A student plans to prepare propanone from propan-2-ol and test the product. Reagents provided to the student and some of their hazards are shown in the table. | reagent | hazard | | :---------------------- | :------------ | | propan-2-ol | flammable | | concentrated sulfuric acid | corrosive | | potassium dichromate(VI) | oxidising | | distilled water | non-hazardous |

1. (a)(i)The full equation for the reaction between propan-2-ol and acidified potassium dichromate(VI) is shown. 3CH₃CH(OH)CH₃ + K₂Cr₂O₇ + 4H₂SO₄ → 3(CH₃)₂CO + K₂SO₄ + Cr₂(SO₄)₃ + 7H₂O Calculate the minimum mass of potassium dichromate(VI) that is needed for complete oxidation of 5.00 g of propan-2-ol to propanone. Give your answer to three significant figures. [Ar: K, 39.1; Cr, 52.0; O, 16.0; C, 12.0; H, 1.0] mass K₂Cr₂O₇ = .............................................. g[2]
2. (a)(ii)The student is provided with a set of instructions to prepare the propanone. step 1 Add concentrated sulfuric acid to 5.0 g of propan-2-ol in a round-bottomed flask, a few drops at a time. step 2 Dissolve the mass of potassium dichromate(VI) calculated in (a)(i) in a few cm³ of distilled water. step 3 Add this aqueous potassium dichromate(VI) slowly to the mixture in the round-bottomed flask. step 4 Heat the mixture under reflux. step 5 Separate the propanone from the reaction mixture using distillation. The student is also provided with the boiling points of propan-2-ol and propanone. | compound | boiling point/°C | | :---------- | :--------------- | | propan-2-ol | 82.5 | | propanone | 56.5 | Complete the diagram to show how the propanone is separated from the reaction mixture in step 5. Label your diagram fully including the location of propan-2-ol and propanone after distillation has taken place. There is no need to include clamps. [Incomplete distillation apparatus diagram][3]
3. (a)(iii)The reaction mixture needs heating for reflux to take place. Explain why a water-bath is used to heat the mixture.[1]
4. (a)(iv)The propanone separated from the mixture in step 5 contains sulfuric acid as an impurity which needs to be removed. Name a reagent that could be added to remove the sulfuric acid and explain how the student would ensure that all of the acid is no longer present. reagent ..................................................... explanation .....................................................[2]
5. (b)(i)When propanone reacts with a solution of 2,4-DNPH an insoluble compound, X, is produced according to the following equation. [Chemical reaction diagram with structures for 2,4-DNPH, CH₃COCH₃, X, H₂O] The melting point of X can be used to confirm the identity of the carbonyl compound that has reacted with 2,4-DNPH. To do this, solid X must be separated from the mixture. This can be done using method A or method B. [Diagrams of filtration apparatus for Method A and Method B] method A: gravity filtration using a filter funnel, filter paper and a conical flask method B: filtration under reduced pressure using a Buchner funnel and Buchner flask, filter paper and a suction pump to reduce the pressure in the Buchner flask Suggest one major advantage of using method B rather than method A.[1]
6. (b)(ii)The student places a washed sample of X in a drying oven for an hour. The student records the mass of X. The student wants to ensure that X is completely dry. Describe what the student should do to ensure that X is completely dry.[1]
7. (b)(iii)5.00 cm³ of propanone reacts with an excess of 2,4-DNPH. The mass of dry X produced is 11.84 g. Calculate the percentage yield of X in this reaction. Mr X = 238 Mr CH₃COCH₃ = 58 density CH₃COCH₃ = 0.789gcm⁻³ percentage yield of X = .............................................. %[3]
8. (b)(iv)Explain why a 100% yield in the preparation of a pure sample of X is not possible.[1]

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