Unit 3B

09. An experiment was carried out to prepare iodoethane, CH3CH2I. Procedure 1. Put some solid, moist red phosphorus into a flask. 2. Add ethanol to the flask. 3. Set up the apparatus as shown in diagram 1. Diagram 1 Equations 2P + 3I2 2PI3 3CH3CH2OH + PI3 3CH3CH2I + H3PO3

4. Add 25.4 g of powdered iodine, in small portions, to the flask. 5. Before each addition, remove the condenser. Add the iodine and then immediately replace the condenser. 6. When all the iodine has been added, allow the flask to stand for 10 minutes and then heat the flask for one hour as shown in diagram 1. 7. Separate the iodoethane from the reaction mixture and dry it. 8. Finally, purify the iodoethane using the apparatus shown in diagram 2. Collect the iodoethane over a suitably narrow temperature range.

Diagram 2 Equations 2P + 3I2 2PI3 3CH3CH2OH + PI3 3CH3CH2I + H3PO3

Data Name Appearance flammability Boiling temperature C Ethanol Iodoethane Colourless liquid Flammable 78 72 Equations 2P + 3I2 2PI3 3CH3CH2OH + PI3 3CH3CH2I + H3PO3 (a) (i) Identify the technique shown in each diagram. Diagram 1..... (heating under reflux Diagram 2….. distillation (ii) Explain why a stopper should not be placed in the top of the condenser shown in diagram 1. (Expansion of vapour will) ,build up pressure / prevent explosion

The reaction is vigorous OR the reaction is exothermic (b) (i) Give one reason why the iodine was added over a period of time and in small amounts. The reaction is vigorous OR the reaction is exothermic OR the reaction is (very) fast or violent Or To stop a reactant or product escaping produced (ii) Explain why water baths were used in both step 6 and step 8 rather than heating the flasks directly with a Bunsen flame. (One or both of) the liquids flammable / the mixture is flammable/ the organic compounds are flammable OR ethanol and iodoethane are flammable OR ethanol is flammable OR iodoethane is flammable OR to keep the temperature below 100°C OR to control the temperature throughout the heating OR for uniform heating OR to prevent uneven heating (iii) Suggest the temperature range suitable for the collection of iodoethane shown in From ………to ………………… °C diagram 2. Any lower temperature: 69 to 71 ( C) Any upper temperature: 73 to 75 ( C)

Use the relative atomic mass of I = 127 0.1(00) (mol) (c) (i) Calculate the number of moles of iodine, I2, in 25.4 g of iodine. Use the relative atomic mass of I = 127 0.1(00) (mol) (ii) In this reaction, 1 mol I2 forms 2 mol CH3CH2I. Calculate the maximum mass of iodoethane, in g, that could be formed from 25.4 g of iodine. Use the following relative atomic masses: C = 12, H = 1, I = 127 I2 2CH3CH2I Mr (CH3CH2I) = 156 so the amount of iodine is 25.4 = 0.1 mol 0.2(00) mol of iodoethane 254 0.2(00) x 156 = 31.2 g (iii) In a preparation, the mass of iodoethane collected was 23.4 g. Calculate the percentage yield in this preparation. 23.4 x 100 % = 75% 31.2

This question is about the alcohol, propan-1-ol. (a) Give two observations when propan-1-ol reacts with a small piece of sodium. Observation 1 Observation 2 (b) A student investigated the rate of reaction of propan-1-ol with sodium. Suggest one suitable measurement which could be made to determine the rate of this reaction. (c) A small amount of phosphorus(V) chloride (phosphorus pentachloride), PCl5, is added to propan-1-ol in a test tube. (i) Describe the appearance of the fumes at the mouth of the test tube. (ii) An open bottle of concentrated ammonia is held near the mouth of the tube. Describe what would be seen at the mouth of the test tube.

Shake the mixture and leave X to dissolve. Propanoic acid may be prepared by oxidizing propan-1-ol in acidic conditions. X + H2SO4 CH3CH2CH2OH CH3CH2COOH Procedure 1. Pour 10 cm3 of distilled water into a boiling tube and add 12 g of oxidizing agent X. Shake the mixture and leave X to dissolve. 2. Pour 3 cm3 of propan-1-ol into a round-bottom flask and add 10 cm3 of distilled water and a few anti-bumping granules. Set up the apparatus for heating under reflux. 3. Add 4 cm3 of concentrated sulfuric acid, drop by drop, to the propan-1-ol. While the mixture is still warm, add the solution of oxidizing agent X, drop by drop. The energy released from the reaction should cause the mixture to boil without external heating.

(b) What colour change does X undergo when it oxidizes propan-1-ol? 4. When all of the solution of X has been added, use a low Bunsen burner flame to keep the mixture boiling for 10 minutes, not allowing any vapour to escape. 5. Distil the mixture in the flask using the apparatus shown below. Collect 5–6 cm3 of distillate, which is an aqueous solution of propanoic acid. Suggest, by name or formula, a suitable oxidizing agent, X, for this reaction. (b) What colour change does X undergo when it oxidizes propan-1-ol? From ……………………. to …………. (c) Draw a labelled diagram showing the apparatus for heating under reflux. (d) Give two reasons why the escape of vapour in step 4 should be prevented. Reason 1 Reason 2 (e) How does the reflux apparatus prevent escape of vapour?

(i) Suggest a suitable solid drying agent. (f) Some water can be removed from the distillate in step 5 by adding a solid drying agent. The solution of propanoic acid can then be decanted leaving the drying agent behind. (i) Suggest a suitable solid drying agent. (ii) Suggest why removing excess solid drying agent by decanting, rather than filtering through filter paper, improves the yield. (g) In a larger scale preparation of propanoic acid, 10.0 g of propan-1-ol was used. (i) Calculate the maximum mass of propanoic acid which could be formed from 10.0 g of propan-1-ol. Propan-1-ol Propanoic acid Molar mass / g mol 60.1 74.1 -1

(ii) After purification, 6.0 cm3 of dry propanoic acid was obtained. Calculate the percentage yield in the preparation. The density of propanoic acid is 0.99 g cm–3. (h) In another experiment, the same reaction mixture (propan-1-ol, X and concentrated sulfuric acid) was heated in the apparatus shown in step 5. Identify the main organic product which would be collected and explain why propanoic acid is not produced. Product Explanation

The steps of the experimental procedure are as follows. 08. Bromoethane may be prepared by reacting ethanol with bromine and red phosphorus. 10C2H5OH(l)+2P(s)+5Br2(l) 10C2H5Br(l)+2H3PO4(aq) + 2H2O(l) The steps of the experimental procedure are as follows. 1. Measure 10.0 cm3 of ethanol into a round-bottom flask. 2. Add 1.5 g of red phosphorus to the ethanol. 3. Pre-cool 5 cm3 of liquid bromine in an ice bath, then slowly add it to the mixture of ethanol and red phosphorus, while cooling the flask under running water. 4. Gently reflux the mixture for about 10 minutes. 5. Rearrange the apparatus for distillation, immersing the receiver in ice-cold water and distil until no more bromoethane is formed.

6. Decant as much water as possible and then wash the product with dilute sodium carbonate solution and distilled water, decanting off the aqueous layer each time. 7. Transfer the washed product to a separating funnel and, from this, run off the organic layer into a small distillation flask. 8. Add anhydrous calcium chloride, stopper the flask and allow it to stand until the liquid turns clear. 9. Distil the bromoethane over a suitable temperature range, immersing the receiver in ice-cold water.

Burette or pipette volumetric flask Data Suggest the apparatus most suitable for measuring the volume of ethanol to an accuracy of + 0.1 cm (step 1). Burette or pipette volumetric flask (b) Explain why it is necessary to pre-cool the bromine (step 3). Bromine volatile or low boiling point or evaporates easily Or To ensure that the bromine does not evaporate (c) Suggest why it is also necessary to cool the mixture while adding the bromine (step 3). Reaction is exothermic or gives off heat orallow reaction is vigorous Property Ethanol Bromoethane Density / g cm 0.789 1.47 Molar mass / g mol 46.0 109 Boiling temperature / °C 78.4 38.4 -3 -1 3

Or To ensure bromoethane is liquid (d) Draw a labelled diagram of the apparatus that you would use to heat the mixture under reflux (step 4). (e) Suggest why, in both the distillations, the receiver is immersed in ice-cold water (steps 5 and 9). Product / bromoethane is volatile or has a low boiling point or evaporates easily Or To prevent evaporation of the bromoethane Or Bromoethane boils at 38.4 (ºC) Or To ensure bromoethane is liquid (f ) State the purpose of the following in this procedure: Washing the product with dilute sodium carbonate solution (step 6). Neutralize the (phosphoric) acid / bromine Or remove the acid / bromineacid / bromine (ii) Adding anhydrous calcium chloride to the organic layer (step 8). Drying agent or to remove water

(step 9), giving the temperatures in whole numbers. (g) Suggest a suitable temperature range for the collection of the product in the final distillation (step 9), giving the temperatures in whole numbers. From . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35, 36, 37 or 38 (ºC) To: 39, 40, 41 or 42 (ºC) (h) (i) Calculate the number of moles of ethanol used in the preparation. 10 x 0.789/46 (=0.17152) = 0.172g (ii) Given that one mole of ethanol forms one mole of bromoethane, calculate the maximum mass, in grams, of bromoethane that may be prepared using 10 cm of ethanol. 0.17152 x 109 = 18.6959 = 18.7 (g) 0.172 x 109 = 18.748 = 18.7 (g) 0.17 x 109 = 18.53 = 18.5 (g) 3

Calculate the percentage yield of bromoethane in this preparation. (iii) Using the procedure described, a student prepared 13.3 g of bromoethane. Calculate the percentage yield of bromoethane in this preparation. 100 x 13.3/18.7 = 71.123 = 71.1 (%) 100 x 13.3/18.5 = 71.8919 = 71.9 (%) (iv) Suggest why the yield is calculated in relation to the ethanol rather than the bromine. Bromine is in excess or All the ethanol is used up (v) Suggest one reason, other than volatility of the reactants or products, why the preparation does not produce a 100 % yield. Transfer losses or handling losses or specific examples of these (e.g. some product remains in the aqueous layer during separation or in the flask during distillation. Reaction incomplete or Side / competing reactions

The process has an 80 % yield after purification of the 1-bromobutane. 10. An experiment to prepare 0.100 mol of 1-bromobutane uses the reaction of butan-1-ol with hydrogen bromide. Hydrogen bromide is formed in the reaction mixture from potassium bromide and moderately concentrated sulfuric acid. The process has an 80 % yield after purification of the 1-bromobutane. KBr + H2SO4 KHSO4 + HBr CH3CH2CH2CH2OH + HBr CH3CH2CH2CH2Br + H2O The steps of the experimental procedure are as follows. 1.Add measured amounts of potassium bromide and butan-1-ol to 10 cm of water into a 50 cm two-necked flask. 2. Fit the two-necked flask with a reflux condenser and a tap funnel. 3. Immerse the flask in a beaker of cold water and add 10 cm of concentrated sulfuric acid from the tap funnel, a few drops at a time. 3 3 3

10. Decant the 1-bromobutane into a 50 cm flask. 4. Remove the flask from the cold water and close the tap on the tap funnel. Heat the mixture under reflux for 30 minutes. 5. Allow the mixture to cool. Then set up the apparatus for distillation. Boil the mixture and collect the distillate in a measuring cylinder. 6. Transfer the distillate to a separating funnel. The distillate consists of two layers, an aqueous layer and impure 1-bromobutane. Separate the two layers. 7. Wash the impure 1-bromobutane with concentrated hydrochloric acid and separate the two layers. 8. Wash the 1-bromobutane layer with sodium hydrogencarbonate solution, releasing any gas formed. 9. Collect the 1-bromobutane layer in a conical flask and add anhydrous sodium sulfate. 10. Decant the 1-bromobutane into a 50 cm flask. 3

Data Property Butan-1-ol 1-bromobutane Water Density /g cm 0.81 1.3 1.0 Molar mass g mol 74 137 18 Boiling temperature / °C 117.3 101.7 100.0 -3 -1 (a) (i) Show, by calculation, that 0.125 mol of butan-1-ol is needed to make 0.100 mol of 1-bromobutane. number of moles of butan-1-ol 0.1 x 100 = 0.125 mol 80 (ii) Calculate the volume of 0.125 mol of butan-1-ol, in cm. 74 x 0.125 = 9.25 g 9.25 = 11.419 cm 0.81 3

[The molar mass of potassium bromide is 119 g mol–1] (iii) Calculate the minimum mass of potassium bromide required in step 1. [The molar mass of potassium bromide is 119 g mol–1] 0.125 x 119 = 14.875 /14.87/14.88/14.9/15 (g) (b) Complete and label the diagram below of the apparatus assembled in steps 1, 2 and 3. [You may assume that the apparatus is suitably clamped.] water out tap funnel concentrated sulphuric acid water out two- necked flask reactants beaker with cold water

Lower layer as more dense or Lower layer is (c) (i) State, with a reason, whether the upper or lower layer contains 1-bromobutane in step 6. Lower layer as more dense or Lower layer is 1-bromobutane because it is denser layer as denser than water (ii) The product is washed with concentrated hydrochloric acid in step 7 to remove unreacted butan-1-ol. In step 8, why is the product then washed with sodium hydrogencarbonate solution and what causes a build up of gas? To remove /neutralize hydrochloric acid/H2SO4 by a 2 reove / neutralize / react with remaining hydrochloric acid/HCl/acid/sulfuric by reacting to form carbon dioxide (gas) (d) (i) What further step is necessary to purify the 1-bromobutane obtained in step 10? distillation / Fractional distillation (ii) How does the step in (d)(i) give information about the purity of the product? Measure Tb or Tm of a liquid and compare with data booklet value

Both alcohols cause the same colour change of the mixture on heating. 11. This question is about two isomeric alcohols, X and Y, each with molar mass 60 g mol . A solution of potassium dichromate(VI) in dilute sulfuric acid is added to each alcohol. Both alcohols cause the same colour change of the mixture on heating. (a) A colourless liquid, B, is distilled from the mixture containing alcohol X. The liquid B forms a red precipitate when it is boiled with Benedict’s or Fehling’s solution. Give the displayed formula of liquid B, and the name of alcohol X. Liquid B H H O Name of alcohol X H C C C H propan-1-ol/1-propanol H H -1

Give the names of liquid C and alcohol Y. Y propan-2-ol/2-propanol (b) A colourless liquid, C, is distilled from the mixture containing alcohol Y. C does not react when it is boiled with Benedict’s or Fehling’s solution. Give the names of liquid C and alcohol Y. Liquid C propanone Alcohol Y Y propan-2-ol/2-propanol

(CH3)3COH + HCl (CH3)3CCl + H2O 12. An experiment to prepare a sample of 2-chloro-2-methylpropane uses the reaction of 2-methylpropan-2-ol with concentrated hydrochloric acid. (CH3)3COH + HCl (CH3)3CCl + H2O The steps of the experimental procedure are as follows 1. Place 0.20 mol of 2-methylpropan-2-ol and 70 cm3 of concentrated hydrochloric acid in a large conical flask. 2. Stopper and shake the flask at intervals, releasing any pressure after each shaking. 3. Separate the 2-chloro-2-methylpropane from the aqueous solution using a separating funnel. 4. To the 2-chloro-2-methylpropane in the separating funnel, add 20 cm3 of sodium hydrogencarbonate solution. Shake the separating funnel, carefully releasing carbon dioxide frequently.

5. Separate the 2-chloro-2-methylpropane and repeat the washing with sodium hydrogencarbonate solution until this washing step is no longer necessary. 6. Transfer the 2-chloro-2-methylpropane to a small conical flask and add a suitable drying agent. 7. Filter off the drying agent, collecting the 2-chloro-2-methylpropane into a distillation flask. Heat the flask, collecting the fraction that distils off between 50 °C and 52 °C. Data Property 2-methylpropan-2-ol 2-chloro-2-methylpropane Density g cm 0.789 0.842 Molar mass g mol 74.1 92.6 Boiling Temperature °C 82.4 50.8 -3 -1

Calculate the volume of 2-methylpropan-2-ol used in the preparation. 0.2 x 74.1 = 18.78 cm =18.8 0.789 (b) Draw a diagram of a separacmting funnel that could be used in step 3. Label the 2-chloro-2-methylpropane layer. (c) (i) Suggest why the product is washed with sodium hydrogencarbonate solution (step 4). (ii) How would you know that no further washing with sodium hydrogencarbonate was necessary? (d) Suggest a suitable drying agent to dry the 2-chloro-2-methylpropane (step 6). (e) Draw a labelled diagram of the apparatus you would use to carry out the final distillation (step 7).

(i) Suggest why ethanol is added to the mixture. (f) A reaction produced 18.7 cm3 of 2-chloro-2-methylpropane starting from 0.20 mol 2-methylpropan-2-ol. Calculate the percentage yield of the product of this reaction. (g) A suitable chemical test for the chlorine in a chloroalkane, such as 2-chloro-2-methylpropane, is to add the chloroalkane to a mixture of aqueous silver nitrate solution and ethanol. (i) Suggest why ethanol is added to the mixture. (ii) Give the expected result of this test.

(CH3)2C(OH)CH2CH3 + HCl → (CH3)2C(Cl)CH2CH3 + H2O 13. 2-chloro-2-methylbutane may be prepared by reacting 2-methylbutan-2-ol with concentrated hydrochloric acid: (CH3)2C(OH)CH2CH3 + HCl → (CH3)2C(Cl)CH2CH3 + H2O The steps of the experimental procedure are as follows. 1. Place 5.00 cm3 of 2-methylbutan-2-ol and about 20 cm3 of concentrated hydrochloric acid into a separating funnel. 2. Continuously shake the mixture for 10 minutes. 3. Remove the aqueous layer and slowly add about 10 cm3 of dilute sodium hydrogencarbonate solution to the separating funnel. 4. Shake the mixture gently, inverting the separating funnel and opening the tap at regular intervals. 5. Remove the aqueous layer and transfer the organic layer to a conical flask. 6. Add a few pieces of anhydrous calcium chloride to the conical flask and shake the mixture. 7. Decant the liquid into a distillation flask and distil it to collect the pure 2-chloro-2-methylbutan

[The density of concentrated hydrochloric acid is 1.18 g cm−3.] Data (a) Draw a diagram of the separating funnel, clearly labelling the 2-methylbutan-2-ol and the concentrated hydrochloric acid layers (step 1). [The density of concentrated hydrochloric acid is 1.18 g cm−3.] 2-methylbutan-2-ol 2-chloro-2-methylbutane Density / g cm−3 0.805 0.866 Molar mass / g mol−1 88 106.5 Boiling temperature / °C 102 85.5

(iv) What is the purpose of the calcium chloride (step 6)? (b) (i) Why is it necessary to continuously shake the 2-methylbutan-2-ol and the concentrated hydrochloric acid for the reaction to occur (step 2)? (ii) Explain the purpose of the sodium hydrogencarbonate solution (step 3). (iii) Why is the tap of the separating funnel opened at regular intervals (step 4)? (iv) What is the purpose of the calcium chloride (step 6)? (v) What is meant by decant the liquid (step 7)? (c) An incomplete diagram of the distillation apparatus is shown below. (i) Draw a thermometer in the diagram, showing clearly where the bulb of the thermometer is placed. (ii) Draw clearly labelled arrows on the diagram to show the flow of water into and out of the condenser.

Q14 The compound with the formula, COOH ,was formerly known as ethylene glyco COOH (a) (i) Give the systematic name for ethylene glycol. (ii) Is ethylene glycol likely to be soluble in water? Give a reason for your answer. (b) Write a balanced equation for the complete combustion of ethylene glycol. State symbols are not required. (c) In each of the following cases, give the structural formula of the organic compound formed when (i) excess sodium is added to ethylene glycol. (ii) ethylene glycol is refluxed with excess acidified sodium dichromate(VI) solution. (d) Ethylene glycol can be manufactured from epoxyethane, which has the following structural formula: Suggest a reagent which could be added to epoxyethane to carry out this conversion.

15. Consider the following reaction scheme: Step 1 C3H7Br (major product) S C3H6 propene Step 2 C3H8O P oxidation CH3COCH3

a) (i) Give the reagent and condition needed for step 1. (ii) Give the structural formula of S. (b) (i) Give the structural formula of P. (ii) State the type of reaction in: step 1............................................................................................. the conversion of S to P................................................................. (c)Give the reagent and the condition needed for step 2. If S is reacted with a solution of hydroxide ions in ethanol, P is not the product. Draw the structure of the compound that is produced in this reaction.

polymers and glues and also in the food industry as an acidity 16. Ethanoic acid is used industrially in the manufacture of polymers and glues and also in the food industry as an acidity regulator. It can be synthesized in the laboratory by the reaction of ethanol with excess sodium dichromate(VI) solution, acidified with concentrated sulfuric acid. Ethanol is placed in a suitable flask along with some anti-bumping beads. The concentrated sulfuric acid is then added a drop at a time. The sodium dichromate(VI) solution is then added a drop at a time causing the mixture to boil spontaneously. When the addition of the sodium dichromate(VI) solution is complete, the mixture is heated under reflux for approximately 15 minutes. The ethanoic acid formed can then be separated from the reaction mixture.

Na2Cr2O7 CH3CH2OH CH3COOH H2SO4/heat,1 atm Ethanoic acid can be produced industrially by the Cativa™ process. Methanol, which can be obtained from wood, is reacted with carbon monoxide in the presence of an iridium catalyst. Iridium catalyst 20-30 atmosphere 1900C CH3OH(g) + CO(g) CH3COOH(g)   (a) (i) Balance the half-equation for the reduction of dichromate(VI) ions. Cr2O72– + ......H+ + .....e− ........Cr3+ + ......H2O (ii) The half-equation for the oxidation of ethanol is CH3CH2OH + H2O CH3COOH + 4H+ + 4e–

Use this and your answer to (a)(i) to write a full equation for the overall reaction between acidified dichromate(VI) ions and ethanol. State symbols are not required. (b) (i) Why are the concentrated sulfuric acid and sodium dichromate(VI) added a drop at a time in the laboratory process? (ii) Draw a labelled diagram of the apparatus that could be used to heat the mixture under reflux. (iii) What colour would the mixture be after it was heated under reflux? (c) A solution containing both water and ethanoic acid is produced by distillation of the final reaction mixture. Explain why the other products and any excess reactants are

left behind in the distillation flask. (ii) Suggest a method to separate pure ethanoic acid, boiling temperature 118°C, from the water. (d) (i) In the Cativa™ process what effect, if any, would increasing the pressure have on the yield of ethanoic acid? Justify your answer. (ii) Suggest TWO reasons why it might be difficult, or undesirable, to produce ethanoic acid in industry by scaling up the laboratory process. (e) An alternative industrial process for the production of ethanoic acid is the oxidation of butane using a transition metal catalyst at 150°C and 55–60 atm. 2C4H10(l) + 5O2(g) 4CH3COOH(aq) + 2H2O(l) Evaluate the ‘greenness’ and sustainability of the two industrial processes. Suggest TWO additional pieces of information that would help you make a more informed decision.