experiment 5: determination of ascorbic acid in vitamin C tablets by acid-base titration

Question 1

title of experiment

Answer 1

determination of ascorbic acid in vitamin C tablets by acid-base titration

Question 2

vitamin C or ascorbic acid is a _____ acid

Answer 2

water soluble

Question 3

where can vitamin C or ascorbic acid be found

Answer 3

chili pepper
guava
citrus fruits (lemon & oranges)

Question 4

what happens if there is deficiency in vitamin C

Answer 4

scurvy

Question 5

how can the amount of ascorbic acid in vitamin C be determined

Answer 5

direct titration with a standardized solution of NaOH

Question 6

what does not affect the results of the analysis in the tablet

Answer 6

excipients like fillers and binder

Question 7

it relies on the basic principles of stoichiometry to determine the exact amount of pure substances present in a sample

Answer 7

titrimetric sample

Question 8

scribe the process of titrimetric sample

Answer 8

it is the gradual addition of a solution of known concentration (titrant/ standard solution) with an unknown concentration (analyte)

Question 9

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

Answer 9

equivalence point

Question 10

the equivalence point coincides (occur at the same time) with the ____, which is observed when an indicator gives a ____

Answer 10

end point
sharp color change

Question 11

what indicator will be used

Answer 11

phenolphthalein

Question 12

briefly explain how phenolphthalein changes color

Answer 12

colorless to pink (acid to basic)
pink to colorless (basic to acid)

Question 13

what is the signal of the end of titration in direct titration of vitamin C with NaOH

Answer 13

appearance of persistent faint pink

Question 14

briefly explain back-titration

Answer 14

excess of standard NaOH solution can be added to the sample then titrated with the standard HCI soln. until color is light pink

Question 15

what will be standardized from previous experiment

Answer 15

prepared NaOH soln. with a concentration of 0.1 M NaOH

Question 16

the prepared NaOH soln. with a concentration of 0.1 M NaOH will be titrated against _____ to determine the exact concentration of _____

Answer 16

known amt of dried potassium hydrogen phthlalate
dilute NaOH

Question 17

formula of direct titration

Answer 17

mass = M NaOH x V NaOH x molar mass ascorbic acid

Question 18

formula of back-titration

Answer 18

mass = [(M excess NaOH x V excess NaOH) – (M HCl x V HCl)] x molar mass ascorbic acid

Question 19

what are the materials that students need to bring

Answer 19

identical brands of 2 500mg vitamin C or ascorbic acid tablets (white-colored tablets only)

Question 20

reagents

Answer 20

phenolphthalein indicator
potassium hydrogen phthalate (KHP) standard – pre-dried and stored in desiccator

Question 21

what is the procedure for day 1

Answer 21

preparation of burette
standardization of dilute NaOH
standardization of dilute HCI

Question 22

what is the procedure for day 2

Answer 22

direct titration of ascorbic acid in vitamin C tablet
back titration of ascorbic acid in vitamin C tablet

Question 23

waste disposal of titrated solutions and excess titrants

Answer 23

poured down the sink
flush with plenty of water

Question 24

what temp and how long should you place the primary standard KPH.
who will conduct the and where will it be placed.

Answer 24

110 °C for 2 hours
placed in a desiccator will be prepared by the lab technician