Learn Chemistry with Prof. Kiran Patil

 A buffer solution is a solution that resists changes in pH when small amounts of acid or base are added to it. It is a mixture of a weak acid and its conjugate base, or a weak base and its conjugate acid. Buffer solutions are used in a variety of applications, including:  * Chemical reactions: Buffer solutions are used to maintain a constant pH during chemical reactions.  * Biological systems: Buffer solutions are used to maintain the pH of blood and other bodily fluids.  * Industrial processes: Buffer solutions are used in a variety of industrial processes, such as food production and wastewater treatment. Here are some examples of buffer solutions:  * A mixture of acetic acid and sodium acetate  * A mixture of ammonium chloride and ammonia  * A mixture of citric acid and sodium citrate The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]) where:  * pKa is the negative logarithm of the ...

 Dry cells are a type of battery commonly used in many portable electronic devices. While they have some advantages, they also have several disadvantages:  * Non-rechargeable: Dry cells are primary batteries, meaning they cannot be recharged once they are depleted. This leads to increased waste and the need for frequent replacements.  * Limited applications: Due to their non-rechargeable nature, dry cells are not suitable for devices that require a continuous power supply or high current demands.  * Lower energy density: Compared to some other battery types, dry cells have a lower energy density, meaning they store less energy for the same size and weight. This can result in shorter operating times for devices.  * Environmental concerns: Dry cells contain hazardous materials, such as heavy metals and chemicals, which can leach into the environment if they are not disposed of properly. This can cause soil and water contamination, posing risks to human health and ...

  The SN2 mechanism describes  a type of nucleophilic substitution reaction where a nucleophile replaces a leaving group in a one-step process. In the specific case of methyl bromide reacting with aqueous KOH, the nucleophile is the hydroxide ion (OH-) from KOH, and the leaving group is the bromide ion (Br-). Here's a step-by-step breakdown of the SN2 mechanism:  * Nucleophile Attack: The hydroxide ion (OH-) acts as a nucleophile, meaning it is attracted to positive charges. It approaches the methyl bromide molecule from the opposite side of the bromine atom. This is called "backside attack."  * Transition State: As the hydroxide ion approaches, it starts forming a bond with the carbon atom, while the bond between carbon and bromine starts breaking. This leads to a transition state where the carbon atom is partially bonded to both the hydroxide ion and the bromine atom. The transition state is unstable and high in energy.  * Leaving Group Departure: The carbon-b...

  Haloarenes are indeed less reactive than haloalkanes, particularly in nucleophilic substitution reactions. Here's a breakdown of the key reasons: 1. Resonance Effect  * In haloarenes, the halogen atom's lone pair of electrons interacts with the pi electron system of the aromatic ring. This leads to resonance, where the electrons are delocalized across the ring.  * This resonance gives the carbon-halogen bond a partial double bond character, making it stronger and more difficult to break compared to the single bond in haloalkanes. 2. Hybridization of Carbon  * The carbon atom attached to the halogen in haloarenes is sp² hybridized, while in haloalkanes, it's sp³ hybridized.  * sp² hybridized carbons have a higher s-character, making them more electronegative. This means they hold onto the electrons in the C-X bond more tightly, making it less polarized and less susceptible to nucleophilic attack. 3. Instability of Phenyl Cation  * If a nucleophilic substit...

(a) Why are cations Lewis acids?  * Lewis acids are defined as species that can accept an electron pair.  * Cations are ions with a positive charge. This positive charge indicates that they have a deficiency of electrons compared to the neutral atom.  * To achieve stability, cations tend to accept electrons to neutralize their positive charge.  * Therefore, since cations have a tendency to accept electron pairs, they fit the definition of Lewis acids. Example:  H+  +  :NH3  ==>  [H3NH]+ *  H+ (cation) acts as a Lewis acid by accepting the lone pair from :NH3. (b) Why is ammonia (NH3) a Lewis base?  * Lewis bases are defined as species that can donate an electron pair.  * Ammonia (NH3) has a lone pair of electrons on the nitrogen atom.  * This lone pair is available for donation to another species to form a coordinate bond.  * Therefore, since ammonia has the ability to donate an electron pair, it fits the definitio...

In a crystalline compound, atoms C occupy CCP lattices while atoms D occupy 2/3rd tetrahedral voids. What is the formula of the compound? Solution Data: In CCP unit lattice points are 8 corners and 6 face centres where atoms C are present.  Number of C atoms = ⅛×8 + ½×6                                  =1+3=4  In cubic unit cell, there are 8 tetrahedral voids.  Number of D atoms = ⅔×8 = 16/3 The formula of the compound is C₃D₄

   What is metallic bond? Ans. The bonding between metal atoms in a crystal of pure metal is called as metallic bond. Why is the conductivity of doped n-type semiconductor higher than that of pure semiconductor? (i) n-type semiconductor is an extrinsic semi conductor (doped semiconductor) which contains increased number of electrons in the conduction band. ii ) An n-type semiconductor is obtained by adding group 15 element to intrinsic semiconductor of group 14 element. e.g. doping of Si with P. (iii) As a result of doping, there are more number of electrons (charge carriers) in the conduction band of the doped n-type semiconductor, than those in the pure semiconductor. (iv) The electrons in the conduction band move under the influence of an applied potential and hence conductivity of the doped n-type semiconductor is higher.

 Explain n-type semiconductor with an example. (i) n-type semiconductor is an extrinsic semiconductor obtained by doping an intrinsic semiconductor with increased number of electron in the conduction band. (ii) Doping of Silicon with Phosphorus Silicon is a crystal structure in which each Si atom is tetrahedrally linked to four other Si atoms. (iii) When a small quantity of P is added to pure Si, the P atoms occupy some vacant sites in the lattice in place of Si atoms. (iv) Four of the five valence electrons of P are utilized in bonding the closest of the four Si atoms, thus P has one extra electron than needed for bonding. (vi) Therefore, the number of electrons in the conduction band of the doped Si are more than those in the conduction band of pure Si. This increases the conductivity of the doped Silicon.  examples of n-type semiconductor. Ans. Si or Ge doped with group 15 elements such as P,As,Sb or Bi are examples of n- type of semiconductor.

What are the conditions and consequence of Frenkel defect.. Ans. Conditions for the formation of Frenkel defect (i) Frenkel defect occurs in ionic compounds with large difference between sizes of cation and anion. (ii) The ions of ionic compounds must be having low coordination number. (ii) The crystal as a whole remains electrically neutral because the equal numbers of cation and anions are present. (a) Write examples of ionic solids with Frenkel defect. Ans. ZnS, AgCl, AgBr, AgI, CaF, etc (b) Name the type of point defect that occurs in a crystal of zinc sulphide? (c) Why Frenkel defect is found in AgCI?  Ans. Frenkel defect is found in AgCl due to small size of silver cation (Ag+) (d) Why is Frenkel defect is not found in pure alkali Ans. Frenkel defect is not found in pure alkali metal halide due to large size of alkali metal ions which cannot fit into interstitial sites. (e) Name the ionic compound which shows both Schottky and Frenkel defect? Ans. Silver bromide (AgBr)

Write a note on: Polymorphism. (i) A single substance that exists in two or more crystalline structures is said to be polymorphous. (ii) Polymorphs of a substance are formed under different conditions. (iii) Polymorphism occurring in elements is called (iv) Example of polymorphous forms: CaCO3: (Calcite and aragonite) Silica:  (α quartz,ẞ- quartz, cristobalite, etc.) (v) Example of allotropic forms: Diamond, graphite fullerene etc. [carbon.]  Define. Anisotropy . Ans. The ability of crystalline solids to change values of physical properties when measured in different directions is called anisotrophy.

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