Experiment 5 Determination of Ascorbic Acid in Vitamin C Tablets by AcidBase Titration

Question 1

a water soluble acid commonly found in guava, chili pepper and citrus fruits such as lemons and oranges.

Answer 1

Vitamin C or ascorbic acid

Question 2

Vitamin C or ascorbic acid a water soluble acid commonly found in _____, chili pepper and citrus fruits such as _____and ______.

Answer 2

guava
lemons
oranges

Question 3

Deficiency in Vitamin C leads to ____.

Answer 3

scurvy

Question 4

The amount of ascorbic acid in Vitamin C tablets can be accurately determined by direct _____ with a standardized solution of _______.

Answer 4

titration
NaOH

Question 5

The presence of excipients like _____ and ________ in the tablet does not affect the results of the analysis.

Answer 5

fillers
binders

Question 6

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

Answer 6

Titrimetric analysis

Question 7

It involves the ____ addition of a solution of known concentration (titrant or standard solution) to a measured volume of a _________ with an unknown concentration or to a weighed amount of the sample ________in a given solution (analyte).

Answer 7

gradual
solution
dissolved

Question 8

_________ 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 8

Equivalence point

Question 9

Equivalence point refers to the point when the amount of __________ added is equivalent to the amount needed to react completely with the ________ .

Answer 9

standard solution
unknown sample

Question 10

the equivalence point coincides with the end point, which is observed when an indicator gives a ______ color change.

Answer 10

sharp

Question 11

both direct and back ____ will be performed. ________ is the indicator that will be used.

Answer 11

titration
Phenolphthalein

Question 12

It changes color from colorless to pink when the acidic solution turns basic and the other way around when the basic solution turns acidic.

Answer 12

Phenolphthalein

Question 13

In direct titration of ____with NaOH, the appearance of persistent faint pink signals the end of ______.

Answer 13

Vitamin C
titration

Question 14

an excess of standard NaOH solution can be added to the sample and then titrated with standard HCl solution until the color is ___________. This technique is known as ___________ .

Answer 14

light pink
back titration

Question 15

The prepared NaOH solution from previous experiment with a concentration close to ___________ will be standardized.

Answer 15

0.1 M NaOH

Question 16

It will be titrated against a known amount of _______________ (KHP, HC8H4O4K) to determine the exact concentration of dilute NaOH.

Answer 16

dried potassium hydrogen phthalate

Question 17

The mass of ascorbic acid (HC6H7O6) in the tablet can be calculated using
the following formula:

For direct titration:

Answer 17

mass = MNaOH x VNaOH x molar mass ascorbic acid

Question 18

For back titration:

Answer 18

mass = [(Mexcess NaOH x Vexcess NaOH) – (MHCl x VHCl)] x molar mass ascorbic acid

Question 19

How many and mg of Vitamic C?

Answer 19

2pcs 500 mg Vitamin C or ascorbic acid tablets

Question 20

Reagents:

Answer 20

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

Question 21

Instrument:

Answer 21

analytical balance

Question 22

A. Preparation of Burette

2. Clean both burettes by rinsing it twice (_______ mL) with distilled water using wash bottle.

Answer 22

~5-10 mL

Question 23

A. Preparation of Burette

6. After rinsing, fill up each burette with its corresponding titrant up to the zero mark. Make sure to read properly using eye level and lower meniscus. Remove any air bubbles in the burette. Ask the assistance of your teacher when reading the burette and recording the volume. Record the volume to nearest ______ mL

Answer 23

±0.01

Question 24

7. Please remember not to waste the titrants. If the amount of the titrant will not be enough for the entire experiment, repeat the process from solution preparation to _________ .

Answer 24

standardization

Question 25

B. Standardization of Dilute NaOH

The primary standard KHP was dried at
________ °C for _____ hours and placed in a _______ will be prepared by the lab technician/custodian

Answer 25

110 °C
2 hours
desiccator

Question 26

B. Standardization of Dilute NaOH

4. Titrate the KHP solution with the NaOH solution (titrant inside the burette) until the appearance of a faint _______ color that persists for ______________ Show and have the color of the solution to be validated by the teacher so that in the succeeding trials, you know it already

Answer 26

pink
30 seconds

Question 27

C. Standardization of Dilute HCl

This can be performed without waiting for the calculated concentration of standardized _______. Calculations can be done later. Gather data first.

Answer 27

standardized NaOH

Question 28

C. Standardization of Dilute HCl

2. Add 35 mL of distilled water and 2 drops of __________________ .

Answer 28

phenolphthalein indicator

Question 29

PROCEDURE for DAY 1

Answer 29

A. Preparation of Burette
B. Standardization of Dilute NaOH
C. Standardization of Dilute HCl