Chapter 4 types of chemical reactions and solution stoichiometry
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Chapter 4: TYPES OF CHEMICAL REACTIONS AND SOLUTION STOICHIOMETRY. Aqueous Solutions. Water is the dissolving medium, or solvent. Some Properties of Water Water is “ bent ” or V-shaped . The O-H bonds are covalent . Water is a polar molecule.

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Chapter 4:


Aqueous Solutions

Water is the dissolving medium, or solvent.

Some Properties of Water

Water is “bent” or V-shaped.

The O-H bonds are covalent.

Water is a polar molecule.

Hydration occurs when salts dissolve in water.

Figure 4.1: (Left) The water molecule is polar. (Right) A space-filling model of the water molecule.

Figure 4.2: Polar water molecules interact with the positive and negative ions of a salt assisting in the dissolving process.

Figure 4.3: (a) The ethanol molecule contains a polar O—H bond similar to those in the water molecule. (b) The polar water molecule interacts strongly with the polar O—H bond in ethanol. This is a case of "like dissolving like."

A Solute

dissolves in water (or other “solvent”);

changes phase(if different from the solvent);

is present in lesser amount (if the same phase as the solvent).

A Solvent

retains its phase(if different from the solute);

is present in greater amount (if the same phase as the solute).

Figure 4.4: Electrical conductivity of aqueous solutions.


Strong Electrolytes - conduct current efficiently

NaCl, HNO3

WeakElectrolytes - conduct only a small current

vinegar, tap water

Nonelectrolytes - no current flows

pure water, sugar solution

※ Svante Arrhenius postulated: the extend to which a solution can conduct an electric current depends on the number of ions present.

Strong electrolytes:

Substances that are completely ionized when they are dissolved in water .

soluble salts,

(2) strong acids,

(3) strong bases.

Figure 4.5: When solid NaCl dissolves, the Na+ and Cl- ions are randomly dispersed in the water.

Arrhenius discoveries the nature of acids

Figure 4.6: HCl(aq) is completely ionized.

※ Arrhenius proposed that an acid is a substance that produces H+.

HCl H+(aq) + OH-(aq)

HNO3H+(aq) + NO3-(aq)

H2SO4H+(aq) + HSO4-(aq)

Strong bases - react completely with water to give OH- ions.

Figure 4.7: An aqueous solution of sodium hydroxide.

Figure 4.8: Acetic acid (HC2H3O2) exists in water mostly as undissociated molecules. Only a small percentage of the molecules are ionized.

Weak electrolytes:

Weak bases - react only slightly with water to give OH- ions.

Figure 4.9: The reaction of NH3 in water.


Molarity (M) = moles of solute per volume of solution in liters:

Common Terms of Solution Concentration

Standard solution- concentration is exactly known.

Stock solutions- routinely used solutions prepared in concentrated form.

Concentrated solution-relatively large ratio of solute to solvent. (5.0 M NaCl)

Diluted solution - relatively small ratio of solute to solvent. (0.01 M NaCl)

Figure 4.10: Steps involved in the preparation of a standard aqueous solution.

Figure 4.11: (a) A measuring pipet is graduated and can be used to measure various volumes of liquid accurately. (b) a volumetric (transfer) pipet is designed to measure one volume accurately.

Figure 4.12: Dilution Procedure (a) A measuring pipet is used to transfer 28.7mL of 17.4 M acetic acid solution to a volumetric flask. (b) Water is added to the flask to the calibration mark. (c) The resulting solution is 1.00 M acetic acid.





毛細管 I.D. 25-100 mm








毛細管電泳(Capillary Electrophoresis-CE)儀器結構簡圖

m = er e0x / h













Photograph of the micro-device with attached transfer capillary

m-TAS (micro-TAS) concept:

Miniture -Total Chemical Analysis system.

Precipitation reactions

AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq)

Acid-base reactions

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

Oxidation-reduction reactions

Fe2O3(s) + Al(s)  Fe(l) + Al2O3(s)

Types of Solution Reactions

Figure 4.13: When yellow aqueous potassium chromate is added to a colorless barium nitrate solution, yellow barium chromate precipitates.

Figure 4.14: Reactant Solutions: (a) Ba(NO3)2(aq) and (b) K2CrO4(aq)

Figure 4.15a,b: The reaction of K2CrO4 and Ba(NO3)2(aq).

Figure 4.15c: The reaction of K2CrO4 and Ba(NO3)2(aq). (cont'd)

Figure 4.16: Precipitation of silver chloride by mixing solutions of silver nitrate and potassium chloride. The K+ and NO3- ions remain in solution.

Figure 4.17: The reaction of KCl(aq) with AgNO3 to form AgCl(s).

1.Most nitrate (NO3) salts are soluble.

2.Most alkali (group 1A) salts and NH4+are soluble.

3.Most Cl, Br, and I salts are soluble(NOT Ag+, Pb2+, Hg22+)

4.Most sulfate salts are soluble(NOT BaSO4, PbSO4, HgSO4, CaSO4)

5.Most OH salts are only slightly soluble(NaOH, KOH are soluble, Ba(OH)2, Ca(OH)2 are marginally soluble)

6.Most S2, CO32, CrO42, PO43 salts are only slightly soluble.

Table 4.1 Simple Rules for Solubility of Salts in Water

1. Molecular equation(reactants and products as compounds)

AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq)

2. Complete ionic equation(all strong electrolytes shown as ions)

Ag+(aq) + NO3(aq) + Na+(aq) + Cl(aq) 

AgCl(s) + Na+(aq) + NO3(aq)

3. Net ionic equation(show only components that actually react)

Ag+(aq) + Cl(aq)  AgCl(s)

Na+ and NO3 are spectator ions.

Describing Reactions in Solution

Stoichiometry Steps for reactions in solution.

Performing calculations for acid-base reactions.

Titrant - solution of known concentration used in titration

Analyte - substance being analyzed

Equivalence point - enough titrant added to react exactly with the analyte (Stoichiometric point)

Endpoint - the indicator changes color so you can tell the equivalence point has been reached.

Indicator- a color substance with its color change to mark the endpoint of titration.

Key Titration Terms

Figure 4.18: The titration of an acid with a base.

Figure 4.19: The reaction of solid sodium and gaseous chlorine to form solid sodium chloride.

Sum of oxidation states = 0 in compounds

Sum of oxidation states = charge of the ion

Figure 4.20: A summary of an oxidation-reduction process, in which M is oxidized and X is reduced.

1.Write separate reduction, oxidation reactions.

2.For each half-reaction:

Balance elements (except H, O)

Balance O using H2O

Balance H using H+

Balance charge using electrons

3. If necessary, multiply by integer to equalize electron count.

4.Add half-reactions.

5.Check that elements and charges are balanced.

Balancing by Half-Reaction Method

Cr2O72-(aq) + SO3-(aq) Cr3+(aq) + SO42-(aq)

How can we balance this equation?

Balancing Oxidation-Reduction Reactions

Cr2O72-(aq) 2Cr3+(aq)

SO3-(aq) SO42-(aq)

How many electrons are involved in each half reaction?

Method of Half Reactions

6e- + Cr2O72-(aq) 2Cr3+(aq)

SO3-(aq) SO42-(aq) + 2e-

How can we balance the oxygen atoms?

Method of Half Reactions (cont.)

6e- + Cr2O72-(aq) Cr3+(aq) + 7H2O

H2O + SO3-(aq) SO42-(aq) + 2e-

How can we balance the hydrogen atoms?

Method of Half Reactions (cont.)

This reaction occurs in an acidic solution.

14H+ + 6e- + Cr2O72-(aq) Cr3+(aq) + 7H2O

H2O +SO3-(aq) SO42-(aq) + 2e- + 2H+

How can we balance the electrons?

Method of Half Reactions (cont.)

14H+ + 6e- + Cr2O72-(aq) Cr3+(aq) + 7H2O

3[H2O +SO3-(aq) SO42-(aq) + 2e- + 2H+]

Cr2O72-(aq) + 3SO3-(aq) + 8H+(aq)

 2Cr3+(aq) + 3SO42-(aq) + 4H2O(l)

Method of Half Reactions (cont.)

1.Balance as in acid.

2.Add OH that equals H+ ions (both sides!)

3.Form water by combining H+, OH.

4.Check elements and charges for balance.

Half-Reaction Method - Balancing in Base

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