10. Group 2
A section of Chemistry, 9701
Listing 10 of 275 questions
Group 2 nitrates decompose when heated. Describe how the thermal stability of Group 2 nitrates changes with increasing proton number. Explain your answer. Copper(nitrate decomposes in a similar manner to Group 2 nitrates. Write an equation for the decomposition of Cu(NO3)2. Cu(NO3)2 is added to water to form solution A. shows some reactions of solution A. solution A Cu(NO3)2solution C solution D precipitate B H2O NH3excess NH3excess concentrated HCl 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 formula of copper‑containing species formed colour of copper‑containing species formed A B C D EDTA4– is a polydentate ligand. Explain what is meant by a polydentate ligand. 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, 2–, as shown. equilibrium 1 [Ca(H2O)6]2+ + EDTA4– 2– + 6H2O Circle on the structure of EDTA4– in the six atoms that form bonds with the metal ion. EDTA4– NCH2CH2N CCH2 –O O CCH2 CH2C CH2C –O O– O– O O O The calcium ions in [Ca(H2O)6]2+ and 2– have a coordination number of 6. Explain what is meant by coordination number. The complex 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 complex Kstab 2– 5.0 × 1010 – 2.5 × 1023 – 1.3 × 1025 2– 1.1 × 1018 An aqueous solution containing 2– is added to a solution containing equal concentrations of Cr 3+, Fe3+and Pb2+. The resulting mixture is left to reach a state of equilibrium. State the type of reaction when 2– reacts with Cr 3+, Fe3+and Pb2+. Deduce the relative concentrations of –, – and 2– present in the resulting mixture. Explain your answer. > > highest concentration lowest concentration 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. • 0.255 g of hydrated chromium(sulfate, Cr2(SO4)3•nH2O, is dissolved in water and made up to 100 cm3 in a volumetric flask. • 25.0 cm3 of this solution requires 26.2 cm3 of 0.00800 mol dm–3 aqueous EDTA4– ions to reach the end‑point. The reaction occurs as shown. [Cr(H2O)6]3+ + EDTA4– – + 6H2O Use the data to calculate the value of n in the formula of Cr2(SO4)3•nH2O. Show your working. n = A solution of Cr 3+and a solution of Fe3+have different colours. Explain why the two complexes have different colours.
9701_s23_qp_41
THEORY
2023
Paper 4, Variant 1
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Group 2 nitrates decompose when heated. Describe how the thermal stability of Group 2 nitrates changes with increasing proton number. Explain your answer. Copper(nitrate decomposes in a similar manner to Group 2 nitrates. Write an equation for the decomposition of Cu(NO3)2. Cu(NO3)2 is added to water to form solution A. shows some reactions of solution A. solution A Cu(NO3)2solution C solution D precipitate B H2O NH3excess NH3excess concentrated HCl 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 formula of copper‑containing species formed colour of copper‑containing species formed A B C D EDTA4– is a polydentate ligand. Explain what is meant by a polydentate ligand. 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, 2–, as shown. equilibrium 1 [Ca(H2O)6]2+ + EDTA4– 2– + 6H2O Circle on the structure of EDTA4– in the six atoms that form bonds with the metal ion. EDTA4– NCH2CH2N CCH2 –O O CCH2 CH2C CH2C –O O– O– O O O The calcium ions in [Ca(H2O)6]2+ and 2– have a coordination number of 6. Explain what is meant by coordination number. The complex 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 complex Kstab 2– 5.0 × 1010 – 2.5 × 1023 – 1.3 × 1025 2– 1.1 × 1018 An aqueous solution containing 2– is added to a solution containing equal concentrations of Cr 3+, Fe3+and Pb2+. The resulting mixture is left to reach a state of equilibrium. State the type of reaction when 2– reacts with Cr 3+, Fe3+and Pb2+. Deduce the relative concentrations of –, – and 2– present in the resulting mixture. Explain your answer. > > highest concentration lowest concentration 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. • 0.255 g of hydrated chromium(sulfate, Cr2(SO4)3•nH2O, is dissolved in water and made up to 100 cm3 in a volumetric flask. • 25.0 cm3 of this solution requires 26.2 cm3 of 0.00800 mol dm–3 aqueous EDTA4– ions to reach the end‑point. The reaction occurs as shown. [Cr(H2O)6]3+ + EDTA4– – + 6H2O Use the data to calculate the value of n in the formula of Cr2(SO4)3•nH2O. Show your working. n = A solution of Cr 3+and a solution of Fe3+have different colours. Explain why the two complexes have different colours.
9701_s23_qp_43
THEORY
2023
Paper 4, Variant 3
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Write an equation showing the thermal decomposition of calcium nitrate, Ca(NO3)2. State and explain how the thermal stabilities of the nitrates vary down Group II. The nitrates of calcium, strontium or barium are often added to firework mixtures to produce red or green flames. The equation for the decomposition of one such mixture is as follows. Sr(NO3)2+ 3C⎯→SrO+ N2+ 2CO2+ COCalculate the volume of gas given off (measured at room temperature and pressure) when a 10.0 g sample of this mixture decomposes. [Mr: Sr(NO3)2, 211.6] Explain in detail how carbon monoxide, produced in this reaction, is poisonous. Use
9701_w06_qp_4
THEORY
2006
Paper 4, Variant 0
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