FST Lab 9 (Determination of titratable acidity)

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LAB – 9 

OBJECTIVE: 

Determination of titratable acidity of milk sample. 

REQUIREMENT: 

  • Analytical balance. 

  • Burette. 

  • 100ml conical flask. 

  • 20 ml pipette, other sizes may be used

CHEMICALS: 

  • 0.1 N NaOH

  • Phenolphthalein

  • 96% Ethanol

THEORY: 

Titratable Acidity (Definition): Titratable acidity is the measure of total acid content in a solution, determined by titration with a base solution to a specific endpoint, expressed in units of concentration. 

TYPES:

1. Total titratable acidity (TTA): Measures the total amount of acid present in a sample, including both volatile and non-volatile acids.

2. Volatile acidity (VA): Specifically measures the amount of volatile acids, such as acetic acid, in a sample.

3. Non-volatile acidity (NVA): Measures the number of non-volatile acids, such as citric acid, in a sample.

4. Free acidity: Represents the amount of unbound or free acid present in a sample.

5. Fixed acidity: Refers to the amount of acid present in a sample that is not easily volatilized or removed.

IMPORTANCE: Titratable acidity is important for assessing the quality, freshness, and stability of food and beverages. It helps determine flavor balance, preservation, and fermentation processes, particularly in products like wine.

PROCEDURE: 

  • Weigh 10ml juice sample in conical flask.

  • Add 250ml distilled water.

  • Titrate with 0.1 M sodium hydroxide, using few drops of phenolphthalein indicator.


OBSERVATION:  wt. of citric acid = 0.1 M 


TRIALS

INITIAL

FINALS

DIFFERENCE

1

0

59

59

2

59

180

21

3

80

137

57


CALCULATION:

  • Molecular Wt. of citric acid= 192.43 gm 

  • Weight of citric acid= 0.1 M of NaOH * Vol of NaOH * 192.43/3

  • 2% of the total activity= weight of acid/ weight of sample * 100

0.1*60*192.43/3= 384.6g

384.6/25*100=1538.4%


RESULT: The percentage of titratable acidity in a milk sample is 1538.4%.


DISCUSSION: 

The purpose of our experiment is to determine the titratable acidity of a milk sample. Titratable acidity measures the total amount of acid in a solution that can be neutralized by a base. This parameter is crucial for assessing the acidity level in food and beverages, as it affects taste, preservation, and shelf stability. The standard value for total acidity in milk typically ranges from 0.15% to 0.2%. However, our experiment found the total acidity to be 2.9%, which is significantly higher. This discrepancy may be due to a machine error.

STUDY QUESTIONS: 

Q1) How does the titratable acidity of juice relate to its freshness and spoilage?

Ans: When juice becomes older or spoils, its titratable acidity increases due to the presence of organic acids produced by microorganisms, indicating a decrease in freshness and an increased risk of spoilage.



Q2) What are some factors that can affect the titratable acidity of juice during spoilage?

Ans: During spoilage, factors such as microbial activity, enzymatic reactions, and the breakdown of sugars can contribute to an increase in the titratable acidity of juice.


Q3) What is the purpose of standardizing the NaOH solution before titration?

Ans: The purpose of standardizing the NaOH solution before titration is to accurately determine its concentration, ensuring precise and reliable results during the titration process.

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