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Reactions in Aqueous

Solution

Chapter 4

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Compounds in Aqueous Solution

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

This is a reaction in which reactants are in solution

Solution – homogeneous mixture composed of two

parts:

solute – the medium which is __________

solvent – the medium which dissolves the solute.

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Compounds in Water

Some compounds conduct electricity when dissolved in

water –_____________

Those compounds which do not conduct electricity when

dissolved in water are called – nonelectrolytes


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Ionic Compounds in Water (Electrolytes)

The conductivity of the solution is due to the formation

of ions when the compound dissolves in water

These ions are not the result of a chemical reaction, they

are the result of a dissociation of the molecule into ions

that compose the solid.

)()()( 2 aqClaqNasNaCl OH


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Molecular Compounds in Water(Nonelectrolytes)

In this case no ions are formed, the molecules just

disperse throughout the solvent.

)()( 2 aqsugarssugar OH


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Molecular Compounds in Water(Nonelectrolytes)

There are exceptions to this, some molecules are strongly

attracted to water and will react with it.

ClOHOHHCl

OHNHOHNH

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423


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Strong and Weak Electrolytes Strong electrolytes – A substance which completely

ionizes in water.

For example:

ClOHOHHCl 32


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Strong and Weak Electrolytes

Weak electrolyte: A substance which partially ionizes

when dissolved in water.

For example:

OHCOCHOHHCOCH 323223


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OHCOCHOHHCOCH 323223


Notice that the arrow in this reaction has two heads,

this indicates that two opposing reactions are

occurring simultaneously.

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OHHCOCHOHCOCH

and

OHCOCHOHHCOCH

223323

323223


Since both reactions occur at the same time,

this is called a chemical equilibrium.

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- A reaction which forms a solid (precipitate)

AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)

- AgCl is classified as an insoluble substance

Precipitation Reaction

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Net Ionic Equation

AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)

- AgNO3 and NaNO3 are electrolytes in solution so they

actually occur as free ions.

Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq)

AgCl(s) + Na+(aq) + NO3-(aq)


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Net Ionic Equation

Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq)

AgCl(s) + Na+(aq) + NO3-(aq)

- Notice that NO3-(aq) and Na+(aq) occur in both the left

and right side of the equation.

-These are called _________________.


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Net Ionic Equation

Ag+(aq) + Cl-(aq) AgCl(s)

- With the spectator ions removed, the resulting

equation shows only the ions involved in the reaction

remain.

- This is a net ionic equation.


Practice

Write the net ionic reaction for the neutralization

of HF by NaOH.

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Solubility Guidelines for Ionic Compounds 1. Most nitrates (NO3

-) and acetates (CH3CO2-) are

soluble in water.

2. All chlorides are soluble except: Hg+, Ag+, Pb2+, Cu+

3. All sulfates are soluble except: Sr2+, Ba2+, Pb2+

4. Carbonates (CO32-), Phosphates (PO4

3-), Borates

(BO33-),Arsenates (AsO4

3-), and Arsenites (AsO33-)

are insoluble.

5. Hydroxides (OH-) of group Ia and Ba2+ and Sr2+ are

soluble.

6. Most sulfides (S2-) are insoluble.


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Solubility Guidelines for Ionic Compounds

Predict the solubility of the following compounds:

PbSO4

AgCH3CO2

(NH4)3PO4

KClO4


Practice

Which one of the following substances is

predicted to be soluble in water?

AgCl Mg(OH)2 FeS PbSO4 Mo(NO3)2

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Acid - substance which ionizes to form hydrogen cations

(H+) in solution

Examples:

Hydrochloric Acid HCl

Nitric Acid HNO3

Acetic Acid CH3CO2H

Sulfuric Acid H2SO4

Sulfuric acid can provide two H+’s - Diprotic acid,

The other acids can provide only one H+

- Monoprotic acid.

Acids and Bases

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Diprotic acid

H2SO4 H+ + HSO4-

HSO4- H+ + SO4

2-

Acids and Bases

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Base - substance which reacts with H+ ions.

Examples:

ammonia NH3

sodium hydroxide NaOH

Acids and Bases

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Acid-Base Reaction

H+ + OH- H2O

- It is clear that the metal hydroxides (NaOH for

example) provide OH- by disassociation.

- Bases like ammonia make OH- by reacting with water

(ionization)

NH3 + H2O NH4+ + OH-

Acids and Bases

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Strong and Weak Acids and Bases

Strong acids and bases are ________electrolytes.

Weak acids and bases are ______electrolytes.

Acids and Bases

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Strong Acids

- The strength of acids and bases are concerned with

the ionization (or dissociation) of the substance, not its

chemical reactivity.

Example:

Hydrofluoric acid (HF) is a weak acid, but it is very

chemically reactive.

- this substance can’t be stored in glass bottles

because it reacts with glass (silicon dioxide).

Acids and Bases

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Common Strong Acids and Bases

Common Strong Acids

Hydrochloric Acid HCl

Hydrobromic Acid HBr

Hydroiodic acid HI

Nitric Acid HNO3

Perchloric Acid HClO4

Sulfuric Acid H2SO4

Acids and Bases

KNOW ALL OF THEM

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Common Strong Acids and Bases

Common Strong Bases

Lithium Hydroxide LiOH

Sodium Hydroxide NaOH

Potassium Hydroxide KOH

Acids and Bases

KNOW ALL OF THEM

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Neutralization Reaction - Reaction between an acid and a base.


“The neutralization between acid and metal hydroxide

produces__________________”

Salt – an ionic compound whose cation comes from a

base and anion from an acid.

Acids, Bases, and Salts

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Neutralization Reaction


- despite the appearance of the equation, the reaction

actually takes place between the ions.


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Neutralization Reaction


Total Ionic Equation

H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)

H2O(l) + Na+(aq) + Cl-(aq)


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Metal Carbonates and Acid

Gas-Forming Reactions

2 HCl(aq) + Na2CO3(aq) 2 NaCl(aq) + H2O(l) +

CO2(g)

- Metal carbonates (or bicarbonates) always form a salt,

water and carbon dioxide

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Metal Sulfide and Acid


2 HCl(aq) + Na2S(s) H2S(g) + 2 NaCl(aq)

- Metal sulfides form a salt and hydrogen sulfide.

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Metal Sulfite and Acid


2 HCl(aq) + Na2SO3(s) SO2(g) + 2 NaCl(aq) +

H2O(l)

- Metal sulfites form a salt, sulfur dioxide and water.

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Ammonium Salt and Strong Base


NH4Cl(s) + NaOH(aq) NH3(g) + NaCl(aq) + H2O(l)

- This reaction forms ammonia, salt and water

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Oxidation-Reduction Reactions

- Reaction where electrons are exchanged.

2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g)

Na(s) Na+(aq) + 1 e-

oxidation- _______________

2 H+(g) + 2 e- H2(g)

reduction – _______________

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- Reaction where electrons are exchanged.

2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g)

- An alternate approach is to describe how one reagent

effects another.

- Reducing Agent, a substance that causes another substance

to be reduced.

Na(s) Na+(aq) + 1 e-

- Oxidizing Agent, a substance that causes another substnace

to be oxidized.

2 H+(g) + 2 e- H2(g)

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Oxidation Numbers 1. Each atom of a pure element has an oxidation number of

zero(0).

2. For monatomic ions, the oxidation number equals the

charge on the ion.

3. Fluorine always has an oxidation state of -1 in compounds.

4. Cl, Br, and I always have oxidation numbers of -1, except

when combined with oxygen or fluorine.

5. The oxidation number of H is +1 and O is -2 in most

compounds.

6. The sum of the oxidation numbers must equal the charge

on the molecule or ion.

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Oxidation Numbers

Examples

PCl5

P 1( ) =

Cl 5( ) = ________

0

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Oxidation Numbers

Example

CO32-

C 1( ) =

O 3( ) = _____

-2

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Oxidation Numbers

Example

K2CrO4

K 2( ) =

O 4( ) =

Cr 1( ) = ________

0

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Molarity(M) Unit of concentration, moles of solute per liter of solution.

solutionofLiters

soluteofMolesMolarity

Solutions

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Example: What is the molarity(M) of a solution which

contains 17.51g of NaCl in 751mL of solution?

F.W. (NaCl): 58.45g/mol

Solutions

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Solutions Molarity

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Dilution

MdiluteVdilute = MconcentratedVconcentrated

Solutions

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If 200. mL of a 2.50 M NaOH

solution is diluted to 500. mL,

what is the new concentration of

NaOH?

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Dilution

Example: What volume of 6.00M NaOH is required to

make 500mL of 0.100M NaOH?

Mconcentrated = 6.00M Mdilute = 0.100M

Vconcentrated = ? Vdilute = 500mL

0.100M(500mL) = 6.00M(Vconcentrated)

Vconcentrated = 8.33mL

Solutions

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pH Scale

Concentration scale for acids and bases.

]log[ HpH

• The square brackets around the H+ indicate that

the concentration of H+ is in molarity.

• So, a change of 1 pH unit indicates a 10X change in

H+ concentration.

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Solution Stoichiometry

- We can now use molarity to determine stoichiometric

quantities.

Example

How many grams of hydrogen gas are produced when

20.0 mL of 1.75M HCl is allowed to react with 15.0g of

sodium metal?

2 HCl(aq) + 2 Na(s) H2(g) + 2 NaCl(aq)

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Solution Stoichiometry

Titrations

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