Complexation & Precipitimetry Copy
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COMPOUND
Analyte: Zinc Oxide Paste Molecular Formula: Molecular Weight:
Indicator Used: Eriochrome Black TS Color Transition/Endpoint: Official Requirement: Zinc Oxide Paste contains not less than 24% and not more than 26% of zinc oxide It may be prepared as follows: Zinc Oxide 250g Starch 250g White Petrolatum 250g TO MAKE 1000g Analysts: Figueroa Marquina Pereyra Zamora
TYPE OF TITRATION AND REACTION Type of Titration: Complexometric Assay Type of Reaction: Complexation Titrant/s: 0.05M EDTA VS Special Conditions: -Ignition
CHEMICAL EQUATIONS AND CALCULATIONS Chemical Equation: Factor: Explanation: Pre- Lab Computations: Post - lab computations:
ASSAY PROCEDURE AND REASONS FOR IMPORTANT STEPS Assay Procedure Using about 600mg of paste, proceed as directed in the Assay under Zinc Oxide Ointment. Weigh accurately in a porcelain crucible 700mg of ointment, heat gently until melted, and continue the heating, gradually raising the temperature until the mass is thoroughly charred. Ignite the mass until the residue is uniformly yellow and cool. Dissolve the residue in 10mL of 2N Sulfuric Acid, warming if necessary to effect complete solution, transfer the solution to a beaker, and rinse the crucible with small portions of water until the combined solutions & rinsings measure 50mL. Add 15mL of Ammonia-ammonium chloride buffer TS & 1mL of Eriochrome Black TS, and titrate with 0.05M Edetate Disodium VS until the solution is blue in color. Each mL of 0.05M Edetate Disodium VS is equivalent to 4.069mg of ZnO. eason/s For Important Steps: R -Use of porcelain crucible when igniting the sample, as the crucible can withstand high temperatures -
Analyte: Sodium Chloride, International Pharmacopoeia Molecular Formula: NaCl Molecular Weight:
Type of Titration: Direct titration Type of Reaction: Precipitimetry (argentometry)
Indicator Used: Potassium Chromate TS Color Transition/Endpoint: White ppt → red ppt Official Requirement:
Titrant/s: 0.1 N Silver Nitrate VS Special Conditions: ● Covering the burette (with titrant) with foil ● Titration in basic medium
Sodium chloride contains NLT 99.0% and NMT 100.5% of NaCl, calculated with reference to the dried substance. Analysts: Casil Juico Nolasco
Chemical Equation:
Assay Procedure
Dissolve about 0.25 g, accurately weighed sodium chloride, in 50 Precipitation reaction between the analyte and mL of water and titrate with silver nitrate (0.1 mol/L) VS, using titrant potassium chromate (100g/L) TS as indicator. Each mL of silver NaCl + AgNO3 → AgCl↓ + NaNO3 nitrate (0.1 mol/L) VS is equivalent to 5.844 mg of NaCl. (white ppt)
Precipitation reaction between the titrant and indicator AgNO3 + K2CrO4 → Ag2CrO4↓ + 2KNO3
(red ppt) Factor: 1 Explanation: Factor is 1 because the valence or charge of silver, the metal cation, is 1. Pre- Lab Computations:
Sol
Reason/s for Important Step/s 1. Weighing the analyte using weighing bottle ● Sodium chloride is a deliquescent substance that absorbs moisture and readily dissolves. 2. Drying the analyte ● To remove any moisture present in the substance 3. Covering the burette (with titrant) with foil ● Standard silver nitrate solution and silver chloride precipitates formed were protected from light at all times because silver nitrate decomposes according to: ● 2AgNO3 → 2Ag↓ + O2 + 2NO2 4. Good stirring or shaking during the addition of silver nitrate ● To have a sharp and reproducible endpoint ● Otherwise, silver chloride that forms locally before the endpoint can become occluded in the silver chloride precipitate instead of re-dissolving.
Post - lab computations: 5. The Mohr titration should be carried out under conditions of 6.5-9
● ●
At higher pH, silver ions may be removed by precipitation with hydroxide ions, forming brownish silver hydroxide. At lower pH, chromate ions may be removed by an acid-base reaction to form hydrogen chromate ions or dichromate ions, affecting the accuracy of the endpoint.
6. Titration done at room temperature ● Because the solubility of silver chromate increases with increasing temperature
Analyte: Sodium chloride Usp Molecular Formula: NaCl Molecular Weight: Indicator Used: Eosine y Color Transition/Endpoint: Yellowish green- pink Official Requirement:
Sodium chloride contains NLT 99.0% and NMT 100.5% of NaCl, calculated with reference to the dried substance.
Type of Titration: Direct titration Type of Reaction: Precipitimetry (argentometry) Titrant/s: 0.1 N Silver Nitrate VS Special Conditions: ● Covering the burette (with titrant) with foil ● Titration in acidic medium
7. Addition of indicator ● The indicator should be prepared by dissolving 1 g of potassium chromate in 10 mL of distilled water and should be added in an exact amount. ● Excessive indicator leads to under titration ● Insufficient indicator leads to over titration Procedure Dissolve 200 mg of nacl, accurately weighed in 10 ml of water and add 10 ml of glacial acetic acid, 75 ml of methanol and 0.5 ml of eosin y ts. Titrate with shaking with 0.1 n silver nitrate vs to a pink endpoint . each ml of 0.1 n silver nitrate is equiv. To 5.894 mg of nacl.
Analyte: Sodium Lauryl Sulfate for Sodium Chloride Content Molecular Formula: Sodium lauryl sulfate: [CH3(CH2)10CH2OSO3Na] Sodium chloride: NaCl Molecular Weight: NaCl = 58.4 g/mol Indicator Used: Potassium chromate TS Endpoint: formation of brick red precipitate Official Requirement: Sodium lauryl sulfate is a mixture of sodium alkyl sulfates consisting chiefly of sodium lauryl sulfate [CH3(CH2)10CH2OSO3Na]. The combined content of sodium chloride and sodium sulfate is not more than 8.0%. Analysts: Encabo Mardo Pausal Velasco
Type of Titration: Direct titration (Argentometric titration) Type of Reaction: Precipitation (Mohr Method) Titrant/s: 0.1 N Silver Nitrate VS Special Conditions: -This titration should be performed at a pH of neutral to slightly alkaline environment. -The buret and erlenmeyer flask should be wrapped in an aluminum foil.
Chemical Equation: AgNO3 + NaCl → AgCl↓ + NaNO3 2AgNO3 + K2CrO4 → Ag2CrO4↓ + 2KNO3 Factor: 1 Explanation: Pre- Lab Computations: NaCl (MW): 58.4 g/mol Na2SO4 (MW): 142.04 g/mol 58.4 g/mol + 142.04 g/mol = 200.44 g/mol 58.4 g/mol 200.44 g/mol = 0.2914
0.2914 x 8 g = 2.3312 g 0.1 N x 10 mL x
58.4 g/mol 1000 x 1 = 0.0584 g
0.0584 g N aCl
Wt. analyte = 2.3312 g N aCl x 100 g SLS = 2.5051 g SLS Post - lab computations:
Assay Procedure Dissolve about 5 g of sodium lauryl sulfate, accurately weighed, in about 50 mL of water. Neutralize the solution with 0.8N nitric acid, using litmus paper as the indicator, add 2 miL of potassium chromate TS, and titrate with 0.1N silver nitrate VS. Each mL of 0.1N silver nitrate is equivalent to 5.844 mg of NaCl. Potassium Chromate TS Dissolve 10 g of potassium chromate in water to make 100 mL. Reason/s For Important Steps: 1. Wrap an aluminum foil around the buret because silver nitrate is photosensitive, it will precipitate when exposed to light. 2. 0.8 nitric acid is added to neutralize the solution. 3. The Mohr titration should be carried out under conditions of pH 6.5-9. At a higher pH, silver hydroxide ions, which is brownish in color, might be precipitated which will mask the endpoint. At a lower pH, dichromate ions are formed. The chromate-ion concentration is reduced and the solubility product of silver chromate may not be exceeded. 4. Because sodium lauryl sulfate is the analyte used, do not shake the erlenmeyer flask as it will form a foam which will mask the endpoint.
Analyte: Calcium Hydroxide topical solution Molecular Formula: Molecular Weight:
Indicator Used: Hydroxy naphthol blue Color Transition/Endpoint: violet to blue Official Requirement:Calcium hydroxide topical solution is a solution containing in each 100mL not less than 140mg of calcium hydroxide
Analysts: Laquindanum Chiu Oloroso
Type of Titration: Complexometric Assay Type of Reaction: Complexation between EDTA and Calcium Titrant/s: 0.05M EDTA VS Special Conditions: basic medium
Chemical Equation: Na2EDTA + Ca(OH)2 = Ca(EDTA) + 2NaOH Factor: n/a Explanation:
Assay Procedure Pipet 100 mL of Topical Solution in a suitable container, add 50 mL of water, 15 mL of 1N sodium hydroxide, and 300 mg of hydroxynaphthol blue, and titrate with 0.05 M edetate disodium VS to a blue endpoint. Each mL of 0.05 M edetate disodium is equivalent to 3.705 mg of calcium hydroxide [Ca(OH)2] eason/s For Important Steps: R 1. The sodium hydroxide alkalinize the solution to a pH of about 13, so that the Ca-EDTA complex would be stable and any magnesium which might be present as a contaminant would not react. 2. Add small amount of indicator to enable to see the color change clearly 3. Be careful with the temperature, solubility of calcium hydroxide varies with the temperature for which it is stored, being about 170mg/mL at 15oC and less at higher temperature. The official concentration is based upon a temperature of 25oC (Remmington) 4. Wash down the sides to get every solution that splattered on the beaker. (middle Tennessee state university, n.d) 5. EDTA is a stronger Complexing agent than the indicator, and displaces the indicator from the metal ion allowing the indicator to return its original color 6. Hydroxynaphthol blue is used as indicator because it is specific for calcium determination.
Analyte: Ammonium Alum Molecular Formula: AlNH4(SO4)2 Molecular Weight: 237.133 g/mol Indicator Used: Dithizone TS Color Transition/Endpoint: Purplish-green to bright rose pink Official Requirement: Ammonium Alum contains not less than 99.0% and not more 100.5% of AlNH4(SO4)2, calculated on the dried basis.
Type of Titration: Residual with blank determination Type of Reaction: Complexation reaction Titrant/s: Back-titrant: 0.05 M Zinc Sulfate Excess titrant: 0.05 M EDTA Special Conditions:
Chemical Equation: Factor: n/a Explanation: Pre-lab computation: Wt. (AlNH4(SO4)2) = 237.15 g/mol 0.05 M x (50.0 mL − 20 mL) x 1000 Wt. (AlNH4(SO4)2) = 0.3557 g Post-lab computation:
RFIS: 1. Complexometric titration (residual) generally performs when the metallic ions form a stable complex with EDTA in a slow reaction or when a metal ion blocks an indicator. The blocked indicator cannot release metallic ions. Thus, no color change will be observable at the endpoint of the complexometric (direct) titration. 2. The buffered solution was heated to increase the buffer formation and the complex formation. This was to ensure that the entire Aluminum has been complexed and only excess EDTA existed in solution.
Analyst: Nacar
Analyte: Alumina & Magnesia Oral Suspension (for Al(OH)3) Molecular formula: Al(OH)3 Molecular weight: 78 g/mol Indicator used: Dithizone TS
Assay Procedure Transfer about 800 mg of Ammonium Alum, accurately weighed to a 400 mL beaker, moisten with 1 mL of glacial acetic acid, and add 50 mL of water, 50.0 mL of disodium edetate titrant, and 20 mL of acetic acid-ammonium acetate buffer TS. Warm on a steam bath until solution is complete, and boil gently for 5 minutes. Cool, add 50 mL of alcohol and 2 mL of dithizone TS, and titrate with 0.05 M zinc sulfate VS to a bright rose-pink color. Perform a blank determination and make any necessary correction. Each mL of 0.05 M disodium edetate titrant is equivalent to 11.86 mg of AlNH4(SO4)2
Type of Titration: Residual w/ blank determination Type of Reaction: Complexation reaction
Chemical Equation: a. Alumina with hydrochloric acid Al(OH)3 + HCl → AlCl3 + H2O b. Excess Na2EDTA with aluminum chloride
Assay Procedure Sample Solution: transfer a volume of oral suspension, previously well shaken in its original container, equivalent to 1200 mg of aluminum
Color Transition/Endpoint: green-violet to rose-pink
AlCl3 + Na2EDTA → Al-EDTA + NaCl Titrants: Excess - 0.05M Disodium EDTA Back - 0.05M Zinc Sulfate
Official Requirement: Alumina & Magnesia Oral Suspension is a mixture Special Conditions: slightly containing aluminum hydroxide [Al(OH)3] and magnesium acidic hydroxide [Mg(OH)2]. It contains the equivalent of NLT 90.0% AND NMT 110.0% of aluminum hydroxide [Al(OH)3] and magnesium hydroxide [Mg(OH)2]
Analyte: Alumina & Magnesia Oral Suspension (for Mg(OH)3)
Type of Titration: Residual w/ blank determination
c. Excess Na2EDTA back titrated with zinc sulfate Na2EDTA + ZnSO4 → Zn-EDTA + Na2SO4 Factor: N/A Pre-lab Computation: moles Weight of analyte = 0.05 10000 x (25-10mL) x 1 mol Al(OH)3 78g/mol x ( 1 mol ZnSO4 ) = 0.0585 g of aluminum hydroxide 0.0585 g x 10 mL = 250 mL 250 mL = sample solution x= 1.4625 g of suspension Labelled claim : 225mg/5mL 5mL 1.4625 g x 0.225 g = 32.5 mL of suspension Post-Lab Computation:
Chemical Equation: a. Magnesia with hydrochloric acid
hydroxid, to a suitable beaker. Add 20mL of water, stir, and slowly add 10mL of hydrochloric acid. Heat gently, if necessary, to aid solution, cool, and filter into a 200-mL volumetric flask. Wash the filter with water into the flask and add water to volume. Analysis: pipet 10mL of water, then add, in the order named and with continuous stirring, 25.0 mL of Edetate disodium titrant and 20 mL of acetic acid-ammonium acetate buffer TS, and heat near the boiling point for 5 minutes. Cool, add 50 mL of alcohol and 2 mL of dithizone TS and mix. Titrate the excess edetate disodium with 0.05M zinc sulfate CS until the color changes from green-violet to rose pink. Perform a blank determination, substituting 10mL of water for the sample solution and make any necessary correction. Each mL of Edetate disodium titrant consumed is equivalent to 3.900mg of aluminum hydroxide [Al(OH)3] RFIS 1. HCl solubilizes aluminum hydroxide by forming aluminum chloride. HCl must be added until solution becomes clear. 2. Filter the sample to filter out any impurities present in the sample 3. Acetic acid-ammonium acetate buffer is added to adjust to the pH in which the complex formed is more stable. This will also minimize change of pH throughout the titration. The ammonium acetate in the buffer prevents precipitation of the hydroxide. 4. Solution is heated near boiling point to stabilize the metal-EDTA complex, since the reaction of aluminum and EDTA is slow 5. Alcohol ensures the solubility of the dithizone 6. Dithizone TS is the indicator used because it is specific with zinc. Procedure: Sample Solution:
Molecular formula: Mg(OH)3 Molecular weight:58.32 g/mol Indicator used: Eriochrome Black T Color Transition/Endpoint: red to blue solution
Type of Reaction: Complexation reaction Titrants: 0.05M Disodium EDTA
Official Requirement: Alumina & Magnesia Oral Special Conditions: basic Suspension is a mixture condition containing aluminum hydroxide [Al(OH)3] and magnesium hydroxide [Mg(OH)2]. It contains the equivalent of NLT 90.0% AND NMT 110.0% of aluminum hydroxide [Al(OH)3] and magnesium hydroxide [Mg(OH)2]
b.
Mg(OH)2 + 2HCl → MgCl2 + 2H2O
Factor: N/A Pre-lab Computation: Label claim: 250mg/5mML Mg(OH)2 250mg/5mL = 1200mg/x x= 30mL Mg(OH)2 Sample solution: 1200mg/250mL = 40mg/x x= 8.33mL sample solution
Post-Lab Computation:
Transfer a volume of Oral suspension, previously well shaken in its original container, equivalent to 1200 mg of magnesium hydroxide, to a suitable beaker. Add 20 ml of water, stir, and slowly add 10 ml of HCl. Heat gently, if necessary, to aid solution, cool, and filter into a 200 ml volumetric flask. Wash the filter with water into the flask and add water to volume. Analysis: Pipet a volume of the sample solution, equivalent to 40 mg of magnesium hydroxide, into a 400 ml beaker. Add 20 ml of water and 20 ml of triethanolamine and stir. Add 10 ml of ammonia-ammonium chloride buffer TS and add 3 drops of an eriochrome black indicator solution (prepared by dissolving 200 mg of eriochrome black T in a mixture of 15 ml of triethanolamine and 5 ml of dehydrated alcohol), and mix. Cool the solution to between 3 and 4 degrees by immersion of the beaker in an ice bath, then remove, and titrate with 0.05M disodium EDTA VS to a blue endpoint. Perform a blank determination, substituting 10 ml of water for the sample solution, and make any necessary correction. Each ml of 0.05M disodium EDTA consumed is equivalent to 2.916 mg magnesium hydroxide. RFIS: 1. The ammonia-ammonium chloride buffer is used to adjust the pH of the solution (pH 10) because the pH must not be too high or the metal hydroxide may precipitate, causing the reaction with EDTA to be very slow (Christian, 2014). 2. pH should be monitored an important because it affects the stability of the complex formed between the indicator ad metal ion, as well as between EDTA and the metal ion (Christian, 2014).
3.
In Edta titrations/reactions, high temperature of solution promotes the ionization of the complex making it unstable that is why the solution is must be cooled between 3 and 4 degrees (Christian, 2014). 4. Triethanolamine is added as a masking agent. TEA will impart enough alkalinity to suppress Al-EDTA complexation in the presence of a Mg-EDTA reaction.
Analyte: Milk of Magnesia Molecular formula: Mg(OH)2 Molecular weight: 58.32 g/mol Indicator used: Eriochrome black TS Color Transition/Endpoint: red to blue color
Type of Titration: Direct titration Type of Reaction: Complexation reaction Titrants: 0.05M Disodium EDTA
Special Conditions: slightly Official Requirement: Milk of Magnesia is a basic suspension of Magnesium Hydroxide. Milk of Magnesia, Double-strength Milk of Magnesia and Triple-strength Milk of Magnesia contain not less than 90.0% and not more than 115.0% of the labeled amount being 80, 160, and 240 mg of Mg(OH)2 per mL, respectively. It may contain not more than 0.05% of a volatile oils, suitable for flavoring purposes.
Chemical Equation:
Factor: N/A Pre-lab Computation: Post-Lab Computation:
Assay Procedure Transfer an accurately measured quantity of Milk of Magnesia, previously shaken in its original container, equivalent to about 800 mg of magnesium hydroxide, to a 250 mL volumetric flask. Dissolve in 30 mL of 3N hydrochloric acid, dilute with water to volume and mix. Filter, if necessary, and transfer 25.0 mL of the filtrate to a beaker containing 75 mL of water, and mix. Adjust the reaction of the solution with 1N sodium hydroxide to a pH of 7 (using pH indicator paper), add 5 mL of ammonia-ammonium chloride buffer TS and 0.15 mL of eriochrome black TS and titrate with 0.05M edetate disodium TS to a blue endpoint. Each mL of 0.05M edetatate disodium is equivalent to 2.916 mg of Mg(OH)2. RFIS 1. Shake or mix the Milk of Magnesia before using - MoM is a white opaque suspended solution. Shaking or mixture is done to ensure representativeness of the sample by having equal distribution of particles that are dispersed throughout the suspension. 2. Dissolve milk of magnesia in 3N HCl, dilute w/ water and mix - secures the complete neutralization of Mg(OH)2, which is waterinsoluble. This will produce a clear solution when neutralization is complete.
3. Adjust reaction of the solution w/ 1N NaOH to a pH of 7 -the excess acid will be reacting with sodium hydroxide and the solution will be basic until pH 7 because Eriochrome black T is blue at pH 6 to 12, which is the target endpoint for this assay. 4. +ammonia-ammonium chloride buffer TS -titration of magnesium with EDTA is done at pH 10 or basic solutions, using ammonia-ammonium chloride buffer. The pH must not be too high or the metal hydroxide may precipitate, causing the reaction with EDTA to be very slow. (Christian, 2004, p. 335) 5. eriochrome black T as indicator - a typical indicator. It contains three ionizable protons, so we will represent it by H3In. This indicator can be used for the titration of Mg2+ with EDTA. A small amount of indicator is added to the sample solution, and it forms a red complex with part of the Mg2+; the color of the uncomplexed indicator is blue. As soon as all the free Mg2+ is titrated, the EDTA displaces the indicator from the magnesium, causing a change in the color from red to blue. 6. 0.05M edetate disodium as titrant -widespread use of its ability to form chelates with all cations but also because most of these chelates are sufficiently stable for titrations.
Analyte: Mercuric Sulfate Molecular formula: HgSo4 Molecular weight: 296.65 g/mol Indicator used: ferric nitrate
solution
Color Transition/Endpoint:Reddish-
Type of Titration:Direct
Chemical Equation:
Assay Procedure
Titration ( Modified Volhard) Type of Reaction: precipitation reaction
HgSo4 + 2HNo3 → Hg(No3)2 + H2So4 Hg(No3)2 + 2NH4SCN →Hg(SCN)2 + 2NH4NO3
Titrants: 0.1 N Ammonium
When all metallic ion has been precipitated as thiocyanate, the thiocyanate will react to ferric nitrate to form red ferric thiocyanate
weigh accurately about 500 mg, and dissolve in 50 mL of dilute Nitric acid (1 in 2). Add 1 ml of ferric nitrate solution (1 in 10), and titrate with 0.1 N Ammonium thiocyanate consumed is equivalent to 10.03 mg of Hg
Thiocyanate
Fe(No3)3 + 3NH4SCN →Fe(SCN)3 + 3(NH4)No3
brown solution Official Requirement:
Mercuric sulfate contains not less than 67 % and not more than 67.5 % of Hg
Special Conditions:
Solution must be Acidified
Factor: 2 because mercuric ion has a valence
of 2
Pre-lab Computation: Analyst: Ham Argana Robles
0.1N x 30mL x 296.65 g/mol 1000 x 2 = 0.4449 g
Post-Lab Computation: N/A
RFIS:
1. Use of Dilute Nitric Acid - According to Knevel, A.M & Digang F.E. (1977) nitric acid is used because it needed an environment of acidic to prevent hydrolysis of that ferric salts undergo in neutral solutions, and mercury dissolves slowly in dilute nitric acid to form mercury(I) nitrate, mercurous nitrate, Hg2(NO3)2. According to Webelement.com (n.d.) 2. Use of 1 ml ferric Nitrate solution - According to chem.uiuc.edu (n.d.) the ferric ion of ferric nitrate solution was used as an indicator and will react to the thiocyanate ion to form a red ferric thiocyanate 3. Performed at Low temperature - titration must be done below 25 C since the ferric thiocyanate complex fades at high temperature
Analyte: Zinc Oxide Paste Molecular Formula: Molecular Weight:
Indicator Used: Eriochrome Black TS Color Transition/Endpoint: Official Requirement: Zinc Oxide Paste contains not less than 24% and not more than 26% of zinc oxide It may be prepared as follows: Zinc Oxide 250g Starch 250g White Petrolatum 250g TO MAKE 1000g Analysts: Figueroa Marquina Pereyra Zamora
TYPE OF TITRATION AND REACTION Type of Titration: Complexometric Assay Type of Reaction: Complexation Titrant/s: 0.05M EDTA VS Special Conditions: -Ignition
CHEMICAL EQUATIONS AND CALCULATIONS Chemical Equation: Factor: Explanation: Pre- Lab Computations: Post - lab computations:
ASSAY PROCEDURE AND REASONS FOR IMPORTANT STEPS Assay Procedure Using about 600mg of paste, proceed as directed in the Assay under Zinc Oxide Ointment. Weigh accurately in a porcelain crucible 700mg of ointment, heat gently until melted, and continue the heating, gradually raising the temperature until the mass is thoroughly charred. Ignite the mass until the residue is uniformly yellow and cool. Dissolve the residue in 10mL of 2N Sulfuric Acid, warming if necessary to effect complete solution, transfer the solution to a beaker, and rinse the crucible with small portions of water until the combined solutions & rinsings measure 50mL. Add 15mL of Ammonia-ammonium chloride buffer TS & 1mL of Eriochrome Black TS, and titrate with 0.05M Edetate Disodium VS until the solution is blue in color. Each mL of 0.05M Edetate Disodium VS is equivalent to 4.069mg of ZnO. eason/s For Important Steps: R -Use of porcelain crucible when igniting the sample, as the crucible can withstand high temperatures -
Analyte: Sodium Chloride, International Pharmacopoeia Molecular Formula: NaCl Molecular Weight:
Type of Titration: Direct titration Type of Reaction: Precipitimetry (argentometry)
Indicator Used: Potassium Chromate TS Color Transition/Endpoint: White ppt → red ppt Official Requirement:
Titrant/s: 0.1 N Silver Nitrate VS Special Conditions: ● Covering the burette (with titrant) with foil ● Titration in basic medium
Sodium chloride contains NLT 99.0% and NMT 100.5% of NaCl, calculated with reference to the dried substance. Analysts: Casil Juico Nolasco
Chemical Equation:
Assay Procedure
Dissolve about 0.25 g, accurately weighed sodium chloride, in 50 Precipitation reaction between the analyte and mL of water and titrate with silver nitrate (0.1 mol/L) VS, using titrant potassium chromate (100g/L) TS as indicator. Each mL of silver NaCl + AgNO3 → AgCl↓ + NaNO3 nitrate (0.1 mol/L) VS is equivalent to 5.844 mg of NaCl. (white ppt)
Precipitation reaction between the titrant and indicator AgNO3 + K2CrO4 → Ag2CrO4↓ + 2KNO3
(red ppt) Factor: 1 Explanation: Factor is 1 because the valence or charge of silver, the metal cation, is 1. Pre- Lab Computations:
Sol
Reason/s for Important Step/s 1. Weighing the analyte using weighing bottle ● Sodium chloride is a deliquescent substance that absorbs moisture and readily dissolves. 2. Drying the analyte ● To remove any moisture present in the substance 3. Covering the burette (with titrant) with foil ● Standard silver nitrate solution and silver chloride precipitates formed were protected from light at all times because silver nitrate decomposes according to: ● 2AgNO3 → 2Ag↓ + O2 + 2NO2 4. Good stirring or shaking during the addition of silver nitrate ● To have a sharp and reproducible endpoint ● Otherwise, silver chloride that forms locally before the endpoint can become occluded in the silver chloride precipitate instead of re-dissolving.
Post - lab computations: 5. The Mohr titration should be carried out under conditions of 6.5-9
● ●
At higher pH, silver ions may be removed by precipitation with hydroxide ions, forming brownish silver hydroxide. At lower pH, chromate ions may be removed by an acid-base reaction to form hydrogen chromate ions or dichromate ions, affecting the accuracy of the endpoint.
6. Titration done at room temperature ● Because the solubility of silver chromate increases with increasing temperature
Analyte: Sodium chloride Usp Molecular Formula: NaCl Molecular Weight: Indicator Used: Eosine y Color Transition/Endpoint: Yellowish green- pink Official Requirement:
Sodium chloride contains NLT 99.0% and NMT 100.5% of NaCl, calculated with reference to the dried substance.
Type of Titration: Direct titration Type of Reaction: Precipitimetry (argentometry) Titrant/s: 0.1 N Silver Nitrate VS Special Conditions: ● Covering the burette (with titrant) with foil ● Titration in acidic medium
7. Addition of indicator ● The indicator should be prepared by dissolving 1 g of potassium chromate in 10 mL of distilled water and should be added in an exact amount. ● Excessive indicator leads to under titration ● Insufficient indicator leads to over titration Procedure Dissolve 200 mg of nacl, accurately weighed in 10 ml of water and add 10 ml of glacial acetic acid, 75 ml of methanol and 0.5 ml of eosin y ts. Titrate with shaking with 0.1 n silver nitrate vs to a pink endpoint . each ml of 0.1 n silver nitrate is equiv. To 5.894 mg of nacl.
Analyte: Sodium Lauryl Sulfate for Sodium Chloride Content Molecular Formula: Sodium lauryl sulfate: [CH3(CH2)10CH2OSO3Na] Sodium chloride: NaCl Molecular Weight: NaCl = 58.4 g/mol Indicator Used: Potassium chromate TS Endpoint: formation of brick red precipitate Official Requirement: Sodium lauryl sulfate is a mixture of sodium alkyl sulfates consisting chiefly of sodium lauryl sulfate [CH3(CH2)10CH2OSO3Na]. The combined content of sodium chloride and sodium sulfate is not more than 8.0%. Analysts: Encabo Mardo Pausal Velasco
Type of Titration: Direct titration (Argentometric titration) Type of Reaction: Precipitation (Mohr Method) Titrant/s: 0.1 N Silver Nitrate VS Special Conditions: -This titration should be performed at a pH of neutral to slightly alkaline environment. -The buret and erlenmeyer flask should be wrapped in an aluminum foil.
Chemical Equation: AgNO3 + NaCl → AgCl↓ + NaNO3 2AgNO3 + K2CrO4 → Ag2CrO4↓ + 2KNO3 Factor: 1 Explanation: Pre- Lab Computations: NaCl (MW): 58.4 g/mol Na2SO4 (MW): 142.04 g/mol 58.4 g/mol + 142.04 g/mol = 200.44 g/mol 58.4 g/mol 200.44 g/mol = 0.2914
0.2914 x 8 g = 2.3312 g 0.1 N x 10 mL x
58.4 g/mol 1000 x 1 = 0.0584 g
0.0584 g N aCl
Wt. analyte = 2.3312 g N aCl x 100 g SLS = 2.5051 g SLS Post - lab computations:
Assay Procedure Dissolve about 5 g of sodium lauryl sulfate, accurately weighed, in about 50 mL of water. Neutralize the solution with 0.8N nitric acid, using litmus paper as the indicator, add 2 miL of potassium chromate TS, and titrate with 0.1N silver nitrate VS. Each mL of 0.1N silver nitrate is equivalent to 5.844 mg of NaCl. Potassium Chromate TS Dissolve 10 g of potassium chromate in water to make 100 mL. Reason/s For Important Steps: 1. Wrap an aluminum foil around the buret because silver nitrate is photosensitive, it will precipitate when exposed to light. 2. 0.8 nitric acid is added to neutralize the solution. 3. The Mohr titration should be carried out under conditions of pH 6.5-9. At a higher pH, silver hydroxide ions, which is brownish in color, might be precipitated which will mask the endpoint. At a lower pH, dichromate ions are formed. The chromate-ion concentration is reduced and the solubility product of silver chromate may not be exceeded. 4. Because sodium lauryl sulfate is the analyte used, do not shake the erlenmeyer flask as it will form a foam which will mask the endpoint.
Analyte: Calcium Hydroxide topical solution Molecular Formula: Molecular Weight:
Indicator Used: Hydroxy naphthol blue Color Transition/Endpoint: violet to blue Official Requirement:Calcium hydroxide topical solution is a solution containing in each 100mL not less than 140mg of calcium hydroxide
Analysts: Laquindanum Chiu Oloroso
Type of Titration: Complexometric Assay Type of Reaction: Complexation between EDTA and Calcium Titrant/s: 0.05M EDTA VS Special Conditions: basic medium
Chemical Equation: Na2EDTA + Ca(OH)2 = Ca(EDTA) + 2NaOH Factor: n/a Explanation:
Assay Procedure Pipet 100 mL of Topical Solution in a suitable container, add 50 mL of water, 15 mL of 1N sodium hydroxide, and 300 mg of hydroxynaphthol blue, and titrate with 0.05 M edetate disodium VS to a blue endpoint. Each mL of 0.05 M edetate disodium is equivalent to 3.705 mg of calcium hydroxide [Ca(OH)2] eason/s For Important Steps: R 1. The sodium hydroxide alkalinize the solution to a pH of about 13, so that the Ca-EDTA complex would be stable and any magnesium which might be present as a contaminant would not react. 2. Add small amount of indicator to enable to see the color change clearly 3. Be careful with the temperature, solubility of calcium hydroxide varies with the temperature for which it is stored, being about 170mg/mL at 15oC and less at higher temperature. The official concentration is based upon a temperature of 25oC (Remmington) 4. Wash down the sides to get every solution that splattered on the beaker. (middle Tennessee state university, n.d) 5. EDTA is a stronger Complexing agent than the indicator, and displaces the indicator from the metal ion allowing the indicator to return its original color 6. Hydroxynaphthol blue is used as indicator because it is specific for calcium determination.
Analyte: Ammonium Alum Molecular Formula: AlNH4(SO4)2 Molecular Weight: 237.133 g/mol Indicator Used: Dithizone TS Color Transition/Endpoint: Purplish-green to bright rose pink Official Requirement: Ammonium Alum contains not less than 99.0% and not more 100.5% of AlNH4(SO4)2, calculated on the dried basis.
Type of Titration: Residual with blank determination Type of Reaction: Complexation reaction Titrant/s: Back-titrant: 0.05 M Zinc Sulfate Excess titrant: 0.05 M EDTA Special Conditions:
Chemical Equation: Factor: n/a Explanation: Pre-lab computation: Wt. (AlNH4(SO4)2) = 237.15 g/mol 0.05 M x (50.0 mL − 20 mL) x 1000 Wt. (AlNH4(SO4)2) = 0.3557 g Post-lab computation:
RFIS: 1. Complexometric titration (residual) generally performs when the metallic ions form a stable complex with EDTA in a slow reaction or when a metal ion blocks an indicator. The blocked indicator cannot release metallic ions. Thus, no color change will be observable at the endpoint of the complexometric (direct) titration. 2. The buffered solution was heated to increase the buffer formation and the complex formation. This was to ensure that the entire Aluminum has been complexed and only excess EDTA existed in solution.
Analyst: Nacar
Analyte: Alumina & Magnesia Oral Suspension (for Al(OH)3) Molecular formula: Al(OH)3 Molecular weight: 78 g/mol Indicator used: Dithizone TS
Assay Procedure Transfer about 800 mg of Ammonium Alum, accurately weighed to a 400 mL beaker, moisten with 1 mL of glacial acetic acid, and add 50 mL of water, 50.0 mL of disodium edetate titrant, and 20 mL of acetic acid-ammonium acetate buffer TS. Warm on a steam bath until solution is complete, and boil gently for 5 minutes. Cool, add 50 mL of alcohol and 2 mL of dithizone TS, and titrate with 0.05 M zinc sulfate VS to a bright rose-pink color. Perform a blank determination and make any necessary correction. Each mL of 0.05 M disodium edetate titrant is equivalent to 11.86 mg of AlNH4(SO4)2
Type of Titration: Residual w/ blank determination Type of Reaction: Complexation reaction
Chemical Equation: a. Alumina with hydrochloric acid Al(OH)3 + HCl → AlCl3 + H2O b. Excess Na2EDTA with aluminum chloride
Assay Procedure Sample Solution: transfer a volume of oral suspension, previously well shaken in its original container, equivalent to 1200 mg of aluminum
Color Transition/Endpoint: green-violet to rose-pink
AlCl3 + Na2EDTA → Al-EDTA + NaCl Titrants: Excess - 0.05M Disodium EDTA Back - 0.05M Zinc Sulfate
Official Requirement: Alumina & Magnesia Oral Suspension is a mixture Special Conditions: slightly containing aluminum hydroxide [Al(OH)3] and magnesium acidic hydroxide [Mg(OH)2]. It contains the equivalent of NLT 90.0% AND NMT 110.0% of aluminum hydroxide [Al(OH)3] and magnesium hydroxide [Mg(OH)2]
Analyte: Alumina & Magnesia Oral Suspension (for Mg(OH)3)
Type of Titration: Residual w/ blank determination
c. Excess Na2EDTA back titrated with zinc sulfate Na2EDTA + ZnSO4 → Zn-EDTA + Na2SO4 Factor: N/A Pre-lab Computation: moles Weight of analyte = 0.05 10000 x (25-10mL) x 1 mol Al(OH)3 78g/mol x ( 1 mol ZnSO4 ) = 0.0585 g of aluminum hydroxide 0.0585 g x 10 mL = 250 mL 250 mL = sample solution x= 1.4625 g of suspension Labelled claim : 225mg/5mL 5mL 1.4625 g x 0.225 g = 32.5 mL of suspension Post-Lab Computation:
Chemical Equation: a. Magnesia with hydrochloric acid
hydroxid, to a suitable beaker. Add 20mL of water, stir, and slowly add 10mL of hydrochloric acid. Heat gently, if necessary, to aid solution, cool, and filter into a 200-mL volumetric flask. Wash the filter with water into the flask and add water to volume. Analysis: pipet 10mL of water, then add, in the order named and with continuous stirring, 25.0 mL of Edetate disodium titrant and 20 mL of acetic acid-ammonium acetate buffer TS, and heat near the boiling point for 5 minutes. Cool, add 50 mL of alcohol and 2 mL of dithizone TS and mix. Titrate the excess edetate disodium with 0.05M zinc sulfate CS until the color changes from green-violet to rose pink. Perform a blank determination, substituting 10mL of water for the sample solution and make any necessary correction. Each mL of Edetate disodium titrant consumed is equivalent to 3.900mg of aluminum hydroxide [Al(OH)3] RFIS 1. HCl solubilizes aluminum hydroxide by forming aluminum chloride. HCl must be added until solution becomes clear. 2. Filter the sample to filter out any impurities present in the sample 3. Acetic acid-ammonium acetate buffer is added to adjust to the pH in which the complex formed is more stable. This will also minimize change of pH throughout the titration. The ammonium acetate in the buffer prevents precipitation of the hydroxide. 4. Solution is heated near boiling point to stabilize the metal-EDTA complex, since the reaction of aluminum and EDTA is slow 5. Alcohol ensures the solubility of the dithizone 6. Dithizone TS is the indicator used because it is specific with zinc. Procedure: Sample Solution:
Molecular formula: Mg(OH)3 Molecular weight:58.32 g/mol Indicator used: Eriochrome Black T Color Transition/Endpoint: red to blue solution
Type of Reaction: Complexation reaction Titrants: 0.05M Disodium EDTA
Official Requirement: Alumina & Magnesia Oral Special Conditions: basic Suspension is a mixture condition containing aluminum hydroxide [Al(OH)3] and magnesium hydroxide [Mg(OH)2]. It contains the equivalent of NLT 90.0% AND NMT 110.0% of aluminum hydroxide [Al(OH)3] and magnesium hydroxide [Mg(OH)2]
b.
Mg(OH)2 + 2HCl → MgCl2 + 2H2O
Factor: N/A Pre-lab Computation: Label claim: 250mg/5mML Mg(OH)2 250mg/5mL = 1200mg/x x= 30mL Mg(OH)2 Sample solution: 1200mg/250mL = 40mg/x x= 8.33mL sample solution
Post-Lab Computation:
Transfer a volume of Oral suspension, previously well shaken in its original container, equivalent to 1200 mg of magnesium hydroxide, to a suitable beaker. Add 20 ml of water, stir, and slowly add 10 ml of HCl. Heat gently, if necessary, to aid solution, cool, and filter into a 200 ml volumetric flask. Wash the filter with water into the flask and add water to volume. Analysis: Pipet a volume of the sample solution, equivalent to 40 mg of magnesium hydroxide, into a 400 ml beaker. Add 20 ml of water and 20 ml of triethanolamine and stir. Add 10 ml of ammonia-ammonium chloride buffer TS and add 3 drops of an eriochrome black indicator solution (prepared by dissolving 200 mg of eriochrome black T in a mixture of 15 ml of triethanolamine and 5 ml of dehydrated alcohol), and mix. Cool the solution to between 3 and 4 degrees by immersion of the beaker in an ice bath, then remove, and titrate with 0.05M disodium EDTA VS to a blue endpoint. Perform a blank determination, substituting 10 ml of water for the sample solution, and make any necessary correction. Each ml of 0.05M disodium EDTA consumed is equivalent to 2.916 mg magnesium hydroxide. RFIS: 1. The ammonia-ammonium chloride buffer is used to adjust the pH of the solution (pH 10) because the pH must not be too high or the metal hydroxide may precipitate, causing the reaction with EDTA to be very slow (Christian, 2014). 2. pH should be monitored an important because it affects the stability of the complex formed between the indicator ad metal ion, as well as between EDTA and the metal ion (Christian, 2014).
3.
In Edta titrations/reactions, high temperature of solution promotes the ionization of the complex making it unstable that is why the solution is must be cooled between 3 and 4 degrees (Christian, 2014). 4. Triethanolamine is added as a masking agent. TEA will impart enough alkalinity to suppress Al-EDTA complexation in the presence of a Mg-EDTA reaction.
Analyte: Milk of Magnesia Molecular formula: Mg(OH)2 Molecular weight: 58.32 g/mol Indicator used: Eriochrome black TS Color Transition/Endpoint: red to blue color
Type of Titration: Direct titration Type of Reaction: Complexation reaction Titrants: 0.05M Disodium EDTA
Special Conditions: slightly Official Requirement: Milk of Magnesia is a basic suspension of Magnesium Hydroxide. Milk of Magnesia, Double-strength Milk of Magnesia and Triple-strength Milk of Magnesia contain not less than 90.0% and not more than 115.0% of the labeled amount being 80, 160, and 240 mg of Mg(OH)2 per mL, respectively. It may contain not more than 0.05% of a volatile oils, suitable for flavoring purposes.
Chemical Equation:
Factor: N/A Pre-lab Computation: Post-Lab Computation:
Assay Procedure Transfer an accurately measured quantity of Milk of Magnesia, previously shaken in its original container, equivalent to about 800 mg of magnesium hydroxide, to a 250 mL volumetric flask. Dissolve in 30 mL of 3N hydrochloric acid, dilute with water to volume and mix. Filter, if necessary, and transfer 25.0 mL of the filtrate to a beaker containing 75 mL of water, and mix. Adjust the reaction of the solution with 1N sodium hydroxide to a pH of 7 (using pH indicator paper), add 5 mL of ammonia-ammonium chloride buffer TS and 0.15 mL of eriochrome black TS and titrate with 0.05M edetate disodium TS to a blue endpoint. Each mL of 0.05M edetatate disodium is equivalent to 2.916 mg of Mg(OH)2. RFIS 1. Shake or mix the Milk of Magnesia before using - MoM is a white opaque suspended solution. Shaking or mixture is done to ensure representativeness of the sample by having equal distribution of particles that are dispersed throughout the suspension. 2. Dissolve milk of magnesia in 3N HCl, dilute w/ water and mix - secures the complete neutralization of Mg(OH)2, which is waterinsoluble. This will produce a clear solution when neutralization is complete.
3. Adjust reaction of the solution w/ 1N NaOH to a pH of 7 -the excess acid will be reacting with sodium hydroxide and the solution will be basic until pH 7 because Eriochrome black T is blue at pH 6 to 12, which is the target endpoint for this assay. 4. +ammonia-ammonium chloride buffer TS -titration of magnesium with EDTA is done at pH 10 or basic solutions, using ammonia-ammonium chloride buffer. The pH must not be too high or the metal hydroxide may precipitate, causing the reaction with EDTA to be very slow. (Christian, 2004, p. 335) 5. eriochrome black T as indicator - a typical indicator. It contains three ionizable protons, so we will represent it by H3In. This indicator can be used for the titration of Mg2+ with EDTA. A small amount of indicator is added to the sample solution, and it forms a red complex with part of the Mg2+; the color of the uncomplexed indicator is blue. As soon as all the free Mg2+ is titrated, the EDTA displaces the indicator from the magnesium, causing a change in the color from red to blue. 6. 0.05M edetate disodium as titrant -widespread use of its ability to form chelates with all cations but also because most of these chelates are sufficiently stable for titrations.
Analyte: Mercuric Sulfate Molecular formula: HgSo4 Molecular weight: 296.65 g/mol Indicator used: ferric nitrate
solution
Color Transition/Endpoint:Reddish-
Type of Titration:Direct
Chemical Equation:
Assay Procedure
Titration ( Modified Volhard) Type of Reaction: precipitation reaction
HgSo4 + 2HNo3 → Hg(No3)2 + H2So4 Hg(No3)2 + 2NH4SCN →Hg(SCN)2 + 2NH4NO3
Titrants: 0.1 N Ammonium
When all metallic ion has been precipitated as thiocyanate, the thiocyanate will react to ferric nitrate to form red ferric thiocyanate
weigh accurately about 500 mg, and dissolve in 50 mL of dilute Nitric acid (1 in 2). Add 1 ml of ferric nitrate solution (1 in 10), and titrate with 0.1 N Ammonium thiocyanate consumed is equivalent to 10.03 mg of Hg
Thiocyanate
Fe(No3)3 + 3NH4SCN →Fe(SCN)3 + 3(NH4)No3
brown solution Official Requirement:
Mercuric sulfate contains not less than 67 % and not more than 67.5 % of Hg
Special Conditions:
Solution must be Acidified
Factor: 2 because mercuric ion has a valence
of 2
Pre-lab Computation: Analyst: Ham Argana Robles
0.1N x 30mL x 296.65 g/mol 1000 x 2 = 0.4449 g
Post-Lab Computation: N/A
RFIS:
1. Use of Dilute Nitric Acid - According to Knevel, A.M & Digang F.E. (1977) nitric acid is used because it needed an environment of acidic to prevent hydrolysis of that ferric salts undergo in neutral solutions, and mercury dissolves slowly in dilute nitric acid to form mercury(I) nitrate, mercurous nitrate, Hg2(NO3)2. According to Webelement.com (n.d.) 2. Use of 1 ml ferric Nitrate solution - According to chem.uiuc.edu (n.d.) the ferric ion of ferric nitrate solution was used as an indicator and will react to the thiocyanate ion to form a red ferric thiocyanate 3. Performed at Low temperature - titration must be done below 25 C since the ferric thiocyanate complex fades at high temperature
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