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Which ONE of the following compounds has the HIGHEST vapour pressure? A - NSC Physical Sciences - Question 1 - 2019 - Paper 2

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Question 1

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Which ONE of the following compounds has the HIGHEST vapour pressure? A. HCOOH B. CH3CHO C. CH3CH2OH D. CH3CH2CH3

Worked Solution & Example Answer:Which ONE of the following compounds has the HIGHEST vapour pressure? A - NSC Physical Sciences - Question 1 - 2019 - Paper 2

Step 1

Identify the Compounds

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Answer

We are given four compounds: HCOOH (formic acid), CH3CHO (acetaldehyde), CH3CH2OH (ethanol), and CH3CH2CH3 (propane).

Step 2

Consider Vapour Pressure Factors

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Answer

Vapour pressure is influenced by intermolecular forces. Compounds with weaker forces tend to have higher vapour pressures. In this case, propane (D) is a non-polar molecule with weak Van der Waals forces, while the others are polar and exhibit hydrogen bonding.

Step 3

Evaluate Each Compound

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Answer

  1. HCOOH: Strong hydrogen bonding, lower vapour pressure.
  2. CH3CHO: Also polar with hydrogen bonding, moderate vapour pressure.
  3. CH3CH2OH: Alcohol, exhibits strong hydrogen bonding, lower vapour pressure than non-polar compounds.
  4. CH3CH2CH3: Non-polar, weak intermolecular forces, expected to have the highest vapour pressure.

Step 4

Conclusion

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Answer

Thus, the compound with the highest vapour pressure is D. CH3CH2CH3 (propane).

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