Types of Chemical Reactions and Solution Stoichiometry

Chapter 4

Water – the common solvent

A Bent polar molecule

•Hydration –positive and negative ends of water attracted to reciprocal ions

-Ionic compounds dissociate when they dissolve.

Water can also dissolve non-ionic compounds if they are “like”

Solution Concentration

Molarity (M) = moles of solute per volume of solution in liters:

M

M

molaritymoles of soluteliters of solution

HClmoles of HCl

liters of solution3

62

Calculate Molarity

A solution contains 1.5 moles of NaCl in 500 ml of water. What is the molar concentration of salt in the solution?

1.5 mol NaCl = 3M NaCl 0.5 L

Solution Concentration terms

Stock - routinely used solutions prepared in concentrated form.

Concentrated - relatively large ratio of solute to solvent. (5.0 M NaCl)

Dilute - relatively small ratio of solute to solvent. (0.01 M NaCl)

Calculating Concentrations of Solutions

M1V1= M2V2

Where M molarity Where V volume Useful equations for dilutions use given volume to

calculate new Molarity Calculate how much volume to dilute a stock

solution to get a desired concentration for an experiment.

Example: Calculate the final concentration of a solution of NaCl where 25mL of a stock concentration of 5.0M has been diluted into 2.0L.

(5.0M) (0.025L) = M2 (2.0L)M2= 0.063M

Aqueous solutions - electrolytes Electrolyte – solution that conducts

electricity Strong electrolytes

NaCl, HCl, NaOH Weak Electrolyte

NH3, CH3COOH Nonelectrolyte

C6H12O6

Classes of Strong Electrolyes

Soluble Ionic Compounds – dissociate in water into anions and cations

Strong acids – acids produce H+ ions when dissolved in water (Arrhenius); strong acid – completely ionizes in aqueous solutions

Like HCl, HBr, HI, HNO3, HClO4, H2SO4 * Strong bases – soluble ionic compound containing

hydroxide Like LiOH, NaOH, KOH, Ba(OH)2, Sr(OH)2

Strong electrolytes

Weak Electrolytes

Weak electrolytes dissociate only to a small extent in aqueous solutions

Weak acids (HC2H3O2 ) Weak bases (NH4OH ) Dissociation – each ion is surrounded by a

shell of water molecules Ionic compounds dissociate while molecular

compounds do not dissociate Acids are an exception. Weak acids are

molecular compounds that dissociate.

Weak electrolytes

Identifying electrolytes

Which of the following are strong electrolytes?

NaCl, C6H12O6, HCl, HC2H3O2, NH4OH, KOH, KNO3

Types of Solution Reactions

Precipitation reactionsAgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)

Acid-base reactionsNaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)

Oxidation-reduction reactionsFeCl2(aq) + Mg(s) Fe(s) + MgCl2(aq)

Precipitation Reactions

Ba(NO3)2 (aq) + K2CrO4 (aq)

2 KNO3(aq) + BaCrO4(s)

Ppt continued

Rules for SolubilityRule Applies to: Exceptions

Group I and ammonium compounds are soluble

Li+, Na+, K+, NH4+ -

“Rule 1”

Acetates and nitrates are soluble

C2H3O2-, NO3

- -

Most chlorides, bromides and iodides are soluble

Cl-, Br-, I- Ag+, Hg22+, Pb2+

Most sulfates are soluble SO42- Sr2+, Ba2+, Hg2

2+, Pb2+

Most carbonates and phosphate are insoluble

CO32-, PO4

3-

See Rule 1

Most sulfides and hydroxides are insoluble

S2-, OH- See Rule 1, and Ca2+, Sr2+, Ba2+

Only learn rules in red

Revised Table for SolubilityRule Applies to: Exceptions

Acetates C2H3O2-,

Most chlorides, bromides and iodides are soluble

Cl-, Br-, I- Ag+, Hg22+, Pb2+

Most sulfates are soluble SO42- Sr2+, Ba2+, Hg2

2+, Pb2+

Most carbonates and phosphate are insoluble

CO32-, PO4

3-

Most sulfides and hydroxides are insoluble

S2-, OH- Ca2+, Sr2+, Ba2+

Missing Red Rules – Available to YouEssentially the Rules show Ksp <0.01mol/L

Describing equations

1. Molecular equation (reactants and products as compounds)

AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq)

2. Complete ionic equation (all strong electrolytes shown as ions)

Ag+(aq) + NO3(aq) + K+(aq) + Cl(aq)

AgCl(s) + K+(aq) + NO3(aq)

Describing Equations continued

3. Net ionic equation (show only components that actually react)

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

K+ and NO3 are spectator ions – do not react

Net Ionic – simple rules

Soluble ionic compounds in solution are written as ions

Strong acids and bases are written as ions Weak acids and bases are written in

“molecular form” Any solid, liquid or gas is written in

“molecular form” Reaction occurs if new compounds form

that must be written in molecular form.

Predicting precipitation reactions(a) Write the complete ionic and net ionic chemical equation that

forms when solutions of BaCl2 and K2SO4 are mixed.

(b) Write the complete ionic and net ionic chemical equation that forms when solutions of Fe2(SO4)3 and LiOH are mixed?

(c) Will a precipitate form when solutions of Ba(NO3)2 and KOH are mixed?

No. both products are soluble. No chemical reaction

Ba2+ + Cl-1 + K+ + SO4-2 BaSO4 + 2K+ + 2Cl-

Ba2+ + Cl-1 + K+ + SO4-2 BaSO4 + 2K+ + 2Cl-

Fe2(SO4)3 + 6LiOH 2Fe(OH)3 + 3Li2SO4

2Fe+3 + 3SO4-2 + 6Li+1 +6 OH-1 2Fe(OH)3 + 3Li+1 +3SO4

-2

2Fe+3 + 6 OH-1 2Fe(OH)3 (proper net ionic)

Conclusion

Water is common solvent that dissolves ionic compounds and polar covalent molecules

Strong electrolytes dissociate in aqueous solutions while weak electrolytes do not.

There are three types of solution reactions: precipitation, acid-base, and oxidation-reduction

Equations can be written in one of three ways – molecular, complete ionic, net ionic