_20260225_235322_0000.jpg)
Q1. What is an asymmetric carbon atom?
Answer:
An asymmetric carbon atom (chiral carbon) is a carbon atom that is attached to four different types of atoms or groups of atoms.
Q2. What properties are different in enantiomers?
Answer:
Enantiomers have identical chemical and physical properties in an achiral environment. Enantiomers rotate the direction of plane polarized light to equal, but to opposite angles and interact with other chiral molecules differently.
Q3. What are the physical properties that make difference in melting point among different molecules?
Answer:
The force of attraction between the molecules affects the melting point of a compound. Stronger intermolecular interactions result in higher melting points. Ionic compounds usually have high melting points because the electrostatic forces holding the ions (ion- ion interaction) are much stronger.
Q4. What is potentiometric titration?
Answer:
Potentiometric titration is a volumetric method in which the potential between two electrodes is measured (referent and indicator electrode) as a function of the added reagent volume.
Types of potentiometric titrations for the determination of analytes in photo processing solutions include acid- base, redox, precipitation, and complexometric.
Q5. What is monomer and polymer?
Answer:
Monomer, a molecule of any of a class of compounds, mostly organic, that can react with other molecules to form very large molecules, or polymers. The essential feature of a monomer is polyfunctionality, the capacity to form chemical bonds to at least two other monomer molecules.
Polymer, any of a class of natural or synthetic substances composed of very large molecules, called macromolecules that are multiples of simpler chemical units called monomers. Polymers make up many of the materials in living organisms, including, for example, proteins, cellulose, and nucleic acids.
Q6. What are molarity, molality and normality?
Answer:
Molarity, molality, and normality are all units of concentration in chemistry.
Molarity (M) is defined as the number of moles of solute per liter of solution.
Molality (m) is defined as the number of moles of solute per kilogram of solvent.
Normality (N) is defined as the number of equivalents per liter of solution.
Q7. What is Mole with example?
Answer:
A mole corresponds to the mass of a substance that contains \(6.023 \times 10^{23}\) particles of the substance. The mole is the SI unit for the amount of a substance. Its symbol is mol. By definition: 1 mol of carbon- 12 has a mass of 12 grams and contains \(6.022140857 \times 10^{23}\) of carbon atoms (to 10 significant figures).
Q8. What do you mean by Avogadro's number?
Answer:
Avogadro's number is defined as the number of elementary particles (molecules, atoms, compounds, etc.) per mole of a substance. It is equal to \(6.022 \times 10^{23}\) mol \(^{- 1}\) and is expressed as the symbol \(\mathrm{NA}\).
Q9. What are the uses of buffer solution?
Answer:
Buffer solutions are used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. In nature, there are many systems that use buffering for pH regulation. For example, the bicarbonate buffering system is used to regulate the pH of blood.
Q10. What is the principle of spectroscopy?
Answer:
The term "spectroscopy" defines a large number of techniques that use electromagnetic radiation to obtain information on the structure and properties of matter.
The basic principle shared by all spectroscopic techniques is to shine a beam of electromagnetic radiation onto a sample, and observe how it responds to such a stimulus.
Q11. What is UV spectroscopy principle?
Answer:
Ultraviolet and visible (UV- Vis) absorption spectroscopy is the measurement of the intensity of a beam of light after it passes through a sample or after reflection from a sample surface. Absorption measurements can be at a single wavelength or over an extended spectral range.
Q12. What is the Principle of ultraviolet- visible absorption?
Answer:
Molecules containing bonding and non- bonding electrons (n- electrons) can absorb energy in the form of ultraviolet or visible light to excite these electrons to higher anti- bonding molecular orbitals. The more easily excited the electrons (i.e. lower energy gap between the HOMO and the LUMO), the longer the wavelength of light it can absorb. There are four possible types of transitions \((\pi - \pi^{*}, \mathrm{n} - \pi^{*}, \sigma - \sigma^{*},\) and \(\mathrm{n} - \sigma^{*}\) ), and they can be ordered as follows: \(\sigma - \sigma^{*} > \mathrm{n} - \sigma^{*} > \pi - \pi^{*} > \mathrm{n} - \pi^{*}\).
Q13. What is vacuum UV region?
Answer:
The term vacuum UV (below \(\approx 200 \mathrm{nm}\) ) refers to the wavelength range where a vacuum apparatus is often used, because the light is strongly absorbed in air. The vacuum UV includes the far and extreme UV.
Q14. What is UV VIS good for?
Answer:
UV/VIS/NIR spectroscopy is a powerful analytical technique to determine the optical properties (transmittance, reflectance and absorbance) of liquids and solids. It can be applied to characterize semiconductor materials, coatings, glass and many other research and manufacturing materials.
Q15. What is definition of electronegativity?
Answer:
Electronegativity is the property of an atom which increases with its tendency to attract the electrons of a bond. If two bonded atoms have the same electronegativity values as each other, they share electrons equally in a covalent bond.
Q16. What are the electronegativity trends on the periodic table?
Answer:
Moving down a group on the periodic table, the electronegativity of an element decreases because the increased number of energy levels puts the outer electrons very far away from the pull of the nucleus. Electronegativity increases as you move from left to right across a period on the periodic table.
Q17. What is Arrhenius concept of acid and base?
Answer:
The Arrhenius acid- base concept classifies a substance as an acid if it produces hydrogen ions \(\mathrm{(H^{+})}\) or hydronium ions in water. A substance is classified as a base if it produces hydroxide ions \(\mathrm{(OH^{- })}\) in water.
Q18. What is Bronsted- Lowry concept of acid and base?
Answer:
A Bronsted- Lowry acid is a chemical species that donates one or more hydrogen ions in a reaction. In contrast, a Bronsted- Lowry base accepts hydrogen ions. When an acid donates its proton, the acid becomes its conjugate base and when a base accepts proton, the base becomes its conjugate acid.
A more general look at the theory is as an acid as a proton donor and a base as a proton acceptor.
Q19. What is S Block, P Block, D Block and F block elements are called?
Answer:
The s- block of elements is the alkali metals and the alkaline earth metals. The d- block of elements is the transition metals. The f- block of elements is the lanthanides (first row) and the actinides (second row).
Q20. What does the P block mean?
Answer:
The p- block elements are unified by the fact that their valence electrons (outermost electrons) are in the p orbital.
Q21. What is meant by D block element?
Answer:
The elements which have partially filled d- orbitals either ground state or in one or more of their ions, are called d- block elements or outer transition elements. Their properties are intermediate between s- block elements and p- block elements.
Q22. What are f block elements?
Answer:
The f block elements are the lanthanides and actinides and are called the inner transition elements because of their placement in the periodic table due to their electron configurations. The f orbitals of the electron shell are filled with "n- 2." Total 28 atoms are.
Q23. What is the definition of electron affinity?
Answer:
In chemistry and atomic physics, the electron affinity of an atom or molecule is defined as the amount of energy released or spent when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion.
Q24. What is the trend for electron affinity?
Answer:
Electron affinity increases upward for the groups and from left to right across periods of a periodic table because the electrons added to energy levels become closer to the nucleus, thus a stronger attraction between the nucleus and its electrons.
Q25. What is the full form of pH?
Answer:
pH stands for Potential of Hydrogen. It refers to the hydrogen ion concentration in a solution. It is the measure of the acidity or alkalinity of a solution. The pH value ranges from 0 to 14 on a pH scale.
Q26. What is the importance of buffer system?
Answer:
A buffer is a chemical substance that helps maintain a relatively constant pH in a solution, even in the face of addition of acids or bases. Buffering is important in living systems as a means of maintaining a fairly constant internal environment, also known as homeostasis.
Q27. What are the 3 buffer systems in the body?
Answer:
There are several buffer systems in the body. The most important include: (1) bicarbonate buffer \((\mathrm{HCO}_{3}^{- } / \mathrm{CO}_{2})\) , (2) haemoglobin buffer (in erythrocytes), (3) phosphate buffer, (4) proteins, and (5) ammonium buffer.
Q28. What are electrolytes in the body?
Answer:
Sodium, calcium, potassium, chloride, phosphate, and magnesium are all electrolytes.
Q29. What is TLC principle?
Answer:
Chromatography works on the principle that different compounds will have different solubility and adsorption to the two phases between which they are to be partitioned. Thin Layer Chromatography (TLC) is a solid- liquid technique in which the two phases are a solid (stationary phase) and a liquid (moving phase).
Q30. What is indicator?
Answer:
Chemical indicator is any substance that gives a visible sign, usually by a color change, of the presence or absence of a threshold concentration of a chemical species, such as an acid or an alkali in a solution. An example is the substance called methyl yellow, which imparts a yellow colour to an alkaline solution.
An indicator is a chemical substance (dye) which indicates whether the given compound is acid or base by changing its colour. The most common indicators are Litmus, Phenolphthalein and Methyl Orange.
Litmus is a weak acid. Methyl orange is a weak base. Phenolphthalein is a weak acid.
indicator pKind pH range
litmus 6.5 5 - 8
methyl orange 3.7 3.1 - 4.4
phenolphthalein 9.3 8.3 - 10.0
Q31. What is an indicator and how does it work?
Answer:
pH indicators detect the presence of \(\mathrm{H + }\) and \(\mathrm{OH - }\). They do this by reacting with \(\mathrm{H + }\) and \(\mathrm{OH - }\) : they are themselves weak acids and bases. If an indicator is a weak acid and is coloured and its conjugate base has a different color, deprotonation causes a color change.
Q32. Why KMnO4 is a self- indicator?
Answer:
First of all the color of KMnO4 is dark purple due to \(+7\) oxidation state of Mn (manganese ). Usually KMnO4 is used in titrations against solutions like oxalic acid, FAS (ferrous ammonium sulfate, etc.). KMnO4 oxidizes these standard solutions. As we do the titration we would reach the end point. The end point indicates that the standard solution was completely oxidized. So once all the permanganate ions are used up in the reaction, the solution loses its pink color. This indicates the end of the reaction and hence potassium permanganate is called a self- indicator as it acts as an indicator apart from being one of the reactants.
Q33. What is universal indicator and what is the color of universal indicator?
Answer:
A universal indicator is a pH indicator made of a solution of several compounds that exhibits several smooth color changes over a wide range pH values to indicate the acidity or alkalinity of solutions.
A universal indicator is typically composed of thymol blue (1.2 - 2.8) & (8.0 - 9.6), methyl orange (3.1 - 4.4), methyl red (4.4 - 5.8), bromothymol blue (6.0 - 7.6) and phenolphthalein (8.3 - 10.0).
The colors that indicate the pH of a solution, after adding a universal indicator, are:
pH range Description Colour
< 3 Strong acid Red
3-6 Weak acid Orange or yellow
7 Neutral Green
8-11 Weak alkali Blue
> 11 Strong alkali Violet or Indigo
When universal indicator is added to a solution, the color change can indicate the approximate pH of the solution. Acids cause universal indicator solution to change from green toward red. Bases cause universal indicator to change from green toward purple.
Q34. What is the role of catalyst?
Answer:
Catalysts called enzymes are important in biology. A catalyst works by providing an alternative reaction pathway to the reaction product. The rate of the reaction is increased as this alternative route has lower activation energy than the reaction route not mediated by the catalyst.
Q35. What are the uses of solvents?
Answer:
Common uses for organic solvents are in dry cleaning (e.g. tetrachloroethylene), as paint thinners (e.g. toluene, turpentine), as nail polish removers and glue solvents (acetone, methyl acetate, ethyl acetate), in spot removers (e.g. hexane, petrol ether), in detergents (citrus terpenes) and in perfumes (ethanol).
Q36. What is the difference between polar solvents and nonpolar solvents?
Answer:
Polar solvents have large dipole moments (aka "partial charges"); they contain bonds between atoms with very different electronegativity, such as oxygen and hydrogen. Non polar solvents contain bonds between atoms with similar electronegativity, such as carbon and hydrogen (think hydrocarbons, such as gasoline).
Q37. What are non- polar solvents?
Answer:
Non- polar solvents are lipophilic as they dissolve non- polar substances such as oils, fats, greases.
Examples: carbon tetrachloride \((\mathrm{CCl}_4)\) , pentane, toluene, benzene \((\mathrm{C}_6\mathrm{H}_6)\) , and diethyl ether \((\mathrm{CH}_3\mathrm{CH}_2\mathrm{OCH}_2\mathrm{CH}_3)\) , hexane \((\mathrm{CH}_3(\mathrm{CH}_2)_4\mathrm{CH}_3)\) , methylene chloride \((\mathrm{CH}_2\mathrm{Cl}_2)\).
Q38. What is meant by polar solvent?
Answer:
A polar solvent is a liquid with molecules that have a slight electrical charge due to its shape.
Example: water, deuterium oxide (heavy water for NMR), ethanol, methanol, acetone, methyl ethyl ketone, isopropanol, n- propanol, acetonitrile, DMSO (dimethyl sulfoxide) or deuterated DMSO (heavy DMSO for NMR), DMF (dimethyl formamide).
Q39. What are the types of chromatography?
Answer:
Chromatographic separations can be carried out using a variety of stationary phases, including immobilized silica on glass plates (thin- layer chromatography), volatile gases (gas chromatography), paper (paper chromatography), and liquids (liquid chromatography).
Q40. What is the basic principle of HPLC?
Answer:
HPLC relies on pumps to pass a pressurized liquid and a sample mixture through a column filled with adsorbent, leading to the separation of the sample components. The active component of the column, the adsorbent, is typically a granular material made of solid particles (e.g., silica, polymers, etc.), 2- 50μm in size.
Q41. What are the types of HPLC?
Answer:
1. Normal Phase HPLC
This method separates analytes on the basis of polarity. NP- HPLC uses polar stationary phase and non- polar mobile phase. Therefore, the stationary phase is usually silica and typical mobile phases are hexane, methylene chloride, chloroform, diethyl ether, and mixtures of these. Polar samples are thus retained on the polar surface of the column packing longer than less polar materials.
2. Reverse Phase HPLC
The stationary phase is nonpolar (hydrophobic) in nature, while the mobile phase is a polar liquid, such as mixtures of water and methanol or acetonitrile. It works on the principle of hydrophobic interactions hence the more nonpolar the material is, the longer it will be retained.
3. Size-exclusion HPLC
The column is filled with material having precisely controlled pore sizes, and the particles are separated according to it's their molecular size. Larger molecules are rapidly washed through the column; smaller molecules penetrate inside the porous of the packing particles and elute later.
4. Ion-Exchange HPLC
The stationary phase has an ionically charged surface of opposite charge to the sample ions. This technique is used almost exclusively with ionic or ionizable samples. The stronger the charge on the sample, the stronger it will be attracted to the ionic surface and thus, the longer it will take to elute. The mobile phase is an aqueous buffer, where both pH and ionic strength are used to control elution time.
Q42. What are the parts of HPLC instrumentation system?
Answer:
HPLC instrumentation includes a pump, injector, column, detector and integrator or acquisition and display system. The heart of the system is the column where separation occurs.
1. Solvent Reservoir
Mobile phase contents are contained in a glass reservoir. The mobile phase, or solvent, in HPLC is usually a mixture of polar and non- polar liquid components whose respective concentrations are varied depending on the composition of the sample.
2. Pump
A pump aspirates the mobile phase from the solvent reservoir and forces it through the system's column and detector. Depending on a number of factors including column dimensions, particle size of the stationary phase, the flow rate and composition of the mobile phase, operating pressures of up to 42000 kPa (about 6000 psi) can be generated.
3. Sample Injector
The injector can be a single injection or an automated injection system. An injector for an HPLC system should provide injection of the liquid sample within the range of 0.1- 100 mL of volume with high reproducibility and under high pressure (up to 4000 psi).
4. Columns
Columns are usually made of polished stainless steel, are between 50 and \(300~\mathrm{mm}\) long and have an internal diameter of between 2 and \(5\mathrm{mm}\). They are commonly filled with a stationary phase with a particle size of \(3 - 10\mu \mathrm{m}\).
Columns with internal diameters of less than \(2\mathrm{mm}\) are often referred to as microbore columns. Ideally the temperature of the mobile phase and the column should be kept constant during an analysis.
5. Detector
The HPLC detector, located at the end of the column detects the analytes as they elute from the chromatographic column. Commonly used detectors are UV- spectroscopy, fluorescence, mass- spectrometric and electrochemical detectors.
6. Data Collection Devices
Signals from the detector may be collected on chart recorders or electronic integrators that vary in complexity and in their ability to process, store and reprocess chromatographic data. The computer integrates the response of the detector to each component and places it into a chromatograph that is easy to read and interpret.
Q43. How many types of detectors are available for HPLC?
Answer:
They are of three types, i.e. fixed wavelength detectors, variable wavelength detectors and the diode array detectors.
1. UV, VIS, and PDA Detectors
2. Refractive-Index Detector (RID)
3. Evaporative Light Scattering Detector
4. Multi-Angle Light Scattering Detector
5. Mass Spectrometer
6. Conductivity Detector
7. Fluorescence Detector
8. Chemiluminescence Detector
9. Optical Rotation Detector
10. Electro Chemical Detector
Q44. Why is HPLC test done?
Answer:
When molecules in the mixture are very similar, direct quantification becomes difficult. HPLC is a form of column chromatography used frequently to separate, identify and quantify compounds. It consists of a stationary phase that absorbs the analytes and holds them for a particular time.
Q45. What is difference between isocratic and gradient?
Answer:
Isocratic means that the mixture of your mobile phase is consistent over the complete testing time. Using a gradient implies that the compounding of the eluent mixture is changed during measurement and so influences the retention of analytes.
Q46. What are the advantages of HPLC?
Answer:
Speed, efficiency and accuracy.
Compared to other chromatographic techniques, such as TLC, HPLC is extremely quick and efficient. It uses a pump, rather than gravity, to force a liquid solvent through a solid adsorbent material, with different chemical components separating out as they move at different speeds.
Q47. What is the retention time in HPLC?
Answer:
Retention time (RT) is a measure of the time taken for a solute to pass through a chromatography column. It is calculated as the time from injection to detection. The RT for a compound is not fixed as many factors can influence it even if the same GC and column are used.
Q48. What is universal detector in HPLC?
Answer:
The refractive index (RI) detector is the only universal detector in HPLC. The detection principle involves measuring of the change in refractive index of the column effluent passing through the flow- cell. The greater the RI difference between sample and mobile phase, the larger the imbalance will become.
Q49. What is System suitability in HPLC?
Answer:
System suitability is defined by ICH as "the checking of a system, before or during analysis of unknowns, to ensure system performance." System suitability criteria may include such factors as plate count, tailing, retention, and/or resolution.
Q50. What is the resolution in HPLC?
Answer:
The resolution of an elution is a quantitative measure of how well two elution peaks can be differentiated in a chromatographic separation. It is defined as the difference in retention times between the two peaks, divided by the combined widths of the elution peaks.
Q51. What is plate count in HPLC?
Answer:
Theoretical plate number (N) is an index that indicates column efficiency. It describes the number of plates as defined according to plate theory, and can be used to determine column efficiency based on calculation in which the larger the theoretical plate number the sharper the peaks.
Q52. What is S/N ratio in HPLC?
Answer:
The noise is measured between two lines bracketing the baseline and the signal is measured from the middle of the baseline to the top of the peak. S/N is merely the signal divided by the noise.
Q53. What is the tailing factor?
Answer:
The tailing factor is a measure of peak tailing. It is defined as the distance from the front slope of the peak to the back slope divided by twice the distance from the center line of the peak to the front slope, with all measurements made at \(5\%\) of the maximum peak height.
Q54. What is LoD and LoQ in HPLC?
Answer:
Limit of detection (LoD) (also called detection limit) - the smallest amount or concentration of analyte in the test sample that can be reliably distinguished from zero.
Limit of quantitation (LoQ) - the lowest concentration of analyte that can be determined with an acceptable repeatability and trueness.
Q55. What is difference between c8 and c18 column?
Answer:
C18 is has 18 carbon atoms while C8 has 8 carbons in the column packing that are bonded to the silica (Si). From what I have seen practically, generally, C18 retains more than C8 such that for a similar compound eluted on the two columns, it will elute later on the C18.
Q56. What is accuracy in method validation?
Answer:
The accuracy of an analytical method is the degree of agreement of test results generated by the method to the true value. Accuracy is measured by spiking the sample matrix of interest with a known concentration of analyte standard and analyzing the sample using the "method being validated.
Q57. What is precision in validation?
Answer:
Precision of an analytical method is the degree of agreement among individual test results when the method is applied repeatedly to multiple samplings of a homogenous sample.
Q58. What is linearity in analytical method validation?
Answer:
The linearity of an analytical method is its ability to elicit test results that are directly proportional to the concentration of the analyte in samples within a given range.
Q59. What is diasteromer?
Answer:
Diastereomers are stereoisomers that are not mirror images of one another and are non- superimposable on one another.
Q60. What is Avogadro's law?
Answer:
Avogadro's law states that "equal volumes of all gases, at the same temperature and pressure, have the same number of molecules."
Q61. What are the advantages of potentiometric titration?
Answer:
Potentiometric titrations are preferred to manual titrations, since they are more accurate and precise. They are also more easily adapted to automation, where automated titration systems can process larger volumes of samples with minimal analyst involvement.
