OCR A Jan 2013 Paper 1 Q3 (with explained solutions) |

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OCR A Jan 2013 Paper 1 Q3

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3 Successive ionisation energies provide evidence for the existence of different shells in atoms. (a) Define, in words, the term first ionisation energy.[3] (b) (i) Write an equation to represent the second ionisation energy of oxygen. Include state symbols.[1] (ii) On the axes below, add crosses to estimate the successive ionisation energies of oxygen. The second ionisation energy has been added for you. It is not necessary to join your points. ionisation energy 2 6 ionisation energy number [2]OCR 2013 Turn over<br />
(c) The first ionisation energy of oxygen is less than the first ionisation energy of fluorine. Explain why.[3] (d) When oxygen reacts with metals it forms oxide ions. Write the electron configurations, in terms of sub-shells, of an oxygen atom and an oxide ion. Hence, explain why this reaction of oxygen is typical of a non-metal. oxygen atomoxide ion[2] (e) Many ions contain oxygen combined with atoms of other elements. For example, the nitrate(V) ion has the formula NO3 . (i) In the table below, write the formula of the sulfate(IV) ion and the chlorate(III) ion. Ion Ionic charge Formula Nitrate(V) Sulfate(IV) Chlorate(III) 1 2 1 NO3 (ii) Write the formula of aluminium nitrate(V).[1] [2]OCR 2013<br />
(iii) Aluminium nitrate(V) can be made by reacting a base with an acid. For this reaction, name a suitable base and write the formula of the acid. name of baseformula of the acid[2] [Total: 16]OCR 2013 Turn over<br />

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F321 Mark Scheme January 2013 Question 3 (a) Answer Energy (needed) to remove an electron (cid:57) from each atom in one mole (cid:57) of gaseous atoms (cid:57) (b) (i) O+(g) (cid:198) O2+(g) + e (cid:57) (ii) x x x x x x x 1 2 3 4 5 6 7 8 All eight ionisation energies showing an increase (cid:57) The biggest increase between the sixth and seventh ionisation energy AND 8th ionisation energy is higher than 7th (cid:57) Marks Guidance ALLOW energy to remove one mole of electrons from one mole of gaseous atoms for three marks IGNORE element ALLOW energy needed to remove an electron from one mole of gaseous atoms to form one mole of gaseous 1+ ions for two marks For third mark: ALLOW ECF if wrong particle is used in second marking point but is described as being gaseous eg molecule instead of atom IGNORE equations ALLOW O+(g)e (cid:198) O2+(g) ALLOW e for electron (ie charge omitted) IGNORE states on the electron IGNORE the 2p/2s true jump IGNORE line if seen IGNORE 0, if included by candidate IGNORE missing 1st IE point BUT DO NOT ALLOW first ionisation energy higher than second DO NOT ALLOW either mark if ionisations energies 3 to 8 inclusive are not shown Place tick for second mark on the x-axis between 6 and 7<br />
F321 Question 3 (c) Mark Scheme January 2013 Marks Guidance Use annotations ie ticks crosses ECF ^ etc for this part Comparison should be used for each mark. Look for ORA from perspective of F throughout. ALLOW all three marks applied to as you go across the period BUT assume the response refers to as you go across the period if not stated ALLOW O has lower proton number BUT IGNORE O has lower atomic number IGNORE O has a smaller nucleus IGNORE O has a smaller charge ie must be nuclear charge IGNORE O has smaller effective nuclear charge ALLOW sub-shell for shell but IGNORE orbitals ALLOW shielding is similar ALLOW outermost electrons of O are further DO NOT ALLOW distance is the same for second mark ALLOW less nuclear pull for less nuclear attraction DO NOT ALLOW less nuclear charge instead of less nuclear attraction for the third mark IGNORE not pulled as close for pulled less strongly Answer Nuclear charge mark O has (one) less proton(s) OR O has smaller nuclear charge OR F has (one) more proton(s) OR F has greater nuclear charge (cid:57) Atomic radius/shielding mark (Outermost) electrons are in the same shell OR energy level OR (Outermost) electrons experience the same shielding OR Atomic radius of O is larger OR Atomic radius of F is smaller (cid:57) Nuclear attraction mark Less nuclear attraction (on outermost electrons) in O OR (outer) electrons are attracted less strongly (to the nucleus) in O OR More nuclear attraction (on outermost electrons) in F OR (outer) electrons are attracted more strongly (to the nucleus) in F (cid:57)<br />
Mark Scheme January 2013 Answer 1s2 2s2 2p4 AND 1s2 2s2 2p6 (cid:57) (In the reaction) oxygen has formed a negative ion (by gaining (two) electrons) (cid:57) Marks Guidance ALLOW subscripts, capitals ALLOW oxidation number of oxygen has decreased ALLOW non metals form negative ions IGNORE oxygen has gained electrons (this is shown in the electron configurations) IGNORE correct formula (ie Al2O3 or Al(OH)3) DO NOT ALLOW correct name with incorrect formula IGNORE correct name (ie nitric acid or nitric(V) acid) DO NOT ALLOW correct formula with incorrect name ALLOW one mark for Al2O3 or Al(OH)3) AND nitric acid or nitric(V) acid (ie name answer and formulae answer has been transposed) F321 Question 3 (d) (e) (i) SO3 ClO2 2 (cid:57)(cid:57) (ii) Al(NO3)3 (cid:57) HNO3 (cid:57) (iii) Aluminium oxide OR aluminium hydroxide (cid:57) Total 16 10<br />

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