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Pharm Chem 135 Lab > Preparation and Standardization > Flashcards

Preparation and Standardization Flashcards

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
[Bromine] Full name and other name
0.1 N Bromine VS | Koppeschaar's Solution
26
[Bromine] Type of titration and reaction
Indirect iodometry | Redox
27
[Bromine] Standard, indicator, endpoint
``` Standard: 0.1 N Na2S2O3 VS Indicator: Starch TS Endpoints: Brown to straw-colored (w/o starch) Intense blue to colorless (w/ starch) ```
28
[Bromine] Titration conditions
Acidic medium Glass-stoppered container Away from light
29
[Bromine] General preparation procedure
Dissolve KBrO3 and KBr in water | Store in amber bottle
30
[Bromine] General standardization procedure
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)
31
[Bromine] RFIS
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
32
[Bromine] Chemical equations and factor
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-)
33
[HCl] Full name
1.0 N Hydrochloric Acid VS
34
[HCl] General preparation procedure
Add HCl to water and dilute to volume
35
[H2SO4] Full name
0.1/0.5/1.0 N Sulfuric Acid VS
36
[H2SO4] General preparation procedure
Add slowly H2SO4 to dehydrated alcohol
37
[HCl/H2SO4] Type of titration and reaction
Direct titration | Neutralization
38
[HCl/H2SO4] Standard, indicator, endpoint
Standard: Tromethamine (TRIS, tris(hydroxymethyl)methylamine) Indicator: Bromocresol green TS (pH 4.0-5.4) Endpoint: Blue to yellow
39
[HCl/H2SO4] General standardization procedure
Weigh dried TRIS and dissolve Add bromocresol green Titrate w/ HCl or H2SO4
40
[HCl/H2SO4] General chemical equation and factor
C4H11NO3 + HA -> C4H12NO3 + A- f = 1 (only 1 H+ is transferred, even in H2SO4)
41
[H2C2O4] Full name
0.1 N Oxalic Acid VS
42
[H2C2O4/KMnO4] Type of titration and reaction
Direct permanganometry | Redox
43
[H2C2O4] Standard. indicator, endpoint
Standard: KMnO4 Indicator: KMnO4 (self-indicating) Endpoint: Colorless to faint pink that persists for 15 s
44
[H2C2O4/KMnO4] Titration conditions
Acidic medium Temperature at endpoint must not be less than 60C Away from light
45
[H2C2O4] General preparation procedure
Dissolve H2C2O4 in water
46
[H2C2O4] General standardization procedure
Dilute oxalic acid Add H2SO4 Heat to 70C Slowly titrate with 0.1 N KMnO4
47
[H2C2O4/KMnO4] RFIS
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
[Ce(SO4)2] Full name
0.1 N Ceric Sulfate VS
49
[Ce(SO4)2] Type of titration and reaction
Direct titration | Redox
50
[Ce(SO4)2] Standard, indicator, endpoint
Standard: Na2C2O4 Indicator: Ce(SO4)2 (self-indicating) Endpoint: Colorless to slight yellow
51
[Ce(SO4)2] Titration conditions
Acidic medium
52
[Ce(SO4)2] General standardization procedure
``` Weigh dried Na2C2O4 and dissolve in water Add H2SO4 previously mixed with water Add HCl Heat (70-75C) Titrate w/ Ce(SO4)2 ```
53
[Ce(SO4)2] RFIS
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
[Ce(SO4)2] Chemical equation and factor
2Ce(SO4)2 + Na2C2O4 -> 2CO2 + Ce2(SO4)3 + Na2SO4 f = 2 (oxalate lost 2 e-)
55
[KMnO4] Full name
0.1 N Potassium Permanganate VS
56
[KMnO4] Standard, indicator, endpoint
Standard: Na2C2O4 Indicator: KMnO4 (self-indicating) Endpoint: Colorless to faint pink that persists for 15 s
57
[KMnO4] General standardization procedure
Dried Na2C2O4 is weighed and dissolved in water Add H2SO4 Heat to 70C Slowly titrate w/ KMnO4
58
[KMnO4] General preparation procedure
Dissolve KMnO4 in water Boil for 15 min Stopper and allow to stand for 2 days Filter through fine-porosity sintered glass crucible
59
[H2C2O4/KMnO4] Chemical equation and factor
2MnO4 - + 16H+ + 5C2O4 2- -> 2Mn2+ + 8H2O + 10CO2 f = 2 (?)
60
[Na2S2O3] Full name
0.1 N Sodium Thiosulfate VS
61
[Na2S2O3] Type of titration and reaction
Indirect iodometry | Redox
62
[Na2S2O3] Standard, indicator, endpoint
``` Standard: K2Cr2O7 Indicator: Starch TS Endpoint: Brown to straw-colored (w/o starch) Intense blue to colorless (w/ starch) ```
63
[Na2S2O3] Titration conditions
Acidic medium Away from light Glass-stoppered container
64
[Na2S2O3] General preparation procedure
Dissolve Na2S2O3 and Na2CO3 in recently boiled and cooled water
65
[Na2S2O3] General standardization procedure
``` 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
[Na2S2O3] RFIS
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
[Na2S2O3] Chemical equations and factor
Liberation of I2: K2Cr2O7 + 6KI + 14HCl -> 3I2 + 2CrCl3 + 8KCl Titration w/ Na2S2O3: 2Na2S2O3 + I2 -> Na2S4O6 + 2NaI f = 6 (because K2Cr2O7 gained 6 e-) (?)
68
[Na2EDTA] Full name
0.05 M Edetate Disodium VS
69
[Na2EDTA] Type of titration and reaction
Direct Complexometry | Complexation
70
[Na2EDTA] Standard, indicator, endpoint
Standard: CaCO3 Indicator: Hydroxynaphthol blue TS Endpoint: Pink to blue
71
[Na2EDTA] Titration conditions
Basic medium (pH 13)
72
[Na2EDTA] General preparation procedure
Dissolve Na2EDTA in water
73
[Na2EDTA] General standardization procedure
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
[Na2EDTA] RFIS
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
[Na2EDTA] Chemical reactions
Dissolution of CaCO3 CaCO3 + 2HCl -> CaCl2 + H2O + CO2 Formation of Ca-EDTA complex: CaC20H9N2Na3O11S3 + Na2EDTA -> H2C20H9N2Na3O11S3 + CaEDTA
76
[AgNO3] Full name
0.1 N Silver Nitrate VS
77
[AgNO3] Type of titration and reaction
``` Direct titration (Fajan's method) Precipitation ```
78
[AgNO3] Standard, indicator, endpoint
Standard: NaCl Indicator: Eosin Y TS (Tetrabromofluorescein) Endpoint: Clumped white to fine magenta precipitate
79
[AgNO3] Titration conditions
``` Acidic medium (pH < 3) Away from light ```
80
[AgNO3] General preparation procedure
Dissolve AgNO3 in water
81
[AgNO3] General standardization procedure
Dried NaCl is dissolve in water Add HOAc, MetOH, and eosin Y TS Stir and titrate
82
[AgNO3] RFIS
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
[AgNO3] Chemical equation and factor
AgNO3 + NaCl → AgCl(s) + NaNO3 f = 1 (valency of Ag+ is 1)
84
[NaOH] Full name
0.1/0.5/1.0 N Sodium Hydroxide VS
85
[NaOH] Type of titration and reaction
Direct titration | Neutralization
86
[NaOH] Standard, indicator, endpoint
Standard: Potassium Biphthalate Indicator: Phenolphthalein TS Endpoint: Colorless to pink
87
[NaOH] Titration conditions
Room temperature
88
[NaOH] General preparation procedure
Dissolve NaOH in CO2-free water | Store in PET bottle
89
[NaOH] General standardization procedure
Crushed and dried KHPh is dissolved in CO2-free water Add phenolphthalein Titrate w/ NaOH
90
[NaOH] RFIS
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
[NaOH] Chemical equation and factor
NaOH + KHC8H4O4 → KNaC8H4O4 + H2O f = 1 (1 replaceable H+ in KHPh)
92
[KMnO4] RFIS (for preparation)
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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