Some Basic Concepts of Chemistry

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Some Basic Concepts of Chemistry — solved practice questions

8 JEE Chemistry questions with step-by-step solutions. Attempt each, then reveal the answer.

1. Q1easy

   How many moles of methane (CH4) are present in 3.2 g of the gas? (Molar mass of CH4 = 16 g/mol)

   • A0.1 mol
   • B0.2 mol
   • C0.32 mol
   • D2.0 mol
   Show answer & solution

   Correct answer: (B) 0.2 mol

   Moles = mass / molar mass = 3.2 / 16 = 0.2 mol. This is a direct application of the mole concept.

2. Q2easy

   What is the molarity of a solution prepared by dissolving 5.85 g of NaCl in enough water to make 500 mL of solution? (Molar mass of NaCl = 58.5 g/mol)

   • A0.05 M
   • B0.1 M
   • C0.2 M
   • D0.4 M
   Show answer & solution

   Correct answer: (C) 0.2 M

   Moles of NaCl = 5.85 / 58.5 = 0.1 mol. Molarity = moles / volume(L) = 0.1 / 0.5 = 0.2 M.

3. Q3easy

   The percentage by mass of nitrogen in ammonium nitrate (NH4NO3) is closest to: (N = 14, H = 1, O = 16)

   • A17.5%
   • B23.3%
   • C28.0%
   • D35.0%
   Show answer & solution

   Correct answer: (D) 35.0%

   Molar mass of NH4NO3 = 14+4+14+48 = 80 g/mol. Nitrogen mass = 2 x 14 = 28. %N = (28/80) x 100 = 35%.

4. Q4medium

   A compound contains 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass. What is its empirical formula? (C = 12, H = 1, O = 16)

   • ACH2O
   • BC2H4O2
   • CCHO
   • DC2H4O
   Show answer & solution

   Correct answer: (A) CH2O

   Mole ratio C:H:O = 40/12 : 6.7/1 : 53.3/16 = 3.33 : 6.7 : 3.33 = 1 : 2 : 1, giving CH2O.

5. Q5medium

   The number of oxygen atoms present in 0.2 mol of H2SO4 is: (NA = 6.022 x 10^23)

   • A1.20 x 10^23
   • B2.41 x 10^23
   • C4.82 x 10^23
   • D1.20 x 10^24
   Show answer & solution

   Correct answer: (C) 4.82 x 10^23

   Each H2SO4 has 4 O atoms, so moles of O atoms = 0.2 x 4 = 0.8 mol. Number of O atoms = 0.8 x 6.022 x 10^23 = 4.82 x 10^23.

6. Q6medium

   Commercial concentrated sulphuric acid is 98% H2SO4 by mass and has a density of 1.84 g/mL. Its molarity is approximately: (Molar mass H2SO4 = 98 g/mol)

   • A9.2 M
   • B18.4 M
   • C1.84 M
   • D36.8 M
   Show answer & solution

   Correct answer: (B) 18.4 M

   In 1 L, mass of solution = 1840 g; mass of H2SO4 = 0.98 x 1840 = 1803.2 g; moles = 1803.2/98 = 18.4. Molarity = 18.4 M.

7. Q7medium

   For the reaction N2 + 3H2 -> 2NH3, if 3 mol of N2 react with 6 mol of H2, how many moles of NH3 can be formed?

   • A6 mol
   • B3 mol
   • C2 mol
   • D4 mol
   Show answer & solution

   Correct answer: (D) 4 mol

   H2 is the limiting reagent: 6 mol H2 needs 2 mol N2 (only 2 of the 3 mol N2 react). Moles NH3 = 6 x (2/3) = 4 mol.

8. Q8easy

   The volume occupied by 0.5 mol of an ideal gas at STP (where molar volume = 22.4 L/mol) is:

   • A11.2 L
   • B22.4 L
   • C5.6 L
   • D44.8 L
   Show answer & solution

   Correct answer: (A) 11.2 L

   Volume = moles x molar volume = 0.5 x 22.4 = 11.2 L at STP.

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