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Pharm Chem 135 Lab > Preparation and Standardization > Flashcards

Preparation and Standardization Flashcards

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0
Q

[ZnSO4] Type of titration and reaction

A

Direct complexometry

Complexation

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1
Q

[ZnSO4] Full name and formula

A

0.05 M Zinc Sulfate VS

ZnSO4•7H2O

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2
Q

[ZnSO4] Standard, indicator, endpoint

A

Standard: 0.05 M edetate disodium VS
Indicator: Dithizone TS (Diphenylthiocarbazone)
Endpoint: Dark green-violet to rose pink

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3
Q

[ZnSO4] Titration conditions and rationale

A

pH = 4.6

EDTA-Zn2+ complex is favored and stable at pH of 4.6

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4
Q

[ZnSO4] General preparation procedure

A

Dissolve ZnSO4 in water

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5
Q

[ZnSO4] General standardization procedure

A

Transfer disodium edetate VS to EF

Add (in order):
HOAc-NH4OAc buffer TS + alcohol + dithizone TS

Titrate w/ ZnSO4 solution

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6
Q

[ZnSO4] RFIS

A

Buffer added to maintain pH at 4.6

Alcohol as solvent since dithizone is insoluble in water alone

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7
Q

[ZnSO4] Chemical equation and factor

A

Na2EDTA + ZnSO4 -> ZnEDTA + Na2SO4

f = 1

Metal ions combine w/ EDTA in a 1:1 mole ratio regardless of charge

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8
Q

[Iodine] Full name

A

0.1 N Iodine VS

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9
Q

[Iodine] Type of titration and reaction

A

Titration: Direct iodimetric
Reaction: Redox

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10
Q

[Iodine] Standard, indicator, endpoint

A 
Standard: 0.1 N sodium thiosulfate VS
Indicator: Starch TS
Endpoint:
Brown to straw-colored (w/o starch)
Intense blue to colorless (w/ starch)
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11
Q

[Iodine] Titration conditions

A

pH not higher than 8
Away from light
Use glass-stoppered flask

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12
Q

[Iodine] General preparation procedure

A

Dissolve iodine in 36% KI
Add HCl (3 gtt)
Dilute to volume w/ water
Transfer to amber bottle

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13
Q

[Iodine] General standardization procedure

A 
Transfer iodine solution to IF
Dilute to 100 mL
Add 1 N HCl
Swirl and titrate w/ 0.1 N Na2S2O3 VS
When solution is pale yellow, add starch TS
Continue titration
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14
Q

[Iodine] RFIS

A

Weigh iodine and KI in weighing bottles since I2 sublimes and Ki is deliquescent (Do not use steel spatula)

KI decreases vapor pressure and increases solubility of I2 (formation of triiodide ion)

HCl added to prevent iodine hydrolysis
(I2 + H2O -> HIO + HI)
(2HIO -> 2HI + O2)
and to increase sensitivity of starch

Dilute to prevent decomposition of Na2S2O3 in acid
(Na2S2O3 + HCl -> S + H2O + SO2)

Iodine flask to prevent escape of I2

Starch because inexpensive, sensitive, highly visible even at low concentrations

Starch is added when solution is straw-colored because:
I2 may cause starch decomposition
Complex formation reversibility is decreased

Keep away from light because I2 may decompose

Room temp. is optimally 25C because indicator sensitivity is decreased by high temp.

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15
Q

[NH4SCN] Full name

A

0.1 N Ammonium Thiocyanate VS

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16
Q

[Iodine] Chemical Equations and factor

A

I2 + 2Na2S2O3 -> 2NaI + Na2S4O6

f = 2 (2 e- gained by I2)

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17
Q

[NH4SCN] Type of titration and reaction

A

Direct argentometric titration (Volhard method)

Volumetric precipitation

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18
Q

[NH4SCN] Standard, indicator, endpoint

A

Standard: 0.1 N AgNO3 VS
Indicator: Ferric ammonium sulfate TS (FeNH4(SO4)2)
Endpoint: Colorless to reddish brown solution (Fe(SCN)3)

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19
Q

[NH4SCN] Titration conditions

A

Room temperature

Away from light

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20
Q

[NH4SCN] General preparation procedure

A

Dissolve NH4SCN in water

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21
Q

[NH4SCN] General standardization procedure

A

Accurately measure 0.1 N AgNO3 VS into glass-stoppered flask
Dilute with water
Add HNO3 + FeNH4(SO4)2 TS
Titrate w/ NH4SCN

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22
Q

[NH4SCN] RFIS

A

NH4SCN must be protected from air because deliquescent (also, slight excess is used in preparation to account for deliquescence)

AgNO3 undergoes photo catalytic decomposition to Ag, so keep away from light

HNO3 is used to acidify the solution to prevent ferric salt hydrolysis (common in neutral solutions)

FeNH4(SO4)2 is used as indicator because it forms reddish brown complex w/ excess SCN- (FeSCN 2+)

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24
Q

[NH4SCN] Chemical equations and factor

A

Precipitation:
AgNO3 + NH4SCN -> AgSCN + NH4NO3

Rxn w/ indicator:
FeNH4(SO4)2 + 3NH4SCN -> Fe(SCN)3 + 2(NH4)2SO4

f = 1 (valency of precipitating cation is 1)

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25
Q

[Bromine] Full name and other name

A

0.1 N Bromine VS

Koppeschaar’s Solution

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26
Q

[Bromine] Type of titration and reaction

A

Indirect iodometry

Redox

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27
Q

[Bromine] Standard, indicator, endpoint

A 
Standard: 0.1 N Na2S2O3 VS
Indicator: Starch TS
Endpoints:
Brown to straw-colored (w/o starch)
Intense blue to colorless (w/ starch)
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28
Q

[Bromine] Titration conditions

A

Acidic medium
Glass-stoppered container
Away from light

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29
Q

[Bromine] General preparation procedure

A

Dissolve KBrO3 and KBr in water

Store in amber bottle

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30
Q

[Bromine] General standardization procedure

A

In iodine flask, dilute bromine solution
Add HCl, stopper, and shake
Add KI TS, stopper, shake, and allow to stand for 5 min
Titrate I2 w/ Na2S2O3 (add starch near endpoint)

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31
Q

[Bromine] RFIS

A

KI is deliquescent (use weighing bottle)

Iodine flask to prevent volatilization of I2 and Br2

KBrO3 and KBr are more stable in solution that Br2

HCl added to:
Liberate Br2
Increase starch sensitivity

Standing for 5 min after add’n of KI: complete liberation of I2

Starch added later to prevent:
Decomposition of starch due to I2
Decreased reversibility of starch-iodo complex

Freshly prepared starch used bec. starch easily decomposes

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32
Q

[Bromine] Chemical equations and factor

A

Liberation of Br2:
KBrO3 + 5KBr + 6HCl -> 3Br2 + 3H2O + 6KCl

Oxidation of I-:
2KI + Br2 -> 2KBr + I2

Titration of iodine:
I2 + Na2S2O3 -> 2NaI + Na2S4O6

f = 2 (Br2 gains 2 e-)

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33
Q

[HCl] Full name

A

1.0 N Hydrochloric Acid VS

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34
Q

[HCl] General preparation procedure

A

Add HCl to water and dilute to volume

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35
Q

[H2SO4] Full name

A

0.1/0.5/1.0 N Sulfuric Acid VS

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36
Q

[H2SO4] General preparation procedure

A

Add slowly H2SO4 to dehydrated alcohol

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37
Q

[HCl/H2SO4] Type of titration and reaction

A

Direct titration

Neutralization

38
Q

[HCl/H2SO4] Standard, indicator, endpoint

A

Standard: Tromethamine (TRIS, tris(hydroxymethyl)methylamine)
Indicator: Bromocresol green TS (pH 4.0-5.4)
Endpoint: Blue to yellow

39
Q

[HCl/H2SO4] General standardization procedure

A

Weigh dried TRIS and dissolve
Add bromocresol green
Titrate w/ HCl or H2SO4

40
Q

[HCl/H2SO4] General chemical equation and factor

A

C4H11NO3 + HA -> C4H12NO3 + A-

f = 1 (only 1 H+ is transferred, even in H2SO4)

41
Q

[H2C2O4] Full name

A

0.1 N Oxalic Acid VS

42
Q

[H2C2O4/KMnO4] Type of titration and reaction

A

Direct permanganometry

Redox

43
Q

[H2C2O4] Standard. indicator, endpoint

A

Standard: KMnO4
Indicator: KMnO4 (self-indicating)
Endpoint: Colorless to faint pink that persists for 15 s

44
Q

[H2C2O4/KMnO4] Titration conditions

A

Acidic medium
Temperature at endpoint must not be less than 60C
Away from light

45
Q

[H2C2O4] General preparation procedure

A

Dissolve H2C2O4 in water

46
Q

[H2C2O4] General standardization procedure

A

Dilute oxalic acid
Add H2SO4
Heat to 70C
Slowly titrate with 0.1 N KMnO4

47
Q

[H2C2O4/KMnO4] RFIS

A

H2SO4 is used and not HCl because HCl may liberate Cl2

H2SO4 is added to:
Keep [H+] constant
Prevent formation of MnO2

Heating is done because reaction is slow

Slow add’n of titrant is done:
To prevent local concentration of H+ w/c may cause MnO2 formation
Because reaction becomes faster with more Mn2+ formed

Light catalyzes formation of MnO2

48
Q

[Ce(SO4)2] Full name

A

0.1 N Ceric Sulfate VS

49
Q

[Ce(SO4)2] Type of titration and reaction

A

Direct titration

Redox

50
Q

[Ce(SO4)2] Standard, indicator, endpoint

A

Standard: Na2C2O4
Indicator: Ce(SO4)2 (self-indicating)
Endpoint: Colorless to slight yellow

51
Q

[Ce(SO4)2] Titration conditions

A

Acidic medium

52
Q

[Ce(SO4)2] General standardization procedure

A 
Weigh dried Na2C2O4 and dissolve in water
Add H2SO4 previously mixed with water
Add HCl
Heat (70-75C)
Titrate w/ Ce(SO4)2
53
Q

[Ce(SO4)2] RFIS

A

Na2C2O4 is dried to eliminate adsorbed moisture

H2SO4 is added to:
Dissolve Na2C2O4 (insoluble in water)
Increase stability of Na2C2O4 and Ce(SO4)2

HCl is added to:
Maintain acidity of the solution
Prevent precipitation of basic salts

Heating to 70-75C is done to:
Increase rate of reaction completion
Allow appearance of slight yellow color

54
Q

[Ce(SO4)2] Chemical equation and factor

A

2Ce(SO4)2 + Na2C2O4 -> 2CO2 + Ce2(SO4)3 + Na2SO4

f = 2 (oxalate lost 2 e-)

55
Q

[KMnO4] Full name

A

0.1 N Potassium Permanganate VS

56
Q

[KMnO4] Standard, indicator, endpoint

A

Standard: Na2C2O4
Indicator: KMnO4 (self-indicating)
Endpoint: Colorless to faint pink that persists for 15 s

57
Q

[KMnO4] General standardization procedure

A

Dried Na2C2O4 is weighed and dissolved in water
Add H2SO4
Heat to 70C
Slowly titrate w/ KMnO4

58
Q

[KMnO4] General preparation procedure

A

Dissolve KMnO4 in water
Boil for 15 min
Stopper and allow to stand for 2 days
Filter through fine-porosity sintered glass crucible

59
Q

[H2C2O4/KMnO4] Chemical equation and factor

A

2MnO4 - + 16H+ + 5C2O4 2- -> 2Mn2+ + 8H2O + 10CO2

f = 2 (?)

60
Q

[Na2S2O3] Full name

A

0.1 N Sodium Thiosulfate VS

61
Q

[Na2S2O3] Type of titration and reaction

A

Indirect iodometry

Redox

62
Q

[Na2S2O3] Standard, indicator, endpoint

A 
Standard: K2Cr2O7
Indicator: Starch TS
Endpoint:
Brown to straw-colored (w/o starch)
Intense blue to colorless (w/ starch)
63
Q

[Na2S2O3] Titration conditions

A

Acidic medium
Away from light
Glass-stoppered container

64
Q

[Na2S2O3] General preparation procedure

A

Dissolve Na2S2O3 and Na2CO3 in recently boiled and cooled water

65
Q

[Na2S2O3] General standardization procedure

A 
Weigh pulverized and dried K2Cr2O7
Dissolve in water in glass-stoppered flask
Add KI, NaHCO3, HCl
Stopper, swirl, and allow to stand in the dark for 10 min
Rinse the stopper and walls w/ water
Titrate w/ Na2S2O3 until yellowish-green
Add Starch TS and continue titration
Perform blank determination
66
Q

[Na2S2O3] RFIS

A

Na2S2O3 is efflorescent (use weighing bottle)

[See starch RFIS from I2 and Br2]

Recently boiled and cooled water is used to eliminate CO2 w/c imparts acidity to the solution. Na2S2O3 is decomposed by acids.
Na2S2O3 + 2H2CO3 -> 2NaHCO3 + H2S2O3
H2S2O3 -> H2SO3 + S

Recently boiled water is also used to sterilize the solution. Thiobacillus thioparus causes decomposition of Na2S2O3.

Na2CO3 is added to prevent acid-catalyzed hydrolysis (see above).

K2Cr2O7 is pulverized to increase surface area for reaction w/ KI. Drying is done to remove adsorbed moisture.

Glass-stoppered flask to prevent:
Escape of I2 and CO2
Air oxidation of KI

KI provides the source of I- to form I2. Excess KI is added to increase I2 solubility.

HCl is added to promote I- -> I2

NaHCO3 is added to prevent HI from forming more I2
Without NaHCO3: 2HI + O2 → I2 + H2O
With NaHCO3: HI + NaHCO3 → H2O + CO2 + NaI

In the presence of light, I2 is hydrolyzed to hypoiodous acid (HIO).

Rinsing is done to decrease green color imparted by Cr3+ and to return I2 to solution.

Blank determination is done to account for I2 formed w/o K2Cr2O7.

67
Q

[Na2S2O3] Chemical equations and factor

A

Liberation of I2:
K2Cr2O7 + 6KI + 14HCl -> 3I2 + 2CrCl3 + 8KCl

Titration w/ Na2S2O3:
2Na2S2O3 + I2 -> Na2S4O6 + 2NaI

f = 6 (because K2Cr2O7 gained 6 e-) (?)

68
Q

[Na2EDTA] Full name

A

0.05 M Edetate Disodium VS

69
Q

[Na2EDTA] Type of titration and reaction

A

Direct Complexometry

Complexation

70
Q

[Na2EDTA] Standard, indicator, endpoint

A

Standard: CaCO3
Indicator: Hydroxynaphthol blue TS
Endpoint: Pink to blue

71
Q

[Na2EDTA] Titration conditions

A

Basic medium (pH 13)

72
Q

[Na2EDTA] General preparation procedure

A

Dissolve Na2EDTA in water

73
Q

[Na2EDTA] General standardization procedure

A

Dried chelometric CaCO3 is weighed and added to water to form slurry
Beaker is covered w/ watch glass
HCl is introduced via pipet through beaker lip
Swirl to dissolve CaCO3
Wash w/ water: sides of beaker, outer surface of pipet, watch glass
Dilute w/ water
Add about 30 mL Na2EDTA via buret
Add NaOH TS and hydroxynaphthol blue
Continue titration

74
Q

[Na2EDTA] RFIS

A

Beaker is covered to prevent loss of sample from splattering and liberation of CO2

HCl is added to dissolve CaCO3

Dilution is done since most titrations require 0.25 mmol metal ion per 50-150 mL solution. High concentrations may cause difficulty in endpoint visualization.

For 30 mL titrant, only 20 mL is added at first to prevent overtitration

Hydroxynaphthol blue is used due to its sharp color change and its lower stability constant compared to metal-EDTA complex

Na2EDTA is preferred over EDTA for standard solutions because it is more water-soluble, non-hygroscopic, and very stable.

NaOH is added to:
Stabilize Ca-EDTA complex
Prevent Mg2+ from competing in the reaction

75
Q

[Na2EDTA] Chemical reactions

A

Dissolution of CaCO3
CaCO3 + 2HCl -> CaCl2 + H2O + CO2

Formation of Ca-EDTA complex:
CaC20H9N2Na3O11S3 + Na2EDTA -> H2C20H9N2Na3O11S3 + CaEDTA

76
Q

[AgNO3] Full name

A

0.1 N Silver Nitrate VS

77
Q

[AgNO3] Type of titration and reaction

A 
Direct titration (Fajan's method)
Precipitation
78
Q

[AgNO3] Standard, indicator, endpoint

A

Standard: NaCl
Indicator: Eosin Y TS (Tetrabromofluorescein)
Endpoint: Clumped white to fine magenta precipitate

79
Q

[AgNO3] Titration conditions

A 
Acidic medium (pH < 3)
Away from light
80
Q

[AgNO3] General preparation procedure

A

Dissolve AgNO3 in water

81
Q

[AgNO3] General standardization procedure

A

Dried NaCl is dissolve in water
Add HOAc, MetOH, and eosin Y TS
Stir and titrate

82
Q

[AgNO3] RFIS

A

AgNO3 is photocatalytically degraded to metal silver and may impart dark color to ppt

NaCl needs to be dried because it is slightly hygroscopic

HOAc is added to prevent eosin Y from adsorbing before endpoint and to induce sharper endpoint

MetOH is added to keep AgCl in colloidal state. AgCl needs to be highly dispersed to better visualize endpoint.

Excess Ag+ is adsorbed on AgCl. This adsorbed Ag+ complexes w/ eosin Y to form the magenta-colored precipitate. Free eosin Y is yellowish-green in color.

83
Q

[AgNO3] Chemical equation and factor

A

AgNO3 + NaCl → AgCl(s) + NaNO3

f = 1 (valency of Ag+ is 1)

84
Q

[NaOH] Full name

A

0.1/0.5/1.0 N Sodium Hydroxide VS

85
Q

[NaOH] Type of titration and reaction

A

Direct titration

Neutralization

86
Q

[NaOH] Standard, indicator, endpoint

A

Standard: Potassium Biphthalate
Indicator: Phenolphthalein TS
Endpoint: Colorless to pink

87
Q

[NaOH] Titration conditions

A

Room temperature

88
Q

[NaOH] General preparation procedure

A

Dissolve NaOH in CO2-free water

Store in PET bottle

89
Q

[NaOH] General standardization procedure

A

Crushed and dried KHPh is dissolved in CO2-free water
Add phenolphthalein
Titrate w/ NaOH

90
Q

[NaOH] RFIS

A

NaOH is deliquescent and reacts w/ atmospheric CO2 to form Na2CO3, so use a weighing bottle.

Crushing KHPh was done to facilitate drying.

CO2-free water was used to eliminate the acidity imparted by H2CO3 and to increase sharpness of endpoint by preventing carbonate formation.

Water is allowed to cool to room temp. because hot alkali solutions rapidly absorb CO2.

Phenolphthalein gives a sharper endpoint compared to other indicators.

91
Q

[NaOH] Chemical equation and factor

A

NaOH + KHC8H4O4 → KNaC8H4O4 + H2O

f = 1 (1 replaceable H+ in KHPh)

92
Q

[KMnO4] RFIS (for preparation)

A

KMnO4 added in excess to account for possible loss due to oxidation of organic substances in water used.

Boiling facilitates oxidation of organic substances in water used. Boiling also coagulates the MnO2 formed.

Standing for 2 days ensures the oxidation of all organic substances in the solvent.

Filtration removes the MnO2 formed which will cause the autocatalysis of the permanganate into the Mn4+ ion if not removed.

Pharm Chem 135 Lab (1 decks)

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