9701_w13_qp_22
A paper of Chemistry, 9701
Questions:
5
Year:
2013
Paper:
2
Variant:
2
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1
Valence Shell Electron Pair Repulsion theory (VSEPR) is a model of electron-pair repulsion (including lone pairs) that can be used to deduce the shapes of, and bond angles in, simple molecules. Complete the table below by using simple hydrogen-containing compounds. One example has been included. number of bond pairs number of lone pairs shape of molecule formula of a molecule with this shape trigonal planar BH3 Tellurium, Te, proton number 52, is used in photovoltaic cells. When fl uorine gas is passed over tellurium at 150 °C, the colourless gas TeF6 is formed. Draw a ‘dot-and-cross’ diagram of the TeF6 molecule, showing outer electrons only. What will be the shape of the TeF6 molecule? What is the F–Te–F bond angle in TeF6?
3. Chemical bonding  →  3.5. Shapes of molecules
13. An introduction to AS Level organic chemistry  →  13.3. Shapes of organic molecules; σ and π bonds
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2
For Examiner’s Use The molecular formula C3H6 represents the compounds propene and cyclopropane. CH3CH CH2 propene cyclopropane C H H C H H C H H What is the H–C–H bond angle at the terminal =CH2 group in propene? Under suitable conditions, propene and cyclopropane each react with chlorine. With propene, 1,2-dichloropropane, CH3CHCl CH2Cl is formed. State fully what type of reaction this is. When cyclopropane reacts with chlorine, three different compounds with the molecular formula C3H4Cl 2 can be formed. Draw displayed structures of each of these three compounds.
14. Hydrocarbons  →  14.2. Alkenes
14. Hydrocarbons  →  14.1. Alkanes
13. An introduction to AS Level organic chemistry  →  13.1. Formulas, functional groups and the naming of organic compounds
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3
For Examiner’s Use Chlorine gas is manufactured by the electrolysis of brine using a diaphragm cell. Write half-equations, including state symbols, for the reactions occurring at each of the electrodes of a diaphragm cell. anode cathode In the diaphragm cell, the anode is made of titanium and the cathode is made of steel. Suggest why steel is never used for the anode. Chlorine is very reactive and will form compounds by direct combination with many elements. Describe what you would see when chlorine is passed over separate heated samples of sodium and phosphorus. In each case write an equation for the reaction. sodium phosphorus For Examiner’s Use Chlorine reacts with aqueous sodium hydroxide in two different ways, depending on the conditions used. In each case, water, sodium chloride and one other chlorine-containing compound are formed. For each condition below, give the formula of the other chlorine-containing compound and state the oxidation number of chlorine in it. condition formula of other chlorine-containing compound oxidation number of chlorine in this compound cold dilute NaOHhot concentrated NaOH Magnesium chloride, MgCl 2, and silicon tetrachloride, SiCl 4, each dissolve in or react with water. Suggest the approximate pH of the solution formed in each case. MgCl 2 SiCl 4 Explain, with the aid of an equation, the difference between the two values.
11. Group 17  →  11.4. The reactions of chlorine
9. The Periodic Table: chemical periodicity  →  9.2. Periodicity of chemical properties of the elements in Period 3
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For Examiner’s Use Compound R is a weak diprotic acid which is very soluble in water. A solution of R was prepared which contained 1.25 g of R in 250 cm3 of solution. When 25.0 cm3 of this solution was titrated with 0.100 mol dm–3 NaOH, 21.6 cm3 of the alkali were needed for complete reaction. Using the formula H2X to represent R, construct a balanced equation for the reaction between H2X and NaOH. Use the data above to calculate the amount, in moles, of OH– ions used in the titration. Use your answers to and to calculate the amount, in moles, of R present in 25.0 cm3 of solution. Calculate the amount, in moles, of R present in 250 cm3 of solution. Calculate Mr of R. Three possible structures for R are shown below. S T U HO2CCH=CHCO2H HO2CCH(OH)CH2CO2H HO2CCH(OH)CH(OH)CO2H Calculate the Mr of each of these acids. Mr of S = Mr of T = Mr of U = Deduce which of the structures, S, T or U, correctly represents the structure of the acid, R. R is represented by For Examiner’s Use It is possible to convert S, T, or U into one another. State the reagentand essential conditions that would be used for the following conversions. S into T S into U T into S Give the structural formula of the organic product formed in each of the following reactions. T reacting with an excess of Na U reacting with an excess of Na2CO3 The acid S shows stereoisomerism. Draw structures to show this isomerism. Label each isomer. When one of the isomers of S is heated at 110 °C in the absence of air, a cyclic compound V, with molecular formula C4H2O3, is formed. The other isomer of S does not react at this temperature. Suggest the displayed formula of V.
13. An introduction to AS Level organic chemistry  →  13.1. Formulas, functional groups and the naming of organic compounds
18. Carboxylic acids and derivatives  →  18.1. Carboxylic acids
16. Hydroxy compounds  →  16.1. Alcohols
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5
For Examiner’s Use Propane, C3H8, and butane, C4H10, are components of Liquefi ed Petroleum Gas (LPG) which is widely used as a fuel for domestic cooking and heating. To which class of compounds do these two hydrocarbons belong? Write a balanced equation for the complete combustion of butane. When propane or butane is used in cooking, the saucepan may become covered by a solid black deposit. What is the chemical name for this black solid? Write a balanced equation for its formation from butane. Propane and butane have different values of standard enthalpy change of combustion. Defi ne the term standard enthalpy change of combustion. A 125 cm3 sample of propane gas, measured at 20 °C and 101 kPa, was completely burnt in air. The heat produced raised the temperature of 200 g of water by 13.8 °C. Assume no heat losses occurred during this experiment. Use the equation pV = nRT to calculate the mass of propane used. For Examiner’s Use Use relevant data from the Data Booklet to calculate the amount of heat released in this experiment. Use the data above and your answers to and to calculate the energy produced by the burning of 1 mol of propane. The boiling points of methane, ethane, propane, and butane are given below. compound CH4 CH3CH3 CH3CH2CH3 CH3(CH2)2CH3 boiling point / K Suggest an explanation for the increase in boiling points from methane to butane. The isomer of butane, 2-methylpropane, (CH3)3CH, has a boiling point of 261 K. Suggest an explanation for the difference between this value and that for butane in the table above.
5. Chemical energetics  →  5.1. Enthalpy change, \(\Delta H\)
14. Hydrocarbons  →  14.1. Alkanes
2. Atoms, molecules and stoichiometry  →  2.4. Reacting masses and volumes (of solutions and gases)
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