FYUG EVEN SEMESTER EXAM, 2024 CHEMISTRY (2nd Semester) Course No.: CHMSEC-151T (Basic Analytical Chemistry)

Time: 3 Hours | Full Marks: 50 | Pass Marks: 20

SECTION-A

Answer any fifteen questions: 1 x 15 = 15

1. What is analytical chemistry?

Analytical chemistry is the science of obtaining, processing, and communicating information about the composition and structure of matter.

2. Define the term 'systematic error'.

Systematic error refers to reproducible inaccuracies that are consistently in the same direction, often caused by faulty equipment or flawed experimental design.

3. What is the full form of TLC?

The full form of TLC is Thin Layer Chromatography.

4. Choose the correct answer: Which one of the following is not an analytical technique?

(c) Stock analysis. (Titration, Gravimetric analysis, and Spectroscopy are all analytical techniques) .

5. Define pH.

pH is a numeric scale used to specify the acidity or basicity of an aqueous solution, defined as the negative logarithm of the hydrogen ion concentration (pH = -log[H+]).

6. What do you mean by an indicator?

An indicator is a chemical substance that undergoes a visible change (usually color) to signal the completion of a chemical reaction, such as the endpoint of a titration.

7. Define pure water.

Pure water is water that contains only hydrogen and oxygen atoms (H2O) and is free from dissolved solids, minerals, gases, or biological contaminants.

8. Give one example of chelating agent.

EDTA (Ethylenediaminetetraacetic acid) is a common chelating agent.

9. Define cosmetic.

A cosmetic is any substance or preparation intended to be applied to the human body for cleansing, beautifying, promoting attractiveness, or altering the appearance.

10. What are the basic constituents of talcum powder?

The primary constituent is talc (hydrated magnesium silicate), often mixed with fragrance and sometimes zinc oxide or cornstarch.

11. Write different types of cosmetics.

Types include skincare (lotions), haircare (shampoos), decorative (makeup), fragrances, and hygiene products (deodorants).

12. Give one example of antiperspirants.

Aluminum chlorohydrate is a frequently used active ingredient in antiperspirants.

13. What are the basic macronutrients present in soil?

The primary macronutrients are Nitrogen (N), Phosphorus (P), and Potassium (K).

14. What are the adulterants present in coffee?

Common coffee adulterants include chicory powder, roasted date seeds, and tamarind seeds.

15. What are the functions of preservatives?

Preservatives function to prevent microbial growth (bacteria, mold, yeast) and slow down oxidation to extend the shelf life of food or cosmetics.

16. What is the full form of FSSAI?

The full form is Food Safety and Standards Authority of India.

17. What will happen to aquatic life when DO level of water is very high?

While high DO is generally good, extreme supersaturation (very high levels) can cause "gas bubble disease" in fish, where bubbles form in the blood and tissues.

18. What is the pH of neutral, acidic and alkaline water?

  • Neutral: pH = 7.
  • Acidic: pH < 7.
  • Alkaline: pH > 7.

19. Name two reagents mostly used in complexometric titration.

EDTA and Eriochrome Black T (as an indicator) are standard reagents.

20. Name the macronutrients present in soil.

Macronutrients include Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, and Sulfur.

SECTION-B

Answer any five questions: 2 x 5 = 10

21. Distinguish between qualitative and quantitative chemical analysis.

  • Qualitative Analysis: Focuses on identifying "what" substances or elements are present in a sample.
  • Quantitative Analysis: Focuses on determining "how much" of a particular substance or element is present.

22. Explain the difference between accuracy and precision.

  • Accuracy: Refers to how close a measured value is to the true or accepted value.
  • Precision: Refers to the consistency or reproducibility of a set of measurements, regardless of how close they are to the true value.

23. Explain how pH of the soil can be determined.

Soil pH is determined by mixing a soil sample with distilled water (usually 1:2 ratio), stirring, and allowing it to settle. The pH of the resulting liquid is measured using a pH meter or pH indicator paper.

24. What are the major sources of contamination of surface water?

Major sources include industrial waste discharge, agricultural runoff containing pesticides and fertilizers, sewage disposal, and urban runoff.

25. What are the major components present in cosmetic products?

Components include water, emulsifiers, preservatives, thickeners, moisturizers (emollients), colors, and fragrances.

26. What is the use of emulsifiers in cosmetics? Give one example.

Emulsifiers are used to prevent oil and water components from separating, creating a stable, smooth mixture. Example: Polysorbates or Lecithin.

27. Give one example of natural and chemical preservative each and mention their uses.

  • Natural: Salt or Vinegar; used in food preservation to inhibit bacteria.
  • Chemical: Parabens (in cosmetics) or Sodium benzoate (in food); used to prevent microbial growth and spoilage.

30. Give the principle of flame photometry.

The principle is based on the measurement of the intensity of emitted light when a metal salt is introduced into a flame. The heat of the flame excites the atoms, which then emit light of a characteristic wavelength as they return to ground state.

SECTION-C

Answer any five questions: 5 x 5 = 25

31. Illustrate the procedure for the separation of a mixture of polar and non-polar compounds by TLC. [5]

Procedure:

  1. Apply a small spot of the mixture onto a TLC plate (stationary phase).
  2. Place the plate in a developing chamber containing a suitable solvent (mobile phase).
  3. As the solvent rises, compounds distribute themselves between the mobile and stationary phases.
  4. Non-polar compounds move faster/higher because they have less affinity for the polar stationary phase.
  5. Polar compounds move slower/lower due to strong interaction with the stationary phase.

32. Types of errors and their minimization. [3+2=5]

Types of Errors: 1. Determinate (Systematic) Errors: Constant errors like instrumental faults or reagent impurities. 2. Indeterminate (Random) Errors: Unpredictable fluctuations.

Minimization: Use calibrated instruments, run "blank" determinations, use standard reference materials, and perform replicate measurements to average out random errors.

33. Basic principle of complexometric titration and chelation. [3+2=5]

Principle: It is based on the formation of a stable, soluble complex between a metal ion and a ligand (complexing agent like EDTA). The endpoint is detected using a metal-ion indicator.

Chelation: It is a type of bonding where a single ligand (chelating agent) forms multiple bonds with a central metal ion, creating a ring-like structure that is highly stable.

34. Adverse effects of contaminated water and purification methods. [3+2=5]

Adverse Effects: Leads to waterborne diseases like Cholera, Typhoid, and Dysentery; heavy metal poisoning (lead/arsenic) can cause organ damage.

Purification Methods: 1. Boiling (kills pathogens). 2. Reverse Osmosis (RO) or Chlorination.

37. Properties of a preservative and use of salt. [2+3=5]

Properties: It must be effective against a wide range of microbes, non-toxic at used concentrations, stable, and should not alter the product's flavor or appearance.

Salt as a Preservative: Salt works by osmosis; it draws water out of microbial cells, dehydrating them and inhibiting their growth.

39. Procedure for determining the dissolved oxygen (DO) in water. [5]

DO is commonly determined using the Winkler Method:

  1. Fix the oxygen in the water sample using Manganese sulfate and Alkali-iodide-azide reagent.
  2. Acidify the sample to release iodine equivalent to the amount of oxygen present.
  3. Titrate the released iodine against a standard Sodium thiosulfate solution using starch as an indicator.
  4. The volume of thiosulfate used is used to calculate the DO concentration.

40. Determination of Calcium and Magnesium by complexometric titration. [5]

  1. Total Hardness (Ca + Mg): Titrate the sample with EDTA at pH 10 using Eriochrome Black T indicator.
  2. Calcium alone: Adjust pH to 12-13 (this precipitates Magnesium). Titrate with EDTA using Murexide indicator.
  3. Magnesium: Calculated by subtracting the Calcium value from the Total Hardness value.

Exam Focus Enhancements

Important Formulas / Concepts

  • pH = -log[H+].
  • Rf (TLC) = Distance moved by solute / Distance moved by solvent.
  • Chelation increases complex stability significantly.

Exam Tips

  • In Section C, always list steps for experimental procedures (TLC, DO determination).
  • Clearly differentiate between error types to score high on measurement questions.
  • Remember the specific pH requirements for Ca and Mg titration (pH 10 vs pH 12).

Common Mistakes

  • Confusing precision with accuracy.
  • Forgetting the role of the mobile vs. stationary phase in TLC.