Short Questions (Q.No.2 & Q.No.3)
Q.No.2
- Mass Spectrum
- What it is: A graph showing different masses of atoms/molecules in a sample.
- How it works: Heavy particles appear on the right, light ones on the left. Taller peaks mean more of that particle exists.
- Example: If you analyze air, nitrogen (N₂) will show a big peak at 28 g/mol.
- Limiting Reactant Steps
- Step 1: Write the chemical equation (e.g., H2+O2→H2O
- H2
- +O2
- →H2
- O).
- Step 2: Calculate moles of each reactant (e.g., 2 g H₂ = 1 mole; 32 g O₂ = 1 mole).
- Step 3: Compare ratios. For H2O
- H2
- O, you need 2 H₂ for every O₂. If you have 1 mole of each, H₂ is the limiting reactant (runs out first).
- % Nitrogen in Urea (NH₂CONH₂)
- Step 1: Molar mass of urea = 60 g/mol (N=14, H=1, C=12, O=16).
- Step 2: Total mass of nitrogen = 2 × 14 = 28 g.
- Step 3: 2860×100=46.67%
- 60
- 28
- ×100=46.67%.
- Why?: Urea is a common fertilizer because it’s rich in nitrogen.
- Uses of Chromatography
- Ink separation: Black ink is a mix of colors; chromatography separates them into bands.
- Drug testing: Detects illegal substances in blood or urine by separating chemicals.
- Why Liquids Are Less Common
- Reason: Most substances are solid (e.g., rocks) or gas (e.g., air) at Earth’s temperature. Liquids (like water) exist in a narrow range between 0–100°C.
- Diffusion vs. Effusion
- Diffusion: Perfume spreads in a room (molecules mix slowly).
- Effusion: Air leaks from a balloon (gas escapes through a tiny hole).
- Critical Temperature of Water > Argon
- Water: Needs very high heat (374°C) to become gas because of strong hydrogen bonds.
- Argon: Weak forces between atoms, so it becomes gas at -186°C.
- Reversible Reaction Example
- Example: N2+3H2⇌2NH3
- N2
- +3H2
- ⇌2NH3
- .
- Why?: Ammonia (NH₃) can break back into nitrogen and hydrogen under heat.
Q.No.3
- Ice Floats on Water
- Why?: Ice has a "honeycomb" structure with gaps, making it less dense than liquid water.
- Importance: Lakes freeze from the top, protecting fish below.
- Vacuum Distillation
- Use: Purifies heat-sensitive liquids (e.g., essential oils) by boiling them at lower temperatures (no air pressure).
- Example: Extracting lavender oil without burning it.
- Ionic Crystals Are Brittle
- Reason: Layers of ions shift, causing same charges to repel and crack (like pushing same poles of magnets together).
- Anion > Parent Atom
- Example: Chlorine (Cl) gains an electron to become Cl⁻. The extra electron repels others, making the ion larger.
- Burning Candle is Spontaneous
- Why?: It releases heat/light naturally (no external energy needed).
- Non-spontaneous example: Melting ice requires heat from outside.
Long Questions (Q.No.4 & Part-II)
Q.No.4
- Electronic Configuration
- Na (11): 1s22s22p63s1
- 1s2
- 2s2
- 2p6
- 3s1
- . The last electron is in the 3s orbital (shiny, reactive metal).
- Cr (24): 4s13d5
- 4s1
- 3d5
- (not 4s23d4
- 4s2
- 3d4
- ) because half-filled d-orbitals are more stable.
- Hund’s Rule
- Rule: Electrons fill orbitals one by one before pairing (like people sitting alone on a bus before sharing seats).
- Example: Oxygen (1s22s22p4
- 1s2
- 2s2
- 2p4
- ) has 2 unpaired electrons in the 2p subshell.
- CuSO₄ is Acidic
- Reason: Cu²⁺ reacts with water:
- Cu2++2H2O→Cu(OH)2+2H+
- Cu2+
- +2H2
- O→Cu(OH)2
- +2H+
- The H⁺ ions make the solution sour (pH < 7).
Part-II
Q.No.5: Empirical Formula
- Given: Ethylene glycol has 38.7% C, 9.7% H, 51.6% O.
- Steps:
- Assume 100 g sample → 38.7 g C, 9.7 g H, 51.6 g O.
- Convert to moles:
- C: 38.712=3.225
- 12
- 38.7
- =3.225
- H: 9.71=9.7
- 1
- 9.7
- =9.7
- O: 51.616=3.225
- 16
- 51.6
- =3.225
- Divide by smallest (3.225): C₁H₃O₁ → CH₃O.
Q.No.7: Ethyne (C₂H₂) Structure
- Hybridization: Carbon uses sp orbitals (mixes one s and one p orbital).
- Shape: Linear (180° bond angle), like a straight line: H―C≡C―H.
Q.No.8: Balancing Redox Reaction
- Equation:
- 3CN−+2MnO4−+H2O→3CNO−+2MnO2+2OH−
- 3CN−
- +2MnO4
- −
- +H2
- O→3CNO−
- +2MnO2
- +2OH−
- Steps:
- Balance atoms (C, N, Mn).
- Add OH⁻ to balance charge (right side had extra negative charge).
Q.No.9: Mole Fraction
- Given: 92 g ethanol, 96 g methanol, 90 g water.
- Moles:
- Ethanol (C₂H₅OH): 9246=2
- 46
- 92
- =2
- Methanol (CH₃OH): 9632=3
- 32
- 96
- =3
- Water (H₂O): 9018=5
- 18
- 90
- =5
- Total moles: 10.
- Mole fractions:
- Ethanol = 210=0.2
- 10
- 2
- =0.2
- Methanol = 310=0.3
- 10
- 3
- =0.3
- Water = 510=0.5
- 10
- 5
- =0.5.