1. Reactions in Aqueous Solutions Course Instructor: HbR
GENERAL CHEMISTRY CHE 101
Reactions in Aqueous Solutions
Course Instructor: HbR

2. Lecture Plan General properties Precipitation Reaction
Acid-Base Reaction
Oxidation-Reduction Reaction
Electronegativity
Concentration of Solutions
Dilutions of Solutions

3. Solution A solution is a homogenous mixture of 2 or more substances.
The solute is (are) the substance(s) present in smaller amount(s) in a solution.
The solvent is the substance present in larger amount in solution
Solution Solvent Solute
Soft drink (l) H2O Sugar, CO2

4. Properties of Aqueous Solution
Electrolyte : Is a substance that, when dissolved in water, results in a solution that can conduct electricity.
Nonelectrolyte: is a substance, that, when dissolved, results in a solution that does not conduct electricity.
Nonelectrolyte weak electrolyte strong electrolyte

5. Electrolytic Solutions
Cations (+) and Anions (-) Strong electrolyte – 100% dissociation NaCl (s) Na+ (aq) + Cl- (aq) Weak electrolyte – not completely dissociated CH3COOH CH3COO-(aq) + H+(aq)
H2O
H2O

6. Electrolytic Solutions
Ionization of acetic acid CH3COOH CH3COO-(aq) + H+(aq) A reversible reaction. The reaction can occur in both directions. Acetic acid is a weak electrolyte because its ionization in water is incomplete.

7. Electrolytic Solutions

8. Electrolytic Solutions
Water is a very effective solvent for ionic compounds.
Although water is an electrically neutral molecule, it has a positive region (the H atoms) and a negative region (the O atom),
or positive and negative “poles”; for this reason it is a polar solvent.

9. Electrolytic Solutions
When an ionic compound such as sodium chloride dissolves in water, the three-dimensional network of ions in the solid is destroyed. The Na+ and Cl- ions are separated from each other.
NaCl (s) Na+ (aq) + Cl- (aq)
H2O

10. Electrolytic Solutions

11. Reactions in aqueous solution
Precipitation Reaction
Acid-Base Reaction
Oxidation-Reduction Reaction

12. Ca(OH)2 (s) Ca2+(aq) + OH-(aq)
H2O
Ca(OH)2 (s) Ca2+(aq) OH-(aq)
Dissolving in water breaks the ionic bonds.
s aq
Precipitation
Dissolution
Dissolution is the process by which a solute (solid) forms a solution in a solvent (water).
Precipitation is the formation of a solid in a solution during a chemical reaction

13. Precipitation reactions
Precipitate : insoluble solid that separates from solution.
Solubility: Maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature.
Solubility is a qualitative measure (e. g., soluble, slightly soluble, insoluble)
Ionic compounds are strong electrolytes /solubility varies
Insoluble compounds can also be soluble to a certain extent (depending on Temp)

14. Precipitation reactions

15. Examples of Precipitation Reaction
CdS, PbS, Ni(OH)2, AL(OH)3

16. Classify the solubility

17. Precipitation reactions
Molecular equation
Pb(NO3)2(aq)+2KI(aq) PbI2(s)+2KNO3(aq)
Ionic equation
Pb2+(aq)+2NO3-(aq)+2K+(aq)+2I-(aq) PbI2(s)+2K+(aq)+2NO3-(aq)
Net Ionic equation
Pb2++ 2I PbI2 (s)
K+ and NO3- are spectator ions.
PbI2

18. Precipitation reactions
Pb2+ + 2I PbI2 (s)

19. silver nitrate with sodium chloride.
Net Ionic Equation
Write the balanced molecular equation.
Write the ionic equation showing the strong electrolytes completely dissociated into cations (+) and anions (-).
Cancel the spectator ions on both sides of the ionic equation.
Check that charges and numbers of atoms are balanced in the net ionic equation.
Write the net ionic equation for the reaction of
silver nitrate with sodium chloride.
AgNO3(aq) + NaCl (aq) AgCl(s) + NaNO3(aq)
Ag+(aq) +NO3-(aq) + Na+(aq) + Cl- (aq) AgCl (s) + Na+(aq) +NO3-(aq)

20. Reactions in aqueous solution
Precipitation Reaction
Acid-Base Reaction
Oxidation-Reduction Reaction

21. Acid-Base Reaction Properties of acid:
Have a sour taste.
(Vinegar owes its taste to acetic acid. Citrus fruits contain citric acid.)
Cause color changes in litmus test (blue- red)
React with certain metals to produce hydrogen gas.
2HCl(aq) + Mg(s) MgCl2(aq) +H2(g)
React with carbonates and bicarbonates to produce carbon dioxide gas.
2HCl(aq) + CaCO3(s) CaCl2(aq) + CO2(g) + H2O(l)
Aqueous acid solutions conduct electricity.

22. Acid-Base Reaction Properties of Base: Have a bitter taste.
Feel slippery. Many soaps which contain bases, show this property.
Cause color changes in litmus test (red-blue)
Aqueous base solutions conduct electricity.
Example:
NH OH-

23. Acid-Base Reaction
Arhenius acid is a substance that produces H+ (H30+) in water.
Arhenius base is a substance that produces OH- in water.

24. Acid-Base Reaction A Bronsted acid is a proton donor.
A Bronsted base is a proton accepter.
A Bronsted acid must contain at least one ionizable proton.

25. Acid-Base Reaction Monoprotic acids
HCl H+ + Cl Strong electrolyte, strong acid
HNO H+ + NO Strong electrolyte, strong acid
CH3COOH H+ + CH3COO weak electrolyte, weak acid
Diprotic acids
H2SO H+ + HSO Strong electrolyte, strong acid
HSO H+ + SO weak electrolyte, weak acid
Triprotic acids
H3PO4- H+ + H2PO weak electrolyte, weak acid
H2PO42- H+ + HPO weak electrolyte, weak acid
HPO42- H+ + PO weak electrolyte, weak acid

26. Neutralization Reaction
A neutralization reaction is a reaction between an acid and a base. (if they are strong)
Acid + Base  Salt + Water
HCl(aq) + NaOH(aq) NaCl(aq) + H2O
H+ + Cl- + Na+ + OH Na+ + Cl- + H2O
H+ + OH H2O

27. Neutralization Reaction
Weak acid + base salt + water
HCN(aq) + NaOH (aq) NaCN (aq) + H2O
HCN + Na+ + OH Na+ + CN- + H2O
HCN + OH CN- + H20
Neutralization reaction producing a Gas
Acid + base salt + water + gas
HCl(aq) + Na2CO3(aq) NaCl(aq) + H2O + CO2
2H+ + 2Cl- + 2Na+ + CO Na+ + Cl- + H2O + CO2
2H+ + CO H2O + CO2

28. Reactions in aqueous solution
Precipitation Reaction
Acid-Base Reaction
Oxidation-Reduction Reaction

29. Redox Reaction-Transfer of electrons
‘X’ id oxidized
Loss of electron
Oxidation number increase.
Mg is reducing agent.
‘Y’ is reduced
Gain of electron
Oxidation number decreases
O2 is oxidizing agent. Y
2Mg(s) + O2 (g)  2MgO (s) X

30. Oxidation-Reduction Reaction
2Mg Mg2+ + 4e- Oxidation half-reaction (lose e-)
O2 + 4e O2- Reduction half-reaction (gain e-)
2Mg + O2 + 4e Mg2+ + 2O e-
2Mg + O MgO

31. Electronegativity Tendency to attract electron to it.
What happens if two atoms of equal electronegativity bond together? example, H2 or Cl2molecules.
What happens if B is slightly more electronegative than A? example; H2O
What happens if B is a lot more electronegative than A? example; NaI

32. Electronegativity The most electronegative element is fluorine (F).
Exception is Hydrogen (H).

33. Formal charge
Formal charge: pretending all the electrons are shared/ perfectly covalent.
H • • O • • H
Formal charge (FC) is the charge assigned to an atom in a molecule, assuming that electrons in a chemical bond are shared equally between atoms, regardless of relative Electronegativity.
Formal Charge = [# of valence electrons on atom] – [non-bonded electrons + number of bonds]
Valence e
Formal charge

34. Let’s try it! Calculate the formal charge on each atom in O3? 0 +1 -1
Can we infer it from Lewis structure ?
Knowing the formal charge on a particular atom in a structure is an important part of keeping track of the electrons and is important for establishing and predicting the reactivity.

35. Rules to imply…
For molecules, the sum of the charges must add up to zero because molecules are electrically neutral species
For cations, the sum of formal charges must equal the positive charge
For anions, the sum of formal charges must equal the negative charge

36. Oxidation number
Oxidation number: assuming all the bonds are perfectly ionic bonds.
H • • O • • H
e- in ions
Oxidation num
(NH4)2MoO4  
Calculate the oxidation number for each atom underneath…
Oxidation number is assigned to an element in chemical combination that represents the number of electrons lost (positive) or gained (negative)
(NH4)2MoO4 contains the NH4+ ion, in which H is (+1) and N is (-3). Because there are two NH4+ ions, the other half of the compound must be an MoO42- ion, in which Mo is (+6) and O is (-2)

37. Oxidation numbers

38. Oxidation-Reduction Reactions
Combination Reaction A+B C 2Al + 3Br2 2AlBr3 Decomposition Reaction C A + B 2KClO3 2KCl + 3O2
Types of Redox reactions..

39. Oxidation-Reduction Reactions
Combination Reaction A+B C 2Al + 3Br2 2AlBr Decomposition Reaction C A + B 2KClO3 2KCl + 3O2 +1/+5/-2 +1/-1 0

40. Oxidation-Reduction Reactions
Combustion reaction
A + O B
S+ O SO2
2Mg +O MgO

41. Oxidation-Reduction Reactions
Displacement reaction:
Hydrogen displacement
Metal displacement
Halogen displacement

42. Oxidation-Reduction Reactions
Disproportion reaction:
The same element is simultaneously oxidized and reduced.
reduced
oxidized
Disproportion reactant always contains an element as reactant who have at least 3 oxidation numbers

43. Solution Stoichiometry
The concentration of a solution is the amount of solute present in a given quantity of solvent or solution.
Molarity(M) or Molar concentration =
Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution.
X volume of solution(in liters) = moles of solute
M V = n /// MiVi = MfVf
Moles of solute
Liters of solution
Moles of solute
Liters of solution

44. Solve:
How many grams of potassium dichromate (K2Cr2O7 ) are required to prepare a 250-mL solution whose concentration is 2.16 M ? (K2Cr2O7 =294.2 g)
Molarity(M) = 2.16 M
Volume = 250 ml = L
We know, MV = n,
moles of K2Cr2O7 = 2.16 M X L
= mol of K2Cr2O7
the molar mass of K2Cr2O7 is g
So, moles have (0.540 x 294.2) g = 159 grams

45. Solution Stoichiometry
How would prepare 60.0 ml of M HNO3 from a stock solution of 4.00 M HNO3?
M1V1 = M2V2
M1 = 4.00 M
M2= M
V1= L
V2= ?
V2 = M1V1/M2
= M x L/4.00 M
= L = 3.00 ml
Dilute 3.00 ml of acid with water to a total volume of 60.0 ml

46. Titration
In a titration, a solution of accurately known concentration is added gradually to another solution of unknown concentration until the chemical reaction between the two solutions is complete.
Equivalence point: the point at which the reaction is complete.
Indicator: substance that changes color at (or near) the equivalence point. Slowly add base to unknown acid until the indicator changes color

47. Try It!
Titration reveals that 11.6 mL of 3.0 M sulfuric acid are required to neutralize mL of NaOH solution. What is the molarity of the NaOH solution?
2.8 M NaOH

48. Thank you! All the best for final!! Stay healthy and keep striding !!!