2nd Exam - ACID-BASE TITRIMETRY

Question 1

substances which can act either as an acid or as a
base (can either donate protons or accept protons
depending on the environment), an example of
which is water.

Answer 1

Amphiprotic Substances

Question 2

leveling effect of water

Answer 2

solvent effect

Question 3

Standard
solutions of strong acids and bases are used
extensively for determining analytes that are
themselves acids or bases or analytes that can be
converted to such species by chemical treatment

Answer 3

Theory of Neutralization Titrations

Question 4

The standard solutions employed in the neutralization
titrations are __________ or ________ because these substances react more completely with
an analyte than do their weaker counterparts and thus
yield sharper end points

Answer 4

strong acids (SA) or strong bases (SB)

Question 5

is an observable physical change that occurs at or near the equivalence point Two most widely used end points involve
- a change in the color due to the reagent, the analyte or an indicator
- a change in the potential of an electrode that responds to the concentration of the reagent or the analyte

Answer 5

end point

Question 6

consist of a plot of reagent volume as
the horizontal axis and some function of the analyte or
reagent concentration as the vertical axis

Answer 6

titration curves

Question 7

important observations are
confined to a small region (typically 0 1 to 0 5
mL) surrounding the equivalence point

Answer 7

sigmoidal curve

Question 8

measurements are made
on both sides of, but well away from the
equivalence point Measurements near equivalence
point are avoided The vertical axis is an
instrument reading that is directly proportional to
the concentration of the analyte or reagent

Answer 8

linear-segment curve

Question 9

The ______ offers the advantages of speed and convenience

The _________ is advantageous for reactions that are complete only in the presence of a goodly excess of the reagent or analyte

Answer 9

sigmoidal type ;

linear segment type

Question 10

most commonly used weak acids/bases

Answer 10

HCL, HClO4, H2SO4, NaOH, KOH

Question 11

The hydronium ion in an aqueous solution of a strong
acid has two sources:

Answer 11

the reaction of the acid with water
the dissociation of water

Question 12

To derive the titration curve for a solution of strong acid with a strong base, three types of pH calculations are required

Answer 12

pre-equivalence
equivalence
post equivalence

Question 13

the solution consists of the excess acid
and the hydronium ion concentration is derived directly from the
concentration of the excess acid

Answer 13

pre-equivalence point

Question 14

the hydronium ion and hydroxide ion are
present in equal concentrations and the hydronium ion concentration is derived directly from the ion product constant of water

Answer 14

equivalence point

Question 15

the solution consist of the excess base
and the hydronium ion concentration is derived directly from the
concentration of the excess base and the ion product constant of water

Answer 15

post equivalence point

Question 16

When a weak acid is titrated with a strong base or
a weak base with a strong acid,

consisting of a conjugate acid/base pair is formed

-resists changes in pH

Answer 16

buffer solution

Question 17

Henderson-Hasselbalch Equation

Answer 17

pH = pKa + log [C. Base]/[W. Acid]

pOH = pKb + log [C. Acid]/[W. Base]

Question 18

The Effect of Dilution on Buffer Solutions

Answer 18

The pH of a buffer solution remains essentially
independent of dilution until the concentration of the
species it contains is decreased to the point where
approximations become invalid

Question 19

defined as the number of moles of a strong acid or
a strong base that causes 1 00 L of the buffer to
undergo a 1 00 unit change in the pH

Answer 19

buffer capacity

Question 20

( T or F )A buffer solution of any desired pH can be
prepared by combining calculated quantities of a
suitable conjugate acid/base pair

Answer 20

T

Question 21

COMMON TYPES OF ACID BASE INDICATORS

Answer 21

1. Phthalein indicators (phenolphthalein): 8-10
2. Sulfonphthalein indications (Phenolsulfonphthalein / phenol red): 6.8-8.3
3. Azo indicators (methyl orange: 3.1-4.4 and methyl red: 4.1-6.1)

Question 22

that occurs when the pH at which the
indicator changes color differs from the pH at chemical
equivalence

Answer 22

systematic errors

Question 23

that originates from the limited ability of
the eye to distinguish reproducibly the intermediate
color of the titration

Answer 23

random
error

Question 24

Variables that influence the behavior of indicators

Answer 24

1. Temperature
2. Ionic strength of the medium
3. Presence of organic solvents and colloidal particles

Question 25

Reagents for Neutralization Titrations

Answer 25

1. Standard Acid Solutions
2. Standard Base Solutions

Question 26

• prepared by diluting an approximate volume of concentrated reagent, commonly used is HCl
• standardized against weighed quantities of sodium carbonate, and other primary standards [TRIS or THAM tris-(hydroxymethyl)aminomethane)

Answer 26

Standard Acid Solutions

Question 27

• sodium hydroxide NaOH is the most commonly prepared standard base solution KOH and Ba(OH) 2 are also encountered
• standardized using weak organic acids, most commonly used is potassium hydrogen phthalate (KHP)

Answer 27

Standard Base Solutions

Question 28

APPLICATIONS OF NEUTRALIZATION TITRATIONS

Answer 28

1. Elemental Analysis
2. Determination of Inorganic Substances
3. Determination of the organic functional groups
4. Determination of Salts

Question 29

elements
susceptible to this type of analysis are nonmetallic and
include carbon, nitrogen, chlorine, bromine, and fluorine

Answer 29

elemental analysis

Question 30

element determined using the most common method known as Kjeldahl method, which is based on a neutralization titration

Here, the sample is decomposed in concentrated acid to convert the nitrogen to ammonia The liberated ammonia is distilled, collected in an acidic solution, and determined by a neutralization titration Procedure is straightforward and readily adapted for routine analysis

Answer 30

Nitrogen

Question 31

element determined by burning the sample in a stream of oxygen The sulfur dioxide formed during oxidation in collected by distillation into a dilute solution of hydrogen peroxide The sulfuric acid is the titrated with a standard base

Answer 31

Sulfur

Question 32

determined by the conversion of ammonia
with strong base followed by distillation The ammonia is collected and titrated as in the Kjeldahl method

Answer 32

Ammonium salts

Question 33

here, ions are first reduced to ammonium ion by Devarda’s alloy, and introduced into a strongly alkaline solution of the sample in a Kjeldahl flask The ammonia is then distilled and titrated

Answer 33

Nitrates and Nitrites

Question 34

neutralization titrations are employed to determine the equivalent weight of the purified organic acids. A base range indicator such as phenolphthalein is required.

Answer 34

carboxylic and sulfonic acid groups

Question 35

Aliphatic amines are titrated with a solution of a strong acid. Many amines are titrated in nonaqueous solvents which enhance their basicity.

Answer 35

amine groups

Question 36

determined by saponification using a
standard base and the excess is titrated with a standard acid

Answer 36

ester groups

Question 37

determined by esterification which produces acetic acid The acetic acid is then titrated with a standard solution of alcoholic sodium or potassium
hydroxide

Answer 37

hydroxyl groups

Question 38

determined with a solution of hydroxylamine hydrochloride In the process, HCl is liberated and is titrated with a base

Answer 38

carbonyl groups

Question 39

The total salt content of a solution can be accurately
and readily determined by an acid/base titration The
salt is converted to an equivalent amount of acid or a
base by passage through a column packed with an ion
exchange resin

Answer 39

Determination of salts