A-LevelChemistryChemical bonding9701/43 · Oct/Nov 2018 · Q27 Marks
(a) Ethanedioate ions, C2O42-, are bidentate ligands. Explain what is meant by the term ligand.
- (a)Explain what is meant by the term ligand. [1][1]
- (b)Cr³+(aq) and C2O42-(aq) ions form the complex ion [Cr(C2O4)2(H2O)2]. Draw two stereoisomers of this complex ion. You may use [Figure: C2O42- represented by a curved line with two oxygen atoms linked to a central dot] to represent C2O42-. [2][2]
- (c)The solubility of calcium ethanedioate, CaC2O4, is 6.65 × 10-³gdm-³ at 298 K.
- (c)(i)Write an expression for the solubility product, Ksp, of CaC2O4. Include its units. Ksp = ..................................................... units = ................................. [2][2]
- (c)(ii)Calculate the numerical value of Ksp CaC2O4 at 298 K. Give your answer in standard form to two significant figures. Ksp CaC2O4 = ................................. [2][2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.
- [1] species that forms dative bond(s) to a (central) metal atom/ion
- [1] any two structures
- [1] Ksp = [Ca2+][C2O42-]
- [1] units mol² dm¯⁶
- [1] [Ca²+] = [C2O42-] = 6.65 × 10¯³/128.1 = 5.19 × 10-5 mol dm¯³
- [1] Ksp = (5.19 × 10-5)² = 2.7 × 10¯⁹ mol² dm¯⁶
Write your answer and get it marked
On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.
Sign up free →