Year 12 Applied Science

Transcription

1 Year 2 Applied Science Chemistry Name: Class: Date: Time: 205 minutes Marks: 203 marks Comments:

2 Q. (a) The formula for the chemical compound magnesium sulphate is MgSO 4. Calculate the relative formula mass (M r )of this compound. (Show your working.) Magnesium sulphate can be made from magnesium and dilute sulphuric acid. This is the equation for the reaction. Mg + H 2 SO 4 MgSO 4 + H 2 Calculate the mass of magnesium sulphate that would be obtained from 4g of magnesium. (Show your working.) Answer g (Total 4 marks) Q2. Methanol (CH 3 OH) can be made by reacting methane (CH 4 ) and oxygen (O 2 ). The reaction is exothermic. The equation for the reaction is: (a) The energy level diagram for this reaction is given below.

3 (i) How does the diagram show that this reaction is exothermic? () (ii) A platinum catalyst can be used to increase the rate of this reaction. What effect does adding a catalyst have on the energy level diagram? () The equation can also be written showing the structural formulae of the reactants and the product. (i) Use the bond energies given in the table to help you to calculate the energy change for this reaction. Bond Bond energy in kj

4 464 Energy change = kj (3) (iii) In terms of the bond energies, why is this an exothermic reaction? () (Total 6 marks) Q3. The equation for the reaction of ethene and bromine is: C 2 H 4 (g) + Br 2 (l) C 2 H 4 Br 2 (l) The reaction is exothermic. (a) Complete the energy level diagram. You should label: the activation energy the enthalpy change ( H). (3) (i) The equation for the reaction can be represented as:

5 Bond Bond dissociation energy in kj per mole C H 43 C C 64 Br Br 93 C C 348 C Br 276 Use the bond dissociation energies in the table to calculate the enthalpy change ( H) for this reaction. Enthalpy change ( H) = kj per mole (3) (ii) The reaction is exothermic. Explain why, in terms of bonds broken and bonds formed. (Total 8 marks) Q4. (a) By reference to their structure, explain how the particles in a piece of metal are held together and how the shape of the metal can be changed without it breaking. (You may use a diagram in your answer.)

6 (5) Explain why metals are good conductors of electricity and suggest why this conductivity increases across the periodic table from sodium to magnesium to aluminium. (4) (Total 9 marks) Q5. The extract below was taken from a leaflet on the uses of platinum. One of the uses described was in making electrodes for spark plugs in car engines. The spark plug produces the spark which ignites the fuel in the engine. Spark Plugs

7 The electrodes in a spark plug have to conduct electricity very well. Since they project into the combustion chamber of the engine, they must also be able to withstand extremely high temperatures in a very corrosive atmosphere. Nickel-based plugs have been produced for many years. They only last a fairly short time. As the electrodes wear, combustion becomes less efficient and the petrol is not burnt completely. Platinum and other precious metals can now be used in spark plugs. These last much longer and are more efficient. This can help to reduce air pollution. The table below gives some information about platinum and nickel. MELTING POINT ( C) BOILING POINT ( C) POSITION IN REACTIVITY SERIES COST ( /kg) nickel Higher than gold 2.5 platinum below gold 60 (a) Compare nickel and platinum for use in making the electrodes in spark plugs. A good answer should give advantages and disadvantages of each metal linking these to the properties of the metals. Marks will be given for the way in which you organise your answer. You will need a sheet of lined paper. (8) (i) Describe the structure and bonding in metals. (3) (ii) Explain why metals such as nickel and platinum are good conductors of electricity.

8 (Total 3 marks) Q6. This question is about ethanol. (a) Ethanol is produced by the reaction of ethene and steam: C 2 H 4 + H 2 O C 2 H 5 OH (i) Figure shows the energy level diagram for the reaction. How does the energy level diagram show that the reaction is exothermic? () (ii) A catalyst is used for the reaction. Explain how a catalyst increases the rate of the reaction. Figure 2 shows the displayed structure of ethanol.

9 Complete the dot and cross diagram in Figure 3 to show the bonding in ethanol. Show the outer shell electrons only. (c) A student burned some ethanol. Figure 4 shows the apparatus the student used. (i) The student recorded the temperature of the water before and after heating. His results are shown in Table. Table Temperature before heating 20.7 C Temperature after heating 35. C Calculate the energy used to heat the water. Use the equation Q = m c ΔT The specific heat capacity of water = 4.2 J / g / C

10 Energy used = J (3) (ii) Table 2 shows the mass of the spirit burner before the ethanol was burned and after the ethanol was burned. Table 2 Mass of spirit burner before ethanol was burned Mass of spirit burner after ethanol was burned g 72.0 g Calculate the number of moles of ethanol (C 2 H 5 OH) that were burned. Relative atomic masses (A r ): H = ; C = 2; O = 6 Number of moles burned = (3) (iii) Calculate the energy released in joules per mole. You should assume that all the energy from the ethanol burning was used to heat the water. Energy = J / mole () (d) The names, structures and boiling points of ethanol and two other alcohols are shown in Table 3. Table 3 Name Methanol Ethanol Propanol

11 Structure Boiling point in C Use your knowledge of structure and bonding to suggest why the boiling points increase as the number of carbon atoms increases. (3) (Total 5 marks) Q7. Millions of years ago the Earth formed as a giant ball of molten rock. The outer surface cooled forming a thin, solid outer crust. Volcanic activity on the surface produced an atmosphere containing the compounds carbon dioxide, ammonia, methane and water vapour. Describe the bonding in any one of these compounds. You must include electronic structures in your explanation. (Total 4 marks) Q8.

12 Methane (CH 4 ) is used as a fuel. (a) The displayed structure of methane is: Draw a ring around a part of the displayed structure that represents a covalent bond. () Why is methane a compound? Tick ( ) one box. Methane contains atoms of two elements, combined chemically. Methane is not in the periodic table. Methane is a mixture of two different elements. () (c) Methane burns in oxygen. (i) The diagram below shows the energy level diagram for the complete combustion of methane. Draw and label arrows on the diagram to show: the activation energy the enthalpy change, ΔH. (ii) Complete and balance the symbol equation for the complete combustion of

13 methane. CH 4 + CO 2 + (iii) Explain why the incomplete combustion of methane is dangerous. (iv) Explain why, in terms of the energy involved in bond breaking and bond making, the combustion of methane is exothermic. (3) (d) Methane reacts with chlorine in the presence of sunlight. The equation for this reaction is: Some bond dissociation energies are given in the table. Bond Bond dissociation energy in kj per mole C H 43 C Cl 327 Cl Cl 243 H Cl 432 (i) Show that the enthalpy change, ΔH, for this reaction is 03 kj per mole.

14 (3) (ii) Methane also reacts with bromine in the presence of sunlight. This reaction is less exothermic than the reaction between methane and chlorine. The enthalpy change, ΔH, is 45 kj per mole. What is a possible reason for this? Tick ( ) one box. CH 3 Br has a lower boiling point than CH 3 Cl The C Br bond is weaker than the C Cl bond. The H Cl bond is weaker than the H Br bond. Chlorine is more reactive than bromine. () (Total 5 marks) Q9. This question is about sodium chloride and iodine. (a) Describe the structure and bonding in sodium chloride.

15 (4) When sodium chloride solution is electrolysed, one product is chlorine. Name the two other products from the electrolysis of sodium chloride solution. (c) Many people do not have enough iodine in their diet. Sodium chloride is added to many types of food. Some scientists recommend that sodium chloride should have a compound of iodine added. Give one ethical reason why a compound of iodine should not be added to sodium chloride used in food. () (d) The bonding in iodine is similar to the bonding in chlorine. (i) Complete the diagram below to show the bonding in iodine. Show the outer electrons only. (ii) Explain why iodine has a low melting point. (3)

16 (iii) Explain, in terms of particles, why liquid iodine does not conduct electricity. (Total 4 marks) Q0. This question is about the reaction of ethene and bromine. The equation for the reaction is: C 2 H 4 + Br 2 C 2 H 4 Br 2 (a) Complete the reaction profile in Figure. Draw labelled arrows to show: The energy given out (ΔH) The activation energy. Figure (3) When ethene reacts with bromine, energy is required to break covalent bonds in the molecules. Explain how a covalent bond holds two atoms together.

17 (c) Figure 2 shows the displayed formulae for the reaction of ethene with bromine. Figure 2 The bond enthalpies and the overall energy change are shown in the table below. C=C C H C C C Br Overall energy change Energy in kj / mole Use the information in the table above and Figure 2 to calculate the bond energy for the Br Br bond. Bond energy kj / mole (3) (d) Figure 3 shows the reaction between ethene and chlorine and is similar to the reaction between ethene and bromine. Figure 3 The more energy levels (shells) of electrons an atom has, the weaker the covalent bonds that it forms. Use the above statement to predict and explain how the overall energy change for the reaction of ethene with chlorine will differ from the overall energy change for the reaction of ethene with bromine.

18 (6) (Total 4 marks) Q. Titanium is a transition metal used as pins and plates to support badly broken bones. Titanium is extracted from an ore that contains the mineral titanium oxide. This oxide is converted into titanium chloride. Titanium chloride is heated with sodium to form titanium metal. This reaction takes place in an atmosphere of a noble gas, such as argon. 4Na(s) + TiCl 4 (l) Ti(s) + 4NaCl(s) Calculate the mass of titanium that can be extracted from 570 kg of titanium chloride. Relative atomic masses: Cl 35.5; Ti 48. Mass of titanium = kg (Total 3 marks) Q2. A student carried out a titration to find the concentration of a solution of hydrochloric acid. The following paragraph was taken from the student s notebook. I filled a burette with hydrochloric acid cm 3 of 0.40 mol/dm 3 potassium hydroxide was added to a flask. 5 drops of indicator were added. I added the acid to the flask until the indicator changed colour. The volume of acid used was 35.0 cm 3. (a) What piece of apparatus would be used to measure 25.0 cm 3 of the potassium hydroxide solution? () Name a suitable indicator that could be used. () (c) Calculate the number of moles of potassium hydroxide used.

19 Concentration of hydrochloric acid = mol/dm 3 Moles of potassium hydroxide = mol (d) Calculate the concentration of the hydrochloric acid. The equation for the reaction is: KOH + HCl KCl + H 2 O (Total 6 marks) Q3. Limestone is a useful mineral. Every day, large amounts of limestone are heated in limekilns to produce lime. Lime is used in the manufacture of iron, cement and glass and for neutralising acidic soils. CaCO 3 CaO + CO 2 (i) The decomposition of limestone is a reversible reaction. Explain what this means.

20 (ii) Calculate the mass of lime, CaO, that would be produced from 250 tonnes of limestone, CaCO 3. Relative atomic masses: C 2; O 6; Ca 40. Mass of lime = tonnes (3) (Total 5 marks) Q4. A student carried out a titration to find the concentration of a solution of sulphuric acid cm 3 of the sulphuric acid solution was neutralised exactly by 34.0 cm 3 of a potassium hydroxide solution of concentration 2.0 mol/dm 3. The equation for the reaction is: 2KOH(aq) + H 2 SO 4 (aq) K 2 SO 4 (aq) + 2H 2 O(l) (a) Describe the experimental procedure for the titration carried out by the student. (4) Calculate the number of moles of potassium hydroxide used. Number of moles = (c) Calculate the concentration of the sulphuric acid in mol/dm 3.

21 Concentration = mol/dm 3 (3) (Total 9 marks) Q5. In 96, during the First World War, a German U-boat sank a Swedish ship which was carrying a cargo of champagne. The wreck was discovered in 997 and the champagne was brought to the surface and analysed. (a) 25.0 cm 3 of the champagne were placed in a conical flask. Describe how the volume of sodium hydroxide solution needed to react completely with the weak acids in 25.0 cm 3 of this champagne can be found by titration, using phenolphthalein indicator. Name any other apparatus used. (4) The acid in 25.0 cm 3 of the champagne reacted completely with 3.5 cm 3 of sodium hydroxide of concentration 0.0 moles per cubic decimetre. Calculate the concentration in moles per cubic decimetre of acid in the champagne. Assume that mole of sodium hydroxide reacts completely with mole of acid. Concentration = moles per cubic decimetre (c) Is analysis by titration enough to decide whether this champagne is safe to drink? Explain your answer.

22 () (d) The graph shows how the ph of the solution changes during this titration. Phenolphthalein is the indicator used in this titration. It changes colour between ph 8.2 and ph 0.0. Methyl orange is another indicator. It changes colour between ph 3.2 and ph 4.4. Suggest why methyl orange is not a suitable indicator for this titration. (Total 9 marks) Q6. This question is about chemical analysis. (a) A student has solutions of three compounds, X, Y and Z. The student uses tests to identify the ions in the three compounds. The student records the results of the tests in the table. Test Compound Flame test Add sodium hydroxide solution Add hydrochloric acid and barium Add nitric acid and silver nitrate

23 chloride solution solution X no colour green precipitate white precipitate no reaction Y yellow flame no reaction no reaction yellow precipitate Z no colour brown precipitate no reaction cream precipitate Identify the two ions present in each compound, X, Y and Z. X Y Z (3) A chemist needs to find the concentration of a solution of barium hydroxide. Barium hydroxide solution is an alkali. The chemist could find the concentration of the barium hydroxide solution using two different methods. Method An excess of sodium sulfate solution is added to 25 cm 3 of the barium hydroxide solution. A precipitate of barium sulfate is formed. The precipitate of barium sulfate is filtered, dried and weighed. The concentration of the barium hydroxide solution is calculated from the mass of barium sulfate produced. Method 2 25 cm 3 of the barium hydroxide solution is titrated with hydrochloric acid of known concentration. The concentration of the barium hydroxide solution is calculated from the result of the titration. Compare the advantages and disadvantages of the two methods.

24 (5) (Total 8 marks) Q7. Dilute nitric acid reacts with potassium hydroxide solution. The equation for the reaction is: HNO 3 + KOH KNO 3 + H 2 O A student investigated the temperature change in this reaction. This is the method the student used. Step Step 2 Step 3 Step 4 Step 5 added. Put 25 cm 3 of dilute nitric acid in a polystyrene cup. Use a thermometer to measure the temperature of the dilute nitric acid. Use a burette to add 4 cm 3 of potassium hydroxide solution to the dilute nitric acid and stir the mixture. Use a thermometer to measure the highest temperature of the mixture. Repeat steps 3 and 4 until 40 cm 3 of potassium hydroxide solution have been The dilute nitric acid and the potassium hydroxide solution were both at room temperature. (a) Figure shows part of the thermometer after some potassium hydroxide solution had been added to the dilute nitric acid. What is the temperature shown on the thermometer? The temperature shown is C () Errors are possible in this experiment. (i) Suggest two causes of random error in the experiment.

25 (ii) Another student used a glass beaker instead of a polystyrene cup. This caused a systematic error. Why does using a glass beaker instead of a polystyrene cup cause a systematic error? () (c) The results of the student using the polystyrene cup are shown in Figure 2. (i) How do the results in Figure 2 show that the reaction between dilute nitric acid and potassium hydroxide solution is exothermic? () (ii) Explain why the temperature readings decrease between 28 cm 3 and 40 cm 3 of potassium hydroxide solution added. (iii) It is difficult to use the data in Figure 2 to find the exact volume of potassium hydroxide solution that would give the maximum temperature.

26 Concentration = moles per dm 3 (3) Suggest further experimental work that the student should do to make it easier to find the exact volume of potassium hydroxide solution that would give the maximum temperature (d) The student did further experimental work and found that 3.0 cm 3 of potassium hydroxide solution neutralised 25.0 cm 3 of dilute nitric acid. The concentration of the dilute nitric acid was 2.0 moles per dm 3. HNO 3 + KOH KNO 3 + H 2 O Calculate the concentration of the potassium hydroxide solution in moles per dm 3. (e) The student repeated the original experiment using 25 cm 3 of dilute nitric acid in a polystyrene cup and potassium hydroxide solution that was twice the original concentration. She found that: a smaller volume of potassium hydroxide solution was required to reach the maximum temperature the maximum temperature recorded was higher. Explain why the maximum temperature recorded was higher. (Total 4 marks)

27 Q8. Sodium hydroxide neutralises sulfuric acid. The equation for the reaction is: 2NaOH + H 2 SO 4 Na 2 SO 4 + 2H 2 O (a) Sulfuric acid is a strong acid. What is meant by a strong acid? Write the ionic equation for this neutralisation reaction. Include state symbols. (c) A student used a pipette to add 25.0 cm 3 of sodium hydroxide of unknown concentration to a conical flask. The student carried out a titration to find out the volume of 0.00 mol / dm 3 sulfuric acid needed to neutralise the sodium hydroxide. Describe how the student would complete the titration. You should name a suitable indicator and give the colour change that would be seen. (4) (d) The student carried out five titrations. Her results are shown in the table below. Titration Titration 2 Titration 3 Titration 4 Titration 5

28 Volume of 0.00 mol / dm 3 sulfuric acid in cm Concordant results are within 0.0 cm 3 of each other. Use the student s concordant results to work out the mean volume of 0.00 mol / dm 3 sulfuric acid added. Mean volume = cm 3 (e) The equation for the reaction is: 2NaOH + H 2 SO 4 Na 2 SO 4 + 2H 2 O Calculate the concentration of the sodium hydroxide. Give your answer to three significant figures. Concentration = mol / dm 3 (4) (f) The student did another experiment using 20 cm 3 of sodium hydroxide solution with a concentration of 0.8 mol / dm 3. Relative formula mass (M r ) of NaOH = 40 Calculate the mass of sodium hydroxide in 20 cm 3 of this solution.

29 Mass = g (Total 6 marks) Q9. (a) The electronic structure of a sodium atom can be written 2,8,. Write the electronic structure of a potassium atom in the same way. () The electronic structure of a sodium atom can also be represented as in the diagram below. (i) Draw a similar diagram for a fluorine atom. (ii) Draw similar diagrams to show the electronic structure of the particles in sodium fluoride. (4) (Total 5 marks) Q20. (a) What is the name given to the block of elements in the middle of the Periodic Table which includes vanadium? ()

30 Some of the properties of vanadium are shown in this list. It has a high melting point. It is a solid at room temperature. It is a conductor of electricity. It is a good conductor of heat. It forms coloured compounds. If forms crystalline compounds. It forms compounds that are catalysts. Select two properties, from the list above, which are not typical of a Group metal.. 2. (Total 3 marks) Q2. Limestone (CaCO 3 ) is a raw material. On strong heating it is converted to calcium oxide which is a very useful substance. (a) Calculate the formula mass (M r ) of calcium carbonate. M r of calcium carbonate = About 60 million tonnes of calcium oxide is made in Britain each year. Calculate the mass of calcium carbonate needed to make this amount of calcium oxide. Mass of calcium carbonate needed = million tonnes (4) (c) Water is added to some of the calcium oxide produced in a process known as slaking. The product of this reaction is used to make plaster.

31 CaO (s) + H 2 O () Ca(OH) 2(s) (i) Give the chemical name of Ca(OH) 2. () (ii) What is the physical state of the Ca(OH) 2 formed in the reaction? () (Total 8 marks) Q22. Silicon is an important element used in the electronics industry. (a) Silicon can be made by heating a mixture of sand (silicon dioxide) with magnesium powder. The equation for this reaction is shown below. SiO 2 (s)+ 2Mg (s) 2MgO (s) + Si (s) Calculate the mass of silicon dioxide needed to make g of silicon. Relative atomic masses: O = 6; Si = 28 Mass = g (3) The resulting mixture of magnesium oxide and silicon is added to a beaker containing hydrochloric acid. The silicon is then filtered from the solution.

32 (i) The magnesium oxide reacts with the hydrochloric acid and forms magnesium chloride (MgCl 2 ) solution and water. magnesium oxide + hydrochloric acid magnesium chloride solution + water Write a balanced symbol equation for this reaction, including state symbols. (ii) The gases produced are a mixture of several silicon hydrides. One of the gases produced in the reaction is the silicon hydride with the formula SiH 4. The structure of this molecule is similar to methane, CH 4. Draw a diagram to show the bonding in a molecule of SiH 4. Represent the electrons as dots and crosses and only show the outer shell (energy level) electrons. () (iii) A sample of a different silicon hydride was found to contain.4 g of silicon and 0.5 g of hydrogen. Calculate the formula of this silicon hydride. You must show all your working to gain full marks. Relative atomic masses: H = ; Si = 28 (4) (iv) The silicon hydrides react immediately they come into contact with oxygen in the air. They burst into flames with a small explosion and give out energy.

33 Which letter, A to H, best describes this reaction? Energy involved in breaking and forming bonds Activation energy Rate of reaction Letter The energy released from forming new bonds is greater than the energy needed to break existing bonds high low fast slow fast slow A B C D The energy needed to break existing bonds is greater than the energy released from forming new bonds fast E high slow F low fast G slow H Letter () (c) The structure of silicon is similar to the structure of diamond. Describe the structure of silicon and explain why it has a high melting point. You may draw a diagram if this helps. (4) (Total 5 marks)

34 Mark schemes Q. (a) Mg S O ( 4) or 64 / evidence of all A r s gains mark but (M r ) = 20 gains 2 marks 2 evidence that 24(g) magnesium would produce 20(g) mapesiurn sulphate gains mark or correct scaling by /6 but 20(g) magnesium sulphate gains 2 marks [credit error carried forward from (a) with full marks in ] 2 [4] Q2. (a) (i) energy / heat of products less than energy of reactants allow converse allow products are lower than reactants allow more energy / heat given out than taken in allow methanol is lower allow energy / heat is given out / lost allow ΔH is negative (ii) lowers / less activation energy allow lowers energy needed for reaction or it lowers the peak/ maximum do not allow just lowers the energy (i) (8 435) = 3977 accept: bonds broken: (2 435) = 367 (6 435) + (2 336) + (2 464) = 420 bonds made: (2 336) + (2 464) = = ( ) 233 energy change: = ( ) 233 ignore sign allow ecf correct answer (233) = 3 marks with or without working

35 (ii) energy released forming (new) bonds is greater than energy needed to break (existing) bonds allow converse do not accept energy needed to form (new) bonds greater than energy needed to break (existing) bonds [6] Q3. (a) products are at a lower energy level than reactants if candidate has drawn a profile for an endothermic reaction penalise first marking point only activation energy correctly drawn and labelled ΔH correctly labelled (i) 93 (kj per mole) correct answer with or without working gains 3 marks allow 2 marks for +93 kj per mole if any other answer is seen award up to 2 marks for any two of the steps below: bonds broken ( ) = 807 (kj) or ( (4 43)) = 2459(kJ) bonds formed ( ) = 900(kJ) or (2 276) + (4 43) = 2552(kJ) bonds broken bonds formed allow ecf for arithmetical errors 3 (ii) more energy is released when the bonds (in the products) are formed than is needed to break the bonds (in the reactants) if no other marks gained, allow mark for energy released for bond making and energy used for bond breaking [8] Q4. (a) Idea that the electrons do not belong to specific atoms/delocalised electrons [credit if done on appropriate diagram] metal atoms form positive ions the attraction which exists between particles with opposite charges, holds the metal together no specific bonds exist between adjacent atoms/ions atoms/ions can slide over each other so allowing metals to bend each for mark 5 some electrons in the structure are delocalised/free to move

36 for mark these free electrons carry the electric current for mark from left to right across the period, atoms of elements have more free electrons gains mark but from left to right across the period, atoms of elements have more free electrons because they have more electrons in the outer shells gains 2 marks 4 [9] Q5. (a) 8 marks Particularly well structured answer with most points mentioned. 7-6 marks Well structured answer. The two metals will have been compared rather than simply listing advantages/disadvantages. Most of the advantages and disadvantages of each metal have been mentioned. 5-3 marks Some structure to the answer. An attempt to compare the metals by giving some advantages and disadvantages. 2- marks Little structure or attempt to compare. Marks gained by listing a few advantages or disadvantages. Advantages of Nickel: Relatively low cost which makes the sparking plugs cheaper to produce. Quite high melting point which is needed because the temperature in the engine is very high. Good conductor of electricity needed to carry electricity into combustion chamber to produce spark. Disadvantages of Nickel: Subject to corrosion in engine which means they only last a short time because nickel is higher in reactivity than platinum. Idea that this leads to reduced efficiency, unburnt petrol and air pollution. Advantages of Platinum: Less susceptible to corrosion (not corroded) because platinum is very low in reactivity. Idea that this improves efficiency and reduces pollution.- Higher melting point than nickel to withstand the high temperatures in the combustion chamber. Last a lot longer than nickel electrodes due to low reactivity. (Sensible extension here could be longer service intervals etc.)- Good conductor of electricity as for nickel. Extension here could be linked to the idea that the conductivity does not deteriorate as quickly as nickel.) Disadvantages of Platinum: Cost which will make the sparking plug more expensive. A good candidate might justify cost by longer life, better fuel consumption and less pollution. 8

37 (i) giant structure/lattice/regular arrangements of atoms any for mark of atoms/of ions (provided free electrons mentioned) either for mark delocalised or free electrons for mark 3 (ii) electrons free/can move for mark each 2 [3] Q6. (a) (i) the products are at a lower energy level than the reactants accept products have less energy / less energy at the end than the beginning (ii) because a catalyst provides an alternative / different pathway / mechanism / reaction route accept adsorption or increases concentration at the surface ignore absorption (that has) lower activation energy allow weakens bonds allow idea of increased successful collisions. DO NOT ALLOW answers stating catalysts provide energy for M and M2 one pair of electrons in each overlap (8 pairs in total) allow any combination of dots, crosses or other symbols the rest of the diagram correct with four non-bonding electrons on the oxygen giving a total of eight electrons in oxygen outer energy level. gains 2 marks (c) (i) ±3024 (J) correct answer with or without working gains 3 marks if the answer is incorrect, award up to 2 marks for the following steps: T = 4.4( C) 50 x 4.2 x 4.4 allow ecf for incorrect T

38 3 (ii) 0.05(27393) correct answer with or without working gains 3 marks if answer is incorrect, allow mark each for any of the following steps up to a max of g M r of ethanol = / 46 allow ecf in final answer for arithmetical errors 3 (iii) ±98 720(J / mole) c(i) c(ii) allow ecf from (c)(i) and (c)(ii) 0.05 gives gives gives (d) (as the molecules get bigger or the number of carbon atoms increases) the intermolecular forces allow intermolecular bonds (intermolecular forces) increase allow more / stronger (intermolecular forces) and therefore require more (heat) energy to overcome breaking covalent bonds or unspecified bonds max mark (M3) [5] Q7. answers apply to: accept diagrams and/or descriptions carbon dioxide CO 2 ammonia NH 3 methane CH 4 water H 2 O *outer electronic structure of one atom correct or needs correct number of electrons to complete outer shell *outer electronic structure of other atom correct or needs correct number of electrons to complete outer shell *one shared pair of electrons (as one covalent bond)

39 use of ions or reference to ionic bonding negates this mark *outer electronic structure of compound correct or each atom now has a full outer shell/noble gas electron structure [4] Q8. (a) circle round any one (or more) of the covalent bonds any correct indication of the bond the line between letters Methane contains atoms of two elements, combined chemically (c) (i) activation energy labelled from level of reagents to highest point of curve ignore arrowheads enthalpy change labelled from reagents to products arrowhead must go from reagents to products only (ii) 2 O 2 (iii) (iv) 2 H 2 O if not fully correct, award mark for all formulae correct. ignore state symbols carbon monoxide is made this combines with the blood / haemoglobin or prevents oxygen being carried in the blood / round body or kills you or is toxic or poisonous dependent on first marking point energy is taken in / required to break bonds accept bond breaking is endothermic energy is given out when bonds are made accept bond making is exothermic

40 the energy given out is greater than the energy taken in this mark only awarded if both of previous marks awarded (d) (i) energy to break bonds = 895 calculation with no explanation max = 2 energy from making bonds = (= 03) or energy to break bonds = 656 energy from making bonds = (= 03) allow: bonds broken bonds made = = -03 for 3 marks. (ii) The C Br bond is weaker than the C Cl bond [5] Q9. (a) lattice / giant structure max 3 if incorrect structure or bonding or particles ionic or (contains) ions Na + and Cl - accept in words or dot and cross diagram: must include type and magnitude of charge for each ion electrostatic attraction allow attraction between opposite charges hydrogen allow H 2 sodium hydroxide allow NaOH (c) any one from, eg: people should have the right to choose insufficient evidence of effect on individuals individuals may need different amounts. allow too much could be harmful ignore religious reasons ignore cost

41 ignore reference to allergies (d) (i) one bonding pair of electrons accept dot, cross or e or or any combination, eg (ii) (iii) 6 unbonded electrons on each atom simple molecules max 2 if incorrect structure or bonding or particles accept small molecules accept simple / small molecular structure with intermolecular forces accept forces between molecules must be no contradictory particles which are weak or which require little energy to overcome must be linked to second marking point reference to weak covalent bonds negates second and third marking points iodine has no delocalised / free / mobile electrons or ions so cannot carry charge if no mark awarded iodine molecules have no charge gains mark [4] Q0. (a) line goes up before it goes down energy given out correctly labelled activation energy labelled correctly electrostatic force of attraction between shared pair of negatively charged electrons (c) and both positively charged nuclei bonds formed = (42) + 2(276) = 2548 kj / mol

42 bonds broken bonds formed = (42) + (Br-Br) 2548 = 95 kj / mol 93 (kj / mol) Alternative approach without using C-H bonds For step allow = (276) = 900 kj / mol Then for step 2 allow 62 + (Br-Br) 900 = 95 kj / mol accept (+)93 (kj / mol) with no working shown for 3 marks 93(kJ / mol) scores 2 marks allow ecf from step and step 2 (d) Level 3 (5 6 marks): A detailed and coherent explanation is given, which demonstrates a broad understanding of the key scientific ideas. The response makes logical links between the points raised and uses sufficient examples to support these links. A conclusion is reached. Level 2 (3 4 marks): An explanation is given which demonstrates a reasonable understanding of the key scientific ideas. A conclusion may be reached but the logic used may not be clear or linked to bond energies. Level ( 2 marks): Simple statements are made which demonstrate a basic understanding of some of the relevant ideas. The response may fail to make logical links between the points raised. 0 marks: No relevant content. Indicative content Size and strength chlorine atoms have fewer electron energy levels/shells chlorine atoms form stronger bonds Cl Cl bond stronger than Br Br C Cl bond stronger than C Br Energies required more energy required to break bonds with chlorine more energy given out when making bonds with chlorine overall energy change depends on sizes of energy changes Conclusions if C Cl bond changes less, then less exothermic if C Cl bond changes more, then more exothermic can t tell how overall energy change will differ as do not know which changes more. 6 [4] Q. 44 accept TiCl4 = 90 for mark accept another correct step in calculation eg 570/90 = 3 for mark

43 [3] Q2. (a) pipette / burette named indicator eg methyl orange / phenolphthalein not universal accept litmus but not litmus paper (c) (d) = 0.0 KOH HCl 2 for correct answer 0.0 moles HCl in 35 cm 3 = for correct answer 0.3 = () (with correct working = ) [6] Q3. (i) a reaction in which the products can be changed back to reactants accept a reaction that can go forwards or backwards under certain conditions (ii) M r CaCO 3 = 00 M r CaO = 56 mass of CaO = 40 (tonnes) mark consequentially [5] Q4. (a) any four from:

44 sulphuric acid measure by pipette or diagram potassium hydroxide in burette or diagram if solutions reversed, award note initial reading use of indicator note final reading or amount used 4 (c) = ½ or 0.5 moles H 2 SO 4 react with mole KOH moles H 2 SO 4 in 25.0 cm 3 = moles H 2 SO 4 in dm 3 = =.36 mol/dm 3 [9] Q5. (a) must be description of a titration no titration = no marks NaOH in burette do not accept biuret etc add NaOH until (indicator) changes colour if specific colour change mentioned, must be correct colourless to pink / red or goes pink / red do not accept clear for colourless note (burette) volume used or final reading accept work out the volume one other point: eg repeat accept: (white) tile or add dropwise / slowly or white background or swirling / mix or read meniscus at eye level or wash apparatus 0.054

45 for 2 marks (0. 3.5)/25 for mark (c) don t know insufficient evidence to decide owtte any sensible answer or depends on whether acid level is considered safe or unsafe yes, safe acid level low / weak acids / low compared with stomach acid owtte any sensible answer no, unsafe acid level (too) high / other substances or bacteria may be present / insufficient evidence to decide owtte any sensible answer 2 (d) (methyl orange) would have changed colour (well) before the end-point / ph7 / neutral owtte weak acid present weak acid-strong base (titration) allow methyl orange used for strong acid-weak base titration [9] Q6. (a) X: Fe 2+ / iron(ii), SO 4 2- / sulfate allow iron(ii) sulfate or FeSO 4 Y: Na + / sodium, I - / iodide allow sodium iodide or NaI Z: Fe 3+ / iron(iii), Br - / bromide allow iron(iii) bromide or FeBr 3 correct identification of any two ions = one mark correct identification of any four ions = two marks any five from: allow converse arguments

46 method weighing is accurate not all barium sulfate may be precipitated precipitate may be lost precipitate may not be dry takes longer requires energy allow not all the barium hydroxide has reacted method 2 accurate works for low concentrations allow reliable / precise 5 [8] Q7. (a) 3 (i) any two from: incorrect reading of thermometer / temperature incorrect measurement of volume of acid incorrect measurement of volume of alkali (burette). 2 (ii) glass is a (heat) conductor or polystyrene is a (heat) insulator answer needs to convey idea that heat lost using glass or not lost using polystyrene accept answers based on greater thermal capacity of glass (such as glass absorbs more heat than polystyrene ) (c) (i) temperature increases (ii) (iii) no reaction takes place or all acid used up or potassium hydroxide in excess cool / colder potassium hydroxide absorbs energy or lowers temperature ignore idea of heat energy being lost to surroundings take more readings ignore just repeat around the turning point or between 20 cm 3 and 32 cm 3 accept smaller ranges as long as no lower than 20 cm 3 and no higher than 32 cm 3 (d).6 or.6(2903) correct answer with or without working scores 3 if answer incorrect, allow a maximum of two from: moles nitric acid = (2 25 / 000) = 0.05 for mark

47 (e) moles KOH = (moles nitric acid) = 0.05 for mark concentration KOH = 0.05 / 0.03 answer must be correctly rounded (.62 is incorrect) same amount of energy given out 3 which is used to heat a smaller total volume or mixture has lower thermal capacity or number of moles reacting is the same but the total volume / thermal capacity is less if no other marks awarded award mark for idea of reacting faster [4] Q8. (a) (c) (sulfuric acid is) completely / fully ionised In aqueous solution or when dissolved in water H + (aq) + OH (aq) H 2 O(l) allow multiples mark for equation mark for state symbols adds indicator, eg phenolpthalein / methyl orange / litmus added to the sodium hydroxide (in the conical flask) do not accept universal indicator (adds the acid from a) burette with swirling or dropwise towards the end point or until the indicator just changes colour 2 until the indicator changes from pink to colourless (for phenolphthalein) or yellow to red (for methyl orange) or blue to red (for litmus) (d) titrations 3, 4 and 5 or 27.2 cm 3 accept 27.2 with no working shown for 2 marks

48 allow with no working shown for 2 marks (e) Moles H 2 SO 4 = conc vol = allow ecf from 8.4 Ratio H 2 SO 4 :NaOH is :2 or Moles NaOH = Moles H 2 SO 4 2 = Concentration NaOH = mol / vol = / = (mol / dm 3 ) accept 0.27 with no working for 4 marks accept with no working for 3 marks (f) 0.8 = no of moles or g 0.44 (g) accept 0.44g with no working for 2 marks [6] Q9. (a) 2, 8, 8, for mark for mark Ignore symbol in middle but structure must be drawn NOT 2,7 If covalent; can score mark for changes but not for diagram Arrow showing electron transfer from metal atom to non-metal atom = 2 marks

49 If the ions are not identified then cannot score mark for changes 4 [5] Q20. (a) transition / transitional metals / elements / d-block for one mark coloured catalyst (accept high melting point) for mark each 2 [3] Q2. (a) (3 6) = 00 each for mark M r of CaO = 56 for mark mass required = 60 00/56 for 2 marks 2 = 07. for mark 4 (c) (i) calcium hydroxide (ii) solid [8] Q22. (a) M r (SiO 2 ) = 60 if M r incorrect ecf for max 2 60 g SiO 2 28 g Si correct answer for 3 marks 2.4 g SiO 2 g Si allow 2, 2., 2.4 (or anything rounding to 2.4), 2.6 or 2.2 a unit is not required but an incorrect unit loses the third mark OR M r (SiO 2 ) = 60 ()

50 moles if silicon needed = = mass of SiO 2 needed = () = 2.4 g () allow 2, 2., 2.4 (or anything rounding to 2.4), 2.6 or 2.2 OR M r (SiO 2 ) = 60 () mass SiO 2 = () = 2.4 g () allow 2, 2., 2.4 (or anything rounding to 2.4), 2.6 or 2.2 (i) MgO(s) + 2HCl(aq) MgCl 2 (aq) + H 2 O(l) penalise incorrect symbols correctly balanced equation for mark state symbols for mark allow correct multiples / fractions 3 2 (ii) or ignore inner shell electrons of silicon allow correct drawings without symbols must clearly indicate four shared pairs of electrons with one electron from each atom (iii) Si H = 0.05 = for whole number ratio can be implied

51 Si H 3 accept H 3 Si or any correct formula with :3 ratio if in step they get either of ratios incorrect they lose first 2 marks but can be ecf for 3rd and 4th mark evidence of mass / A r mark proportions of each mark whole number ratio mark correct formula mark (iv) C accept c (c) any four from: giant structure / macromolecule / lattice / giant molecule allow giant molecular / giant atomic structure each silicon atom joined to four other atoms (or diagram) covalent bonds bonds are strong or large amount of energy needed to break bonds accept hard to break bonds large number of bonds to be broken mention of giant ionic structure or intermolecular forces or intermolecular bonds max mark diamond or carbon discussion max 3 marks unless clearly linked to silicon 4 [5]