chapter 4: aqueous reactions

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


Ionic Compounds

When ionic compounds dissolve in water, they dissociate completely

--

-

--+

+

+

+

-

-

+

++ H

2O

NaCl (aq) → Na+ (aq) + Cl- (aq)


Molecular Compounds

Most molecular compounds do not dissociate in water

+ H2O

methanol Methanol dissolved in water


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)


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


Strong, Weak, and Non- Electrolytes

AgI NaCl HCl

Ag+

I- Na+

Cl- Cl-

H+C12H22O11

sugar

Ionic Ionic Molecular(dissociated acid)

Molecular


Formic acid

HCOOH

HCOO-

H+

Electrolytes and Non-Electrolyte definitiononly refers to the molecules/ions that are dissolved

Molecular

Strong, Weak, and Non- Electrolytes


Some reactions involving ionic compounds:

Exchange ot Metathesis Reactions

AX + BY → AY + BX+ - + - + - + -


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


Precipitation Reactions

AgNO3 (aq) + NaI (aq) → AgI (s) + NaNO

3 (aq)

brownish precipitate

heterogeneous mixture!



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


Precipitation ReactionsHow do you know which ionic compounds are soluble?



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



(NH4)

2SO

4

AgCl

CuSO4

FeNO3

Cu(OH)2

CaCO3

LiCl

Ca(C2H

3O

2)2

HW: 90


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


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:


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


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



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



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


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


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


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)


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


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


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+


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


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


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


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


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


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 reactions

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