Reactionsin Solution

AP Chemistry

solvent

solution: a homogeneous mixture of two or more substances

-- The ______ is present in greatest quantity.

-- Any other substance present is called a ______.

aqueous solutions: solutions in which water is the dissolving medium (i.e., the solvent)

electrolyte: any substance whose aqueous solutionwill conduct electricity

e.g., -- as opposed to a nonelectrolyte, e.g.,

solute

HCl, NaCl, KOH

any sugar (C6H12O6, C12H22O11)

or any alcohol (CH3OH, CH3CH2OH)

+

As a general rule, ionic solids dissociate into ions inaqueous solution. The partial (–) charge on the O andthe partial (+) charge on the H atoms allow H2O tointeract strongly with, and “pull out,” ions in the crystallattice. Thus, ionic compounds are often strongelectrolytes.

OH H

– + – + –+ – + – +–

+– – + –+ – + – +–

OH

H+O

H HO

HHO

HHOH H

d+d+

d–

+

For molecular compounds, structural integrity ofmolecules is maintained. Substance may dissolve,but generally won’t split into ions. Thus, mol. comps.tend to be nonelectrolytes.

-- major exceptions: acids and NH3 (ammonia)

** When molecular compounds DO split into ions,it is called ionization, not dissociation.

Strong electrolytes exist almost completely as ions in aqueous solution.

e.g.,

Weak electrolytes produce only a small concentration of ions in reaching equilibrium.

e.g.,

HCl(aq) H+(aq) + Cl–(aq)

KCl(aq) K+(aq) + Cl–(aq)

lots ofproduct

CH3COOH(aq) CH3COO–(aq) + H+(aq)

HF(aq) H+(aq) + F–(aq)

lots ofreactant

(note the one-sided arrow)

(note the double arrow)

Some of the strong electrolytes are thestrong acids and strong bases.

STRONG ACIDS STRONG BASES

the hydroxides of...

“strong base cations”

Li, Na, K, Rb,Cs, Ca, Sr, Ba

hydrochloric, HCl

hydrobromic, HBr

hydroiodic, HI chloric, HClO3

perchloric, HClO4

nitric, HNO3

sulfuric, H2SO4

If… “most”

Be careful to distinguish betweendissolution and dissociation/ionizationin regard to strongs or weaks. Forexample, CH3COOH dissolves completely, but ionizesonly slightly; it is therefore a weak electrolyte. On theother hand, Ba(OH)2 dissolves very little, but theamount that does dissolve dissociates almostcompletely. Ba(OH)2 is a strong electrolyte.

The question is: Of the amount that dissolves, whatfraction dissociates/ionizes?

If… “not much”

STRONG

WEAK

Precipitation reactions are reactions in solution that form an insoluble product.

The insoluble product is called a... precipitate.

Solubility Guidelines for Selected Ionsin Aqueous Solution

Soluble

Insoluble

no exceptions

except with Hg22+, Ag+, and Pb2+

except with Hg22+, Ba2+, Sr2+, and Pb2+

except with Alk+ and NH4+

except with NH4+ and “strong base cations”

CH3COO–, Alk+,

Br–, I–, Cl–

SO42–

PO43–, CrO4

2–, CO32–

S2–, OH–

NO3–, NH4

+

Soluble no exceptions

except with Hg22+, Ag+, and Pb2+

except with Hg22+, Ba2+, Sr2+, and Pb2+

CH3COO–, Alk+,

Br–, I–, Cl–

SO42–

NO3–, NH4

+

sol Br–, I–, Cl– Hg22+ Ag+ Pb2+

sol SO42– Hg2

2+ Pb2+ Ba2+ Sr2+

Saul Sulf ate two huge bars… and peanut butter, too.

Saul Brickell double-hugged Agatha… and Paul Bunyan, too.

Saul ‘Chuck’ Cooawlkay knows exceptions? Naaaah.

sol CH3COO– Alk+ NH4+ NO3

–

Insoluble except with Alk+ and NH4+

except with NH4+ and “strong base cations”

PO43–, CrO4

2–, CO32–

S2–, OH–

“The poor crow was cold; he huddled with everyone, but Al K. said, “Naaaah.”

PO43– Alk+ NH4

+

“Soooooo… You two are always combined.” “Naaaaht when we’re strongly basic.”

CrO42– CO3

2–

S2– OH– NH4+ SBCs

Saul ‘Chuck’ Cooawlkay knows exceptions? Naaaah.

the honorable, no-nonsense judge: Saul ‘Chuck’ Cooawlkay

sol CH3COO– Alk+ NH4+ NO3

–

Saul Brickell double-hugged Agatha… and Paul Bunyan, too.

sol Br–,I–,Cl– Hg22+ Ag+ Pb2+

Saul Brickell double-hugging Agatha

Saul Brickell double-huggingthe Paul Bunyan trophy

Saul Sulf ate two huge bars… and peanut butter, too.

the slightly sickenedSaul Sulf

sol SO42– Hg2

2+ Pb2+ Ba2+ Sr2+

two HUGE, “I’m-going-into-a-sugar-coma” bars

peanutbutter

The poor crow was cold; he huddled with everyone, but Al K. said, “Naaaah.”

PO43– Alk+ NH4

+ CrO42– CO3

2–

the poorcrow whowas cold

the poor crowwho was coldattempting tohuddle with

everyone

the somewhat aloof Al K. politelydeclining the

crow’s overturesto huddle

‘Soooooo… You two are always combined.’ “Naaaaht when we’re strongly basic.”

S2– OH– NH4+ SBCs

“OH!”

(aq)

Suppose you mix solutions oflead(II) nitrate and sodium iodide.

The ions present are... Pb2+, NO3–, Na+, I–

Pb2+ + 2 NO3– + 2 Na+ + 2 I–

Pb(NO3)2 NaI

Write the overall ionic equation…

PbI2 + 2 NO3– + 2 Na+

(aq) (aq) (aq) (aq) (aq)(ppt)

Cancel the spectator ions toget the net ionic equation…

Pb2+ + 2 I– PbI2(aq) (aq) (ppt)