to

supporting life on Earth

INTRODUCTIONWATER AS A MEDIUM Water has an exceptional ability to dissolve a wide variety

of substances

Water on Earth invariably contains a variety of dissolved

substances

Water is the medium for most of the chemical reactions

that take place within us and around us

INTRODUCTIONWATER AS A MEDIUM

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Figure 4.1 Cenote formation

4.1 GENERAL PROPERTIES OF AQUEOUS SOLUTIONS

ELECTROLYTIC PROPERTIES Consider two aqueous solutions: NaCl (aq) & C6H12O6 (aq)

Electrolyte & nonelectrolyte

Solution, solvent, and solute

4.1 GENERAL PROPERTIES OF AQUEOUS SOLUTIONS IONIC & MOLECULAR COMPOUNDS IN

WATER Dissolution (solvation) process in water We can predict the nature of ionic compounds (Na2SO4) in

water from the chemical formula Most molecular compounds are nonelectrolytes Glucose, CH3OH, and HCl (ionic)

4.1 GENERAL PROPERTIES OF AQUEOUS SOLUTIONSSTRONG AND WEAK

ELECTROLYTES Strong electrolytes exist in solution (nearly) completely as ions; NaCl, HCl

Weak electrolytes exist in solution mostly in the form of molecules with only a small fraction in the form of ions; CH3COOH (about 1% ionized)

Dissolution & ionization (CH3COOH & Ba(OH)2 ) (weak) (strong)

Soluble ionic compounds are strong electrolytes: metal+nonmetal compounds & ammonium containing compounds (NaCl, FeSO4, Al(NO3)3, NH4Br, (NH4)2CO3)

4.2 PRECIPITATION REACTIONSPRECIPITATION REACTION

4.2 PRECIPITATION REACTIONSSOLUBILITY GUIDELINES FOR IONIC

COMPOUNDS Solubility: the amount of a substance dissolved in a given

quantity of solvent at a given temperature Some ionic substances are insoluble in water because the

attraction between the opposite charges is too great for the water molecules to separate the ions

No general rules to predict solubility of a substance

All ionic compounds containing NO3-, or CH3COO-

All ionic compounds containing the alkali metal ions or,

NH4+

4.2 PRECIPITATION REACTIONSSOLUBILITY GUIDELINES FOR IONIC COMPOUNDS

4.2 PRECIPITATION REACTIONS

EXCHANGE (METATHESIS) REACTIONS

IONIC EQUATIONS Molecular equations

Ionic equations (complete ionic equations)

Net ionic equations

Spectator ions

4.3 ACID-BASE REACTIONS Many acids and bases are industrial and household

substances Hydrochloric acid: important industrial chemical & main

component of gastric juice in our stomach.

4.3 ACID-BASE REACTIONS

ACIDS Substances that ionize in water to form H+,

thereby increasing the concentration of H+

Proton donors

Monoprotic acids: HCl and HNO3

Diprotic acids: H2SO4

CH3COOH (acetic acid)

4.3 ACID-BASE REACTIONS

BASES Substances that accept (react with) H+ Bases produce hydroxide ions (OH-) when they dissolve in

water

NaOH, KOH and Ca(OH)2 are common bases

NH3 is also a common base although it does not have OH-

4.3 ACID-BASE REACTIONS

STRONG AND WEAK ACIDS AND BASES Strong acids and bases

•Acids and bases that are completely ionized in solution Weak acids and bases

•Acids and bases that are partly ionized in solution

4.3 ACID-BASE REACTIONS IDENTIFYING STRONG AND WEAK

ELECTROLYTES

4.3 ACID-BASE REACTIONSNEUTRALIZATION REACTIONS AND

SALTS Differences in the properties of acids and bases

•Sour and bitter taste

•Color changes with certain dyes Neutralization reaction occurs when a solution of an acid

and a solution of a base are mixed

4.3 ACID-BASE REACTIONSNEUTRALIZATION REACTIONS AND SALTS

4.3 ACID-BASE REACTIONSNEUTRALIZATION REACTIONS AND

SALTSSample Exercise 4.7 Writing Chemical Equations for a

Neutralization ReactionFor the reaction between aqueous solutions of acetic acid (CH3COOH) and barium hydroxide, Ba(OH)2, write (a) the balanced molecular equation, (b) the complete ionic equation, (c) the net ionic equation.

4.3 ACID-BA SE REACTIONSACID-BASE REACTIONS WITH GAS

FORMATION Consider a acid-base reaction:

Carbonic acid is unstable

Heartburn, reflux, indigestion, and sour stomach

Histamine-2 (H2) blockers including cimetidine (Tagamet), famotidine (Pepcid), and ranitidine (Zantac), and the proton pump inhibitor (PPI) omeprazole (Prilosec)

4.4 OXIDATION-REDUCTION REACTIONS

OXIDATION AND REDUCTION

Oxidation – loss of electrons by a substance

Reduction – gain of electrons by a substance

4.4 OXIDATION-REDUCTION REACTIONS

OXIDATION AND REDUCTION

Ca(s) is oxidized and O2(g) is reduced

4.4 OXIDATION-REDUCTION REACTIONS

OXIDATION NUMBERS The degree of oxidation of an atom in a chemical compound Assigning oxidation number

• Elements in their elemental form have an oxidation number of 0.

• The oxidation number of a monatomic ion is the same as its charge.

• Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions

- O: -2 (-1 in O2-2), H: +1 (-1 when bonded to metals),

F: -1, other halogens: -1 (+N when bonded to oxygen)• The sum of the oxidation numbers in a neutral compound is 0.• The sum of the oxidation numbers in a polyatomic ion is the

charge on the ion.

4.4 OXIDATION-REDUCTION REACTIONS

OXIDATION NUMBERS

4.4 OXIDATION-REDUCTION REACTIONSOXIDATION OF METALS BY ACIDS AND

SALTS By acids

By salts

4.4 OXIDATION-REDUCTION REACTIONSOXIDATION OF METALS BY ACIDS AND

SALTS

4.4 OXIDATION-REDUCTION REACTIONS

ACTIVITY SERIES Can we predict whether a certain metal will be oxidized either

by an acid or by a particular salt? It would be unwise to store a solution of nickel nitrate,

Ni(NO3)2, in an iron container.

Different metals vary in the ease with which they are oxidized Zn is oxidized by aqueous solution of Cu2+, but Ag is not. Activity series of metals in aqueous solution

•A list of metals arranged in order of decreasing ease of oxidation

4.4 OXIDATION-REDUCTION REACTIONSACTIVITY SERIES

Any metal on the listcan be oxidizedby the ions of elements below it

4.4 OXIDATION-REDUCTION REACTIONSACTIVITY SERIES

4.4 OXIDATION-REDUCTION REACTIONSACTIVITY SERIES

• Why is gold a special metal? - intrinsic beauty and rarity - soft and easy to be formed - the least active metal• Gold can be found in nature as a

pure element rather than combined with oxygen or other elements, which account for its early discovery.

• Used in jewelry (73%), coins (10%), and electronics (9%).

4.5 CONCENTRATIONS OF SOLUTIONSMOLARITY

The concentration of a solution as the number of moles of solute in a liter of solution

Figure 4.16 Preparing 0.250 L of a 1.00M solution of CuSO4.

4.5 CONCENTRATIONS OF SOLUTIONS

FW 142 g/mol

MOLARITY

4.5 CONCENTRATIONS OF SOLUTIONSTHE CONCENTRATION OF AN

ELECTROLYTE Some substances produce multiple cations and/or anions

(Na2SO4, MgCl2)

4.5 CONCENTRATIONS OF SOLUTIONS

INTERCONVERTING M, mol, AND VOLUME

FW 142 g/mol

DILUTION How would you prepare 250.0 mL of 0.100 M cupric sulfate

solution from 1.00 M solution?

4.5 CONCENTRATIONS OF SOLUTIONS

DILUTION – PREPARATION OF SOLUTIONS

4.5 CONCENTRATIONS OF SOLUTIONS

Figure 4.17

4.6 SOLUTION STOICHIOMETRY AND CHEMICAL ANALYSIS Let’s consider a question:

4.6 SOLUTION STOICHIOMETRY AND CHEMICAL ANALYSIS

FW 74.1 g/mol

4.6 SOLUTION STOICHIOMETRY AND CHEMICAL ANALYSIS

NaOH, FW 40.0 g/mol

4.6 SOLUTION STOICHIOMETRY AND CHEMICAL ANALYSIS

TITRATIONS Titration is an analytical technique in which one can

determine the concentration of a solute in a solution. Standard solution Equivalence point Indicators

4.6 SOLUTION STOICHIOMETRY AND CHEMICAL ANALYSIS

TITRATIONS

Figure 4.19

4.6 SOLUTION STOICHIOMETRY AND CHEMICAL ANALYSIS

4.6 SOLUTION STOICHIOMETRY AND CHEMICAL ANALYSIS

FW 212.3 g/mol

Ag3PO4, FW 212.3 g/mol

1.

2.

3.