Experiment 19 Titration

Question 1

Experiment 19

Answer 1

Titration: Determination of the Vitamin C content of citrus juices

Question 2

is a WATER-SOLUBLE vitamin that is present in foods such as CITRUS FRUIT and GREEN VEGETABLES

Answer 2

Vitamin C or ascorbic acid

Question 3

It is CHEMICALLY UNSTABLE because it is a STRONG REDUCING AGENT and can be deactivated by a wide range of oxidizing agents

Answer 3

Vitamin C or ascorbic acid

Question 4

The FORMULA for ascorbic acid is

Answer 4

C6H8O6

Question 5

Oxidized form of ascorbic acid

Answer 5

Dehydroascorbic acid

Question 6

The experiment studies ______________ concentration in different brands of COMMERCIAL CITRUS JUICES

Answer 6

Vitamin C

Question 7

The AMOUNT of ascorbic acid can be DETERMINED by a REDOX TITRATION with a standardized SOLUTION OF

Answer 7

Iodine

Question 8

The iodine is REDUCED by the ascorbic acid to form

Answer 8

IoDIDE

Question 9

The TITRATION END POINT is reached when a ___________________ is added to the ascorbic acid solution

Answer 9

Slight excess of IODIDE

Question 10

is used to DETERMINE the ENDPOINT

Answer 10

Starch

Question 11

Objectives

Answer 11

1. To determine the CONCENTRATION of Vitamin C in a sample of citrus juices
2. To learn the TECHNIQUE of titration

Question 12

Apparatus

Answer 12

125-mL Erlenmeyer flask
10-mL graduated cylinder
buret
buret clamp
medicine droppers

Question 13

Materials

Answer 13

Citrus juice sample
0.01N Iodine (I2) solution
1% starch
6N Acetic acid (CH3COOH)

Question 14

Procedure

Answer 14

1. Measure 25 mL of the the JUICE SAMPLE into the 125-mL erlenmeyer flask
2. Add 2 mL of Acetic acid, 3 mL of 1% starch, and 10 mL of water
3. Clean an ACID BURET and RINSE it with a SMALL AMOUNT of the standard solution (0.01 Iodine). Fill it with standard solution
4. Drain it to just BELOW the FIRST VOLUME MARK . Ensure that there are no air bubbles at the TIP of the buret. Read and record the INITIAL VOLUME
5. Add slowly the Iodine solution from the acid buret to the sample, SWIRLING the flask DURING each ADDITION. Stop adding the IODINE when the contents of the flask turn BLUE BLACK. Record the FINAL VOLUME of the iodine solution
6. Make 2 DETERMINATIONS
7. Calculate the concentration of vitamin C in g/mL sample

Question 15

Formula

Answer 15

g Vit. C/mL =

Volume of sample x 2000

Question 16

N

Answer 16

Normality concentration

Question 17

Dilution equation

Answer 17

N1 V1 = N2 V2

Question 18

N2=

Answer 18

V2

Question 19

N2

Answer 19

Concentration of Iodine in sample

Question 20

V1

Answer 20

Initial volume on the buret; mL

Question 21

V2

Answer 21

Final volume remained in the buret; mL

Question 22

N1

Answer 22

Initial concentration of iodine (0.01 I2)

Question 23

Round off answers to

Answer 23

4 decimal places

Question 24

Blue black

Answer 24

Lugol’s reagent