IB Questionbank

User interface language: English | Español

Date	November 2020	Marks available	1	Reference code	20N.3.sl.TZ0.1
Level	SL	Paper	3	Time zone	TZ0
Command term	Suggest	Question number	1	Adapted from	N/A

Question

In order to determine the oil content of different types of potato crisps (chips), a student weighed $5.00 g$ of crushed crisps and mixed them with $20.0 {cm}^{3}$ of non-polar solvent.

She assumed all the oil in the crisps dissolved in the solvent.

The student then filtered the mixture to remove any solids, and gently heated the solution on a hot plate to evaporate the solvent.

She measured the mass of the oil that remained from each type of crisps

Suggest why a non-polar solvent was needed.

[1]

State one reason why the mixture was not heated strongly.

[1]

Non-polar solvents can be toxic. Suggest a modification to the experiment which allows the evaporated solvent to be collected.

[1]

Suggest one source of error in the experiment, excluding faulty apparatus and human error, that would lead to the following:

[2]

Markscheme

oil is non-polar «and dissolves best in non-polar solvents»
OR
oil does not dissolve in polar solvents ✔

Do not accept “like dissolves like” only.

solvent/oil is flammable
OR
solvent/oil must be kept below its flash point
OR
oxidation/decomposition of oil
OR
mixture has a low boiling point ✔

Accept “to prevent evaporation of oil”.

distillation «instead of evaporation» ✔

Accept “pass vapour through a condenser and collect liquid”.

Do not accept “condensation” without experimental details.

Experimental mass greater than actual mass of oil in crisps:
other substances «in the crisps» are soluble in the solvent
OR
not all the solvent evaporates ✔

Experimental mass less than actual mass of oil in crisps:
not all oil dissolved/extracted ✔

Accept “oil evaporated” OR “oil burned/decomposed” OR “oil absorbed by the filter” OR “assumption «all oil dissolved» was wrong” for M2.

Do not accept examples of human errors OR faulty apparatus.

Examiners report

A well answered question where replies used all the alternatives provided. Very few candidates limited their answer to "like dissolves like" and while this expression was used most student elaborated with higher quality answer. Some common incorrect responses included students talking about dissolving the crisps (chips) or indicating the oil was a polar compound.

Another correctly answered question. As accepted by notes many candidates scored by stating "to prevent evaporation of oil". This resulted in the same argument scoring twice as often used for 1d as well. Some students incorrectly indicated the problem was to prevent the evaporation of the solvent which was the point of this step in the experiment. This could indicate a general lack of understanding of experimental methods.

A bit disappointing as the number of correct answers were substantially lower than expected. Many students responded using a fume hood or other method to remove the solvent. Once again this indicates a general misunderstanding about experimental methods.

Even weak candidates scored at least one point and often both. One common pitfall was to invert the arguments or provide answers excluded by the stem. A frequent incorrect answer was identification of faulty apparatus and human error which was specifically excluded in the question.

Syllabus sections

Core » Topic 4: Chemical bonding and structure » 4.4 Intermolecular forces

Show 79 related questions

Hide related questions

Core » Topic 4: Chemical bonding and structure

Core

Question

Markscheme

Examiners report

Syllabus sections

View options