Chemistry
Question from maharashtra board chemistry book of 12th maharashtra board
- Which of the following reactions has 100% atom economy? Answer: B. CH2=CH2 + H2 → C2H6 In an addition reaction all reactant atoms end up in the product, so the atom economy is 100%. 1
- Which of the following undergoes SN1 reaction fastest? Answer: D. (CH3)3CBr S_N1 rate depends on carbocation stability; the tertiary carbocation is the most stable. 1
- Chlorobenzene reacts with methyl chloride and sodium in dry ether. The main product is Answer: C. toluene Wurtz–Fittig reaction: C₆H₅Cl+CH₃Cl+2Na→ C₆H₅CH₃+2NaCl . 1
- The pH of 0.1 M acetic acid (\(K_a=1.8\times10^{-5}\)) is approximately Answer: B. 2.87 [H^+]=√(K_aC)=sqrt1.8×10⁻⁶=1.34×10⁻³ M; pH ≈2.87 . 1
- The solubility of Ag2CrO4 in water is \(1\times10^{-4}\) mol L-1. Its solubility product is Answer: A. 4×10⁻¹² K_sp=(2s)²s=4s³=4×10⁻¹² . 1
- A buffer contains 0.02 M acetic acid and 0.2 M sodium acetate. If p\(K_a\) of acetic acid is 4.74, the pH of the buffer is Answer: B. 5.74 pH =pK_a+log[salt]/[acid]=4.74+log10=5.74 . 1
- The packing efficiency of a body-centred cubic (bcc) unit cell is Answer: C. 68% In bcc, 4r=sqrt3a ; two atoms occupy 2·4/3π r³/a³≈0.68 of the cell. 1
- An element with molar mass 60 g mol-1 forms an fcc lattice with edge length 400 pm. Its density is approximately (\(N_A=6.022\times10^{23}\)) Answer: D. 6.23 g cm-3 ρ=ZM/a³N_A=frac4×60(4×10⁻⁸)³×6.022×10²³=240/38.54≈6.23 g cm⁻³. 1
- In a cubic solid, atoms A occupy the corners and atoms B occupy the face centres. If one A atom is missing from one corner of each unit cell, the formula of the compound is Answer: D. A7B24 A =7×1/8=7/8 , B =6×1/2=3 . Ratio 7/8:3=7:24 . 1
- Which of the following defects does NOT change the density of an ionic crystal? Answer: D. Frenkel defect In a Frenkel defect an ion only shifts to an interstitial site, so mass and volume stay the same. 1
- 1.8 g of glucose (molar mass 180 g mol-1) is dissolved in 100 g of water. The elevation in boiling point is (\(K_b=0.52\) K kg mol-1) Answer: D. 0.052 K m=0.01/0.1=0.1 mol kg⁻¹; Δ T_b=0.52×0.1=0.052 K. 1
- The osmotic pressure of a 0.1 M aqueous solution of a non-electrolyte at 300 K is (R = 0.082 L atm K-1 mol-1) Answer: C. 2.46 atm π=CRT=0.1×0.082×300=2.46 atm. 1
- Which of the following liquid pairs shows a negative deviation from Raoult's law? Answer: C. Acetone + chloroform Acetone and chloroform form hydrogen bonds with each other, so the A–B attraction is stronger than A–A and B... 1
- The spin-only magnetic moment of Fe2+ ion (Z of Fe = 26) is Answer: A. 4.90 BM Fe²⁺ is 3d⁶ with 4 unpaired electrons: μ=√(4×6)=√(24)≈4.90 BM. 1
- In acidic medium, the number of moles of KMnO4 required to oxidise 1 mole of Fe2+ to Fe3+ is Answer: A. 0.2 mathrmMnO₄^-+5Fe²⁺+8H^+→ Mn²⁺+5Fe³⁺+4H₂O ; 1 mol Fe²⁺ needs 1/5 mol MnO₄⁻. 1
- A 0.1 m solution of K2SO4 in water has a freezing point of – 4.3 °C. Given: Molality of K₂SO₄ solution = m = 0.1 m Freezing point of solution = T_f = – 4.3 °C K_f of water = 1.86 K kg mol^(–1)To find: van’t Ho... 1
- Write the equation relating boiling point elevation to the concentration of the solution. The boiling point elevation is directly proportional to the molality of the solution. Thus, Δ Tb ∝ m ∴ Δ Tb ∝ Kb m where, m is the molality... 1
- An element with molar mass 27 g/mol forms cubic unit cell with edge length of 405 pm Given : Molar mass = M= 27 g m0l_‘ Nature of crystal = cubic unit cell Edge length = a = 405 pm = 4.05 x 10⁻⁸ cm Density = ρ = 2.7 g cm⁻³ Na... 1
- An element has a bcc structure with unit cell edge length of 288 pm. Given: Types of unit cell = bcc, for bcc unit cell n = 2 Edge length (a) = 288 pm = 2.88 x 10^(-8 )cm³ Mass of element (x) =200g Density of... 1
- In an ionic crystalline solid atoms of element Y form hcp lattice. In the given hcp lattice, Y atoms are present at 12 corners and 2 face centres. ∴ Number of Y atoms = 1/6×12 +1/2×2 = 2+1= 3 There are 6 tet... 2
- Aluminium crystallizes in cubic close packed structure with unit cell edge length of 353.6 pm. Given : Structure of Al = Cubic close packed structure = ccp structure Edge length of unit cell = a = 353.6 pm = 3.536 x 10⁻⁸ cm r = ? Numbe... 1
- The density of iridium is 22.4 g/cm3. The unit cell of iridium is fcc. Calculate the radius of iridium atom. Given : Crystal structure of iridium = fcc Molar mass of iridium = 192.2 gmol⁻¹ Density = ρ = 22.4 gcm⁻³ Radius of iridium = ? In fcc struct... 1
- Cu crystallizes in fcc unit cell with edge length of 495 pm. Given : a = 495 pm Radius, r = ? For fcc structure, Radius = r = a/2√(2)= 495/2√(2) = 175pm Ans. Radius of Cu atom = 175 pm. 1
- Cesium chloride crystallizes in cubic unit cell with Cl- ions at the corners and a Cs+ ion in the centre of the cube. Number of Cs⁺ ion at body centre = 1 A Number of Cl⁻ ions due to 8 comers = 1/8×8 = 1 Hence unit cell contains 1 CsCl molecule. 1