10. Group 2
A section of Chemistry, 9701
Listing 10 of 275 questions
When a sample of hydrated lithium ethanedioate, Li2C2O4•H2O, is gently heated, two gaseous products are formed and a white solid residue remains. The residue is added to HNO3. A gas is produced that turns limewater milky. Complete the equation for the decomposition of Li2C2O4•H2O. Li2C2O4•H2O + + The trend in the decomposition temperatures of the Group 2 ethanedioates is similar to that of the Group 2 nitrates. Suggest which of CaC2O4 and BaC2O4 will decompose at the lower temperature. Explain your answer. Potassium iron(ethanedioate, K3[Fe(C2O4)3], dissolves in water to form a green solution. Explain why transition elements can form coloured complexes. The anhydrous iron(compound K3[Fe(C2O4)3] decomposes on heating to form a mixture of K2[Fe(C2O4)2], K2C2O4 and CO2. Complete the equation for the decomposition of K3[Fe(C2O4)3]. K3[Fe(C2O4)3] K2[Fe(C2O4)2] + K2C2O4 + CO2 The [Fe(C2O4)3]3– complex ion shows stereoisomerism. Complete the three-dimensional diagrams in to show the two stereoisomers of [Fe(C2O4)3]3–. The C2O4 2– ligand can be represented using O O. isomer 1 Fe isomer 2 Fe Buffer solutions are used to regulate pH. Write two equations to describe how a solution containing HC2O4 – ions acts as a buffer solution when small amounts of acid or alkali are added. A fuel cell is an electrochemical cell that can be used to generate electrical energy by using oxygen to oxidise a fuel. Ethanedioic acid, (COOH)2, dissolved in an alkaline electrolyte is being investigated as a fuel. The relevant standard electrode potentials, Eo, for the cell are shown. O2+ 2H2O+ 4e– 4OH–Eo = +0.40 V 2CO2+ 2e– C2O4 2–Eo = –0.59 V Use these equations to deduce the overall cell reaction. Calculate the value of E o cell. overall cell reaction E o cell = V
9701_s24_qp_43
THEORY
2024
Paper 4, Variant 3
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Use Describe and explain the trend in the solubilities of the sulphates of the Group II elements. The salts formed by the Group II elements with other divalent anions show a similar trend in their solubilities, whereas most of their salts with monovalent anions are very soluble. Use this information to predict the identities of compounds A and B in the following description of some reactions of Group II compounds, and write balanced equations for the reactions. Magnesium hydroxide, Mg(OH)2, is almost insoluble in water. Stirring a mixture of magnesium hydroxide and aqueous ethanedioic acid, H2C2O4, produces a clear colourless solution containing A. When a solution of calcium nitrate, Ca(NO3)2, is added, a white precipitate of B is formed. identity of A identity of B equations The solubility product, Ksp, of magnesium hydroxide has a numerical value of 2.0 × 10–11. Write an expression for the Ksp of magnesium hydroxide, stating its units. Use the value of Ksp given to calculate the concentration of Mg(OH)2 in a saturated solution. Explain whether magnesium hydroxide would be more or less soluble in 0.1 mol dm–3 MgSO4than in water.
9701_w07_qp_4
THEORY
2007
Paper 4, Variant 0
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Use Describe and explain the trend observed in the thermal stability of the carbonates of the Group II elements. By quoting suitable data from the Data Booklet suggest how the thermal stabilities of • zinc carbonate and • lead carbonate might compare to that of calcium carbonate. Malachite is an ore of copper. It contains the following percentages by mass. copper 57.7% oxygen 36.2% carbon 5.4% hydrogen 0.9% Malachite reacts with dilute H2SO4 producing a gas B that turns limewater milky and leaving a blue solution C. When heated in the absence of air, malachite produces gas B and steam, and leaves a black solid D. D reacts with dilute H2SO4 to produce the same blue solution C. Adding iron filings to C produces a pink solid E and a pale green solution F. Calculate the empirical formula of malachite. Examiner’s Use Suggest the formula of the ion responsible for the blue colour of solution C. Identify the black solid D and calculate the mass of D that could be obtained by heating 10 g of malachite. Use data from the Data Booklet to identify the pink solid E and the solution F, and suggest an equation for the reaction producing them. What type of reaction is the reaction that produces E and F? Describe and explain what you would see happen when dilute NH3is added slowly to the solution C until it is in an excess.
9701_w08_qp_4
THEORY
2008
Paper 4, Variant 0
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Radium was discovered in the ore pitchblende by Marie and Pierre Curie in 1898, and the metal was first isolated by them in 1910. The metal was obtained by first reacting the radium present in the pitchblende to form insoluble radium sulfate which was converted into aqueous radium bromide. This solution was then electrolysed using a mercury cathode and a carbon anode. Radium has chemical reactions that are typical of Group II metals and forms ionic compounds. What is the characteristic feature of the electronic configurations of all Group II metals? Radium sulfate is extremely insoluble. From your knowledge of the simple salts of Group II metals, suggest another very insoluble radium salt. During their electrolysis of aqueous radium bromide, the Curies obtained radium at the cathode and bromine at the anode. Write half-equations for the two electrode reactions that take place during this electrolysis. anode cathode Describe what you would see when magnesium reacts with cold water, steam. Write an equation for the reaction with steam. Radium reacts vigorously when added to water. Write an equation, with state symbols, for this reaction. State two observations that could be made during this reaction. Suggest the approximate pH of the resulting solution. ……………… Will the reaction be more or less vigorous than the reaction of barium with water? Explain your answer.
9701_w09_qp_21
THEORY
2009
Paper 2, Variant 1
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Questions Discovered
275