Aqueous Reactions and Solution Stoichiometry Chapter 4.

Aqueous Reactions and Solution Stoichiometry

Chapter 4Chapter 4

Aqueous Reactions

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 dissolvedsolvent – the medium which dissolves the solute.

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

of solution.

solutionofLiters

soluteofMolesMolarity

Solutions

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

Solution volume

molmolg

gNaClmoles 2996.0

/45.58

51.17

LmL

LmLsolutionofLiters 751.0

1000

1751

Solutions

Example: What is the molarity (M) of a solution which contains 17.51g of NaCl in 751mL of solution?

M

L

molmolarity

399.0

751.0

2996.0

Solutions

SolutionsSolutionsMolarity

MdiluteVdilute = MconcentratedVconcentrated

SolutionsSolutionsDilution

Example: What volume of 6.00M NaOH is required to make 500mL of 0.100M NaOH?

Mconcentrated = 6.00M Mdilute = 0.100MVconcentrated = ? Vdilute = 500mL

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

Vconcentrated = 8.33mL

SolutionsSolutionsDilution

Some compounds conduct electricity when dissolved in water – electrolytes

Those compounds which do not conduct electricity when dissolved in water are called – nonelectrolytes

Properties of SolutesProperties of SolutesCompounds in Water

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.

Properties of SolutesProperties of Solutes

)()()( 2 aqClaqNasNaCl OH

Ionic Compounds in Water (Electrolytes)

Properties of SolutesProperties of SolutesIonic Compounds in Water

In this case no ions are formed, the molecules just disperse throughout the solvent.


)()( 2 aqsugarssugar OH

Molecular Compounds in Water (Nonelectrolytes)

There are exceptions to this, some molecules are strongly attracted to water and will react with it.

Properties of SolutesProperties of SolutesMolecular Compounds in Water(Nonelectrolytes)

There are exceptions to this, some molecules are strongly attracted to water and will react with it.


ClOHOHHCl

OHNHOHNH

32

423

Molecular Compounds in Water (Nonelectrolytes)

Strong electrolytes – A substance which completely ionizes in water.

For example:


ClOHOHHCl 32

Strong and Weak Electrolytes

Weak electrolyte: A substance which partially ionizes when dissolved in water.

For example:

Notice that the arrow in this reaction has two heads, this indicates that two opposing reactions are occurring simultaneously.


OHCOCHOHHCOCH 323223


Since both reactions occur at the same time, this is called a chemical equilibrium


OHHCOCHOHCOCH

and

OHCOCHOHHCOCH

223323

323223


Acid - substance which ionizes to form hydrogen cations (H+) in solution Examples:

Hydrochloric Acid HCl Nitric Acid HNO3

Acetic Acid CH3CO2HSulfuric Acid H2SO4

Notice that sulfuric acid can provide two H+’s – Diprotic acid,

the other acids can provide only one H+ – Monoprotic acid.

Acids, Bases, and SaltsAcids, Bases, and Salts

H2SO4 H+ + HSO4-

HSO4- H+ + SO4

2-

Acids, Bases, and SaltsAcids, Bases, and SaltsDiprotic acid

Bases - substances which reacts with H+ ions formed by acids.

Examples: ammonia NH3

sodium hydroxide NaOH

Acids, Bases, and SaltsAcids, Bases, and SaltsBases

H+ + OH- H2O

- Metal hydroxides (NaOH for example) provide OH- by disassociation.

- Bases like ammonia make OH- by reacting with water (ionization)

NH3 + H2O NH4+ + OH-

Acids, Bases, and SaltsAcids, Bases, and SaltsAcid-Base Reactions

- The strength of acids and bases are concerned with the The strength of acids and bases are concerned with the ionization (or dissociation) of the substance, ionization (or dissociation) of the substance, notnot its its chemical reactivity.chemical reactivity.

Example:Example:Hydrofluoric acid (HF) is a weak acid, but it is very Hydrofluoric acid (HF) is a weak acid, but it is very chemically reactive.chemically reactive.- this substance can’t be stored in glass bottles because - this substance can’t be stored in glass bottles because it reacts with glass (silicon dioxide).it reacts with glass (silicon dioxide).

Acids, Bases, and SaltsAcids, Bases, and SaltsStrong Acids

Common Strong AcidsCommon Strong AcidsHydrochloric AcidHydrochloric Acid HCl HCl Hydrobromic AcidHydrobromic Acid HBrHBrHydroiodic acidHydroiodic acid HIHINitric AcidNitric Acid HNOHNO33

Perchloric AcidPerchloric Acid HClOHClO44

Chloric AcidChloric Acid HClOHClO33

Sulfuric AcidSulfuric Acid HH22SOSO44

Acids, Bases, and SaltsAcids, Bases, and SaltsCommon Strong Acids and Bases

Common Strong BasesCommon Strong BasesLithium HydroxideLithium Hydroxide LiOHLiOHSodium HydroxideSodium Hydroxide NaOHNaOHPotassium HydroxidePotassium Hydroxide KOHKOHRubidium HydroxideRubidium Hydroxide RbOHRbOHCesium HydroxideCesium Hydroxide CsOHCsOHCalcium HydroxideCalcium Hydroxide Ca(OH)Ca(OH)22

Strontium HydroxideStrontium Hydroxide Sr(OH)Sr(OH)22

Barium HydroxideBarium Hydroxide Ba(OH)Ba(OH)22

Acids, Bases, and SaltsAcids, Bases, and SaltsCommon Strong Acids and Bases

- Reaction between an acid and a base.


“The reaction between an acid and a metal hydroxide produces water and a salt”

Salt – an ionic compound whose cation comes from a base and anion from an acid.

Acids, Bases, and SaltsAcids, Bases, and SaltsNeutralization Reaction


- despite the appearance of the equation, the reaction actually takes place between the ions.



Total Ionic EquationH+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)

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

(aq)





(aq)

Some of the ions appear unchanged in both the reactants and products – spectator ion





(aq)

Net Ionic EquationH+(aq) + OH-(aq) H2O(l)


AX + BY AY + BX

Three driving forces for the reaction: - Formation of an insoluble solid (precipitation reaction)- Formation of a weak electrolyte or nonelectrolyte- Formation of a gas that escapes from solution

Metathesis ReactionsMetathesis Reactions

Precipitation Reaction


- A reaction which forms a solid (precipitate)

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

- AgCl is classified as an insoluble substance

Solubility – amount of substance that can be dissolved in a specific amount of water (g/L or mg/L)

- for this textbook, any substance with a solubility less than 0.01mol/L is considered insoluble.

Metathesis ReactionsMetathesis ReactionsPrecipitation Reaction

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 (AsO43-), and Arsenites (AsO3

3-) are insoluble.5. Hydroxides (OH-) of group Ia and Ba2+ and Sr2+ are soluble.6. Most sulfides (S2-) are insoluble.

Reactions Which Form Weak and Non-electrolytes


- One example of this type of reaction is a neutralization reaction.

Mg(OH)2 + 2 HCl MgCl2 + 2 H2O

- Insoluble metal oxide (base) and a strong acid.

MgO(s) + 2 HCl(aq) MgCl2(aq) + H2O(l)

Reactions Which Form Gases


- Carbonates and Hydrogen Carbonates decompose to give CO2

- Carbonate and Acid2 HCl(aq) + Na2CO3(aq) 2 NaCl(aq) + CO2(g) + H2O(l)

- Hydrogen Carbonate and AcidHCl(aq) + NaHCO3(aq) NaCl(aq) + CO2(g) + H2O(l)

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 – loss of electrons

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

reduction – gain of electrons

Oxidation-Reduction ReactionsOxidation-Reduction Reactions

- Oxidation of metals by acids to form saltsMg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

- Oxidation of metals saltsFe(s) + Ni2+(aq) Fe2+(aq) + Ni(s)

Notice that the Fe is oxidized to Fe2+ and the Ni2+ is reduced to Ni.


- Oxidation of metals by acids to form saltsMg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

- Oxidation of metals saltsFe(s) + Ni2+(aq) Fe2+(aq) + Ni(s)

but,Fe2+(aq) + Ni(s) no reaction


- Some metals are more easily oxidized than others.- The relative ability of an element to be oxidized is

summarized in a table.

Activity series - a list of metals arranged in decreasing ease of oxidation.

- The higher the metal on the activity series, the more active that metal.

- Any metal can be oxidized by the ions of elements below it.

The Activity Series

Oxidation-Reduction ReactionsOxidation-Reduction ReactionsThe Activity Series

Solution StoichiometrySolution Stoichiometry

- We can now use molarity to determine stoichiometric quantities.

ExampleHow 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)

Solution StoichiometrySolution StoichiometryTitrations

Solution StoichiometrySolution StoichiometryTitrationsHow many milliliters of 0.155M HCl are needed to neutralizeCompletely 35.0 mL of 0.101 M Ba(OH)2 solution?

2 HCl(aq) + Ba(OH)2(aq) BaCl2(aq) + 2 H2O(l)

Aqueous Reactions and Solution Stoichiometry Chapter 4.

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