9701_s13_qp_22 - revisedeck

9701_s13_qp_22

A paper of Chemistry, 9701

Questions:

5

Year:

2013

Paper:

2

Variant:

2

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1

Ammonium sulfate is a fertiliser which is manufactured by the reaction between ammonia and sulfuric acid. Ammonia is described as a weak base and sulfuric acid as a strong acid. By using an equation, explain clearly what is meant by the term weak base. Ammonia and sulfuric acid are both manufactured by processes which involve chemical equilibria. Sulfuric acid is produced from sulfur trioxide which is made by the Contact process. State three important operating conditions for the Contact process for the manufacture of sulfur trioxide. For each of your conditions, you should avoid the use of vague phrases such as ‘high temperature’. condition 1 condition 2 condition 3 How is the sulfur trioxide produced converted into sulfuric acid? For Examiner’s Use Chloropropanols such as 1,3-dichloropropan-2-ol (1,3-DCP) are present in some foods. Cl CH2CH(OH)CH2Cl 1,3-DCP What will be produced when 1,3-DCP is reacted separately with the following reagents under suitable conditions? In each case give the structural formula. concentrated sulfuric acid an excess of ammonia Describe as fully as you can what type of reaction occurs with ammonia.

12. Nitrogen and sulfur → 12.1. Nitrogen and sulfur

11. Group 17 → 11.3. Some reactions of the halide ions

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2

For Examiner’s Use Chile saltpetre is a mineral found in Chile and Peru, and which mainly consists of sodium nitrate, NaNO3. The mineral is puriﬁ ed to concentrate the NaNO3 which is used as a fertiliser and in some ﬁ reworks. In order to ﬁ nd the purity of a sample of sodium nitrate, the compound is heated in NaOHwith Devarda's alloy which contains aluminium. This reduces the sodium nitrate to ammonia which is boiled off and then dissolved in acid. 3NaNO3+ 8Al + 5NaOH+ 18H2O→ 3NH3+ 8NaAl (OH)4The ammonia gas produced is dissolved in an excess of H2SO4 of known concentration. 2NH3 + H2SO4 → (NH4)2SO4 The amount of unreacted H2SO4 is then determined by back-titration with NaOH of known concentration. H2SO4 + 2NaOH → Na2SO4 + 2H2O A 1.64 g sample of impure NaNO3 was reacted with an excess of Devarda's alloy. The NH3 produced was dissolved in 25.0 cm3 of 1.00 mol dm–3 H2SO4. When all of the NH3 had dissolved, the resulting solution was titrated with NaOH. For neutralisation, 16.2 cm3 of 2.00 mol dm–3 NaOH were required. Calculate the amount, in moles, of H2SO4 present in the 25.0 cm3 of 1.00 mol dm–3 H2SO4. Calculate the amount, in moles, of NaOH present in 16.2 cm3 of 2.00 mol dm–3 NaOH. Use your answer to to calculate the amount, in moles, of H2SO4 that reacted with 16.2 cm3 of 2.00 mol dm–3 NaOH. Use your answers to and to calculate the amount, in moles, of H2SO4 that reacted with the NH3. For Examiner’s Use Use your answer to to calculate the amount, in moles, of NH3 that reacted with the H2SO4. Use your answer to to calculate the amount, in moles, of NaNO3 that reacted with the Devarda's alloy. Hence calculate the mass of NaNO3 that reacted. Use your answer to to calculate the percentage by mass of NaNO3 present in the impure sample. Write your answer to a suitable number of signiﬁ cant ﬁ gures. The above reaction is an example of a redox reaction. What are the oxidation numbers of nitrogen in NaNO3 and in NH3? NaNO3 NH3

12. Nitrogen and sulfur → 12.1. Nitrogen and sulfur

11. Group 17 → 11.4. The reactions of chlorine

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3

For Examiner’s Use This question refers to the elements in the section of the Periodic Table shown below. H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca transition elements Ga Ge As Se Br Kr From this list of elements, identify in each case one element that has the property described. Give the symbol of the element. An element that when placed in cold water sinks and reacts readily. An element whose molecules contain π bonding. An element that forms a gaseous toxic oxide. The element which has a giant molecular structure and forms an oxide which also has a giant molecular structure. An element that forms a covalent chloride which dissolves in water to give a conducting solution. The element in Period 3 (Na to Ar) with the greatest electrical conductivity. For Examiner’s Use Some of the elements in Period 3 (Na to Ar) burn with a coloured ﬂ ame when heated in oxygen or chlorine. Give the symbol of one such element, the formula of the oxide formed, and state the ﬂ ame colour that would be seen. symbol of element formula of oxide ﬂ ame colour For the element you have used in , give the formula of the chloride formed, and state the pH of the solution produced when this chloride is shaken with water. formula of chloride pH of solution Chlorine reacts with both bromine and iodine to form BrCl and ICl respectively. The melting points of chlorine and the two chlorides are shown in the table. substance Cl 2 BrCl ICl m.p. / °C –101 –66 Showing outer electrons only draw a 'dot-and-cross' diagram of the bonding in ICl . Suggest why the melting points increase from Cl 2 to ICl . Suggest which of these three molecules has the largest permanent dipole. Explain your answer.

9. The Periodic Table: chemical periodicity → 9.2. Periodicity of chemical properties of the elements in Period 3

11. Group 17 → 11.1. Physical properties of the Group 17 elements

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4

For Examiner’s Use Crotyl alcohol, CH3CH=CHCH2OH, is a colourless liquid which is used as a solvent. In the boxes below, write the structural formula of the organic compound formed when crotyl alcohol is reacted separately with each reagent under suitable conditions. If you think no reaction occurs, write 'NO REACTION' in the box. A Br2 in an inert organic solvent B PCl 5 C H2 and Ni catalyst D NaBH4 E K2Cr2O7 / H+ heat under reﬂ ux Draw the displayed formula of the organic compound formed when crotyl alcohol is reacted with cold, dilute acidiﬁ ed potassium manganate(. Draw the skeletal formula of the compound formed in reaction E. For Examiner’s Use Crotyl alcohol is obtained from crotonaldehyde, CH3CH=CHCHO. Describe one test that would conﬁ rm the presence of a small amount of unreacted crotonaldehyde in the crotyl alcohol. Give the name of the reagent used and state what you would see. reagent observation What type of reaction is the conversion of crotonaldehyde into crotyl alcohol? Compound P, another unsaturated compound, is found in some blue cheeses. The percentage composition by mass of compound P is C: 73.7%; H: 12.3%; O: 14.0%. Calculate the empirical formula of compound P.

16. Hydroxy compounds → 16.1. Alcohols

13. An introduction to AS Level organic chemistry → 13.1. Formulas, functional groups and the naming of organic compounds

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5

For Examiner’s Use A student reacted together an alcohol and a carboxylic acid under appropriate conditions to produce an ester. A sweet smelling organic liquid, Q, with the empirical formula C2H4O was produced. The Mr of Q was found by experiment to be 87.5. What is the molecular formula of Q? In the boxes below, draw the structural formulae of four isomers with this formula that are esters. W X Y Z For Examiner’s Use A sample of Q was hydrolysed by heating with aqueous sulfuric acid. The resulting mixture was heated under reﬂ ux with acidiﬁ ed potassium dichromate(to give a single organic product, R. The product, R, was collected and subjected to the following tests. A sample of R gave no reaction with Tollens’ reagent. A second sample of R gave no reaction with 2,4-dinitrophenylhydrazine reagent. A third sample of R gave an effervescence with sodium carbonate. What does the result of the test with Tollens’ reagent show about R? What does the result of the test with 2,4-dinitrophenylhydrazine reagent show about R? What functional group does the result of the test with sodium carbonate show to be present in R? What is the identity of the single organic compound, R? Which of your structures, W, X, Y or Z, represents the ester, Q? Which, if any, of your esters, W, X, Y or Z, is chiral?

13. An introduction to AS Level organic chemistry → 13.1. Formulas, functional groups and the naming of organic compounds

18. Carboxylic acids and derivatives → 18.2. Esters

17. Carbonyl compounds → 17.1. Aldehydes and ketones

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