More practice questions

3. Q3. Arrange CH₃CH₂CH₃, CH₃OCH₃, CH₃CHO and CH₃CH₂OH in increasing order of boiling point.

   Show answerHide answer

   CH₃CH₂CH₃ < CH₃OCH₃ < CH₃CHO < CH₃CH₂OH: the alkane has only weak van der Waals forces, the ether is weakly polar, the aldehyde has stronger dipole–dipole attraction, and the alcohol is hydrogen bonded (NCERT Intext Question 8.3, page 236; reasoned from page 235).

4. Q4. Which of methanal, ethanal and propanone are gases at 25 °C and 1 atm?

   Show answerHide answer

   Methanal and ethanal are gases; propanone is a liquid. Ethanal’s normal boiling point is about 20–21 °C (NIST), so it is a liquid only below that. If a question uses NCERT’s wording and asks which is a gas at room temperature, answer methanal, and call ethanal “a volatile liquid”, as NCERT does (page 235).

5. Q5. Check that NCERT’s five compounds in Section 8.3 all have molar masses of 58 or 60. (C = 12, H = 1, O = 16.)

   Show answerHide answer

   n-Butane C₄H₁₀: 48 + 10 = 58. Methoxyethane C₃H₈O: 36 + 8 + 16 = 60. Propanal and acetone C₃H₆O: 36 + 6 + 16 = 58. Propan-1-ol C₃H₈O: 60 (reasoned from NCERT page 235).

6. Q6. Propanal and acetone are isomers. Which boils higher by NCERT’s data, and by how much?

   Show answerHide answer

   Acetone, 329 K against 322 K: 7 K higher (NCERT page 235).