9701_s18_qp_42
A paper of Chemistry, 9701
Questions:
8
Year:
2018
Paper:
4
Variant:
2
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1
Silicontetrachloride, SiCl 4, is formed when silicon reacts with chlorine under suitable conditions. It is a colourless liquid with a low boiling point. Explain why SiCl 4 has a low boiling point. SiCl 4 reacts with water to produce an acidic solution. Write an equation for this reaction. Describe two visual observations when silicontetrachloride is added drop by drop to a small amount of water. A sample of 0.8505 g of SiCl 4 is added to 800 cm3 of water. All of the soluble acidic product is dissolved in the water. Calculate the pH of the solution obtained. pH = Silicontetrachloride can be prepared according to reaction1. reaction1 Si+ 2Cl 2SiCl 4ΔS o = –225.7 J K–1 mol–1 standard entropy of silicon, S o Si18.7 J K–1 mol–1 standard entropy of silicon tetrachloride, S o SiCl 4 239.0 J K–1 mol–1 Calculate the standard entropy of chlorine, S o Cl 2. Show all your working. S o Cl 2= J K–1 mol–1 Explain why the entropy change for reaction1 is negative. The standard enthalpy change of formation of silicon tetrachloride, SiCl 4, is – 640 kJ mol‑1. Reaction 1 is spontaneous at lower temperatures, but it is not spontaneous at very high temperatures. Calculate the temperature above which reaction1 is not spontaneous. temperature = K
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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Iodine monochloride, ICl, is a yellow-brown gas. It reacts with hydrogen gas under certain conditions as shown. 2ICl + H22HCl + I2Experiments are performed using different starting concentrations of ICl and H2. The initial rate of each reaction is measured. The following results are obtained. experiment [ICl ] / mol dm–3 [H2] / mol dm–3 relative rate of reaction 4.00 × 10–3 4.00 × 10–3 1.00 4.00 × 10–3 7.00 × 10–3 1.75 4.00 × 10–3 1.00 × 10–2 2.50 5.00 × 10–3 8.00 × 10–3 2.50 7.00 × 10–3 8.00 × 10–3 3.50 Identify a change, taking place in the reaction mixture, that would enable measurements of the rate of this reaction to be made. Use the data in the table to show that the reaction is first order with respect to H2. Use the data in the table to show that the reaction is first order with respect to ICl . Complete the rate equation for the reaction between ICl and H2. rate = Use experiment3 to calculate a numerical value for the rate constant, k. k = The reaction 2ICl + H22HCl + I2is first order with respect to ICl and first order with respect to H2. Suggest a mechanism for this reaction. You should assume ● the mechanism has two steps, ● the first step is much slower than the second step. first step second step An alternative method is used to show that the reaction is first order with respect to H2. This method uses a large excess of ICl and measures how the concentration of H2varies with time. Describe two ways of using these results to show the reaction is first order with respect to H2concentration. Explain the reason for using a large excess of ICl . A chemical reaction may be speeded up by the presence of a catalyst. Explain why a catalyst increases the rate of a chemical reaction.
8. Reaction kinetics  →  8.1. Rate of reaction
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Complete the table by predicting the identity of the substance liberated at each electrode during electrolysis with inert electrodes. electrolyte substance liberated at the anode substance liberated at the cathode NaOHdilute CuCl 2concentrated MgCl 2 The electrolysis of molten ZnBr2 is a redox process. Identify the ion that is oxidised and the ion that is reduced. Use ionic half-equations to explain your answer. Describe one visual observation that would be made during this electrolysis. Dilute sulfuricacid is electrolysed for 50.0minutes using inert electrodes and a current of 1.20 A. A different gas is collected above each electrode. The volumes of the two gases are measured under room conditions. Calculate the maximum volume of gas that could be collected at the cathode. volume = cm3
6. Electrochemistry  →  6.1. Redox processes: electron transfer and changes in oxidation number (oxidation state)
2. Atoms, molecules and stoichiometry  →  2.3. Formulas
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Cobalt is a transition element with atomic number 27. Cobalt forms ions with charges of +2 and +3. Both these ions form complexes. Complete the electronic configurations of a Co atom and a Co2+ ion. Co atom 1s22s22p6 Co2+ ion 1s22s22p6 One Co2+ ion can form a tetrahedral complex ion with four Cl – ions. This complex is blue. What is meant by the term complex ion? Draw the tetrahedral complex ion formed by one Co2+ ion with four Cl – ions. Your drawing should clearly show three-dimensional shape, and should include the overall charge on the ion. Co Explain why many transition metal complexes are coloured. Using ideas from your answer to suggest why the colour of the complex formed by one Co2+ ion with four Cl – ions is blue. Describe the colour change that occurs when water is added to blue crystals of the cobalt(‑chloride complex. Name the type of reaction responsible for this colour change. colour change type of reaction Co2+can be oxidised to Co3+. Use the Data Booklet to suggest a suitable oxidising agent for this reaction. Calculate the of this reaction. = V Write an equation for the reaction between Co2+ and the oxidising agent you chose in . Cobalt(forms two isomeric octahedral complexes with the formula [Co(NH3)3(NO2)3]. The NO2 – ion is monodentate. Complete the diagrams to show the three-dimensional structures of the two isomers and suggest the type of isomerism shown here. isomer 1 Co isomer 2 Co type of isomerism
2. Atoms, molecules and stoichiometry  →  2.3. Formulas
3. Chemical bonding  →  3.4. Covalent bonding and coordinate (dative covalent) bonding
17. Carbonyl compounds  →  17.1. Aldehydes and ketones
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Phenol is an important industrial chemical used in the manufacture of dyestuff and other substances. Suggest two different substances that react with phenol to produce potassiumphenoxide, C6H5O– K+. Identify the second product formed in each case. substance second product substance second product OH 2-naphthol 2-naphthol can show similar properties to phenol. It can be used to produce Sudan I, an orange coloured dyestuff. N OH N Sudan I On the diagram of SudanI above circle the bond or bonds that make this substance a dyestuff. Describe how SudanI can be made using phenylamine and 2-naphthol as the organic starting materials. Phenol can be used to make 2-nitrophenol. OH 2-nitrophenol NO2 The nitration reaction of phenol to form 2‑nitrophenol shows that phenol is more reactive than benzene. Describe the conditions used for the nitration of phenol. Explain how these conditions show phenol to be more reactive than benzene. conditions explanation  Suggest why phenol is more reactive than benzene. Complete the mechanism for the nitration of phenol to form 2-nitrophenol. You should assume that the mechanism is the same as that for the nitration of benzene. ● Include all relevant charges and curly arrows to show the movement of electron pairs. ● Draw the structure of the intermediate. ● You do not need to draw the products. phenol intermediate products OH +NO2 Name the isomer of 2‑nitrophenol which is also a major product of this reaction.
21. Organic synthesis  →  21.1. Organic synthesis
14. Hydrocarbons  →  14.2. Alkenes
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Asparagine and valine are two naturally occurring amino acids. O O asparagine NH2 NH2 OH O valine NH2 OH Give the molecular formula of asparagine. Name all of the functional groups in an asparagine molecule. Draw the structure of the dipeptide formed by valine and asparagine. The peptide bond should be shown displayed and should be clearly labelled. A solution of valine in water acts as a buffer solution. Explain what is meant by a buffer solution. Write two equations to explain how valine can act as a buffer. Use the formula H2NCHRCO2H for valine in your equations. Each valine molecule has one chiral carbon atom. Draw three-dimensional diagrams to show the two optical isomers of valine. The (CH3)2CH group can be represented as R. Asparagine is hydrolysed when heated with aqueous sulfuricacid. Write an equation for this reaction.
13. An introduction to AS Level organic chemistry  →  13.1. Formulas, functional groups and the naming of organic compounds
13. An introduction to AS Level organic chemistry  →  13.4. Isomerism: structural isomerism and stereoisomerism
11. Group 17  →  11.3. Some reactions of the halide ions
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Calcitriol is a steroid hormone found in human blood. HO HO OH calcitriol Give the number of primary, secondary and tertiary alcohol groups in one molecule of calcitriol. primary secondary tertiary Give the number of chiral carbon atoms in one molecule of calcitriol. Calcitriol shows geometrical isomerism. Give the number of geometrical isomers of calcitriol, including calcitriol. A sample of calcitriol is treated with an excess of hot, concentrated, acidified potassium manganate(. There are three different carbon‑containing products of this reaction. One of these three products, X, is shown. O O X O O Predict the number of peaks in the carbon-13 NMR spectrum of X. For the carbon‑13 NMR spectrum of X, state the expected chemical shift ranges (δ) of the peaks predicted in and the number of peaks in each range. Predict the number of peaks this compound would show in its proton NMR spectrum. For each of the peaks in the proton NMR spectrum you have identified in give the expected splitting pattern. Explain your reasoning. In addition to the product shown in , two other carbon-containing products are formed when a sample of calcitriol is treated with an excess of hot, concentrated, acidified potassiummanganate(. Of these two other carbon-containing products, identify the product with the smaller molecular mass. Explain how this product is formed. Of these two other carbon-containing products, identify the product with the larger molecular mass by drawing its skeletal formula in the space below.
22. Analytical techniques  →  22.2. Mass spectrometry
14. Hydrocarbons  →  14.2. Alkenes
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