Daniel L. RegerScott R. GoodeDavid W. Ball

http://academic.cengage.com/chemistry/reger

Chapter 4Chemical Reactions in

Solution

• Solvent: compound that has the same physical state as the solution - frequently a liquid. • Solute: substance being dissolved.• Aqueous solution: water is the solvent.• Strong electrolyte: compound that

separates completely into ions in water.• Weak electrolyte: molecule that only

partially ionizes when dissolved in water.

Solutions

Solubility Experiments

NiCl2 Hg2Cl2 CoCl2 Fe(NO3)3 NaNO3 Cr(NO3)3

Solubility Rules

Solubility of Ionic CompoundsPredict the solubility of (a) (NH4)2SO4 and

(b) PbCl2.

• A precipitation reaction involves the formation of an insoluble product or products from the reaction of soluble reactants.

• Example: Mixing AgNO3 and LiCl, both of which are soluble, produces insoluble AgCl.

AgNO3(aq) + LiCl(aq)AgCl(s) + LiNO3(aq)

Precipitation Reactions

Precipitation Reactions

What insoluble compound, if any, will form when solutions of Pb(NO3)2 and Na2SO4 are mixed? Write the chemical equation.

Precipitation Reactions

Build a table of the reactants and possible products; label each as soluble or insoluble. Cations

Anions Na+ Pb2+

NO3- soluble NaNO3 soluble Pb(NO3)2

SO42- soluble Na2SO4 insoluble PbSO4

PbSO4 is insoluble and the equation is:

Pb(NO3)2(aq) + Na2SO4(aq)

PbSO4(s) + 2NaNO3(aq)

Precipitation Reactions

• Complete ionic equation shows all strong electrolytes as ions in solution

Overall equation: Pb(NO3)2(aq) + Na2SO4(aq)

PbSO4(s) + 2NaNO3(aq)

Complete ionic equation:

Pb2+(aq) + 2NO3-(aq) + 2Na+(aq) + SO4

2-(aq) PbSO4(s) + 2Na+(aq) + 2NO3

-(aq)

Complete Ionic Equation

• Net ionic equation shows only those species in the solution that actually undergo a chemical change.

Overall equation: Pb(NO3)2(aq) + Na2SO4(aq)

PbSO4(s) + 2NaNO3(aq)

Net ionic equation:

Pb2+(aq) + SO42-(aq) PbSO4(s)

• Spectator ions are those that do not participate in the chemical reaction.

Net Ionic Equation

Test Your Skill• Write the net ionic equation for the

reaction of HCl(aq) and KOH(aq).

• Molarity (M) is the number of moles of solute in one liter of solution.

moles of soluteMolarity =

liters of solution

Molarity

Example: Molarity of Solution

• What is the molar concentration of NaF in a solution prepared by dissolving 2.51 g of NaF in enough water to form 200 mL of solution?

Molarity of Ions• One mole of K2SO4 dissolves in water to

form two moles of K+ ions and one mole of SO4

2- ions.

K2SO4(s) 2K+(aq) + SO42-(aq) OH2

Dilution

• Solutions of lower concentration can be prepared by dilution of more concentrated solutions of known molarity.

Volume (L)of dilute solution

Moles of solute

Molarity

of dilutesolution

Molarity

ofconcentrated

solution

Volume (L)of concen-

trated solution

Dilution

• In a dilution problem: moles of solute in dilute solution = moles of solute in the concentrated solution molarity(conc) x volume(conc) =

molarity(dil) x volume(dil)

• Use this formula only for dilution problems, not for problems involving equations.

Example: Dilution• Calculate the volume of 6.00 M H2SO4

that is needed to prepare 2.00 L of a 0.200 M solution of H2SO4.

Test Your Skills (a) Calculate the volume of 4.00 M K2SO4

that is needed to prepare 600 mL of a 0.0200 M solution of K2SO4.

(b) Calculate the molar concentration of K+ ions in the 0.0200 M solution.

• In stoichiometric calculations, molarity is used to calculate moles from volume of solution analogous to using molar mass from mass of a solid.

Solution Stoichiometry Calculations

• Calculate the mass of lead(II) sulfate formed in the reaction of 145 mL of 0.123 M lead(II) nitrate and excess sodium sulfate.

Pb(NO3)2(aq) + Na2SO4(aq) PbSO4(s) + 2NaNO3(aq)

Solution Stoichiometry Calculations

Test Your Skills• Calculate the mass of magnesium

hydroxide need to react completely with 356 mL of 6.92 M H2SO4.

Titrations• In a titration, the concentration and

volume of a solution of known concentration is used to determine the concentration of an unknown solution.• Equivalence point: the point in a

titration where stoichiometrically equivalent amounts of the two reactants have been added.

Titrations

• An indicator is a compound that changes color as an acidic solution becomes basic or basic solution becomes acidic.• The indicator changes color at the end

point – the end point of the indicator should match the equivalence point.

Titration with Phenolphthalein Indicator

• Left: acidic solution with indicator added• Center: end point - very slight pink color• Right: pink color after excess base added

Example: Titrations• Calculate the molarity of an HCl solution

if 26.4 mL of the solution neutralizes 30.0 mL of 0.120 M Ba(OH)2.

Test Your Skills• Calculate the molarity of an NaOH

solution if 33.4 mL of the solution is neutralized by 16.0 mL of a 0.220 M solution of H2 SO4.

Gravimetric Analysis• Calculate the molarity of Cl- ions in a 250

mL solution if addition of excess silver nitrate yielded 1.34 g of silver chloride.

Test Your Skill• What mass of lead(II) chloride forms in

the reaction of 24.3 mL of 1.34 M lead(II) nitrate and 38.1 mL of 1.22 M sodium chloride?