DP Chemistry (last assessment 2024)

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Question 19M.2.hl.TZ2.1d(iii)

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Date May 2019 Marks available [Maximum mark: 3] Reference code 19M.2.hl.TZ2.1d(iii)
Level hl Paper 2 Time zone TZ2
Command term Explain Question number d(iii) Adapted from N/A
d(iii).
[Maximum mark: 3]
19M.2.hl.TZ2.1d(iii)

Ethyne, C2H2, reacts with oxygen in welding torches.

Product B, CH3CHO, can also be synthesized from ethanol.

(d(iii))

Explain why product B is water soluble.

[3]

Markscheme

Any three of:

has an oxygen/O atom with a lone pair      [✔]

that can form hydrogen bonds/H-bonds «with water molecules»     [✔]

hydrocarbon chain is short «so does not disrupt many H-bonds with water molecules»     [✔]

«large permanent» dipole-dipole interactions with water      [✔]

Examiners report

Candidates did not understand that they must mention the IMF responsible for the solubility. Most candidates explained the polarity of the aldehyde and water but did not mention that this results in permanent dipole-dipole interactions; many did mention H-bonding. The mention of the lone pair on O atom and short hydrocarbon chain were very rare.

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