Quantitative Analysis Part 1

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Topic: Determination of pKa and pI values of an amino acids by Titrimetic method

1. What are Proteins?

Ans: Proteins are the most abundant organic molecules of the living system. They occur in every part of the cell and constitute about 50% of the cellular dry weight. Proteins are organic substances of high molecular weight formed by a number of amino acids united by a peptide linkage.

2. Define pH?

Ans: It is the inverse logarithm of hydrogen ion concentration or it is the logarithm of hydrogen ion concentration (or) is the logarithm of the reciprocal of hydrogen ion concentration.

                              pH = -log[H+] = log 1 / [H+]

3. Define Buffer?

Ans: It is a mixture of weak acids with their salts of strong bases and resists and sudden changes in hydrogen ion concentration even after the addition of hydrogen (or) hydroxyl ions.

4. What is the Principle of amino acid pKa and pI values determination experiment?

Ans: Every amino acids has two ionizable groups namely COOH (Carboxyl group) and NH3 (amino group). These ionizations are shown as:

-COOH  –> COO + H+ ————-(1)

-NH2 + H+ –>  -NH3+ ————-(2)

Since H+ takes part in both above ionization reaction the process is pH dependent. At very high pH ion concentration is at low at pH value: reaction (1) will be pushed backward and reaction (2) pushed forward.

5. What do mean by the Isoelectric pH (pI) of an amino acid?

Ans: The isoelectric pH is the pH midway between pK values on either side of the isoionc species.

              pK1 + pK2

pI = ————————


6. What are ampholytes (or) Zwitter ions?

Ans: The amino acids forming proteins contain both acidic and basic groups and react with both alkalies and acids to form salts. These amino acids are amphoteric and are called Ampholytes (or) Zwitter ion.

7. Why are the Amino acids Ornithine, Cirtulline, Arginosuccinic acid not found in the classification of amino acids?

Ans: Because they are not involved in proten formation but they fulfil important roles in metabolisc process.

8. Define amino acid?

Ans: It is the hydrolytic product of protein. It has at least one amino group and a carboxyl group. The amino group is attached to the alpha (a) carbon atom of this acid.

9. What is the importance of Indicator?

Ans: It indicates the completion of the reaction by changing one color to another color.

10. Mention the sensitivity of Phenapthalein indicator?

Ans: Sensitivity between pH 8.0 to 10.0.

11. What is the molecular weight of Glycine?

Ans: The molecular weight of Glycine is 75.07

12. Write the molecular formula of Glycine?

Ans: the molecular formula of Glycine is C2 H5 O2 N.

       (NH2 CH2 COOH).

13.What is the IUPAC name of the Glycine?

Ans: Amino acetic acid

14.. Write the molecular formula and molecular weight of the Sodium Hydroxide?

Ans: NaOH; 40.00

15. What the molecular formula, molecular weight, specific gravity and Molarity of the Hydrochloric acid?

Ans: Molecular formula- HCl; Molecular weight-36.46, Specific gravity-1.18, Molarity – 11.6

16. What is Molarity (M) ?

Ans: The number of moles of solute per litre of solution

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