Chem Salt/Polyprotic acids/Buffers/titrations/SolEqual 14.4-15.1

How to Predict whether a salt solution will be acidic basic, or neutral practice question 30 on page 100 ka=kw/kb

How to Predict whether a salt solution will be acidic basic, or neutral practice question 30 on page 100

Monoprotic acids: vice versa with bases

1 h+ can be donated

Diprotic acids vice versa with bases

2 h+ can be donated over the course of 3 ionizations

Triprotic acids vice versa with bases

3 h+ can be donated over the course of 3 ionizations

What defines a buffer & why are buffers useful?

Consists of an acid and its conjugate base OR a base and its conjugate acid. Buffers help maintain pH (prevent large pH changes when acid/base is added to a solution)

Calculate the pH of a buffer before and after addition of acid/base pH=pKa + log(b/a)

Before: Use the relevant Henderson-Hasselbalch Equation

After: Assume the strong acid/base reacts completely with the weak base/acid. Then use the Henderson-Hasselbalch Equation.

a solution containing appreciable (good) amounts of an acid-base conjugate pair

Buffer

What have we learned about buffered vs. unbuffered solutions

prevent drastic changes in pH!

Can buffers maintain the pH of a solution indefinitely

no

amount of acid or base that can be added to a given volume of buffer solution before the pH changes significantly (by ≥ 1 pH unit)

buffer capacity

the greater the concentration of acid/conjugate base (or base/conjugate acid), the

greater the buffering capacity of the solution.

Rules for picking a good buffer:

Aim for equal concentrations of each component

Choose a system with a pKa near your desired pH

Interpret titration curves for strong and weak acid-base systems

What is the nature of the unknown solution—is it a weak acid or a weak base? How do you know? What’s the approximate Kb of the base? How do you know? What is the nature of the titrant? How do you know?

Calculate solution pH at different points in a titration & use titration data to calculate the concentration of an unknown solution

See worked example here & CoursePak #22-24 (p. 114-115) Calculate solution pH at different points in a titration

What is the purpose of acid-base indicators?

To detect pH changes; visualize equivalence points/end points in titrations

plot of some solution property as a function of amount of titrant added (usually a plot of pH vs. volume of strong acid or base added)

titration curve

equal amount of acid and base present (stoichiometric amounts of acid/base reacted)

Equivalence point

Why does this part of the curve flatten a bit (have its own inflection point)?

Here it acts as a buffer!

What’s the point of doing a titration

can be used to quantify acid/base concentrations in solution

Manual titration: Remember: at the equivalence point (visualized as the “ending point” or “end point”)

the amount of acid and base present are equal.

substances (weak organic acids or weak organic bases) used to determine the pH of a solution (via visual color change)

acid-base indicators

Write chemical equations & equilibrium constant expressions (Ksp) for solubility equilibria

See worked examples here (remember not to include solids!) Write chemical equations & equilibrium consta

Determine the molar solubility or Ksp for a compound

See worked examples here (write equations, Ksp expressions, and use ICE charts) Determine the molar solubility

Predict whether a precipitate will form given specified concentrations of aqueous ions (and Ksp values for the corresponding solid(s)

Calculate Qsp and compare it to Ksp (if Qsp < Ksp à no precipitation; if Qsp > Ksp à precipitation

Explain how common ions and solution pH affect ionic compound solubility in aqueous solution

Effects on solubility determined by how other ions in solution alter solid-derived dissolved ion levels (equilibria shifts according to Le Chatelier’s Principle)

*Remember: Q is found using the same expression as K

but at unknown or non-equilibrium conditions

If Q < K, in which direction will the reaction proceed?

forward

If Q > K, in which direction will the reaction proceed?

reverse

If Qsp < Ksp, the compound will

dissolve (stay in solution)

If Qsp > Ksp, the compound will

precipitate

Forward =

Dissolve (stay in solution)

Reverse =

precipitate

Compounds that dissociate to give weak base ions

dissolve better in acidic solutions.

Compounds that dissociate to give weak acid ions

dissolve better in basic solutions

Solids that produce basic anions will become

more soluble at low pH

Metal hydroxide solubility decreases in basic solutions where

Hydroxide concentrations are high

Solids that produce acidic anion are more

soluble in basic solutions

In buffer FRQ look for

find Ph of before addition of strong acid or base. Use H.H equation. You can use mol or Molarity in division but remember to add new mL amount

Percent ionization also is called

percent dissociation

percent ionization equation for acids

H30+ (AT EQUALIBRIUM) // HA (INITIAL) X 100

percent ionization equation for bases

OH- (AT EQUALIBRIUM) /// B (INITIAL) X 100

Id you see a FRQ asking for Ka of a weak acid or base first

Set up ice chart ***at equalibrium assume x is too small and disregard

In saturated solution FRQ Separate the solid into its

ions. Ksp = new ionic side without solid side! Stochiometric goes in exponent in the KSP expression

What do you always forget

SIGFIGS!!!!!!!!

When adding a product equilibrium will shift

in reverse to counter added product

If adding sodium to a solution

no change will be made

If you see a titration FRQ

M1*V1=M2*V2 remember to stay consistent with mL or L

Equation for molar mass

g/mol

equation for mols

L*M

Equation for Molarity

mol/L

pH = -log(M concentration)

pOH = -log(M concentration)

14 - pH = pOH

14 - pOH = pH