SAMPLE CHEMISTRY QUESTIONS MIXTURE OF UNIT 3 & 4 MATERIALS

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1 SAMPLE CHEMISTRY QUESTIONS MIXTURE OF UNIT 3 & 4 MATERIALS QUESTION 1 The equation describing the production of butyl ethanoate is given below. Catalyst C4H 9OH CH 3COOH CH 3COOC 4H 9 H 2O( l ) mol of ethanoic acid and mol of butanol were allowed to reach equilibrium at 0 90 C for 2 hours, and then quickly cooled in an ice bath to 0 C 3 out at a constant volume of 1.00 dm cm of.00 M 25. The reaction was carried 1 NaOH was added to the mixture, and was then titrated with 1.00 M hydrochloric acid using phenolphthalein as the indicator. this reaction. CH 3COOH NaOH CH 3COONa( aq) H 2O( l) NaOH HCl NaCl 2 ( l) cm of acid was required for H O a. (i) Calculate the amount, in mol, of NaOH that reacted with the 1.00 M hydrochloric acid solution. (ii) Calculate the amount, in mol, of solution. CH 3 COOH that reacted with the 1.00 M NaOH The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 1

2 (iii) Calculate the amount, in mol, of butanol, mixture. C 9 4 H OH, that reacted in the initial (iv) Hence calculate the amount, in mol, of each species at equilibrium at 25 0 C. b. (i) Write an expression for the equilibrium constant for this reaction. (ii) Hence determine the equilibrium constant at 25 0 C. The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 2

3 c. The table below describes some features relating to the organic molecules involved in the production of butyl ethanoate. Catalyst C4H 9OH CH 3COOH CH 3COOC 4H 9 H 2O( l ) Molar Mass ( g / mol ) Boiling Point ( C Ethanoic Acid Butanol Butylethanoate (i) Explain how heating the equilibrium mixture to 110 o C will improve the yield of ester. (ii) What catalyst is typically used in the production of esters and why? o ) (ii) The reactants used to make small chain esters are highly soluble in aqueous solutions, but the esters themselves are not. Explain. The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 3

4 d. Esters may be linked to produce long chains known as polyesters. Could the molecules below be used to produce a polyester? Explain your answer. CH 3 O C O CH 2 CH 3 Total 16 marks The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 4

5 QUESTION 2 A student decides to investigate the equilibrium properties and rates of the reaction involving vitamin C ( C 6H 8O6 ) and iodine ( I 2 ) solution, as described in the reaction below. C6H 8O6( aq) I 2 C6H 6O6( aq) 2HI Equimolar amounts of vitamin C and iodine were originally added to a vessel at 25 o C. The concentration of iodine was then monitored using colorimetry at a wavelength of 400 nm. The absorption of a series of standard solutions containing iodine, which is brown in colour, is given below. A sample of the reaction mixture was removed at 30 second intervals. The reaction was stopped and the absorbance of each sample was determined using colorimetry. The absorbances were then plotted against time, as illustrated in the graph below. The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 5

6 a. (i) At what time did the system described by the reaction C6H 8O6( aq) I 2 C6H 6O6( aq) 2HI reach equilibrium? (ii) What is the concentration of iodine when the system reaches equilibrium? b. (i) Write an expression for the equilibrium constant for this reaction. (ii) Calculate the equilibrium constant at 25 o C. 3 marks The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 6

7 c. (i) On the axes below, sketch one possible curve that reflects the changes in absorbance you could expect to observe if a catalyst was added to the reaction mixture. (ii) On the axes below, sketch one possible curve that reflects the changes in absorbance you could expect to observe if C 6H 6O6( aq) were regularly removed from the reaction mixture, keeping volume and temperature constant. Total 10 marks The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 7

8 QUESTION 3 The production of ethanol from ethene is given by the reaction: C H H O C 2H 5OH ( g ) 2 4 ( g ) 2 ( g) H3PO4 a. Identify the type of reaction that is occurring in the above equation. Circle the correct response(s): Addition Substitution Hydration Condensation Esterification The graph below shows the variation in the equilibrium constant for this reaction at different temperatures. K Temperature b. (i) Use this graph to determine whether the production of ethanol is exothermic or endothermic. (ii) State whether the formation of ethanol is favoured by high or low pressures and temperatures. The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 8

9 Alkenes are typically more reactive than their corresponding alkanes due to the presence of unsaturated C-C bonds. c. Outline a procedure to compare the reactivity of an alkene such as ethene with its corresponding alkane. Describe the results that would be obtained, including the relevant chemical equations. 4 marks Total 7 marks The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 9

10 QUESTION 4 The high cost of traditional hydrocarbon fuels has led to intense research into alternative fuels such as ethanol. Ethanol is a common alcohol with molar mass 46 gmol 1, density g/ml and a heat of combustion of kjmol 1. a. A group of students decide to investigate the energy released during the combustion of ethanol using a form of calorimetry, as illustrated below. Thermometer Ethanol The results obtained during this investigation include: Volume of water in the beaker Volume of ethanol used during combustion Initial temperature of the water Maximum temperature of the water Note: Specific heat capacity of water 500 ml 5.00 ml 22.4 C 75.2 C J 1 g 1 C 1 (i) What amount of energy was released when the ethanol was burned? (ii) Why is the measured heat of combustion in this investigation lower than the true heat of combustion for ethanol? The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 10

11 (iii) Use the results of this experiment to write the corresponding thermochemical equation for the combustion of ethanol. 4 marks b. Assume that all the heat released during the combustion of the ethanol sample in this investigation was transferred to the water. (i) Determine the calibration factor of this calorimeter in kj K 1. (ii) A 15.0 ml sample of pure olive oil contains 505 kj of energy. What temperature change should the students observe during the complete combustion of a 2.50 ml sample using the illustrated calorimeter? The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 11

12 c. Olive oil contains 55-85% oleic acid (CH 3 (CH 2 ) 7 CHCH(CH 2 ) 7 COOH) by weight. (i) What type of fatty acid is oleic acid? (ii) State one difference that would be observed in the physical properties of olive oil if it contained 85% stearic acid (CH 3 (CH 2 ) 16 COOH) by weight? Total 1 The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 12

13 QUESTION 5 Consider the flow diagram below, which shows the pathways of ingested fat and starch in humans. Triglyceride Starch A Fatty Acid + Glycerol CH3( CH 2) 14COOH CHO Glucose CH O O 2 CO H O 2 2 a. (i) State the type of reaction involved in process A. (ii) Explain what is meant by the term triglyceride. (iii) Determine the correct molecular formula of the triglyceride = 5 marks The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 13

14 b. (i) When g of pure glucose is completely combusted in a calorimeter, 3114J of energy is released. Calculate the H in kjmol -1 for the oxidation reaction below. C 6 H 12 O 6 (s) + 6O 2 (g) 6CO 2 (g) + 6H 2 O (l) (ii) The reaction above occurs in all living animal cells and is termed respiration. Give one major difference between the manner in which glucose is oxidized in living cells compared to its oxidation in a bomb calorimeter. (iii) Excess glucose in the blood that does not undergo oxidation in cells is converted to other substances. One possible pathway is the conversion of glucose to fat. State the other possible pathway for glucose that occurs in animal cells. (iv) Glucose is very soluble in water. Describe, using a diagram if you wish, the nature of the chemical bonding responsible for this observation = 6 marks Total 1s The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 14

15 QUESTION 6 When phenol red, C 5 19 H14O S is dissolved in water, the following equilibrium is set up. C19H14O5S C19H Yellow Red 13 O S 5 H In aqueous solutions, the molecule C 5 19 H14O S is yellow, and the ion C 5 19 H13O S is red. Phenol red is a weak acid, whose K a at o C a. (i) Write the expression for the acid dissociation constant. (ii) Calculate the concentration of hydrogen ions in a M solution of phenol red. b. Another solution of phenol red, also at a concentration of M, is 1.5% hydrolysed at 35 o C. (i) Calculate the K a for the dissociation reaction of phenol red at 35 o C. The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 15

16 (ii) Use these results to determine whether the forward reaction for the dissociation of phenol red is endothermic or exothermic. c. Phenol red can be used as an acid/base indicator, changing from yellow to red between ph Phenol red was used as the indicator in the following titration. A M solution of sodium hydroxide was slowly added from a burette, to a conical flask containing ml HCl and a few drops of phenol red. A titre of ml was required during this titration. (i) What was the initial colour displayed by the indicator? Explain. (ii) Explain why the indicator changes colour when excess sodium hydroxide is added to the conical flask. (iii) Calculate the molarity of the HCl solution. Total 11 Marks The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 16

17 QUESTION 7 The following structures represent some biologically important molecules. A H NCHCH 3COOH 2 B C 18H 34O2 C C 3H8O3 D E F ( CH COOH CH 3 2 ) 14 G CH 3 COOH H C 12H 22O11 I C 16H 32O2 J CO (NH 2 ) 2 K CO 2 L H 2 O H 2 COH O M HC O C ( CH 2 ) 16 CH 3 H 2 COH a. Circle the response(s) that best answer the questions below. (i) Which structure(s) represent fatty acids? A B C D E F G H I J K L M (ii) Which structure(s) represent the components from which unsaturated fats are derived? A B C D E F G H I J K L M (iii) Which structure(s) represent the product(s) of photosynthesis? A B C D E F G H I J K L M (iv) Which structure(s) represent the product(s) of the hydrolysis of carbohydrates? A B C D E F G H I J K L M (v) Which structure(s) represent the product(s) of the oxidation of fats? A B C D E F G H I J K L M 5 marks The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 17

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19 b. The nutritional information relating to 5 grams of a particular food that is based on the components of larger molecules in Part (a) is given below. Structure A Structure B Structure E grams 4.1 grams 0.03 grams The energy available to the body from the combustion of foods is given below. Nutrient Energy Available (kj/g) Carbohydrates 17 Fats 37 Proteins 17 Calculate the energy content per 100 gram serving of this food. Total Marks = 7 The School For Excellence 2014 Unit 3 & 4 Chemistry Mixed Questions Page 19