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800 most-asked Class 11 & 12 (+1 / +2) questions across Physics, Chemistry, Maths and Biology — each with a model answer and the exact marking-scheme points examiners reward. Revise smart, walk in calm.
ChemistryClass 112 marksmedium
Equilibrium
State Le Chatelier's principle. What is the effect of increasing pressure on the equilibrium N2(g) + 3H2(g) <=> 2NH3(g)?
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Le Chatelier's principle states that if a system at equilibrium is subjected to a change in concentration, pressure or temperature, the equilibrium shifts in the direction that tends to counteract (reduce) the effect of that change. Increasing the pressure shifts this equilibrium in the forward direction (towards NH3), because the forward reaction reduces the number of gas moles from 4 (1 + 3) to 2, thereby lowering the pressure.
Marking-scheme points
- ✓System shifts to oppose the imposed change
- ✓Higher pressure favours the side with fewer gas moles
- ✓Here forward reaction (4 -> 2 moles) is favoured -> more NH3
ChemistryClass 112 markseasy
Equilibrium
Define an acid and a base according to the Bronsted-Lowry concept. What is a conjugate acid-base pair?
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According to the Bronsted-Lowry concept, an acid is a substance that donates a proton (H+) and a base is a substance that accepts a proton. A conjugate acid-base pair is a pair of species that differ by a single proton; for example, in HCl + H2O -> H3O+ + Cl-, HCl/Cl- and H2O/H3O+ are conjugate acid-base pairs.
acid <=> base + H+
Marking-scheme points
- ✓Bronsted acid = proton donor; base = proton acceptor
- ✓Conjugate pair differs by one proton (H+)
- ✓Example: HCl/Cl- and H2O/H3O+
ChemistryClass 112 markseasy
Equilibrium
Calculate the pH of a 0.001 M HCl solution.
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HCl is a strong acid and dissociates completely, so [H+] = 0.001 M = 1 x 10^-3 M. pH = -log[H+] = -log(10^-3) = 3. The solution is acidic (pH < 7).
pH = -log[H+]
Marking-scheme points
- ✓Strong acid: [H+] = 10^-3 M
- ✓pH = -log[H+]
- ✓pH = 3 (acidic)
ChemistryClass 112 marksmedium
Equilibrium
What is the ionic product of water (Kw)? State its value at 298 K and its relation with pH.
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Equilibrium
What is the common ion effect? Explain with a suitable example.
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Redox Reactions
Define oxidation and reduction in terms of electron transfer and oxidation number.
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Redox Reactions
Calculate the oxidation number of manganese in KMnO4 and of chromium in K2Cr2O7.
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Redox Reactions
Define an oxidising agent and a reducing agent with one example each.
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Redox Reactions
What is a disproportionation reaction? Give one example.
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Redox Reactions
In the reaction Zn + CuSO4 -> ZnSO4 + Cu, identify the species oxidised, the species reduced, the oxidising agent and the reducing agent.
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Hydrogen
Why is the position of hydrogen anomalous in the periodic table?
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Hydrogen
Explain why hydrogen peroxide (H2O2) can act both as an oxidising agent and as a reducing agent.
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The s-Block Elements
Why are alkali metals strong reducing agents?
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The s-Block Elements
What is a diagonal relationship? Why do lithium and magnesium show similar properties?
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The s-Block Elements
Why does lithium show anomalous behaviour compared with the other alkali metals?
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The p-Block Elements
What is the inert pair effect? Illustrate with an example from group 14.
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The p-Block Elements
Why does boron trifluoride (BF3) behave as a Lewis acid?
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The p-Block Elements
What is catenation? Why does carbon show it to a maximum extent? Name three allotropes of carbon.
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The p-Block Elements
Why is diamond very hard while graphite is soft and a good conductor of electricity?
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Organic Chemistry: Some Basic Principles and Techniques
Give the IUPAC names of (CH3)2CHCH2CH3 and CH3COOH.
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