L8. 9. 10. Salts, Buffers, Titrations

Question 1

Three conditions for buffer systems

Answer 1

1. Weak Acid + Weak Base
2. Weak Acid cannot react w/ Weak Base
3. Conjugate Acid-Base Pair

Question 2

What equation is used to find the pH or pOH of a buffer solution?

Answer 2

The Henderson-hasselbalch

is used to determine the pH ot pOH id a buffer solution

pH = pKa + log [A-] / [HA]

pOH = pKb + log [B+] / [BOH]

Question 3

Four ways acids and bases react to form salts.

Answer 3

1. Strong Acid + Stong Base ( Neutral Salt)
2. Strong Base + Weak Acid (Basic Salt)
3. Strong Acid + Weak Base (Acidic Salt)
4. Weak Acid + Weak Base (competition between conjugate acid and base ka & kb)

Question 4

What is Titration?

Answer 4

A procedure used to determine the concentration of a known reactant in a solution.

• The titrant has a known concentration and is added slowly to the titrand to reach the equivalence point.
• The titrand has an unknown concentration but a known volume

Types; Acid/base, oxidation /reduction and complexometric (metal ion)

Question 5

Equivalence point

Equation to calculate unknown concentration of titrand

Answer 5

The equivalence point is indicated by the steepest slope in a titration curve; it is reached when the number of acid equivalents in the original solution equals the number of base equivalents added, or vice-versa.

M1V1 = M2V2

• Stong Acid and Base pH = 7
• Stong Acid & Weak Base pH < 7
• Stong Base & Weak Acid pH >7
• Weak Acid and base can have above or below pH 7 depending on the relative strength

Question 6

The half-equivalence point

Answer 6

Is the midpoint of the buffering region,

in which half of the titrant has been protonated (or deprotonated)

thus; [HA] = [A-] & a BUFFER is formed

Question 7

What are Indicators?

Answer 7

Indicators are weak acids or weak bases that display different colors in their protonated and deprotonated forms.

• The indicators chosen for a titration should have a pKa close to the pH of the expected equivalence point.
• The endpoint of a titration is when the indicator reaches its final color
• Multiple buffering regions & equivalence points are observed in polyvalent acid & base titrations.

Question 8

What are buffer solutions?

Answer 8

Buffer solutions consist of a mixture of

weak acid & its conjugate salt or a weak base & its conjugate salt;

they resist large fluctuations in pH

Question 9

Buffering capacity

Answer 9

• Refers to the ability of a buffer to resist changes in pH
• Maximal buffering capacity is seen within 1 pH point of the pKa of the acid in the buffer solution
• Optimal buffered solution; pH = pka & pOH = pkb

Question 10

What is the common ion effect?

Answer 10

The common ion effect states that in a chemical solution in which several species reversibly associate with each other by an equilibrium process increase concentration of any one of its dissociate components will raise amounts of association.

CH3OOH + H2O —-> H3O = CH3COO-

Le’chatliers Principle

Question 11

When you add reactions together, to get a net reaction constant you..

Answer 11

multiply the individual equilibrium constants

to get the equilibrium constant for the net reaction

ka x kb = kw

Question 12

Strong Acid + Strong Base Titration Curve

Answer 12

Question 13

Weak Acid + Strong Base Titration Curve

Answer 13

Question 14

Weak Base + Strong Acid Titration Curve

Answer 14

Question 15

The bicarbonate Buffer System Equation

Answer 15

Question 16

p scale value approximation

Answer 16

p ≈ m - 0.n

• log ( n ) - log ( 10^-m )

= m - log ( n )

n = Value betwwe 1 - 10

log 1 = 0

log 10 = 1

The closer n is to 1, the closer n is to 0