experiment 5: determination of ascorbic acid in vitamin C tablets by acid-base titration Flashcards
title of experiment
determination of ascorbic acid in vitamin C tablets by acid-base titration
vitamin C or ascorbic acid is a _____ acid
water soluble
where can vitamin C or ascorbic acid be found
chili pepper
guava
citrus fruits (lemon & oranges)
what happens if there is deficiency in vitamin C
scurvy
how can the amount of ascorbic acid in vitamin C be determined
direct titration with a standardized solution of NaOH
what does not affect the results of the analysis in the tablet
excipients like fillers and binder
it relies on the basic principles of stoichiometry to determine the exact amount of pure substances present in a sample
titrimetric sample
scribe the process of titrimetric sample
it is the gradual addition of a solution of known concentration (titrant/ standard solution) with an unknown concentration (analyte)
it refers to the point when the amount of standard solution added is equivalent to the amount needed to react completely with the unknown sample
equivalence point
the equivalence point coincides (occur at the same time) with the ____, which is observed when an indicator gives a ____
end point
sharp color change
what indicator will be used
phenolphthalein
briefly explain how phenolphthalein changes color
colorless to pink (acid to basic)
pink to colorless (basic to acid)
what is the signal of the end of titration in direct titration of vitamin C with NaOH
appearance of persistent faint pink
briefly explain back-titration
excess of standard NaOH solution can be added to the sample then titrated with the standard HCI soln. until color is light pink
what will be standardized from previous experiment
prepared NaOH soln. with a concentration of 0.1 M NaOH
the prepared NaOH soln. with a concentration of 0.1 M NaOH will be titrated against _____ to determine the exact concentration of _____
known amt of dried potassium hydrogen phthlalate
dilute NaOH
formula of direct titration
mass = M NaOH x V NaOH x molar mass ascorbic acid
formula of back-titration
mass = [(M excess NaOH x V excess NaOH) – (M HCl x V HCl)] x molar mass ascorbic acid
what are the materials that students need to bring
identical brands of 2 500mg vitamin C or ascorbic acid tablets (white-colored tablets only)
reagents
phenolphthalein indicator
potassium hydrogen phthalate (KHP) standard – pre-dried and stored in desiccator
what is the procedure for day 1
preparation of burette
standardization of dilute NaOH
standardization of dilute HCI
what is the procedure for day 2
direct titration of ascorbic acid in vitamin C tablet
back titration of ascorbic acid in vitamin C tablet
waste disposal of titrated solutions and excess titrants
poured down the sink
flush with plenty of water
what temp and how long should you place the primary standard KPH.
who will conduct the and where will it be placed.
110 °C for 2 hours
placed in a desiccator will be prepared by the lab technician
