| Date | November 2020 | Marks available | 2 | 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 of crushed crisps and mixed them with 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.
State one reason why the mixture was not heated strongly.
Non-polar solvents can be toxic. Suggest a modification to the experiment which allows the evaporated solvent to be collected.
Suggest one source of error in the experiment, excluding faulty apparatus and human error, that would lead to the following:
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
- 18M.1.sl.TZ1.28: Which value of q, in J, has the correct number of significant figures? q = mcΔT where m =...
- 18M.1.sl.TZ1.13: The enthalpy of combustion of ethanol is determined by heating a known mass of tap water in a...
-
18M.3.sl.TZ1.2d.i:
Justify why it is inappropriate to record the uncertainty of the mean as ±0.01 s.
-
22M.2.sl.TZ2.1b(iii):
Suggest a reason why the volume of hydrogen gas collected was smaller than predicted.
-
22M.1.sl.TZ1.28:
A student performed an experiment to find the melting point of sulfur, obtaining 118.0 °C. The literature value is 115.2 °C. What was the percentage error?
A.B.
C.
D.
-
22M.2.hl.TZ1.1b(ii):
Determine the percentage uncertainty of the mass of product after heating.
-
22M.2.hl.TZ1.2c(iii):
Carbonates also react with HCl and the rate can be determined by graphing the mass loss. Suggest why this method is less suitable for the reaction of Mg with HCl.
- 17N.1.sl.TZ0.30: A student performs an acid-base titration using a pH meter, but forgets to calibrate it....
- 22M.1.sl.TZ2.29: What is the uncertainty, in cm3, of this measurement?A. ±0.01 B. ±0.1 C. ±0.15 D. ±1
- 17M.1.hl.TZ1.38: The molar mass of a gas, determined experimentally, is 32 g mol−1. Its literature molar...
-
17M.3.sl.TZ1.5f:
Outline why the thermochemical method would not be appropriate for 0.001 moldm−3 hydrochloric acid and aqueous sodium hydroxide of a similar concentration.
- 18M.1.sl.TZ2.29: How are the uncertainties of two quantities combined when the quantities are multiplied...
- 18N.1.sl.TZ0.30: What are the absolute and percentage uncertainties for the change in mass? Initial mass:...
-
17M.1.sl.TZ1.29:
What is the density, in gcm−3, of a 34.79 g sample with a volume of 12.5 cm3?
A. 0.359
B. 0.36
C. 2.783
D. 2.78
-
18N.3.sl.TZ0.1d.ii:
Deduce the appropriate number of significant figures for your answer in (d)(i).
-
18N.3.hl.TZ0.1e.ii:
Deduce the appropriate number of significant figures for your answer in (e)(i).
- 19M.1.hl.TZ1.38: How should a measurement of 5.00 g from a balance be recorded? A. 5.00 ± 0.1 g B. 5.00 ±...
- 19M.1.hl.TZ2.38: The following data were recorded for determining the density of three samples of silicon,...
-
21N.2.sl.TZ0.6b:
A student dissolved 0.1240 ± 0.0001 g of Na2S2O3 to make 1000.0 ± 0.4 cm3 of solution to use in the Winkler Method.
Determine the percentage uncertainty in the molar concentration.
-
19M.2.hl.TZ2.2e:
The experiment gave an error in the rate because the pressure gauge was inaccurate.
Outline whether repeating the experiment, using the same apparatus, and averaging the results would reduce the error.
-
19M.3.hl.TZ2.2c(ii):
Identify one error associated with the use of an accurate stopwatch.
-
19M.3.sl.TZ2.2c(ii):
Identify one error associated with the use of an accurate stopwatch.
- 19M.1.sl.TZ1.28: How should a measurement of 5.00 g from a balance be recorded? A. 5.00 ± 0.1 g B. 5.00 ±...
- 19M.1.sl.TZ2.27: What is the name of this compound using IUPAC rules? A. 2,3-diethylbutane B....
- 19M.1.sl.TZ2.28: The following data were recorded for determining the density of three samples of silicon,...
-
19M.2.hl.TZ2.5d(iv):
The uncertainty of the 100.0cm3 volumetric flask used to make the solution was ±0.6cm3.
Calculate the maximum percentage uncertainty in the mass of NaHCO3 so that the concentration of the solution is correct to ±1.0 %.
-
17M.2.sl.TZ2.2b.i:
Calculate the percentage uncertainty for the mass of K2Cr2O7(s) from the given data.
-
17M.3.sl.TZ1.5b:
Heat losses would make this method less accurate than the pH probe method. Outline why the thermometric method would always give a lower, not a higher, concentration.
- 16N.2.sl.TZ0.3g: Suggest one reason why the values of rates of reactions obtained at higher temperatures may...
-
17N.3.sl.TZ0.2c:
Calculate the uncertainty in the change in pH.
-
16N.1.sl.TZ0.30:
A student measured the change in mass on heating a sample of calcium carbonate, CaCO3(s). What is the mass loss?
Mass before heating: 2.347 g ± 0.001
Mass after heating: 2.001 g ± 0.001A. 0.346g ± 0.001
B. 0.346g ± 0.002
C. 0.35g ± 0.002
D. 0.35g ± 0.001
-
18M.3.sl.TZ1.2d.iii:
Another student, working alone, always dropped the marble chips into the acid and then picked up the stopwatch to start it. State, giving a reason, whether this introduced a random or systematic error.
- 19N.1.sl.TZ0.14: Which quantity is likely to be the most inaccurate due to the sources of error in this...
-
17N.3.sl.TZ0.3c:
Calculate the percentage of water by mass in the NaCl•2H2O crystals. Use the data from section 6 of the data booklet and give your answer to two decimal places.
- 19N.2.sl.TZ0.2b(ii): Suggest a modification to the procedure that would make the results more reliable.
-
19N.2.sl.TZ0.2b(i):
Calculate the percentage uncertainty of the day 5 titre.
- 19N.3.sl.TZ0.1b(iii): Suggest a source of error in the procedure, assuming no human errors occurred and the balance...
-
19M.2.sl.TZ2.2d:
The experiment gave an error in the rate because the pressure gauge was inaccurate. Outline whether repeating the experiment, using the same apparatus, and averaging the results would reduce the error.
-
17M.3.sl.TZ1.1b:
Suggest how the precision of this measurement could be improved.
-
19M.3.hl.TZ2.2c(i):
Describe one systematic error associated with the use of the gas syringe, and how the error affects the calculated rate.
- 19N.1.sl.TZ0.29: What is the value of the temperature change? Initial temperature: 2.0 ± 0.1 °C Final...
-
18M.3.sl.TZ1.2d.ii:
If doubling the concentration doubles the reaction rate, suggest the mean time you would expect for the reaction with 2.00 mol dm−3 hydrochloric acid.
-
17M.2.sl.TZ2.1a.ii:
Suggest why the final mass of solid obtained by heating 3.760 g of AgxOy may be greater than 3.275 g giving one design improvement for your proposed suggestion. Ignore any possible errors in the weighing procedure.
-
19M.3.sl.TZ2.2c(i):
Describe one systematic error associated with the use of the gas syringe, and how the error affects the calculated rate.
- 20N.2.hl.TZ0.5f(i): Potassium hydroxide solutions can react with carbon dioxide from the air. The solution was...
-
17M.3.sl.TZ2.1b:
O2 is consumed in producing CO2 for electricity generation. The graph shows the relationship between the world’s electricity generation and CO2 production between 1994 and 2013.
Calculate the mass, in million tonnes, of oxygen gas ultimately found in CO2 which is consumed in generating 18000 terawatts of electricity using the equation given for the best fit line. Give your answer to 2 significant figures.
Assume coal is the only energy source.
-
20N.1.sl.TZ0.28:
A student obtained the following data to calculate , using .
What is the percentage uncertainty in the calculated value of ?
A.
B.
C.
D.
-
20N.2.hl.TZ0.5f(ii):
Potassium hydroxide solutions can react with carbon dioxide from the air. The solution was made one day prior to using it in the titration.
Predict, giving a reason, the effect of this error on the calculated concentration of ethanoic acid in 5(e).
- 21M.1.sl.TZ1.29: Burette readings for a titration are shown. What is the mean titre? A. 11.1 cm3 ±...
- 21M.1.sl.TZ1.28: The enthalpy of combustion of a fuel was determined using the calorimeter shown. The final...
-
18N.2.hl.TZ0.1b.iii:
The only significant uncertainty is in the temperature measurement.
Determine the absolute uncertainty in the calculated value of ΔH if the uncertainty in the temperature rise was ±0.2 °C.
- 21M.1.sl.TZ2.29: How should the difference between 27.0 ± 0.3 and 9.0 ± 0.2 be shown? A. 18.0 ± 0.1 B. ...
-
17M.3.sl.TZ2.2b.ii:
Suggest one improvement to the investigation.
-
20N.3.sl.TZ0.2e:
Calculate the percentage uncertainty and percentage error in the experimentally determined value of for methanol.
-
18N.2.sl.TZ0.1b.iii:
The only significant uncertainty is in the temperature measurement.
Determine the absolute uncertainty in the calculated value of ΔH if the uncertainty in the temperature rise was ±0.2 °C.
-
17M.3.sl.TZ2.1c.iii:
The change in APO O2/N2 ratio, per meg, is measured relative to an O2/N2 reference.
Calculate the APO Δ(O2/N2) value for an oxygen concentration of 209400 ppm assuming that any change in N2 concentration is negligible. Reference values for O2 and N2 are 209 460 and 790 190 ppm respectively.
-
22M.2.hl.TZ1.1c(ii):
Suggest an explanation, other than product being lost from the crucible or reacting with nitrogen, that could explain the yield found in (b)(iii).
-
22M.2.sl.TZ1.1b(ii):
Determine the percentage uncertainty of the mass of product after heating.
-
22M.2.sl.TZ1.1c(ii):
Suggest an explanation, other than product being lost from the crucible or reacting with nitrogen, that could explain the yield found in (b)(iii).
-
21N.2.hl.TZ0.6b:
A student dissolved 0.1240 ± 0.0001 g of Na2S2O3 to make 1000.0 ± 0.4 cm3 of solution to use in the Winkler Method.
Determine the percentage uncertainty in the molar concentration.
