ACID-BASE TITRATIONS

Standard Solution or titrant

An acid/base solution whose concentration is known

End point

The point at which an indicator changes color

Equivalence Point

The point at which moles of H+ ion from the acid equals moles of OH- ion from the base. An abrupt change in pH occurs at the ______

Standard solutions

_____ employed are strong acids or strong bases

Acid/base indicator

_____ is a weak organic acid or a weak organic base whose undissociated form differs in color from its conjugate form.

pre-equivalence stage

we compute the concentration of the acid from its starting concentration and the amount of base added.

equivalence point

the hydronium and hydroxide ions are present in equal concentrations, and the hydronium ion concentration can be calculated directly from the ion-product constant for water, Kw

post-equivalence stage

the analytical concentration of the excess base is computed, and the hydroxide ion concentration is assumed to be equal to or a multiple of the analytical concentration

buffer solution

Whenever a weak acid is titrated with a strong base or a weak base with a strong acid, a ______ is formed.

Buffer solution

_____ is a solution of conjugate acid/ base pair that resists changes in the pH.

Acidic Buffer

solution of mixture of weak acid and salt of this weak acid with strong base (conjugate base)

Basic Buffer

solution of mixture of weak base and a salt of this weak base with strong acid (conjugate acid)

Ratio of acid and its conjugate base

buffer capacity is optimal when the ratio is 1:1 that is when pH=pKa

Total buffer concentration

for example, it will take more acid or base to deplete a 0.5 M buffer than a 0.05 M buffer.

optimum cellular activity

Buffer maintains constant [H+] in the body required for _____

bicarbonate

The pH of blood (around 7.4) is controlled by ______ (H2CO3 /HCO3 - ) buffer system.

phosphate buffer system

The ______ (HPO4 -2 /H2PO4 - ) plays a role in plasma and erythrocytes.

methyl green

0.2 - 1.8

color change (lower to higher pH): yellow to blue

thymol blue

1.2 - 2.8

color change (lower to higher pH): red to yellow

methyl orange

3.2 - 4.4

color change (lower to higher pH): red to yellow

ethyl red

4.0 - 5.8

color change (lower to higher pH): colorless to red

methyl purple

4.8 - 5.4

color change (lower to higher pH): purple to green

bromocresol purple

5.2 - 6.8

color change (lower to higher pH): yellow to purple

bromothymol blue

6.0 - 7.6

color change (lower to higher pH): yellow to blue

phenol red

6.4 - 8.2

color change (lower to higher pH): yellow to red/violet

litmus

4.7 - 8.3

color change (lower to higher pH): red to blue

cresol red

7.0 - 8.8

color change (lower to higher pH): yellow to red

thymol blue

8.0 - 9.6

color change (lower to higher pH): yellow to blue

phenolphthalein

8.2 - 10.0

color change (lower to higher pH): colorless to pink

thymolphthalein

9.4 - 10.6

color change (lower to higher pH): colorless to blue

alizarin yellow R

10.1 - 12.0

color change (lower to higher pH): yellow to red

clayton yellow

12.2 - 13.2

color change (lower to higher pH): yellow to amber