Two technicians are asked to prepare separate 250 mL solutions that are each 0.100…
CHEMISTRY · Multi-part · A Level · Chemistry · Amount of substance · Amount of substance
Problem
Two technicians are asked to prepare separate 250 mL solutions that are each 0.100 mol L⁻¹ in nitrate ion at 25 °C. Technician A is given only crystalline Ca(NO₃)₂·4H₂O, while Technician B is given anhydrous KNO₃.
(a) For each technician, calculate the mass of solid that must be dissolved to produce the required nitrate ion concentration.
(b) Compare the calculated masses and explain, at the particulate level, why the amounts differ even though both solutions contain the same concentration of nitrate ions.
(c) Suppose Technician A, unaware of the hydrate’s water content, mistakenly uses the molar mass of anhydrous Ca(NO₃)₂ in the calculation. Quantitatively determine the resulting nitrate ion molarity in the solution that would be produced and discuss the potential impact on any experiment that assumes the nominal 0.100 mol L⁻¹ concentration.