Reactions in Aqueous Solution - Assumption University Chem... · Reactions in Aqueous Solution prepared by A. Kyi Kyi Tin Ref: Raymong Chang. Chemistry Twelfth Edition, McGraw –

Reactions in Aqueous Solutionprepared by A. Kyi Kyi Tin

Ref: Raymong Chang. Chemistry Twelfth Edition, McGraw – Hill International Edition

4.1 General Properties of Aqueous Solutions4.2 Precipitation Reactions4.3 Acid- Base Reactions4.4 Oxidation – Reduction Reactions4.5 Concentration of Solutions

Chapter 4 (semester 1/2016)

4.1

4.1 General Properties of Aqueous SolutionsSolution = [ solute + solvent]

[smaller amount + larger amount]

[CLEAR, HOMOGENEOUS MIXTURE]

Aqueous solution = solute (liquid “or” solid (gas)) + solvent (water)

Solution Solvent Solute

Sea water

Air (g)

Alloy

H2O

N2

Cu

Salt (NaCl)

O2, Ar, CH4

Ni

Two types of Solutes

nonelectrolyte weak electrolyte strong electrolyte

4.2

Non-electrolyte

When dissolved in water does not conduct electricity

Electrolyte

When dissolved in water can conduct electricity

Incomplete dissociation/reversible

100%dissociation/One-sided reaction

Ref: Raymond Chang Chemistry, Eleventh Edition

Strong Electrolyte – 100% dissociation

NaCl (s) Na+ (aq) + Cl- (aq)H2O

Weak Electrolyte – not completely dissociated

CH3COOH CH3COO- (aq) + H+ (aq)

Conduct electricity in solution?

Dissociation means breaking up into..Cations (+) and Anions (-)

4.3

Note: Pure water contains very few ions, can conduct electricity slightly (extremely weak

electrolyte)

Hydration: is the process in which an ion is surroundedby water molecules arranged in a specific manner.

Water, electrically neutral molecule has a positive polesand negative poles, ∴it is a polar solvent.

Ex: when NaCl dissolves in water Na+ ions and Cl-ions are separated from each other and undergo

“hydration”.

Hydration helps to stabilize ions in solution and prevents cations from combining with anions.

4.4

6

Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner.

δ+

δ−

H2O

Ionization of acetic acid

CH3COOH CH3COO- (aq) + H+ (aq)

4.5

A reversible reaction. The reaction can occur in both directions.

Acetic acid is a weak electrolyte because its ionization in water is incomplete.

Nonelectrolyte does not conduct electricity?

No cations (+) and anions (-) in solution

4.6

C6H12O6 (s) C6H12O6 (aq)H2O

Ref: Raymond Chang Chemistry, Ninth Edition

Page 121

4.2 Precipitation Reactions (Metathesis reaction) or (Double Displacement reaction)

One product is insoluble solid

molecular equation

ionic equation

net ionic equation

Pb2+ + 2NO3- + 2Na+ + 2I- PbI2 (s) + 2Na+ + 2NO3

-

Na+ and NO3- are spectator ions

Pb(NO3)2 (aq) + 2NaI (aq) PbI2 (s) + 2NaNO3 (aq)

precipitate

Pb2+ + 2I- PbI2 (s)

4.7

4.8

Solubility: Maximum amount of solute that will dissolve in a given quantity of solvent in a specific temperature.

Substances:

soluble

Slightly soluble

insoluble

Soluble : fair amount is visibly dissolves when added to water

-All ionic compounds are strong electrolytes, but they are not equally soluble.

-Even insoluble compounds dissolve to a certain extent

Examples are: (NH4)2CO3, (NH4)3PO4,(NH4)2S,(NH4)2CrO4

ACID: Arrhenius acid is a substance that produces H+ (H3O+) in water

BASE: Arrhenius base is a substance that produces OH- in water

4.9

4.3 Acid-Base Reactions

Ref: Raymond Chang Chemistry, Ninth EditionFigure 4.7,4.8 Page 128,129

Electrostatic potential map of the Hydronium ion, hydrated proton, H3O+

4.10

Ref: Raymond Chang Chemistry, Eleventh Edition

the most electron- rich

region

the most electron-poor

region

A Brønsted acid is a proton donorA Brønsted base is a proton acceptor

acidbase acid base

4.11

A Brønsted acid must contain at least one ionizable proton!

Ref: Raymond Chang Chemistry, Ninth Edition

Figure 4.8, Page 129

Monoprotic acidsHCl H+ + Cl-

HNO3 H+ + NO3-

CH3COOH H+ + CH3COO-

Strong electrolyte, strong acid

Strong electrolyte, strong acid

Weak electrolyte, weak acid

Diprotic acidsH2SO4 H+ + HSO4

-

HSO4- H+ + SO4

2-

Strong electrolyte, strong acid

Weak electrolyte, weak acid

Triprotic acidsH3PO4 H+ + H2PO4

-

H2PO4- H+ + HPO4

2-

HPO42- H+ + PO4

3-

Weak electrolyte, weak acidWeak electrolyte, weak acidWeak electrolyte, weak acid

4.12

Practice question: Identify each of the following species as a Brønsted acid, base, or both. (a) HI, (b) CH3COO-, (c) H2PO4

-

HI (aq) H+ (aq) + Br- (aq) Brønsted acid

CH3COO- (aq) + H+ (aq) CH3COOH (aq) Brønsted base

H2PO4- (aq) H+ (aq) + HPO4

2- (aq)

H2PO4- (aq) + H+ (aq) H3PO4 (aq)

Brønsted acid

Brønsted base

4.13

Neutralization Reaction

acid + base salt + water

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

H+ + Cl- + Na+ + OH- Na+ + Cl- + H2O

H+ + OH- H2O

4.14

4.4 Oxidation-Reduction ReactionsREDOX REACTIONS(electron transfer reactions)

2Mg (s) + O2 (g) 2MgO (s)

2Mg 2Mg2+ + 4e-

O2 + 4e- 2O2-

Oxidation half-reaction (loss of e-)

Reduction half-reaction (gain e-)

2Mg + O2 2MgO

4.15

Oxidized∴Reducing Agent (donates electrons

to oxygen and causes oxygen to

be reduced)

Reduced∴Oxidizing Agent (accepts electrons from Magnesium

and causes Magnesium to be

oxidized)

OIL RIG

Oxidation Is Loss

Reduction Is Gain

Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s)

Zn is oxidizedZn Zn2+ + 2e-

Cu2+ is reducedCu2+ + 2e- Cu

Zn is the reducing agent

Cu2+ is the oxidizing agent

4.16

Copper wire reacts with silver nitrate to form silver metal.What is the oxidizing agent in the reaction?

Cu (s) + 2AgNO3 (aq) Cu(NO3)2 (aq) + 2Ag (s)

Cu Cu2+ + 2e-

Ag+ + 1e- Ag Ag+ is reduced Ag+ is the oxidizing agent

NaIO3

Na = +1 O = -2

3x(-2) + 1 + ? = 0

I = +5

IF7

F = -1

7x(-1) + ? = 0

I = +7

K2Cr2O7

O = -2 K = +1

7x(-2) + 2x(+1) + 2x(?) = 0

Cr = +6

Oxidation numbers of all the elements in the following ?

4.17

Types of Redox Reactions

(i) Combination Reaction

Two or more substances combine to form a single product.

0 0 +4 -2

S(s) + O2 (g) SO2(g)

(ii) Decomposition Reaction

Breakdown of a compound into two or more components.

+2 -2 0 0

2 HgO(s) 2Hg(l) + O2(g)

4.18

(iii) Displacement ReactionHalogen displacement

According to Activity Series

F2 > Cl2 > Br2 > I2i.e Molecular fluorine can replace chloride, bromide and iodide ions in solution. On the other hand, Molecular chlorine can replace bromide and iodide ions in solution

0 -1 -1 0

Cl2 (g) + 2 KBr(aq) 2KCl(aq) + Br2(l)

0 -1 -1 0Cl2 (g) + 2 NaI(aq) 2NaCl(aq) + I2(l)

4.19

Ca2+ + CO32- CaCO3

NH3 + H+ NH4+

Zn + 2HCl ZnCl2 + H2

Ca + F2 CaF2

Precipitation

Acid-Base

Redox (H2 Displacement)

Redox (Combination)

Classify the following reactions.

4.20

4.5 Concentration of Solutions

concentration : amount of solute present in a given quantity of solvent or solution.

M = molarity =moles of solute

liters of solution

4.21

Most commonly used unit is “Molarity”

VnM =

Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution.

DilutionAdd Solvent

Moles of solutebefore dilution (i)

Moles of soluteafter dilution (f)=

MiVi MfVf=4.22

How would you prepare 60.0 mL of 0.2 MHNO3 from a stock solution of 4.00 M HNO3?

MiVi = MfVf

Mi = 4.00 Mf = 0.200 Vf = 0.06 L Vi = ? L

4.23

Vi =MfVf

Mi= 0.200 x 0.06

4.00= 0.003 L = 3 mL

3 mL of acid + 57 mL of water = 60 mL of solution