Zadanie 10a
Wzorowane na: Chemistry HL Paper 3, November 2024, pytanie 10(a). Treść, dane i kontekst są zmienione; sprawdzane umiejętności, format i punktacja jak w oryginale.
Darmowe konto pozwoli wrócić do niego później.
Polecenie
The concentration of copper(II) ions in wastewater from a plating works was determined by colorimetry. Excess ammonia solution was added to each solution so that all the copper(II) ions formed the deep blue complex ion [Cu(NH3)4]2+, and the absorbance was measured at a fixed wavelength. A calibration curve was drawn from standard solutions.
A 5.00 cm3 sample of the wastewater was diluted to 100.0 cm3 with water before the ammonia was added. The absorbance of this diluted sample was 0.35. Estimate the concentration of copper(II) ions in the undiluted wastewater, in mol dm−3.
Sprawdź rozwiązanieUkryj rozwiązanieKlucz i punktacja
Odpowiedź z klucza
«diluted sample: absorbance 0.35 corresponds to» 0.50 × 10−3 mol dm−3
«dilution factor 100.0/5.00 = 20»
«undiluted wastewater:» 1.0 × 10−2 mol dm−3 ✔
Schemat punktowania
Accept values in the range 0.95 × 10−2 to 1.05 × 10−2 mol dm−3. Award [0] if the dilution is not taken into account; a reading of 0.50 × 10−3 alone earns nothing.
Komentarz
Reading the concentration at the given absorbance and then multiplying by the dilution factor are both required.