FYUG Even Semester Exam, 2025

CHEMISTRY (Basic Analytical Chemistry)

Course No.: CHMSEC-151

Full Marks: 50 | Pass Marks: 20 | Time: 2 Hours

UNIT-I

1. (a) Define the term relative error. 1

Relative error is the ratio of the absolute error of a measurement to the true or accepted value, often expressed as a percentage or parts per thousand.

1. (b) What is retention factor in chromatography? 1

The retention factor (Rf) is the ratio of the distance traveled by the solute to the distance traveled by the solvent front in a chromatographic separation.

1. (c) What do you mean by significant figures in analytical measurements? 1

Significant figures are the digits in a measured value that are known with certainty plus one final digit that is somewhat uncertain or estimated.

1. (d) What is the role of a developing reagent in chromatography? 1

A developing reagent is used to visualize colorless spots on a chromatogram by reacting with the separated components to form colored products.

2. (a) Differentiate between accuracy and precision in analytical measurements. 2

Accuracy Precision
Refers to how close a measured value is to the true or accepted value. Refers to the closeness of agreement between a series of measurements obtained in the same way.
Determined by systematic errors. Determined by random errors.

2. (b) What are the different types of errors in analytical chemistry? 2

Errors are generally classified into two types: Determinate (Systematic) Errors, which have a definite value and assignable cause (e.g., instrumental or personal errors), and Indeterminate (Random) Errors, which arise from uncontrollable variables in the measurement.

3. (a) Explain the concept of sampling in analytical chemistry. Why is it important? 5

Sampling is the process of collecting a small portion of a material that is truly representative of the entire bulk (population) being studied.

  • Process: It involves defining the population, collecting a gross sample, and reducing it to a laboratory-sized sample without changing its composition.
  • Importance: Analytical results are only as good as the sample; if the sample is not representative, even the most accurate laboratory analysis will lead to incorrect conclusions about the bulk material.

3. (b) Describe the principle and procedure of thin layer chromatography. 5

Principle: TLC is based on the differential adsorption of components of a mixture between a stationary phase (usually silica gel or alumina coated on a plate) and a mobile phase (solvent) that moves up the plate by capillary action.

Procedure:

  1. A small spot of the sample is applied near the bottom of the TLC plate.
  2. The plate is placed in a developing chamber containing a small amount of mobile phase.
  3. As the solvent rises, components move at different rates based on their affinity for the phases.
  4. Once the solvent reaches near the top, the plate is removed, dried, and visualized (using UV light or reagents).

UNIT-II

4. (a) What are the major components of soil? 1

Soil is composed of mineral matter, organic matter (humus), water, and air.

4. (b) What is the purpose of using an indicator in complexometric titrations? 1

The indicator (usually a metallochromic indicator) changes color at the equivalence point when it is displaced from the metal ion by the stronger chelating agent (like EDTA).

4. (c) Name one commonly used chelating agent in complexometric titrations. 1

Ethylenediaminetetraacetic acid (EDTA) is the most common chelating agent used.

4. (d) What is chelation? 1

Chelation is the formation of a stable, ring-like structure between a metal ion and a multidentate ligand (chelating agent) that provides multiple points of attachment.

5. (a) Explain the principle and procedure of pH measurement in soil analysis. 2

Principle: Soil pH is measured to determine the acidity or alkalinity of the soil solution, which affects nutrient availability.

Procedure: A soil-water suspension is prepared (usually in a 1:2 or 1:5 ratio), stirred thoroughly, allowed to settle, and the pH of the supernatant is measured using a calibrated pH meter.

6. (b) What is complexometric titration and how is it applied in soil analysis? 5

Complexometric titration is a form of volumetric analysis where the formation of a colored complex is used to indicate the end point of a titration.

Application in Soil: It is primarily used to determine the concentration of metal ions such as Calcium (Ca2+) and Magnesium (Mg2+), which represent soil hardness and essential plant nutrients. [span_28](start_span)EDTA is typically titrated against a soil extract using Eriochrome Black T (EBT) as an indicator.[span_28](end_span)

UNIT-III

7. (a) What is the role of boric acid in cosmetics? 1

Boric acid acts as a mild antiseptic, preservative, and pH buffering agent in various cosmetic products.

8. (a) What is the role of ZnO in talcum powder? 2

Zinc Oxide (ZnO) serves as a mild astringent, provides a soothing effect on the skin, and acts as a physical UV filter to protect against sun exposure.

9. (a) Discuss the major and minor constituents of cosmetics and their functions. 5

Major Constituents:

  • Vehicles/Solvents: Water or alcohol used to dissolve other ingredients.
  • Surfactants: Used for cleansing and emulsification (e.g., in shampoos).
  • Emollients: Soften and smooth the skin (oils, fats).

Minor Constituents:

  • Preservatives: Prevent microbial growth (e.g., parabens).
  • Fragrances & Colors: Enhance aesthetic appeal.
  • Active Ingredients: Vitamins or antioxidants for specific skin benefits.

UNIT-IV

10. (a) What is food adulteration? 1

Food adulteration is the practice of adding inferior substances to food or removing valuable ingredients from it to increase quantity or profit, thereby lowering its quality and safety.

11. (b) Explain the importance of checking for adulterants in food products. 2

Checking for adulterants is crucial to ensure food safety, prevent health hazards (like toxicity or allergies), and protect consumers from economic fraud.

12. (b) Describe different methods used to detect adulteration in food products with examples. 5

  • Physical Tests: Visual inspection or simple tests like checking for chalk in sugar by dissolving it in water.
  • Chemical Tests: Using specific reagents, such as adding iodine to milk to detect starch (turns blue).
  • Microscopic Analysis: Used to detect extraneous matter like insect parts or saw dust in spices.
  • Chromatography: Advanced methods to detect prohibited synthetic dyes in oils or powders.

UNIT-V

13. (a) Name one method used to determine dissolved oxygen (DO) in water sample. 1

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Winkler’s Method is the standard chemical method for DO determination.[span_46](end_span)

14. (a) What are the sources of alkalinity in water? 2

Alkalinity is primarily caused by the presence of bicarbonate (HCO3-), carbonate (CO32-), and hydroxide (OH-) ions.

15. (a) What are the chemical reactions involved in the Winkler's method for DO determination? 5

  1. MnSO4 + 2KOH → Mn(OH)2 + K2SO4
  2. 2Mn(OH)2 + O2 → 2MnO(OH)2 (Brown precipitate)
  3. MnO(OH)2 + 2H2SO4 → Mn(SO4)2 + 3H2O
  4. Mn(SO4)2 + 2KI → MnSO4 + K2SO4 + I2
  5. I2 + 2Na2S2O3 → Na2S4O6 + 2NaI

Exam Focus Enhancements

  • Common Mistakes: Do not confuse Accuracy (closeness to truth) with Precision (consistency). In Winkler's method, always ensure the sample is collected without air bubbles.
  • Key Formula: Retention Factor ($R_f$) = (Distance traveled by substance) / (Distance traveled by solvent front).
  • Important FAQ: Why use EDTA? It forms highly stable 1:1 complexes with most metal ions, making it an ideal universal titrant.