9701_w13_qp_42
A paper of Chemistry, 9701
Questions:
8
Year:
2013
Paper:
4
Variant:
2
Login to start this paper & get access to powerful tools
1
Gaseous ammonia reacts with gaseous hydrogen chloride to form solid ammonium chloride. NH3 + HCl → NH4Cl The bonding in ammonium chloride includes ionic, covalent and co-ordinate (dative covalent) bonds. Complete the following ‘dot-and-cross’ diagram of the bonding in ammonium chloride. For each of the six atoms show all the electrons in its outer shell. Three electrons have already been included. Use the following code for your electrons. ● electrons from chlorine x electrons from hydrogen o electrons from nitrogen H H H N Cl H + – ● xo When a sample of dry ammonia is needed in the laboratory, the gas is passed through a tower containing lumps of solid calcium oxide, CaO. Suggest why the usual drying agent for gases, concentrated H2SO4, is not used for ammonia. Write an equation for the reaction between CaO and H2O. Suggest why CaO rather than MgO is used to dry ammonia. For Examiner’s Use 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.
12. Nitrogen and sulfur  →  12.1. Nitrogen and sulfur
3. Chemical bonding  →  3.4. Covalent bonding and coordinate (dative covalent) bonding
11. Group 17  →  11.4. The reactions of chlorine
Open
2
For Examiner’s Use The melting points of some Group IV elements are given below. element melting point / K C Si Ge Sn Suggest an explanation for each of the following. The melting point of silicon is less than that of carbon. The melting point of tin is less than that of germanium. Using data from the Data Booklet where appropriate, write equations for the following reactions of compounds of Group IV elements. SiCl 4+ H2Othe action of heat on PbCl 4SnCl 2+ FeCl 3SnO2+ NaOH
10. Group 2  →  10.1. Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds
9. The Periodic Table: chemical periodicity  →  9.1. Periodicity of physical properties of the elements in Period 3
Open
3
For Examiner’s Use Using the symbol HZ to represent a Brønsted-Lowry acid, write equations which show the following substances acting as Brønsted-Lowry bases. NH3 + → CH3OH + → Using the symbol B– to represent a Brønsted-Lowry base, write equations which show the following substances acting as Brønsted-Lowry acids. NH3 + → CH3OH + → State briefl y what is meant by the following terms. reversible reaction dynamic equilibrium Explain what is meant by a buffer solution. Explain how the working of a buffer solution relies on a reversible reaction involving a Brønsted-Lowry acid such as HZ and a Brønsted-Lowry base such as Z–. For Examiner’s Use Propanoic acid, CH3CH2CO2H, is a weak acid with Ka = 1.34 × 10–5 mol dm–3. Calculate the pH of a 0.500 mol dm–3 solution of propanoic acid. Buffer solution F was prepared by adding 0.0300 mol of sodium hydroxide to 100 cm3 of a 0.500 mol dm–3 solution of propanoic acid. Write an equation for the reaction between sodium hydroxide and propanoic acid. Calculate the concentrations of propanoic acid and sodium propanoate in buffer solution F. [propanoic acid] = mol dm–3 [sodium propanoate] = mol dm–3 Calculate the pH of buffer solution F. pH = Phenyl propanoate cannot be made directly from propanoic acid and phenol. Suggest the identities of the intermediate G, the reagent H and the by-product J in the following reaction scheme. O ONa O + J G CH3CH2CO2H H G is H is J is
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
Open
4
For Examiner’s Use Explain what is meant by the term bond energy. Describe and explain the trend in bond energies of the C–X bond in halogenoalkanes, where X = F, Cl, Br or I. Describe the relationship between the reactivity of halogenoalkanes, RX, and the bond energies of the C–X bond. Use the Data Booklet to suggest an explanation as to why CFCs such as CF2Cl 2 are much more harmful to the ozone layer than fl uorocarbons such as CF4 or hydrocarbons such as butane, C4H10. Predict the products of the following reactions and draw their structures in the boxes below. The molecular formula of each product is given, where X = Cl , Br or I. H2O C3H5O2X + Cl Cl O H2O C3H7OX + I Cl H2O C7H7OX + Br Br For Examiner’s Use Ethane reacts with chlorine according to the following equation. C2H6 + Cl 2 → C2H5Cl + HCl State the conditions needed for this reaction. State the type of reaction occurring here. One of the steps during this reaction is the following process. Cl ● + CH3CH3 → HCl + CH3CH2 ● Use the Data Booklet to calculate the enthalpy change, ∆H, of this step. ∆H = kJ mol–1 Use the Data Booklet to calculate the enthalpy change, ∆H, of the similar reaction: I● + CH3CH3 → HI + CH3CH2 ● ∆H = kJ mol–1 Hence suggest why it is not possible to make iodoethane by reacting together iodine and ethane. Complete the following equations of some possible steps in the formation of chloroethane. Cl 2 → Cl ● + CH3CH3 → HCl + CH3CH2 ● CH3CH2 ● + → + + → CH3CH2Cl
15. Halogen compounds  →  15.1. Halogenoalkanes
Open
5
For Examiner’s Use Super-absorbent polymers have the ability to absorb 200-300 times their own mass of water. They are classifi ed as hydrogels and they are widely used in personal disposable hygiene products such as babies’ nappies . These polymers are commonly made by the polymerisation of compound K mixed with sodium hydroxide in the presence of an initiator. CH2 C H CO2H K Explain what is meant by the term polymerisation. What type of polymerisation is involved in the formation of hydrogels? Describe the changes in chemical bonding that occur during the polymerisation of K. Acrylic acid is the common name for compound K. Suggest the systematic name of K. Draw the structure of at least two repeat units of the polymer formed by the above method from acrylic acid, K, when mixed with NaOH. The C–C–C bond angle in compound K changes when the polymer is formed. State and explain how the C–C–C bond angle differs between a molecule of K and the polymer. angle changes from to explanation For Examiner’s Use Draw a detailed diagram of a portion of the polymer you have drawn in to explain how it can absorb a large volume of water. A student added 0.10 g of the polymer to 10 cm3 of aqueous copper(sulfate solution. Predict, with a reason, what you expect to observe. Compound L, CH2=CHCONH2, can also be polymerised to form a super-absorbent polymer. Name the two functional groups in compound L. Compound K can be converted into compound L by the following two-step route. H2C CO2H H C H2C CO2 –NH4 + H C K H2C CONH2 H C L step 1 step 2 Suggest a reagent for step 1. What other product is formed in step 2? State the reagents and conditions necessary to re-form K from L.
20. Polymerisation  →  20.1. Addition polymerisation
14. Hydrocarbons  →  14.2. Alkenes
Open
6
Protein molecules are formed by the polymerisation of amino acids in the body. The structures of three amino acids are given. OH H2N O OH HO NH2 O OH NH2 O glycine serine valine How many different tripeptides can be made using one molecule of each of the amino acids shown? Draw the tripeptide ser-gly-val, showing the peptide bonds in displayed form. Within the tripeptide, which amino acid provides a hydrophobic side chain? Polypeptide chains can form bonds giving proteins their secondary and tertiary structures. Using the tripeptide in , state two types of bonding that can be formed and the groups in the tripeptide that are involved in this bonding. bond groups bond groups For Examiner’s Use Enzymes are particular types of proteins that catalyse chemical reactions. The effi ciency of enzymes can be reduced by the presence of other molecules known as inhibitors. Explain how both competitive and non-competitive inhibitors prevent enzymes from working effi ciently. competitive inhibitors non-competitive inhibitors The graph shows the rate of an enzyme-catalysed reaction against the substrate concentration in the absence of an inhibitor. rate of reaction concentration of substrate On the same axes, sketch a graph showing the rate of this reaction if a non-competitive inhibitor was present.
3. Chemical bonding  →  3.4. Covalent bonding and coordinate (dative covalent) bonding
21. Organic synthesis  →  21.1. Organic synthesis
14. Hydrocarbons  →  14.2. Alkenes
Open
7
For Examiner’s Use Electrophoresis is a technique which can be used to separate amino acids or peptide fragments present in a mixture. Draw a diagram to show the apparatus used to carry out electrophoresis. You should label each of the relevant parts of the apparatus. How far an amino acid will travel during electrophoresis depends on the pH of the solution. For a given potential difference, state two other factors that will affect how far a given amino acid travels in a fi xed time during electrophoresis. 1. 2. A number of analytical and separation techniques rely on substances having different partition coeffi cients. State what is meant by the term partition coeffi cient. For Examiner’s Use The partition coeffi cient of X between ethoxyethane and water is 40.0. A solution contains 4.00 g of X dissolved in 0.500 dm3 of water. Calculate the mass of X that can be extracted from this aqueous solution by shaking it with 0.050 dm3 of ethoxyethane, two successive portions of 0.025 dm3 of ethoxyethane.
22. Analytical techniques  →  22.2. Mass spectrometry
2. Atoms, molecules and stoichiometry  →  2.3. Formulas
Open
8
For Examiner’s Use In a world with a rapidly increasing population, access to clean drinking water is critical. For many countries, groundwater sources, rather than stored rainwater or river-water, are vital. Groundwater is water that exists in the pore spaces and fractures in rock and sediment beneath the Earth's surface. The World Health Organisation (WHO) provides maximum recommended concentrations for different ions present in drinking water. The geological nature of the soil determines the chemical composition of the groundwater. The table shows some ions which may contaminate groundwater. ion present WHO maximum permitted concentration / mg dm–3 Ba2+ 0.30 Cl – 250.00 NO3 – 50.00 Pb2+ 0.01 Na+ 20.00 SO4 2– 500.00 Nitrate, NO3 –, ions are diffi cult to remove from groundwater. What is the reason for this? State which ions in the table above are likely to be removed from the water by treatment with powdered limestone, CaCO3, giving reasons for each of your answers. Nitrates and phosphates can enter water courses such as rivers or streams as a result of human activity. Both of these ions are nutrients for algae. What is the origin of these nitrates? For Examiner’s Use Suggest an origin for the phosphates found in water courses. What effect do nitrates and phosphates have on water courses? Acid rain can have a major impact on natural waters, particularly lakes. In recent years there has been a worldwide effort to reduce the amount of acid rain produced. Write equations to show the production of acid rain from sulfur dioxide, SO2. The use of fossil fuels is one major source of sulfur dioxide. Name another major industrial source.
9. The Periodic Table: chemical periodicity  →  9.2. Periodicity of chemical properties of the elements in Period 3
12. Nitrogen and sulfur  →  12.1. Nitrogen and sulfur
Open