৪৯তম বিসিএস ⎯ রসায়ন [৫৩১] · তারিখ অনির্ধারিত · ৩০ প্রশ্ন
We know,
specific conductance= conductance x cell constant
If, specific conductance & conductance of a solution are same
Then, cell constant= 1.0 unit
So the right answer is B
Source: Essentials of physical chemistry (Bahl, Tuli)/Any text book from HSC level
Unit of molar conductance Ω -1 cm2 mol-1
Molar conductance is a measure of a solution's ability to conduct electricity, specifically when considering the contribution of one mole of an electrolyte.
Molar conductance= (specific conductance x 1000)/C
where, C is the concentration of solution in Molarity unit
Source: Essentials of physical chemistry (Bahl, Tuli)/Any text book from HSC level
According to Faraday's Law:
2F charge is required to produce 63.5 g of Cu
So, 0.5F charge is required to produce (63.5x0.5)/2 g of Cu = 15.9 g
Source: Essentials of physical chemistry (Bahl, Tuli)/Any text book from HSC level
The more reactive metal is the more easily oxidized metal.
Reactivity series:
So the right answer is D
Source: Any text book from HSC level
When electrolyzing an aqueous solution of silver sulfate, silver metal is deposited at the cathode, and oxygen gas is produced at the anode
Cathode (Reduction): Silver ions (Ag+) from silver sulfate are attracted to the negatively charged cathode
Ag⁺ + e⁻ → Ag
Anode (Oxidation): Hydroxide ions (OH⁻) from the water are attracted to the positively charged anode
4OH⁻ → O₂ + 2H₂O + 4e⁻
Source: Essentials of physical chemistry (Bahl, Tuli)/Any text book from HSC level
The metal which is less reactive than hydrogen does not react with HCl(aq)
So the right answer is C
Source: Any text book from HSC level
With a rise in temperature, the conductance of an electrolyte solution generally increases
Because higher temperatures increase the kinetic energy of ions, leading to faster movement and increased mobility within the solution. This enhanced mobility allows ions to carry more charge, resulting in a higher conductance.
Conductance: The conductance of an electrolyte solution refers to its ability to conduct electricity, which is facilitated by the movement of ions in the solution. This conductance is affected by several factors, including
1. the type and concentration of the electrolyte,
2. the temperature
3. the viscosity of the solvent.
Source: Essentials of physical chemistry (Bahl, Tuli)/Any text book from HSC level
Kohlrausch’s law : the molar conductivity of an electrolyte at infinite dilution can be expressed as the sum of the contributions of its individual ions.
λα = λa + λc
Applications of Kohlrausch's law:
1. Determining limiting molar conductivity of weak electrolytes
2. Calculating the degree of dissociation of weak electrolyte
3. Determining the solubility of sparingly soluble salts
So the right answer is D
Source: Essentials of physical chemistry (Bahl, Tuli)/Any text book from HSC level.
We know,
Molar conductance= (conductance x cell constant x 1000)/Concentration in Molarity= 2.8x10-3 x 0.5 x 1000/0.01 = 140
Source: Essentials of physical chemistry (Bahl, Tuli)/Any text book from HSC level.
Explanation: Potential jump indicates equivalence point
In potentiometric titrations, the equivalence point is determined by observing the inflection point on the titration curve, which is a plot of electrode potential (E) or pH versus the volume of titrant added. This inflection point represents the point of maximum slope and signifies the completion of the reaction.
Titration Curve:
A potentiometric titration involves measuring the potential difference between two electrodes as a titrant is added to a solution
Equivalence Point:
The equivalence point is the point in the titration where the reactants are in stoichiometric proportions
Inflection Point:
The inflection point on the titration curve is where the curve changes direction most rapidly.
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch
Explanation: Spectroscopy is an analytical (identification) method, not separation.
Chromatography: Chromatography is a laboratory technique used to separate components of a mixture based on their differing affinities for a stationary phase and a mobile phase.
Spectroscopy: a technique used to study how light interacts with matter.
Electrophoresis: a laboratory technique that separates molecules based on their size and electrical charge by applying an electric field.
Solvent extraction: a separation technique that utilizes the differences in solubility of substances in two immiscible liquids to isolate and purify compounds.
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch/ Any text book from HSC level.
The Beer-Lambert Law: describes the relationship between the absorbance of light by a solution and its concentration and path length.
A=∈lc
Where,
A= absorbance
∈= Molar absorptivity
l= path length
c= concentration
Source: Any text book from HSC level
Gas Chromatography: An analytical technique used to separate and analyze the chemical components of a sample mixture
Key Concepts:
Mobile Phase: An inert gas, typically helium or nitrogen, that carries the vaporized sample through the system.
Stationary Phase: A liquid or solid material coated on a column that interacts with the sample components, slowing their movement based on their chemical properties
Column: The heart of the GC system, where separation occurs, can be packed or capillary.
Detector: Measures the amount of each separated component as it elutes from the column
So the right answer is B
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch/ Any text book from HSC level
Atomic Absorption Spectroscopy: An analytical technique used to determine the concentration of a specific element in a sample by measuring the absorption of electromagnetic radiation by free atoms of that element in the gaseous state
So the right answer is A
Principle of AAS:
AAS relies on the fact that ground-state atoms absorb specific wavelengths of light when exposed to radiation. The amount of light absorbed is directly proportional to the concentration of the element in the sample, following the Beer-Lambert Law.
Explanation: In chromatography, the component that moves with the mobile phase is called Analyte.
The mobile phase, which can be a liquid or a gas, carries the analyte through the stationary phase, where the separation occurs. The analyte is the substance being analyzed and separated
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch
In gravimetric analysis, the precipitate should be of low solubility (easily filterable), high purity, and known composition (stable).
Gravimetric analysis: A quantitative method in analytical chemistry that determines the amount of a substance by measuring its mass.
Principle: Gravimetric analysis relies on the principle that the mass of a substance can be directly related to its quantity. By isolating the analyte in a pure and measurable form, its mass can be used to determine its concentration or amount in the original sample.
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch.
The most common indicator used in complexometric titrations with EDTA is Eriochrome Black T (EBT)
Complexometric titration with EDTA (ethylenediaminetetraacetic acid): It is a type of titrimetric analysis where a metal ion's concentration is determined by forming a soluble complex with EDTA. EDTA, a chelating agent, binds to metal ions in a 1:1 ratio, allowing for accurate quantification. The titration involves adding EDTA solution to a metal ion solution until the reaction is complete, as indicated by a color change of a metallochromic indicator.
How EBT works: EBT is blue in its deprotonated form. When it binds to metal ions, it forms a red or wine-red colored complex
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch
Explanation:
Conductometric titration: is an analytical method that determines the concentration of a substance by measuring changes in the electrical conductivity of a solution as a titrant is added.
Principle:
1. Conductometric titrations are based on the principle that electrical conductivity is directly related to the concentration of ions in a solution.
2. As a titrant is added to the analyte, the reaction between the two causes a change in the ionic composition of the solution
3. This change in ion concentration directly affects the solution's conductivity, allowing for the determination of the equivalence point.
Advantages:
1. Suitable for Colored or Turbid Solutions
2. Conductometric titration can be done even when indicators fail.
3. Versatile (Strong Acid vs. Strong Base, Weak Acid vs. Strong Base, Weak acid–weak base etc )
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch
Explanation: At infinite dilution, H+ (hydronium ion) exhibits the highest molar conductivity. This is due to the unique Grotthuss mechanism of proton hopping, which allows H+ to move much faster than other ions in solution.
So the right answer is B
Source: Any text book from HSC level.
Equivalent conductance of an electrolyte solution generally increases with dilution due to increased ionization and ionic mobility
Explanation: Dilution reduces the attractive forces between ions, allowing them to move more freely and conduct electricity more effectively
Equivalent Conductance: Equivalent conductance (Λ) is a measure of the conducting ability of all the ions produced by one gram equivalent of an electrolyte in a solution. When a solution is diluted, the concentration of ions decreases, but the degree of ionization. Dilution also reduces the interionic interactions, meaning ions experience less attraction or repulsion from each other. This leads to an increase in ionic mobility, which is the speed at which ions move through the solution under the influence of an electric field
Source: Any text book from HSC level.
Explanation: Systematic error is a consistent or proportional difference between the observed and true values of something.
Systematic errors are inherent and require correction, not averaging. Random error, Gross error & Instrumental error can be minimized by increasing the number of measurements.
So the right answer is C
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch
Explanation: Primary standard substances are highly pure, stable, and non-reactive chemicals used to accurately determine the concentration of solutions, particularly in titrations.
So the right answer is B
Option A: hygroscopic substances are highly reactive with water.
Option C: Volatile substances are not suitable for titration.
Option D: Primary standard substances can be base, reductant, oxidant besides acid.
So, Options A, C, D are wrong
Source: Any text book from HSC level
Explanation:
In gravimetric analysis, ignition of a precipitate is primarily done to convert it into a stable, known chemical compound with a constant composition.
This conversion allows for accurate and reliable weighing of the precipitate, which is crucial for quantitative analysis. Specifically, ignition removes water (both absorbed and hydrated) and other volatile impurities, leaving behind a pure, weighed form of the desired compound.
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch
Conductometry: is an electrochemical method used to measure the electrical conductivity of a solution, typically an electrolyte solution
AAS: Analytical technique used to determine the concentration of specific elements (like metal ions, metalloids) in a sample
Potentiometric titration: is a method in analytical chemistry that determines the concentration of a substance (analyte) by measuring the potential difference between two electrodes as a titrant of known concentration is added
Gravimetric analysis: A quantitative chemical analysis method used to determine the amount of a substance (analyte) by measuring its mass.
So the right answer is B
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch.
Explanation: Absorption of infrared (IR) radiation occurs when the frequency of the radiation matches the vibrational frequency of a molecule's bonds.
Infrared (IR) spectroscopy: is a technique that utilizes the interaction of infrared radiation with matter to study the vibrational and rotational energy levels of molecules. This interaction, typically absorption, provides information about the functional groups and molecular structure of a substance, making it a valuable tool in various fields like chemistry, pharmaceuticals, and materials science.
Applications:
Organic Chemistry: Identifying functional groups, determining molecular structure, and analyzing reaction progress.
Materials Science: Studying the properties of polymers, plastics, and other materials.
Pharmaceutical Analysis: Identifying and quantifying drug molecules.
Food Science: Analyzing the composition and quality of food products.
Environmental Science: Monitoring pollutants and contaminants.
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch.
Explanation: In HPLC, column efficiency refers to how effectively a column separates analytes, resulting in narrow, well-defined peaks.
Key factors:
1. the particle size of the stationary phase (Smaller particle size increases surface area → higher efficiency)
2. column dimensions (length and diameter)
3. mobile phase flow rate
4. the properties of the stationary and mobile phases
So the right answer is A
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch
Explanation: In gas chromatography (GC), retention time, which is the time it takes for a compound to travel through the column, primarily depends on the column temperature, the properties of the stationary phase, and the properties of the analyte itself.
So the right answer is C where Stronger interactions = longer retention.
Gas chromatography (GC): is an analytical technique used to separate and analyze the chemical components of a sample mixture. It works by vaporizing the sample and separating the components based on their differing affinities for a stationary phase within a column, which is then detected and quantified
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch
Explanation:
The primary advantage of ICP-OES over AAS is its versatility and ability to detect multiple elements simultaneously.
ICP-OES can analyze a wider range of elements, including some non-metals, and is more efficient for multi-element analysis compared to AAS, which typically analyzes one element at a time.
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch
The most suitable analytical technique for determining the oxidation state of a metal in a complex compound is X-ray photoelectron spectroscopy (XPS)
Explanation: XPS allows for the precise determination of oxidation states by measuring the binding energy of electrons emitted from the metal atom, which is affected by its electronic environment (i.e., the surrounding atoms and their oxidation state)
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch
In mass spectrometry, isotopes of an element are separated based on their mass-to-charge ratio (m/z).
Explanation: This separation occurs because different isotopes of the same element have different numbers of neutrons, leading to variations in their mass, even though they have the same number of protons and electrons.
Mass spectrometry: is a powerful analytical technique used to identify and quantify the chemical components of a sample by measuring the mass-to-charge ratio of ions
Source: "Principles of Instrumental Analysis" by Skoog, Holler, and Crouch