2nd Exam Definitions (2)

Question 1

Substances that can act either as an acid or as a base (like water)

Answer 1

Amphiprotic substances

Question 2

Consists of a plot of reagent volue as x axis and analyte function as y axis

Answer 2

Titration curves

Question 3

Types of titration curves

Answer 3

Sigmoidal curve: observations to a small refion only *+- 0.1 to 0.5 mL) surroundign equivalence point. Speed and convenience

Linear-segment curve: measurements made far away from equivalence point. Measures the concentration of analyte or reagent. helpful if there is too much reagent or analyte

Question 4

pH calculations needed for strong acid and strong base (3)

Answer 4

pre-equivalence point: excess acid and hydronium ion concentration derived exactly from concentration of excess acid

equivalence point: hydronium ion and hydroxide ion are present in equal concentrations

post equivalence point: excess base and the hydornium ion concentration is derived from the concentration of excess base

Question 5

A weak acid is titrated with a strong base or vice versa it is then formed. Resists changes to pH

Number of moles of a strong acif or strong base that causes the buffer to go through a 1.00 pH change

Answer 5

Buffer solution

Buffer capacity

Question 6

Acid base indicators (3)

Answer 6

Phthalein indicators - colorless in acid. ex. phenolphthalein indicator

Sulfonphthalein indicators - colorful in acid and neutral or basic, stable in alkali. ex. phenol red

Azo indicators - red to yellow with increased basicity ex. methyl red

Question 7

Errors encountered in neutralization titrations

Answer 7

Systematic errors: Occurs when pH where indicator changes color differs from pH at chemical equivalence

Random error: from the ability of eye to distinguish the intermediate color of titration

Question 8

Variables that influence the behavior of indicators (3)

Answer 8

Temperature

Ionic strength of medium

Presence of organic solvents and colloidal particles

Question 9

Reagents for neutralization titrations

Answer 9

Standard acid solutions: Prepared by diluting an approx. volume of concentrated reagent. Commonly HCl

Standard base solutions: Most commonly prepared is NaOH sodium hydroxide

Question 10

Applications of neutralization titrations: Elemental Analysis

Answer 10

Elements susceptible to this type of analysis are nonmetallic

Nitrogen decomposed to ammonia. Ammonia is distilled then determined.

Sulfur determined by burning sample in stream of oxygen. Sulfur diozxide collected, distilled into hydrogen peroxide.

Question 11

Applications of neutralization titrations: Determination of Inorganic substances

Answer 11

Inorganic species are determined

Ammonium salts - ammonia process

Nitrates and Nitrites - ammonium ion

Question 12

Applications of neutralization titrations: Determination of organic functional groups

Answer 12

carboxylic and sulfonic acid groups - neutralization employed to determine equivalent weight of these organic acids

Amine groups - Aliphatic amines titrated to enhance basicity

Ester groups - saponification with standard base

Hydroxyl groups - esterification to produce acetic acid and then titrated

carbonyl groups - solution of hydroxylamine hydrochloride

Question 13

Applications of neutralization titrations: Determination of Salts

Answer 13

Amount of salt content can be determined through acid base titration. Salt just has to be converted to an equivalent amount of acid.