Chemistry General I CHE-1031
Dr. Jonathan M. Smith Wednesday, February 25
Today
Solutions to solutions...
Our oceans...
Unexpected Growth Coccolithophores like these may prosper in high-CO2 seas.
Losing Nemo Acidified seawater disrupts the homing ability of orange clownfish. http://pubs.acs.org/cen/science/87/8708sci2.html
Solutions
Chapter 4
Salt vs. Sugar Dissolved in Water
ionic compounds dissociate into ions when they dissolve
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molecular compounds do not dissociate when they dissolve
Acids
acids are molecular compounds that ionize when they dissolve in water
the molecules are pulled apart by their attraction for the water when acids ionize, they form H+ cations and anions
the percentage of molecules that ionize varies from one acid to another acids that ionize virtually 100% are called strong acids HCl(aq) H+(aq) + Cl-(aq) acids that only ionize a small percentage are called weak acids HF(aq) H+(aq) + F-(aq)
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Strong and Weak Electrolytes
strong electrolytes are materials that dissolve completely as ions
ionic compounds and strong acids their solutions conduct electricity well
weak electrolytes are materials that dissolve mostly as molecules, but partially as ions
weak acids their solutions conduct electricity, but not well
when compounds containing a polyatomic ion dissolve, the polyatomic ion stays together Na2SO4(aq) 2 Na+(aq) + SO42-(aq) HC2H3O2(aq) H+(aq) + C2H3O2-(aq)
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Classes of Dissolved Materials
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Solubility of Ionic Compounds
some ionic compounds, like NaCl, dissolve very well in water at room temperature other ionic compounds, like AgCl, dissolve hardly at all in water at room temperature compounds that dissolve in a solvent are said to be soluble, while those that do not are said to be insoluble
NaCl is soluble in water, AgCl is insoluble in water the degree of solubility depends on the temperature even insoluble compounds dissolve, just not enough to be meaningful
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When Will a Salt Dissolve?
Predicting whether a compound will dissolve in water is not easy The best way to do it is to do some experiments to test whether a compound will dissolve in water, then develop some rules based on those experimental results
we call this method the empirical method
Tro, Chemistry: A Molecular Approach 10
Solubility Rules Compounds that Are Generally Soluble in Water
Compounds Containing the Following Ions are Generally Soluble Exceptions (when combined with ions on the left the compound is insoluble)
Li+, Na+, K+, NH4+ NO3, C2H3O2 Cl, Br, I SO42
none none Ag+, Hg22+, Pb2+ Ag+, Ca2+, Sr2+, Ba2+, Pb2+
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Solubility Rules Compounds that Are Generally Insoluble
Compounds Containing the Following Ions are Generally Insoluble Exceptions (when combined with ions on the left the compound is soluble or slightly soluble)
OH S2 CO32, PO43
Tro, Chemistry: A Molecular Approach
Li+, Na+, K+, NH4+, Ca2+, Sr2+, Ba2+ Li+, Na+, K+, NH4+, Ca2+, Sr2+, Ba2+ Li+, Na+, K+, NH4+
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Precipitation Reactions
reactions between aqueous solutions of ionic compounds that produce an ionic compound that is insoluble in water are called precipitation reactions and the insoluble product is called a precipitate
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2 KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2 KNO3(aq)
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No Precipitate Formation = No Reaction
KI(aq) + NaCl(aq) KCl(aq) + NaI(aq) all ions still present, no reaction
Tro, Chemistry: A Molecular Approach
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Process for Predicting the Products of a Precipitation Reaction
1. Determine what ions each aqueous reactant has 2. Determine formulas of possible products
Exchange ions
(+) ion from one reactant with (-) ion from other
Balance charges of combined ions to get formula of each product
3. Determine Solubility of Each Product in Water
Use the solubility rules If product is insoluble or slightly soluble, it will precipitate
4. If neither product will precipitate, write no reaction after the arrow
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Process for Predicting the Products of a Precipitation Reaction 5. If either product is insoluble, write the formulas for the products after the arrow writing (s) after the product that is insoluble and will precipitate, and (aq) after products that are soluble and will not precipitate 6. Balance the equation
Tro, Chemistry: A Molecular Approach
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Example 4.10 Write the equation for the precipitation reaction between an aqueous solution of potassium carbonate and an aqueous solution of nickel(II) chloride 1. Write the formulas of the reactants
K2CO3(aq) + NiCl2(aq)
2. Determine the possible products
a) Determine the ions present
(K+ + CO32-) + (Ni2+ + Cl-)
b) Exchange the Ions (K+ + CO32-) + (Ni2+ + Cl-) (K+ + Cl-) + (Ni2+ + CO32-) c) Write the formulas of the products
cross charges and reduce
K2CO3(aq) + NiCl2(aq) KCl + NiCO3
Example 4.10 Write the equation for the precipitation reaction between an aqueous solution of potassium carbonate and an aqueous solution of nickel(II) chloride
3. Determine the solubility of each product
KCl is soluble NiCO3 is insoluble
4. If both products soluble, write no reaction
does not since apply NiCO3 is insoluble
Tro, Chemistry: A Molecular Approach
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Example 4.10 Write the equation for the precipitation reaction between an aqueous solution of potassium carbonate and an aqueous solution of nickel(II) chloride
5. Write (aq) next to soluble products and (s) next to insoluble products K2CO3(aq) + NiCl2(aq) KCl(aq) + NiCO3(s) 6. Balance the Equation K2CO3(aq) + NiCl2(aq) 2 KCl(aq) + NiCO3(s)
Tro, Chemistry: A Molecular Approach
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Ionic Equations
equations which describe the chemicals put into the water and the product molecules are called molecular equations 2 KOH(aq) + Mg(NO3)2(aq) 2 KNO3(aq) + Mg(OH)2(s) equations which describe the actual dissolved species are called complete ionic equations
aqueous strong electrolytes are written as ions
soluble salts, strong acids, strong bases
insoluble substances, weak electrolytes, and nonelectrolytes written in molecule form
solids, liquids, and gases are not dissolved, therefore molecule form 2K+1(aq) + 2OH-1(aq) + Mg+2(aq) + 2NO3-1(aq) 2K+1(aq) + 2NO3-1(aq) + Mg(OH)2(s)
Tro, Chemistry: A Molecular Approach 21
Ionic Equations
ions that are both reactants and products are called spectator ions
2K+1(aq) + 2OH-1(aq) + Mg+2(aq) + 2NO3-1(aq) 2K+1(aq) + 2NO3-1(aq) + Mg(OH)2(s)
an ionic equation in which the spectator ions are removed is called a net ionic equation
2OH-1(aq) + Mg+2(aq) Mg(OH)2(s)
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Acid-Base Reactions
also called neutralization reactions because the acid and base neutralize each other's properties
2 HNO3(aq) + Ca(OH)2(aq) Ca(NO3)2(aq) + 2 H2O(l)
the net ionic equation for an acid-base reaction is
H+(aq) + OH-(aq) H2O(l) as long as the salt that forms is soluble in water
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Acids and Bases in Solution
acids ionize in water to form H+ ions
more precisely, the H from the acid molecule is donated to a water molecule to form hydronium ion, H3O+
{H+ and H3O+ are often used interchangeably}
bases dissociate in water to form OH- ions
bases, like NH3, that do not contain OH- ions, produce OH- by pulling H off water molecules
in the reaction of an acid with a base, the H+ from the acid combines with the OH- from the base to make water the cation from the base combines with the anion from the acid to make the salt
acid + base salt + water
Tro, Chemistry: A Molecular Approach 24
Common Acids
Chemical Name Perchloric Acid Nitric Acid Sulfuric Acid Hydrochloric Acid Phosphoric Acid Chloric Acid Acetic Acid Hydrofluoric Acid Carbonic Acid Hypochlorous Acid Boric Acid Formula HClO4 HNO3 H2SO4 HCl H3PO4 HClO3 HC2H3O2 HF H2CO3 HClO H3BO3 Uses
explosives, catalyst explosives, fertilizer, dye, glue
Strength Strong Strong
explosives, fertilizer, dye, glue, Strong batteries metal cleaning, food prep, ore Strong refining, stomach acid fertilizer, plastics & rubber, Moderate food preservation explosives Moderate plastics & rubber, food Weak preservation, vinegar metal cleaning, glass etching Weak soda water sanitizer eye wash
Weak Weak Weak
Common Bases
Chemical Name sodium hydroxide potassium hydroxide calcium hydroxide sodium bicarbonate magnesium hydroxide ammonium hydroxide Formula NaOH KOH Ca(OH)2 NaHCO3 Mg(OH)2 NH4OH, {NH3(aq)} Common Name lye, caustic soda caustic potash slaked lime baking soda milk of magnesia ammonia water
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Uses soap, plastic, petrol refining soap, cotton, electroplating cement cooking, antacid antacid detergent, fertilizer, explosives, fibers
Strength Strong Strong Strong Weak Weak Weak
Tro, Chemistry: A Molecular Approach
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
Tro, Chemistry: A Molecular Approach
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Example - Write the molecular, ionic, and netionic equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide
1. 2. Write the formulas of the reactants HNO3(aq) + Ca(OH)2(aq) Determine the possible products
a) Determine the ions present when each reactant dissociates (H+ + NO3-) + (Ca+2 + OH-) b) Exchange the ions, H+1 combines with OH-1 to make H2O(l) (H+ + NO3-) + (Ca+2 + OH-) (Ca+2 + NO3-) + H2O(l) c) Write the formula of the salt cross the charges (H+ + NO3-) + (Ca+2 + OH-) Ca(NO3)2 + H2O(l)
Tro, Chemistry: A Molecular Approach 28
Example - Write the molecular, ionic, and netionic equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide
3. Determine the solubility of the salt
Ca(NO3)2 is soluble
4. Write an (s) after the insoluble products and a (aq) after the soluble products
HNO3(aq) + Ca(OH)2(aq) Ca(NO3)2(aq) + H2O(l)
5. Balance the equation
2 HNO3(aq) + Ca(OH)2(aq) Ca(NO3)2(aq) + 2 H2O(l)
Tro, Chemistry: A Molecular Approach 29
Example - Write the molecular, ionic, and netionic equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide
6. Dissociate all aqueous strong electrolytes to get complete ionic equation
not H2O 2 H+(aq) + 2 NO3-(aq) + Ca+2(aq) + 2 OH-(aq) Ca+2(aq) + 2 NO3-(aq) + H2O(l)
7. Eliminate spectator ions to get net-ionic equation
2 H+1(aq) + 2 OH-1(aq) 2 H2O(l) H+1(aq) + OH-1(aq) H2O(l)
Tro, Chemistry: A Molecular Approach 30