Zadanie 1a, Paper 1B, maj 2025, TZ2, Chemia IB HL
Wzorowane na: Chemistry HL Paper 1B, May 2025, TZ2, pytanie 1(a). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
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Zadanie
Wspólne informacje do wiązki zadań
Copper(II) ions, Cu2+, in the rinse water from a copper-plating workshop must be monitored before the water is discharged. Their concentration can be determined either by complexometric titration with a standard solution of EDTA or by atomic absorption spectroscopy (AAS).
Polecenie
Before use, the EDTA solution was standardized against a standard solution of Cu2+ ions. An accurately weighed piece of pure copper wire was dissolved in the minimum volume of concentrated nitric acid and the mixture was warmed gently until no more brown fumes of nitrogen dioxide were given off. Once the solution had cooled, it was made up to exactly 500.0 cm3. A more dilute standard solution, suitable for the titration, was then prepared from it.
(i) State which piece of glassware is most appropriate for making the Cu2+ solution up to exactly 500.0 cm3.
(ii) Describe the steps that should be followed to prepare the more dilute standard solution from the copper(II) nitrate solution.
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Pokaż rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
(i) «500.0 cm3» volumetric flask ✔
(ii) Any two of:
calculate the volume of the initial solution required «from c1V1 = c2V2» ✔
measure this volume with a volumetric pipette/burette and run it into a «second» volumetric flask ✔
add deionized/distilled water up to the graduation mark ✔
stopper the flask and invert it several times/shake to mix ✔
OR
transfer the solution through a funnel into the volumetric flask, rinsing the beaker and funnel and adding the washings ✔
add deionized/distilled water up to the graduation mark ✔
stopper the flask and invert it several times/shake to mix ✔
Schemat punktowania
(i) [1] for a volumetric flask; accept graduated flask; a measuring cylinder, beaker or conical flask scores 0. (ii) [2 max] for any two steps of the dilution: calculating the volume needed, transferring it with a pipette or burette into a volumetric flask, making up to the mark with deionized water, mixing by inversion. The alternative of transferring the solution with rinsings into a volumetric flask, making up to the mark and mixing is also accepted for [2 max].
Komentarz. The volume of the diluted solution is fixed by the graduation mark of the flask, so the water is added last, after the measured volume of the concentrated solution.