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CHEM 104 LAB 4
Notebook
Experiment
Title: Molarity
Vit C
Purpose: To understand solutions and concentrations, as well as
determine Molarity and mg/ml of Vit C through titrations.
Procedure:
Titration #1: Use a known amount of Vit C from commercial source of
Iodine(I 2
) to determine concentration of I 2
- Weight out approximately 0.5g of Vit C standard into volumetric flask.
- Dilute with water to 250 ml.
- Take 10 ml sample of Vit C solution and add 2 to 3 drops of
acetic acid (source of H+ to help solidify solution) and starch
(for color indication)
Titrate with I 2
- Record ml of I 2
required to reach endpoint.
Titration #2: Use predetermined concentration of I 2 to determine
Molarity and mg/ml of Vit C in orange juice
- Add 20 ml of orange juice to flask and dilute with water to 50 ml
- Take 10 ml of orange juice solution and add 2 to 3 drops of
acetic acid (source of H+ to help solidify solution) and starch
(for color indication)
- Titrate with I 2
- Record ml of I required to reach endpoint.
Titration #3: Use predetermined concentration of I 2
to determine
Molarity and mg/ml of Vit C in lemon juice
- Add 20 ml of lemon juice to flask and dilute with water to 50 ml
- Take 10 ml of lemon juice solution and add 2 to 3 drops of
acetic acid (source of H+ to help solidify solution) and starch
(for color indication)
- Titrate with I 2
- Record ml of I 2
required to reach endpoint.
Titration #3: Use predetermined concentration of I 2
to determine
Molarity and mg/ml of Vit C in lime juice
- Add 20 ml of lime juice to flask and dilute with water to 50 ml
- Take 10 ml of lime juice solution and add 2 to 3 drops of
acetic acid (source of H+ to help solidify solution) and starch
(for color indication)
Titrate with I 2
Record ml of I 2
required to reach endpoint.
mol I 2 = mol Vit C in lime juice (based on balanced equation)
= 0.0000455 mol Vit C / 0.020 L = 0.002275 M Vit C
0.0000455 mol Vit C x (176.12 g/mol) x (1000 mg/1g) = 8.
mg/20mL = 0.4004 mg/mL Vit C in lime juice
Conclusions:
We gained a better understanding of solutions and concentrations by
titrating orange, lemon, and lime juice with a predetermined I 2
concentration. We were able to evaluate the amounts of Vit C in the
juices, and found that orange juice has the highest concentration of
Vit C out of the juices.
Notes:
Endpoint of titration #1 (Vit C standard and I
2
): light shade of
greyish/blue purple
Endpoint of titration #2 (Orange juice and I 2
): blueish green due
to pulp
Endpoint of titration #3 (Lemon juice and I 2
): darkish blue/green
Endpoint of titration #4 (Lime juice and I ): light blue
