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Chapter 4: Aqueous Reactions. Solution : homogeneous mixture of solute and solvent. Solvent: substance present in the larger amount Solute: substance(s) dissolved in solvent, generally present in lesser amounts than solvent. -. -. +. -. +. + H 2 O. -. +. +. +. -. -. +. -. - PowerPoint PPT Presentation
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Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Solution: homogeneous mixture of solute and solvent
Solvent: substance present in the larger amount
Solute: substance(s) dissolved in solvent, generally present inlesser amounts than solvent
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Ionic Compounds
When ionic compounds dissolve in water, they dissociate completely
--
-
--+
+
+
+
-
-
+
++ H
2O
NaCl (aq) → Na+ (aq) + Cl- (aq)
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Molecular Compounds
Most molecular compounds do not dissociate in water
+ H2O
methanol Methanol dissolved in water
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Molecular Compounds
Some molecular compounds dissociate (ionize) in water (acids)
HCl (aq) → H+ (aq) + Cl- (aq)
Strong acids, such as hydrochloric acid, dissociate completely:
Weak acids, such as acetic acid, dissociate only partially:
CH3COOH (aq) H+ (aq) + CH
3COO- (aq)
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Aqueous solutions that contain ions, conduct electricity
Electrolytes: substances that generate ions when dissolved in water
● Ionic compounds
● Strong acids
● Weak acids
For example: strong electrolyte
strong electrolyte
weak electrolyte
Non-Electrolytes: substances that do not generate ions when dissolved in water
● Strong bases
● Weak bases
strong electrolyte
weak electrolyte
HW: 1,3,18,37
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Strong, Weak, and Non- Electrolytes
AgI NaCl HCl
Ag+
I- Na+
Cl- Cl-
H+C12H22O11
sugar
Ionic Ionic Molecular(dissociated acid)
Molecular
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Formic acid
HCOOH
HCOO-
H+
Electrolytes and Non-Electrolyte definitiononly refers to the molecules/ions that are dissolved
Molecular
Strong, Weak, and Non- Electrolytes
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Some reactions involving ionic compounds:
Exchange ot Metathesis Reactions
AX + BY → AY + BX+ - + - + - + -
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Some reactions involving ionic compounds: Exchange ot Metathesis Reactions
If one of the products in insoluble, the reaction is a precipitation reaction:
AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO
3 (aq)
white precipitate
AgNO3 (aq) + NaI (aq) → AgI (s) + NaNO
3 (aq)
brownish precipitate
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Precipitation Reactions
AgNO3 (aq) + NaI (aq) → AgI (s) + NaNO
3 (aq)
brownish precipitate
heterogeneous mixture!
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Precipitation Reactions
Ni(NO3)
2 + NaOH → Ni(OH)
2 + NaNO
3
A:Y:
Ni2+
OH-
B:X:
Na+
NO3-
II) Exchange X and Y:
III) Determine stoichiometryof compounds formed:
Ni2+ + OH-
Na+ + NO3-
=> Ni(OH)2
=> NaNO3
IV) Balance equation!
2
V) Is there an insoluble product?
(aq) (aq) (s) (aq)
Na+
OH-
I) Identify ions: A:X:
B:Y:
Ni2+
NO3-
2
HW: 15
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Precipitation ReactionsHow do you know which ionic compounds are soluble?
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Precipitation Reactions
Digest of solubility rules:
Salts of the following ions are always soluble:
● Group IA metals
Li+, Na+, K+ ...
● Ammonium
NH4
+
● Nitrate
NO3-
● Acetate
C2H
3O
2-
HW: 10,19,22
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Precipitation Reactions
(NH4)
2SO
4
AgCl
CuSO4
FeNO3
Cu(OH)2
CaCO3
LiCl
Ca(C2H
3O
2)2
HW: 90
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Ni(NO3)
2 (aq) + 2 NaOH (aq) → Ni(OH)
2 (s) + 2 NaNO
3 (aq)
Net Ionic Equations
Molecular Equation (shows undissociated compounds):
Ionic Equation:
Net Ionic Equation:
Ni2+ (aq) + 2 NO3- (aq) + 2 Na+ (aq) + 2 OH- (aq) →
Ni(OH)2 (s) + 2 Na+ (aq) + 2 NO
3- (aq)
Ni2+ (aq) + 2 OH- (aq) → Ni(OH)2 (s)
spectator ions
The spectator ions do not participate in the reaction!
HW: 23
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Ca(NO3)
2 (aq) + Na2CO
3 (aq) → CaCO
3(s) + NaNO
3(aq)2
Ca2+ (aq) + CO32- (aq) → CaCO
3 (s)
Spectator ions: 2 Na+, 2 NO3-
Net ionic equation:
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Ca(NO3)
2 (aq) + NaC
2H
3O
2 (aq) → Ca(C
2H
3O
2)
2 + NaNO3
22
Spectator ions: ALL !
If all salts are soluble, no precipitation reaction will take place
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Properties of Acids and Bases
Acids
● taste sour
● turn blue litmus red
● produce CO2 when
reacting with carbonates
● produce H2 when
reacting with metals
● generate protons, H+, whendissolved in water
Bases
● taste bitter
● turn red litmus blue
● generate hydroxide ions, OH-, when dissolved in water
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Properties of Acids and Bases
Strong Acids
HCl Hydrochloric acid
HBr Hydrobromic acid
HI Hydroiodic acid
HNO3 Nitric acid
H2SO
4 Sulfuric acid
HClO3 Chloric acid
HClO4 Perchloric acid
= dissociate completely in water = strong electrolytes
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Properties of Acids and Bases
Strong Bases
Metal Hydroxides of Group IA metals:
NaOH, KOH ...
Metal Hydroxides of Group IIA metals:
Ca(OH)2 , Mg(OH)
2 ...
strong electrolytes
HW: 36
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
The reaction of acids with carbonate salts:
MgCO3
(s) + HCl (aq) → MgCl
2 (aq) + H2CO
3 (aq)2
H2CO3 (aq) → CO
2 (g) + H
2O (l)
unstable
Overall:
MgCO3
(s) + HCl (aq) → MgCl
2 (aq) + CO
2 (g) + H
2O (l)2
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Neutralization Reactions
HNO3 (aq)
+ NaOH (aq) → H
2O (l) + NaNO
3 (aq)
acid base WATER salt
In a neutralization reaction, an acid and a base react to formwater and a salt
net ionic equation:
H+(aq) + NO3- (aq)
+ Na+ (aq) + OH- (aq) → H
2O (l) + Na+ (aq) + NO
3- (aq)
H+(aq) + OH- (aq) → H2O (l)
HW: 39
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Complete and balance the following neutralization reaction:
Mg(OH)2
(aq) + HBr (aq) → MgBr
2 (aq) + H
2O (l)22
net ionic equation:
Mg2+ (aq) + 2 OH-
(aq) + 2 H+
(aq) + 2 Br-
(aq)
→ Mg2+ (aq) + 2 Br-
(aq) + 2 H
2O
(l)
net: 2OH- (aq) + 2H+(aq) → 2H2O (l)
OH- (aq) + H+(aq) → H2O (l)
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Concentrations of Solutions
... are measured in Molarity
Molarity =moles of solute
Volume of solution in L
The concentration of 0.4 L of solution containing 0.25 moles of sugar is
0.25mol0.4 L
= 0.6mol
L= 0.6 M
mLNaClmol
M40010.0
NaClgNaClmol
NaClg5.49
10.5
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Someone is preparing to cook pasta by adding 5.0 g of table salt
(NaCl, formula mass = 49.5 g/mol) to 400 mL of boiling water. What is
the molarity of the resulting NaCl solution?
M =moles of NaClL of solution
(I) convert g NaCl into mol NaCl:
×1000mL1 L
= 0.25mol NaCl
L= 0.25M NaCl
(II) calculate molarity:
NaClmol10.0
HW: 62,73
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
What is the molarity of Na+ ions in a 0.2 M solution of Na2SO
4 ?
Na2SO
4 (aq) → 2 Na+ + SO
42-
SO42-
Na+
Na+
Na+
Na+
SO42-
Each formula unit of Na2SO
4 that dissolves gives rise to
1 SO42- ion and 2 Na+ ions
0.2M Na2SO4 ×2Na
1Na2SO4
+
= 0.4 M Na+
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Proton Concentration in Aqueous Solutions
[H+] ≡ proton concentration pH = -log [H+]
[H+] = 0.001 M [H+] = 0.001 M = 1 x 10-3 M pH = -log(1 x 10-3) = 3
acidic basicneutral
1 2 3 4 5 6 7 8 9 10 12 13 14
The pH scale
[H+] x [OH-] = 10-14 = constant
and [H+] = 10-pH
Neutral solution: [H+] = [OH-] = 10-7 M
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
What are the proton and hydroxide concentrations in a solution that has a pH of 4.3 ?
pH = -log [H+]
[H+] = 10-pH
[H+] = 10-4.3
[H+] x [OH-] = 10-14
[OH-] = 10-14
[H+]
= 10-14 =
5.0 x 10-5
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
How many moles of HF are needed to make 0.15 L of a 0.13M solution?
(how many moles HF are in 0.15 L of a 0.13 M solution?)
0.13mol HFL
1 L of a 0.13 M solution:
0.15 L of a 0.13 M solution: 0.13mol HFL
x 0.15 L = 0.02 mol HF
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Dilutions
add solvent
number of solutemolecules before dilution
number of solute molecules after dilution=
number of moles of solute before dilution
number of moles of solute after dilution=
M conc =mol solute
V conc
M conc × V conc = M dil × V dil
M dil =mol solute
V dil
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
What is the concentration of a solution that is made by adding 0.3Lof water to 15mL of a 0.65M solution?
M conc × V conc = M dil × V dil
Vconc = 15mL = 0.015L Mconc= 0.65M Vdil = 0.3L + 15mL
= 0.3L + 0.015L = 0.315L
dil
concconcdil V
VMM
LLM
M dil 315.0015.065.0 M031.0
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
Solution Stoichiometry and Chemical Analysis
What volume of a 0.30 M HCl solution is needed to completely react 3.5 g of Ca(OH)2 ?
HCl (aq) + Ca(OH)2 (aq) → H2O (aq) + CaCl2 (aq)2 2
3.5 g Ca(OH)2 → moles Ca(OH)2→ moles HCl → Liters HCl
molar mass = 74g/mol stoichiometric factorfrom equation
molarity ofsolution
Strategy:
HW: 79a,d
Solution Stoichiometry and Chemical Analysis
What volume of a 0.30 M HCl solution is needed to completely react 3.5 g of Ca(OH)2 ?
HCl (aq) + Ca(OH)2 (aq) → H2O (aq) + CaCl2 (aq)2 2
2
22 )(74
)(1)(5.3
OHCag
OHCamolOHCag
2)(12
OHCamolHClmol
HClmolHClL
30.01 HClL32.0
Chapter 4: Aqueous ReactionsChapter 4: Aqueous Reactions
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