Zadanie 3d, Paper 1B, listopad 2025, TZ1, Chemia IB SL
Wzorowane na: Chemistry SL Paper 1B, November 2025, TZ1, pytanie 3(d). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
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A student used paper chromatography to find out which coloured dyes had been mixed to make the brown ink of a marker pen, and to compare the polarities of those dyes. A spot of the ink was placed on the start line of each of two identical paper strips. The start line was drawn in pencil 1.5 cm from the bottom edge of the strip, and each strip was placed in a covered beaker containing a different solvent system, both mixtures of ethanol and water. System 1 was 25 % ethanol and 75 % water by volume; system 2 was 75 % ethanol and 25 % water by volume. Each run gave four coloured spots. The positions of the start line, the solvent front and the spots were measured from the bottom edge of each strip.
| Position measured from the bottom edge / cm | System 1 (25 % ethanol) | System 2 (75 % ethanol) |
|---|---|---|
| Start line | 1.5 | 1.5 |
| Solvent front | 17.5 | 15.5 |
| Violet spot | 16.2 | 5.6 |
| Blue spot | 14.1 | 11.3 |
| Orange spot | 11.1 | 7.8 |
| Yellow spot | 3.3 | 3.0 |
PowiększPolecenie
Deduce, giving a reason, which of the two dyes, orange or violet, is the more polar.
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Pokaż rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
violet AND it travels «much» further in the solvent with the higher proportion of water/lower proportion of ethanol
OR
violet AND it travels «much» less far in the solvent with the higher proportion of ethanol/lower proportion of water ✔
the mixture with more water is the more polar solvent
OR
the mixture with more ethanol is the less polar solvent «so the more polar dye is the one carried further by the more polar solvent» ✔
Schemat punktowania
M1: violet, with the observation that its distance depends strongly on the water content of the solvent (orange moves a similar distance in both). M2: the link between the composition of the solvent and its polarity. No mark for 'violet' without a reason.
Komentarz. The stationary phase is the water held on the cellulose fibres; the dye whose position changes most with the water content of the mobile phase is the one held by the strongest polar attractions.