Group 2 nitrates decompose when heated. Describe how the thermal stability of Group 2 nitrates changes with increasing proton number. Explain your answer.

1. (a)Group 2 nitrates decompose when heated. Describe how the thermal stability of Group 2 nitrates changes with increasing proton number. Explain your answer.[3]
2. (b)Copper(II) nitrate decomposes in a similar manner to Group 2 nitrates. Write an equation for the decomposition of Cu(NO3)2.[1]
3. (c)Cu(NO3)2 is added to water to form solution A. Fig. 1.1 shows some reactions of solution A. [Figure 1.1] Complete Table 1.1 to show the formula and colour of each of the copper-containing species present in A, B, C and D. [Table 1.1][4]
4. (d)(i)EDTA4– is a polydentate ligand. Explain what is meant by a polydentate ligand.[2]
5. (d)(ii)Group 2 metal ions can form complexes similar to those of transition elements. A solution of EDTA4– is added to water containing [Ca(H2O)6]2+ to form a new complex, [CaEDTA]2-, as shown. equilibrium 1 [Ca(H2O)6]2+ + EDTA4– ⇌ [CaEDTA]2- + 6H2O Circle on the structure of EDTA4– in Fig. 1.2 the six atoms that form bonds with the metal ion. [Figure 1.2][1]
6. (d)(iii)The calcium ions in [Ca(H2O)6]2+ and [CaEDTA]2- have a coordination number of 6. Explain what is meant by coordination number.[1]
7. (d)(iv)The complex [CaEDTA]2- can be used to remove toxic metals from the body. Table 1.2 shows the numerical values for the stability constants, Kstab, for some metal ions with EDTA4–. [Table 1.2] An aqueous solution containing [CaEDTA]2- is added to a solution containing equal concentrations of Cr3+(aq), Fe3+(aq) and Pb2+(aq). The resulting mixture is left to reach a state of equilibrium. State the type of reaction when [CaEDTA]²– reacts with Cr3+(aq), Fe3+(aq) and Pb2+(aq).[1]
8. (d)(v)Deduce the relative concentrations of [CrEDTA]¯, [FeEDTA]¯ and [PbEDTA]2- present in the resulting mixture. Explain your answer. highest concentration lowest concentration[1]
9. (e)The number of moles of water of crystallisation in a hydrated ionic salt can be determined by titration using aqueous EDTA4– ions with a suitable indicator. • 0.255g of hydrated chromium(III) sulfate, Cr2(SO4)3•nH2O, is dissolved in water and made up to 100cm³ in a volumetric flask. • 25.0cm³ of this solution requires 26.2 cm³ of 0.00800 moldm⁻³ aqueous EDTA4—– ions to reach the end-point. The reaction occurs as shown. [Cr(H2O)6]3+ + EDTA4– → [CrEDTA]– + 6H2O Use the data to calculate the value of n in the formula of Cr2(SO4)3•nH2O. Show your working.[3]
10. (f)A solution of Cr3+(aq) and a solution of Fe3+(aq) have different colours. Explain why the two complexes have different colours.[2]

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