Title : Acid-base Titration of a Diprotic acid and back titration of Unknown

Abstract:

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The purpose of this laboratory experiment was to perform a direct titration of an unknown diprotic acid with a strong base in order to identify and determine the molecular weight of an unknown acid. Back titration of an unknown compound was performed to determine the weight percent of CaCO3 . The molecular weight of a diprotic acid was …… g/mol and it was identified as …… acid ; Also the weight percent of CaCO3 was calculated to be …… % +/- ……. .

Introduction:
The major aspect of acid-base equilibrium was used during this experiment ; The main laboratory technique that was done during this lab is acid-base titration in which a strong base (NaOH) was titrated with a strong acid (HCl) . Two titration methods were used which are direct and back respectively . Originally an unknown diprotic acid is provided and certain amount of it was diluted and titrated directly with a strong base NaOH ( 0.0214M +/-0.0002) .Calibrated pH electrode was used during the titration procedure to measure the solution’ s associated pH , therefore creating a titration curve. The unknown diprotic acid deprotonates twice with two equivalence points and acid dissociation values ( ka1 , ka2 ) . In order to determine the largest incremental change in pH change by volume , the derivative of the titration curve was used. The equivalence point represents the moles of used NaOH at equivalence point can be traced through stoichiometric relation and basic molecular mass calculation to identify the provided unknown diprotic acid .
H2A (aq) < – – – — – > H+(aq) + HA-(aq) ka1
HA- (aq) < – – – – -> H+(aq) + A2-(aq) ka2
The second part of this laboratory experiment involves the back titration of an unknown mixture (3-3)

Title : Acid-base Titration of a Diprotic acid and back titration of Unknown

Abstract:

The purpose of this laboratory experiment was to perform a direct titration of an unknown diprotic acid with a strong base in order to identify and determine the molecular weight of an unknown acid. Back titration of an unknown compound was performed to determine the weight percent of CaCO3 . The molecular weight of a diprotic acid was …… g/mol and it was identified as …… acid ; Also the weight percent of CaCO3 was calculated to be …… % +/- ……. .

Introduction:
The major aspect of acid-base equilibrium was used during this experiment ; The main laboratory technique that was done during this lab is acid-base titration in which a strong base (NaOH) was titrated with a strong acid (HCl) . Two titration methods were used which are direct and back respectively . Originally an unknown diprotic acid (#839) is provided and certain amount of it was diluted and titrated directly with a strong base NaOH ( 0.0214M +/-0.0002) .Calibrated pH electrode was used during the titration procedure to measure the solution’ s associated pH , therefore creating a titration curve. The unknown diprotic acid deprotonates twice with two equivalence points and acid dissociation values ( ka1 , ka2 ) . In order to determine the largest incremental change in pH change by volume , the derivative of the titration curve was used. The equivalence point represents the moles of used NaOH at equivalence point can be traced through stoichiometric relation and basic molecular mass calculation to identify the provided unknown diprotic acid .
H2A (aq) < – – – — – > H+(aq) + HA-(aq) ka1
HA- (aq) < – – – – -> H+(aq) + A2-(aq) ka2
The second part of this laboratory experiment involves the back titration of an unknown mixture (3-3) with strong base NaOH (0.0214M +/-0.0002) to determine the weight percent of present CaCO3 .During direct titration the volume of titrant and the associated pH are used to find the two ka values. However ,by using stoichiometry the molecular formula of diprotic acid is identified and therefore concentration and molecular weight were calculated. The back titration happens only in presence of excess base added to an analyte which is CaCO3 ; therefore an excess titrant can help to determine the concentration of an analyte. Back titration is useful in finding out the concentration of an insoluble diprotic acid salts such as CaCO3 .
CaCO3(aq) < – – – – > Ca2+(aq) + CO3(aq)2. Ksp = 2.7 x 10 ^ -33 pH= 7.00 25C

.During direct titration the volume of titrant and the associated pH are used to find the two ka values. However ,by using stoichiometry the molecular formula of diprotic acid is identified and therefore concentration and molecular weight were calculated. The back titration happens only in presence of excess base added to an analyte which is CaCO3 ; therefore an excess titrant can help to determine the concentration of an analyte. Back titration is useful in finding out the concentration of an insoluble diprotic acid salts such as CaCO3 .
CaCO3(aq) < – – – – > Ca2+(aq) + CO3(aq)2. Ksp = 2.7 x 10 ^ -33 pH= 7.00 25C

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