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 types of chemical reactions and solution stoichiometry

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.

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 4.1: (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 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 "

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
Figure 4.4: Electrical conductivity of aqueous solutions. 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 "


Electrolytes 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 "

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: 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 "

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


Figure 4 6 hcl aq is completely ionized

Arrhenius discoveries the nature of acids 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 "

Figure 4.6: HCl(aq) is completely ionized.


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

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

HNO3H+(aq) + NO3-(aq)

H2SO4H+(aq) + HSO4-(aq)


Figure 4 7 an aqueous solution of sodium hydroxide

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

Figure 4.7: An aqueous solution of sodium hydroxide.


Figure 4.8: Acetic acid (HC 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 "2H3O2) exists in water mostly as undissociated molecules. Only a small percentage of the molecules are ionized.

Weak electrolytes:


Figure 4 9 the reaction of nh 3 in water

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

Figure 4.9: The reaction of NH3 in water.


Molarity 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 "

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


Common Terms of Solution Concentration 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 "

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 4.11: standard aqueous solution.(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.



資料處理 used

系統

毛細管

毛細管 I.D. 25-100 mm

偵測器

注入端

偵檢端

白金電極

電解質緩衝溶液

電解質緩衝溶液

高電壓(KV)

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


m used = er e0x / h


+ used

+

n

-

-

EOF

+

n

Net

-

毛細管電泳的向量圖


CE-in-a-Chip used

Photograph of the micro-device with attached transfer capillary


m used -TAS (micro-TAS) concept:

Miniture -Total Chemical Analysis system.


Precipitation reactions used

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 no 3 2 aq and b k 2 cro 4 aq
Figure 4.14: Reactant Solutions: added to a colorless barium nitrate solution, yellow barium chromate precipitates.(a) Ba(NO3)2(aq) and (b) K2CrO4(aq)


Figure 4 15a b the reaction of k 2 cro 4 and ba no 3 2 aq
Figure 4.15a,b: The reaction of K added to a colorless barium nitrate solution, yellow barium chromate precipitates.2CrO4 and Ba(NO3)2(aq).


Figure 4 15c the reaction of k 2 cro 4 and ba no 3 2 aq cont d
Figure 4.15c: The reaction of K added to a colorless barium nitrate solution, yellow barium chromate precipitates.2CrO4 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 agno 3 to form agcl s
Figure 4.17: The reaction of KCl( solutions of silver nitrate and potassium chloride. The aq) with AgNO3 to form AgCl(s).


1. solutions of silver nitrate and potassium chloride. The 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


Describing reactions in solution

1. Molecular equation solutions of silver nitrate and potassium chloride. The (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
Stoichiometry Steps for reactions in solution. solutions of silver nitrate and potassium chloride. The


Performing calculations for acid base reactions
Performing calculations for acid-base reactions. solutions of silver nitrate and potassium chloride. The


Key titration terms

Titrant solutions of silver nitrate and potassium chloride. The - 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 4.18: The titration of an acid with a base. solutions of silver nitrate and potassium chloride. The


Figure 4 19 the reaction of solid sodium and gaseous chlorine to form solid sodium chloride
Figure 4.19: The reaction of solid sodium and gaseous chlorine to form solid sodium chloride.


Sum of oxidation states = 0 in compounds chlorine to form solid sodium chloride.

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


Balancing by half reaction method

1. in which M is oxidized and X is reduced.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


Balancing oxidation reduction reactions

Cr in which M is oxidized and X is reduced.2O72-(aq) + SO3-(aq) Cr3+(aq) + SO42-(aq)

How can we balance this equation?

Balancing Oxidation-Reduction Reactions


Method of half reactions

Cr in which M is oxidized and X is reduced.2O72-(aq) 2Cr3+(aq)

SO3-(aq) SO42-(aq)

How many electrons are involved in each half reaction?

Method of Half Reactions


Method of half reactions cont

6e in which M is oxidized and X is reduced.- + Cr2O72-(aq) 2Cr3+(aq)

SO3-(aq) SO42-(aq) + 2e-

How can we balance the oxygen atoms?

Method of Half Reactions (cont.)


Method of half reactions cont1

6e in which M is oxidized and X is reduced.- + Cr2O72-(aq) Cr3+(aq) + 7H2O

H2O + SO3-(aq) SO42-(aq) + 2e-

How can we balance the hydrogen atoms?

Method of Half Reactions (cont.)


Method of half reactions cont2

This reaction occurs in an acidic solution. in which M is oxidized and X is reduced.

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.)


Method of half reactions cont3

14H in which M is oxidized and X is reduced.+ + 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.)


Half reaction method balancing in base

1. in which M is oxidized and X is reduced. 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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