Prepare for your next interview with these 55 essential chemistry questions and answers.
Questions
1. What is Valency?
Valency refers to the combining capacity of an element. It represents the number of chemical bonds an atom of that element can form.
2. Define Avogadro’s law?
Avogadro’s law states that equal volumes of all gases, at the same temperature and pressure, contain the same number of molecules.
3. Why graphite rod is used in nuclear reactor?
Graphite rods are used as moderators in nuclear reactors. They slow down neutrons, which increases the probability of nuclear fission.
4. What is oxidation and reduction reaction?
- Oxidation is the loss of electrons.
- Reduction is the gain of electrons. These two processes always occur together in a redox reaction.
5. What does iron ore consist of?
Iron ore consists mainly of iron oxides, such as hematite (Fe2O3) and magnetite (Fe3O4), along with various impurities.
6. Explain what is dextro-rotatory and levorotatory?
These terms refer to the optical activity of chiral molecules. A dextro-rotatory (d or +) molecule rotates plane-polarized light clockwise. A levorotatory (l or -) molecule rotates plane-polarized light counterclockwise.
7. What is the difference between a homogeneous and heterogeneous mixture?
A homogeneous mixture has a uniform composition throughout (e.g., saltwater). A heterogeneous mixture has a non-uniform composition (e.g., sand and water).
8. Explain the concept of chemical equilibrium.
Chemical equilibrium is the state where the rates of the forward and reverse reactions are equal, and the net change in concentrations of reactants and products is zero.
9. What are the different types of intermolecular forces?
- London Dispersion Forces: Weak, temporary forces present in all molecules.
- Dipole-Dipole Interactions: Forces between polar molecules.
- Hydrogen Bonding: Strong dipole-dipole interaction when hydrogen is bonded to a highly electronegative atom (N, O, F).
10. How do you prepare a standard solution?
A standard solution is a solution with a precisely known concentration. You would typically dissolve a precisely weighed amount of solute in a known volume of solvent using volumetric glassware.
11. What is the purpose of a blank in spectrophotometry?
A blank is used to calibrate the spectrophotometer and account for any absorbance or background signal from the cuvette or solvent.
12. What are some common applications of mass spectrometry?
Mass spectrometry is used to identify and quantify the components of a sample, determine molecular structures, and study isotopic abundances. It has applications in fields like drug discovery, environmental monitoring, and forensics.
13. Explain the concept of a Grignard reaction.
A Grignard reaction involves the reaction of an organomagnesium halide (RMgX) with a carbonyl compound (aldehyde or ketone) to form a new carbon-carbon bond. It’s a very important reaction in organic synthesis.
14. What is the difference between SN1 and SN2 reactions?
SN1 (Substitution Nucleophilic Unimolecular) reactions proceed through a two-step mechanism involving a carbocation intermediate. SN2 (Substitution Nucleophilic Bimolecular) reactions are concerted (one-step) reactions. They differ in their kinetics, stereochemistry, and dependence on the nucleophile and substrate.
15. What are polymers, and what are some examples?
Polymers are large molecules made up of repeating subunits (monomers). Examples include polyethylene, polystyrene, nylon, and proteins.
16. What is the role of catalysts in chemical reactions?
Catalysts increase the rate of a chemical reaction by lowering the activation energy, without being consumed themselves in the process.
17. Explain the concept of pH and how it is measured.
pH is a measure of the acidity or basicity of a solution. It is measured using a pH meter or indicators.
18. How do you handle and dispose of hazardous waste in a lab?
Proper handling includes wearing appropriate PPE, labeling containers clearly, and following established safety protocols. Disposal involves segregating waste according to type and following local regulations.
19. What are some important considerations when designing an experiment?
Considerations include defining the research question, formulating a hypothesis, selecting appropriate controls and variables, choosing suitable methods and materials, and planning for data analysis.
20. How do you ensure the accuracy and precision of your experimental results?
Accuracy is how close a measurement is to the true value. Precision is how close repeated measurements are to each other. Ensuring both involves calibration, using appropriate equipment, minimizing errors, and performing replicates.
21. What are some ethical considerations in chemistry research?
Ethical considerations include data integrity, proper attribution of sources, responsible conduct of research, and avoiding plagiarism.
22. Explain the difference between distillation and extraction.
Distillation separates liquids based on their boiling points. Extraction separates components of a mixture based on their solubility in different solvents.
23. What is the purpose of refluxing a reaction?
Refluxing allows a reaction to be heated at its boiling point for an extended period without loss of volatile solvents or reactants.
24. What are some applications of nuclear magnetic resonance (NMR) spectroscopy?
NMR is used to determine the structure and conformation of molecules, study reaction kinetics, and analyze mixtures. It’s particularly important in organic chemistry, biochemistry, and materials science.
25. Explain the principles of mass spectrometry.
Mass spectrometry separates ions based on their mass-to-charge ratio. It is used to identify and quantify the components of a sample and to determine molecular structures.
26. What is the difference between adsorption and absorption?
Adsorption is the adhesion of molecules to the surface of a material. Absorption is the penetration of molecules into the bulk of a material.
27. What are surfactants, and how do they work?
Surfactants are molecules that reduce the surface tension of a liquid. They have both hydrophilic (water-loving) and hydrophobic (water-fearing) parts. They work by accumulating at interfaces between different phases (e.g., water and oil).
28. Explain the concept of chirality.
Chirality refers to the property of a molecule being non-superimposable on its mirror image. Chiral molecules often have a stereocenter (usually a carbon atom bonded to four different groups).
29. What are enantiomers and diastereomers?
Enantiomers are mirror image isomers that are non-superimposable. Diastereomers are stereoisomers that are not mirror images of each other.
30. What is a racemic mixture?
A racemic mixture contains equal amounts of both enantiomers of a chiral molecule and is therefore optically inactive.
31. What are the main classes of biomolecules, and what are their functions?
- Proteins: Carry out a variety of functions, including catalysis, transport, and structural support.
- Carbohydrates: Provide energy and serve as structural components.
- Lipids: Store energy and form cell membranes.
- Nucleic acids: Store and transmit genetic information.
32. What are enzymes, and how do they work?
Enzymes are biological catalysts that speed up chemical reactions in living organisms. They work by lowering the activation energy of reactions.
33. Explain the term Aliquot and Diluent?
An aliquot is a precisely measured portion of a sample. A diluent is the substance (usually a liquid) used to dilute a solution. In simple terms, you take an aliquot of your concentrated solution and add it to the diluent to make a less concentrated solution.
34. What is molality?
Molality (m) is defined as the number of moles of solute per kilogram of solvent. It’s different from molarity, which is moles of solute per liter of solution.
35. What is the purpose of a back titration?
A back titration is used when the direct titration of an analyte with a titrant is difficult or impossible (e.g., if the reaction is slow or if the endpoint is hard to detect). A known excess of the titrant is added to the analyte, and then the excess titrant is titrated with a second standard solution.
36. Explain the principles behind thin-layer chromatography (TLC).
TLC separates compounds based on their differential adsorption to a stationary phase (usually silica gel) and their solubility in a mobile phase (a solvent or mixture of solvents).
37. What is titration?
Titration is a technique used to determine the concentration of a solution by reacting it with a solution of known concentration (the titrant). The reaction between the two solutions is usually monitored by an indicator or a pH meter.
38. What is a buffer?
A buffer is a solution that resists changes in pH when small amounts of acid or base are added.
39. What is the common ion effect, and how does it affect solubility?
The common ion effect describes the decrease in solubility of a sparingly soluble salt when a soluble salt containing a common ion is added to the solution. The presence of the common ion shifts the solubility equilibrium according to Le Chatelier’s principle, reducing the solubility of the sparingly soluble salt.
40. What is the difference between a strong electrolyte and a non-electrolyte?
- Strong electrolytes: Completely dissociate into ions when dissolved in water, resulting in solutions that conduct electricity well (e.g., NaCl, HCl).
- Non-electrolytes: Do not dissociate into ions when dissolved in water, and their solutions do not conduct electricity (e.g., sugar, ethanol).
41. What is the difference between a monoprotic, diprotic, and triprotic acid?
Acids are classified by the number of protons they can donate.
- Monoprotic: Donates one proton (e.g., HCl).
- Diprotic: Donates two protons (e.g., H2SO4).
- Triprotic: Donates three protons (e.g., H3PO4).
42. What are amphoteric substances? Give some examples.
Amphoteric substances can act as both acids and bases, depending on the conditions. Examples include water (H2O), aluminum hydroxide (Al(OH)3), and amino acids.
43. What are isomers?
Isomers are molecules with the same molecular formula but different structures. Different structural arrangements lead to different molecular geometries.
44. What is the difference between ionization energy and electronegativity?
- Ionization energy: The energy required to remove an electron from an atom in its gaseous state.
- Electronegativity: The ability of an atom to attract electrons in a chemical bond.
45. What are some important applications of elements from different groups in the periodic table?
- Alkali metals (Group 1): Used in batteries, soaps.
- Halogens (Group 17): Used in disinfectants, lighting.
- Noble gases (Group 18): Used in lighting, welding.
- Transition metals: Many are used as catalysts, structural materials.
46. Explain Le Chatelier’s principle and its applications.
Le Chatelier’s principle states that if a change of condition (e.g., temperature, pressure, concentration) is applied to a system in equilibrium, the system will shift in a direction that relieves the stress. Applications include predicting the effects of changes on equilibrium systems, optimizing reaction conditions, and understanding how equilibrium systems respond to disturbances.
47. What is the difference between Kc and Kp?
- Kc: The equilibrium constant expressed in terms of concentrations.
- Kp: The equilibrium constant expressed in terms of partial pressures (for gaseous reactions).
48. What factors can affect chemical equilibrium?
- Concentration: Changing the concentration of reactants or products will shift the equilibrium.
- Pressure: Changing the pressure affects equilibria involving gases.
- Temperature: Changing the temperature will change the value of the equilibrium constant and shift the equilibrium.
- Catalyst: A catalyst does not affect the position of equilibrium but speeds up the rate at which equilibrium is reached.
49. What is the difference between a zero-order, first-order, and second-order reaction?
- Zero-order: The reaction rate is independent of the concentration of the reactant.
- First-order: The reaction rate is directly proportional to the concentration of the reactant.
- Second-order: The reaction rate is proportional to the square of the concentration of the reactant.
50. What is the activation energy, and how does it relate to reaction rate?
The activation energy is the minimum energy required for a reaction to occur. A higher activation energy corresponds to a slower reaction rate. The relationship is described by the Arrhenius equation.
51. What are atomic orbitals, and what do they represent?
Atomic orbitals are regions of space around the nucleus of an atom where there is a high probability of finding an electron. They are described by quantum numbers (n, l, ml, s).
52. What are the different types of atomic orbitals (s, p, d, f)?
- s orbitals: Spherical.
- p orbitals: Dumbbell-shaped.
- d orbitals: More complex shapes.
- f orbitals: Even more complex shapes.
53. What are quantum numbers, and what do they describe?
Quantum numbers describe the properties of atomic orbitals and electrons.
- Principal quantum number (n): Energy level.
- Angular momentum quantum number (l): Shape of the orbital.
- Magnetic quantum number (ml): Orientation of the orbital in space.
- Spin quantum number (s): Spin of the electron.
54. What is the Pauli exclusion principle?
The Pauli exclusion principle states that no two electrons in an atom can have the same set of four quantum numbers. This means that each atomic orbital can hold a maximum of two electrons with opposite spins.
55. What is Hund’s rule?
Hund’s rule states that for degenerate orbitals (orbitals with the same energy), electrons will individually occupy each orbital before doubling up in any one orbital. This minimizes electron-electron repulsion.
