Chapter 12: Principles of Neutralization Titrations Flashcards
is a weak organic acid or a weak organic base whose undissociated form differs in color from its conjugate base or its conjugate acid form.
acid-base indicator
2 types of titration error
determinate error
indeterminate error
occurs when the pH at which the indicator changes color differs from the pH at the equivalence point
determinate error
originates from the limited ability of the human eye to distinguish reproducibly the intermediate color of the indicator
indeterminate error
TRUE or FALSE
On average, the visual uncertainty with an acid-base indicator is in the range of 60.5 to 61 pH unit. This uncertainty can often be decreased to as little as 60.1 pH unit by matching the color of the solution being titrated with that of a reference standard containing a similar amount of indicator at the appropriate pH
TRUE
variables that influence the behaviour of indicators
temperature
ionic strength of the medium
presence of organic solents
colloidal particles
what acid-base indicators changes its color from red to yellow
thymol blue
methyl yellow
methyl red
what acid-base indicators changes its color from yellow to blue
thymol blue
bromocresol green
bromothymol blue
what acid-base indicators changes its color from red to orange
methyl orange
what acid-base indicators changes its color from yellow to pink
bromocresol purple
cresol purple
what acid-base indicators changes its color from yellow to red
phenol red
what acid-base indicators changes its color from colorless to red
phenolphthalein
what acid-base indicators changes its color from colorless to blue
thymolphthalein
what acid-base indicators changes its color from colorless to yellow
alizarin yellow GG
The standard solutions used in neutralization titrations are _____________ because these substances react more completely with an analyte than do weak acids and bases, and as a result, they produce sharper end points
strong acids or strong bases
TRUE or FALSE
Hot concentrated perchloric and sulfuric acids are potent oxidizing agents and are very hazardous
TRUE
An acid-base indicator is a _________ whose undissociated form differs in color from its conjugate base or its conjugate acid form
weak organic acid or a weak organic base
The human eye is not very sensitive to color differences in a solution containing a mixture of HIn and In2, particularly when the ratio [HIn]>[In2] is greater than about 10 or smaller than about 0.1/ Due to this restriction, the color change detected by an average observer occurs within a limited range of concentration from about
10 to 0.1
methyl violet
0-1.6
bromophenol blue
3.0- 4.6
methyl orange
3.2- 4.4
chlorophenol red
4.8- 6.7
m-cresol purple
7.4- 9.0
thymol blue
8.0- 9.2
phenolphthalein
8.0-10.0
o-cresolphthalein
8.2-9.8
thymolphthalein
8.8-10.5
bromocresol green
3.80-5.4ali
zarin red
4.6-6.0
bromothymol
6.0-7.0
TRUE or FALSE
[H3O+]= 10Ka
[H3O+]= 0.1Ka
pH (acid color)= -log(10Ka)= pKa + 1
pH (acid color)= -log(0.1Ka)= pKa - 1
TRUE
indicator pH change
indicator pH change = pKa +- 1
The hydronium ions in an aqueous solution of a strong acid have two sources
- reaction of the acid with water
- dissociation of water itself
we compute the concentration of the acid from its starting concentration and the amount of base ad
preequivalence
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.
equivalence point
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
postequivalence
TRUE or FALSE
the selection of an indicator is not critical when the reagent concentration is approximately 0.1 M.
TRUE
used to determine the dissociation constants
half-titration points
TRUE or FALSE
bromocresol green is unsuited for a titration involving the 0.001 M reagent because the
color change occurs over a 5-mL range well before the equivalence point
TRUE
TRUE or FALSE
the choice of indicator is more limited for the titration of a weak acid than for the titration of a strong acid
TRUE
