TLDR;
This YouTube video by Priyeshsir Vidhyapeeth features a chemistry lesson focused on solving multiple-choice questions (MCQs) relevant to board exams. The instructor reviews key concepts, provides shortcuts, and clarifies common mistakes students make while tackling these problems. The session also includes guidance on practical exams and general study tips.
- Focus on understanding concepts rather than rote memorisation.
- Solve previous year question papers and sample papers.
- Time management during exams is crucial.
Introduction and Preparation Tips [0:05]
The instructor greets the students and inquires about their study progress, encouraging them to share what subjects and chapters they have been studying. He urges students to like the stream and share it with their friends, emphasising the importance of focused study time. He addresses a common question about the scope of MCQs, clarifying that while the sessions are helpful, comprehensive preparation is necessary for success.
MCQ 1: Identifying Different Cell Types [3:19]
The first MCQ asks students to identify the cell that operates on a different principle. The options include various electrochemical cells and one electrolytic cell. The instructor explains that electrochemical cells produce electrical energy from chemical reactions, while electrolytic cells use electrical energy to drive chemical reactions. Therefore, the electrolytic cell is the odd one out.
MCQ 2: Reducing Agent Strength [5:00]
This question involves determining the decreasing order of reducing agent strength based on standard electrode potentials. The instructor clarifies that a good reducing agent has a lower reduction potential. By comparing the given reduction potentials of metals X, Y, and Z, the correct order is determined to be Z > X > Y.
MCQ 3: Solubility and KH Values [6:14]
The MCQ requires arranging gases in increasing order of solubility based on their Henry's Law constants (KH). The instructor explains the inverse relationship between KH and solubility: higher KH means lower solubility. By comparing the KH values of Argon, CO2, HCHO, and CH4, the correct order of increasing solubility is determined.
MCQ 4: Relative Lowering of Vapour Pressure and Molality [7:52]
This problem involves finding the molality of a solution given the relative lowering of vapour pressure (RLVP). The instructor provides a shortcut formula: RLVP = molality × (molar mass of solvent / 1000). Knowing that the solvent is water, the molality can be calculated using the given RLVP value.
Practical Exam Guidance Announcement [10:04]
The instructor announces a live session at 8:30 PM to address students' doubts regarding practical exams. This session aims to answer questions about required materials, lab attire, and how to handle supervisor inquiries, providing comprehensive support for practical exam preparation.
MCQ 5: Molality Calculation from Percentage Composition [11:30]
The question asks to calculate the molality of a 10% w/w aqueous solution of NaOH. The instructor explains that 10% w/w means 10 grams of solute in 100 grams of solution. From this, the mass of the solvent (water) can be determined, and the molality calculated using the standard formula.
MCQ 6: Boiling Point Elevation [13:37]
This MCQ involves calculating the boiling point of a one molal urea solution in Kelvin. The instructor uses the formula for elevation in boiling point: ΔTb = i × Kb × molality. Since urea does not dissociate or associate, the van't Hoff factor (i) is 1. The new boiling point is then found by adding the elevation to the normal boiling point of water.
MCQ 7: Positive Deviation from Raoult's Law [15:23]
The question asks which mixture shows positive deviation from Raoult's Law. The instructor notes that alcohol-containing mixtures generally show positive deviation. The correct answer is ethanol plus acetone.
MCQ 8: Osmotic Pressure Comparison [16:27]
This MCQ requires identifying the solution with the highest osmotic pressure under identical conditions. Using the formula π = iCRT, and assuming R and T are constant, the solution with the highest iC value will have the highest osmotic pressure. By calculating the van't Hoff factor (i) for each solution, FeCl3 is identified as having the highest osmotic pressure due to producing the most ions.
MCQ 9: Potential of Hydrogen Electrode [18:06]
The question asks for the potential of a hydrogen electrode in contact with a solution of pH = 1. The instructor explains how to use the Nernst equation, simplifying it for the hydrogen electrode. By relating pH to H+ concentration and applying the Nernst equation, the electrode potential is calculated.
MCQ 10: Faraday's Law of Electrolysis [22:48]
This MCQ involves calculating the amount of electricity in Faradays required to reduce two moles of MnO4- to Mn+2. The instructor explains that the reduction requires 5 moles of electrons per mole of MnO4-. Therefore, for two moles, 10 moles of electrons are needed, which corresponds to 10 Faradays.
Study Advice and Time Management [24:31]
The instructor advises students to maximise their study time and not rely solely on watching videos. He emphasises the importance of self-study, practice, and revision for achieving good marks. He also suggests writing full-length practice papers to prepare for the chemistry board exam.
MCQ 11: Factors Affecting Electronic Conductance [26:27]
The question asks which factor does not affect electronic conductance. The instructor explains that electronic conductance depends on the nature of the metal, the number of valence electrons, and temperature. Pressure, however, does not have a significant effect on the electronic conductance of solid conductors like wires.
MCQ 12: Rate Constant Unit for Second-Order Reaction [28:23]
This MCQ requires determining the unit of the rate constant for a second-order reaction. The instructor provides a shortcut formula: mol^(1-n) * L^(n-1) * s^(-1), where n is the order of the reaction. Substituting n = 2, the correct unit is found to be mol^(-1) * L * s^(-1).
Graph of lnk vs 1/t [29:52]
The instructor discusses the graph of lnk versus 1/t, explaining that the slope of the graph is -Ea/R. He emphasises the importance of remembering this relationship and the difference between using lnk and logk.
MCQ 13: Electrolysis of Concentrated NaCl Solution [32:26]
The question asks about the resulting solution after the electrolysis of concentrated NaCl solution. The instructor explains that the products are H2, Cl2, and NaOH. NaOH is a base, and therefore the solution will turn red litmus paper blue.
Balancing Study with MCQs and Theory [34:04]
The instructor advises students to balance their study time between theory and MCQs. He discourages the idea of cramming everything into a single session and emphasises the importance of consistent, daily study and practice.
MCQ 14: Order of Reaction and Rate [35:23]
This MCQ involves determining how the rate of a reaction changes when the concentration of the reactant is tripled, given that doubling the concentration quadruples the rate. The instructor explains that the order of the reaction is 1/2. Therefore, tripling the concentration will increase the rate by a factor of 3^(1/2).
MCQ 15: Half-Life of a First-Order Reaction [36:52]
The question asks to find the half-life of a first-order reaction given the rate at two different times. The instructor uses the integrated rate law to find the rate constant (k) and then uses the half-life formula t1/2 = 0.693/k to calculate the half-life.
MCQ 16: Arrhenius Equation and Graph [40:26]
This MCQ asks which graph is used to obtain the value of the Arrhenius constant. The instructor explains that the graph of log k versus 1/T is used, where the y-intercept gives log a and the slope is -Ea / 2.303R.
MCQ 17: Number of Ions in a Complex [41:23]
The question asks for the number of ions formed by a given complex in an aqueous solution. The instructor explains that the complex dissociates into one complex ion and three chloride ions, resulting in a total of four ions.
MCQ 18: IUPAC Naming of Coordination Compounds [41:52]
This MCQ involves naming a coordination compound using IUPAC nomenclature. The instructor explains the rules for naming complexes, including identifying the ligands, central metal ion, and oxidation state.
MCQ 19: Colour of Coordination Compounds [43:32]
The question asks to identify the coloured ions. The instructor explains that colour arises from d-d transitions, which occur when there are unpaired electrons in the d orbitals (1 to 9 electrons). Ions with d0 or d10 configurations are colourless.
MCQ 20: Magnetic Moment of Coordination Compounds [45:26]
This MCQ involves determining which compound has the highest magnetic moment. The instructor explains that the magnetic moment depends on the number of unpaired electrons. By determining the electronic configuration of each metal ion, the compound with the most unpaired electrons (Mn+2) is identified as having the highest magnetic moment.
MCQ 21: Identifying Transition Elements [47:46]
The question asks which element is a transition element. The instructor explains that transition elements have partially filled d orbitals in at least one of their oxidation states. Copper is identified as a transition element because Cu+2 has a d9 configuration.
MCQ 22: Colour of K2MnO4 [48:49]
This MCQ asks for the colour of K2MnO4. The instructor provides a list of colours for various compounds, stating that K2MnO4 is green.
MCQ 23: Primary and Secondary Valency [50:17]
This MCQ involves determining the primary and secondary valencies of a coordination compound. The instructor explains that primary valency is the oxidation state of the metal ion, and secondary valency is the coordination number.
MCQ 24: Isomerism in Coordination Compounds [52:00]
The question asks about the type of isomerism exhibited by a given coordination compound. The instructor explains that the compound exhibits both geometrical and optical isomerism, resulting in three isomers.
MCQ 25: High Spin Complexes [54:55]
This MCQ involves identifying the correct relationship for high-spin complexes. The instructor explains that high-spin complexes occur with weak field ligands, where the crystal field splitting energy (Δo) is less than the pairing energy (P).
Conclusion and Further Guidance [57:59]
The instructor concludes the session, summarising the topics covered and providing guidance on where to find additional resources, such as PDF notes on the PVF app. He encourages students to complete all the sessions for thorough preparation and wishes them good luck.
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