Name: Organic chemistry. Class: Foundation revision questions. Date: 67 minutes. Time: 67 marks. Marks: Comments: Page 1 of 27

Transcription

1 Organic chemistry Foundation revision questions Name: Class: Date: Time: 67 minutes Marks: 67 marks Comments: Page of 27

2 Barbecues are heated by burning charcoal or burning hydrocarbons. (a) Use the Chemistry Data Sheet to help you to answer this question. The chemical equation for charcoal burning is: C + O 2 CO 2 Complete the word equation for this reaction. carbon + carbon dioxide () (b) Propane is a hydrocarbon. (i) Complete the displayed structure of propane. Draw in the missing bonds. Write the chemical formula of propane. () () Page 2 of 27

3 (iii) Draw a ring around the correct answer to complete the sentence. hydrogen. Propane burns in air to produce carbon dioxide and hydroxide. water. () (c) The table shows information about six hydrocarbons. Hydrocarbon State at room temperature (20 C) Boiling point in C Ethane (C 2 H 6 ) gas 89 Ethene (C 2 H 4 ) gas 04 Butane (C 4 H 0 ) gas Butene (C 4 H 8 ) gas 6 Hexane (C 6 H 4 ) liquid +69 Hexene (C 6 H 2 ) liquid +64 Tick ( ) two correct statements about the six hydrocarbons. Statement Tick ( ) Ethane and butane boil at temperatures less than 20 C. Hexene and butene are alkanes. Butane and hexane are liquid at 0 C. Ethene and hexene each have a carbon-carbon double bond. (2) (Total 6 marks) Page 3 of 27

4 2 A student investigated the substances produced when fuels burn. The figure below shows the apparatus the student used. (a) The complete combustion of a hydrocarbon produces carbon dioxide and one other substance. Look at the figure above. What would the student see in tube A? () (b) When the student burned the fuel she saw soot in the funnel. Explain why soot forms. (2) Page 4 of 27

5 (c) The student burned another fuel which contained impurities. The substance in tube B is water containing universal indicator. The indicator turned red. Which gas made the indicator turn red? Tick one box. Ammonia Carbon monoxide Nitrogen Sulfur dioxide () (Total 4 marks) 3 There are several different forms of carbon and many different carbon compounds. (a) Figure shows a 3D model of a molecule of methane (CH 4 ). Figure Draw the 2D structure of a methane molecule. () Page 5 of 27

6 (b) Different forms of carbon have different bonding and structure. Draw one line from the form of carbon to the bonding and structure. Form of carbon Bonding and structure (3) Page 6 of 27

7 (c) Crude oil is a mixture of many different carbon compounds. Crude oil can be separated into useful fractions by fractional distillation. Figure 2 shows a column used to separate crude oil. Figure 2 Complete the sentences. Use words from the box. condense evaporate freeze Crude oil is heated so that most of the compounds At different temperatures the compounds cool and (2) Page 7 of 27

8 (d) Which fraction is the most viscous? Tick one box. Engine oil Diesel oil Kerosene Petrol () (e) Which fraction is the most flammable? Tick one box. Diesel oil Kerosene Petrol Refinery gas () (f) Why does kerosene separate out of the mixture before diesel oil? () (Total 9 marks) Page 8 of 27

9 4 Some gas cookers burn natural gas, methane. Methane, CH 4, is a hydrocarbon. (a) What is meant by hydrocarbon? (2) (b) When methane burns there must be a good supply of air. (i) Complete the word equation by choosing the correct two chemicals from the box. carbon dioxide hydrogen oxygen water methane + oxygen + (2) Without a good supply of air, carbon monoxide is formed. Why is carbon monoxide a dangerous gas? () (Total 5 marks) Page 9 of 27

10 5 A student investigated the viscosity of liquid hydrocarbons. A viscous liquid is a liquid that flows slowly. The student used this method. Measure 50 cm 3 of the liquid hydrocarbon. Pour the liquid hydrocarbon into the funnel, as shown in Figure. Time how long it takes for all of the liquid hydrocarbon to run out of the funnel. Repeat the experiment for other liquid hydrocarbons. (a) (i) Give the name of apparatus A in Figure. () Name the apparatus that could be used to measure 50 cm 3 of liquid hydrocarbon. () Page 0 of 27

11 (b) The student s results for six liquid hydrocarbons are shown in Table. Table Formula of liquid hydrocarbon Time for liquid hydrocarbon to run out of the funnel in seconds Experiment Experiment 2 Experiment 3 Mean time in seconds C 5 H C 6 H C 7 H C 8 H C 0 H C 2 H Page of 27

12 (i) The student did the experiment three times with each liquid hydrocarbon. Give two reasons why. (2) Use the data in Table to calculate the mean time, in seconds, for C 7 H 6 Mean time = seconds () (iii) Complete the sentence. As the number of carbon atoms in a molecule of liquid hydrocarbon increases, the time taken for the liquid hydrocarbon to run out of the funnel. () (iv) A ring has been drawn around one result in Table. This result has not been used to calculate the mean time for C 0 H 22 Suggest why this result was not used. () (v) Suggest one error the student may have made to get the ringed result. () Page 2 of 27

13 (c) The student investigated the effect of temperature on the viscosity of one of the liquid hydrocarbons. The liquid hydrocarbon he was using had the hazard symbols shown in Figure 2. (i) Suggest why the student warmed the liquid hydrocarbon using warm water and not a Bunsen flame. () The student wore safety glasses. Give one other safety precaution the student should take, and give a reason for this safety precaution. Safety precaution Reason (2) (d) This is the method the student used to investigate the effect of temperature on the viscosity of one of the liquid hydrocarbons. Measure 50 cm 3 of the liquid hydrocarbon and pour it into a beaker. Stand the beaker of liquid hydrocarbon in a heated water bath. Leave for a few minutes. Measure the temperature of the liquid hydrocarbon. Pour the liquid hydrocarbon into the funnel, as shown in Figure 3. Page 3 of 27

14 Time how long it takes for all of the liquid hydrocarbon to run out of the funnel. Repeat the experiment at different temperatures. (i) The student s results are shown in Table 2. Table 2 Temperature of liquid hydrocarbon in C Time to run out of the funnel in seconds Page 4 of 27

15 Plot the results shown in Table 2 on the graph in Figure 4. Draw a curve of best fit. (3) One of the points is anomalous. Draw a ring around the anomalous point on your graph. () (iii) Predict how long it will take the liquid hydrocarbon to run through the funnel at 70 C. Show your working on your graph. Time = seconds (2) (iv) Describe the relationship between the temperature of the liquid hydrocarbon and the viscosity of the liquid hydrocarbon. (3) (v) The apparatus the student used in Figure 2 could lead to a systematic error in the results. Identify one source of systematic error, and describe how the student could avoid or reduce the error. Page 5 of 27

16 (2) (Total 22 marks) 6 Crude oil is a fossil fuel. (a) To make crude oil more useful it is separated into fractions. Use the correct word from the box to complete each sentence. boiling compound decomposition distillation filtration mixture molecule (i) Crude oil is a of different substances. The substances in crude oil have different points. () () (iii) Crude oil is separated by fractional. () Page 6 of 27

17 (b) Petrol is one of the fractions produced from crude oil. Car engines use a mixture of petrol and air. The diagram shows some of the gases produced. (i) What type of reaction happens to petrol in a car engine? Tick ( ) one box. combustion decomposition neutralisation () Petrol contains octane (C 8 H 8 ). Complete the word equation for the reaction of octane with oxygen. octane + + (2) (iii) Cars use sulfur-free petrol as a fuel. Describe why sulfur should be removed from petrol. (2) Page 7 of 27

18 (c) Some fractions from crude oil contain large hydrocarbon molecules. These molecules can be cracked to produce smaller, more useful molecules. An equation for cracking decane is: C 0 H 22 C 3 H 8 + C 2 H 4 + C 5 H 0 decane propane ethene pentene (i) Why is propane useful? Tick ( ) one box. Propane is a polymer. Propane is an alloy. Propane is a fuel. () Draw bonds to complete the displayed structure of ethene. () (iii) What is the colour change when bromine water reacts with ethene? Tick ( ) one box. Orange to colourless Orange to green Orange to red () Page 8 of 27

19 (iv) Complete the sentence. Pentene is useful because many pentene molecules can join together to form. () (Total 2 marks) 7 Alkanes are hydrocarbons found in crude oil. (a) (i) Complete the sentence. Hydrocarbons contain the elements and only. () Ethane is an alkane with the formula C 2 H 6 Draw a ring around the correct answer to complete the sentence. C n H n Alkanes are hydrocarbons with the general formula C n H 2n C n H 2n+2 () Page 9 of 27

20 (b) Crude oil is separated into useful fractions by fractional distillation. Describe and explain how crude oil is separated into fractions by fractional distillation. Use the diagram to help you answer the question. (4) (c) Dodecane (C 2 H 26 ) from crude oil is cracked to produce ethene (C 2 H 4 ). (i) Complete the equation for this reaction. C 2 H 26 2 C 2 H 4 + () Give two conditions needed for cracking.. 2. (2) (Total 9 marks) Page 20 of 27

21 Mark schemes (a) oxygen must be name do not accept oxide or dioxide (b) (i) 2 x C C and 5 x C H all single (line) bonds C 3 H 8 must be formula do not accept lower case h (iii) water (c) ethane and butane boil at temperatures less than 20 C ethene and hexene each have a carbon-carbon double bond [6] 2 (a) Colourless liquid / condensation / water (b) incomplete combustion of the fuel because not enough oxygen (c) Sulfur dioxide [4] 3 (a) Page 2 of 27

22 (b) Form of carbon Bonding and structure extra lines from the left negate the mark 3 (c) evaporate condense (d) Engine oil (e) Refinery gas (f) because its boiling point is lower [9] 4 (a) hydrocarbon is a compound not mixture not substance containing carbon and hydrogen accept of the elements carbon and hydrogen accept of carbon and hydrogen contains hydrogen and carbon only (2) (b) (i) any order carbon dioxide accept CO 2 exact formulae 2 Page 22 of 27

23 water accept H 2 O not carbon in one box and dioxide in second box (0) ignore any attempt to balance the equation it is poisonous accept toxic can kill you accept any reasonable description of its effect on red blood cells or on haemoglobin in terms of reducing oxygen transport not can explode, harmful, dangerous, flammable [5] 5 (a) (i) (conical) flask measuring cylinder / pipette / burette (b) (i) any two from: so anomalous results could be identified / ignored so a mean / average could be taken (to improve) accuracy 9 2 (iii) increases / gets longer / gets bigger (iv) anomalous / does not agree with other times for C 0 H 22 (v) any one from: shorter hydrocarbon used volume of hydrocarbon too small started timing late stopped timing too early / when liquid left in funnel must suggest why the result is lower than the others. allow the temperature was higher or the students used a wider funnel. Page 23 of 27

24 (c) (i) flammable suitable safety precaution reason that links the safety precaution to the hazard symbols eg: wear gloves (because) it is hazardous to health / harmful / toxic / irritant or do not pour down sink or dispose of properly (because) it is harmful to the environment / kills fish or wear a mask or do it in the fume cupboard or a well-ventilated area respiratory irritant Page 24 of 27

25 (d) (i) points plotted correctly (within half small square) all six points correct scores 2 3, 4 or 5 points correct scores smooth curve of best fit 2 (iii) (iv) (v) point at 46 C circled allow point furthest from the line as drawn working shown on graph value read from graph line drawn (within half small square) the higher the temperature the lower the viscosity allow the higher the temperature the lower / shorter the time taken for mark non-linear or change gets smaller as temperature gets higher answer relating temperature to time taken can score a maximum of 2 marks. identifying source of the error 2 method of avoiding the error eg: the temperature will drop insulate the funnel or runs out before all added put a tap on the funnel [22] 6 (a) (i) mixture (of different substances) (iii) boiling (points) distillation Page 25 of 27

26 (b) (i) combustion (reactant) oxygen allow correct formulae (products) products in any order carbon dioxide allow carbon or carbon monoxide and water allow water vapour or steam or hydrogen oxide (iii) (burning sulfur) produces sulfur dioxide / S0 2 allow it / sulfur reacts with oxygen ignore sulfur oxide causes acid rain (c) (i) propane is a fuel double bond drawn between carbon atoms do not allow any other bonds or symbols (iii) orange to colourless (iv) poly(pentene) allow polymer(s) [2] 7 (a) (i) hydrogen / H and carbon / C answers can be in either order if letters given, must be capital H C n H 2n+2 (b) (most) crude oil vaporises / evaporates or crude oil enters as a vapour (vapour) cools as it rises up the tower / column or tower / column cooler at the top or negative temperature gradient Page 26 of 27

27 (c) (i) C 8 H 8 if one answer is given C 8 H 8 is the only acceptable answer the fractions have different boiling / condensation points / ranges accept the larger the molecules, the higher the boiling point / condensation point so they will condense at different levels in the tower allow will collect at different levels if condensation mentioned allow will condense to give different fractions if no other mark is gained allow mark for mention of heating credit any correct combination of alkanes and alkenes, eg C 5 H 2 and C 3 H 6 hot / high temperature accept any temperature in the range C heat is insufficient catalyst accept a named catalyst alumina or zeolites or aluminosilicates or broken pot ignore other named catalysts allow (mixing with) steam as an alternative to second marking point ignore pressure [9] Page 27 of 27