Isotopes, Mass Spec & RAM/ RMM

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1 Isotopes, Mass Spec & RAM/ RMM Mark Scheme Level Subject Exam Board Topic Sub Topic Booklet International A Level Chemistry Edexcel The Core Principles of Chemistry Isotopes, Mass Spec & RAM/RMM Mark Scheme Time Allowed: 59 minutes Score: /49 Percentage: /100 Grade Boundaries: A* A B C D E U >85% 777.5% 70% 6.5% 57.5% 45% <45%

2 Correct Answer Reject Mark 1 D 1 Correct Answer Reject Mark B 1 Correct Answer Mark 3 B 1 Correct Answer Mark 4 C 1 Correct Answer Mark 5 C 1 Correct Answer Mark 6 D 1 Correct Answer Mark 7 B 1 Correct Answer Reject Mark 8 C 1 Correct Answer Reject Mark 9 B 1 Correct Answer Reject Mark 10 C 1

3 11(a)(i) (RAM = (13.9 x 10) + (86.1 x 11)) = = 10.9 IGNE amu / g mol -1 g/% answers not to 3sf Correct answer without working scores () 11(a)(ii) compared to one twelfth the mass of a carbon-1 (atom/isotope) where (one atom of) carbon-1 has a mass of exactly (a)(iii) 5 protons and 5 electrons 7 neutrons use of letters p, e and n for subatomic particles 11(b)(i) Any one from 1 deflect the ions from their normal path additional/false peaks from particles in the air ions would collide with particles in the air Air molecules IGNE Reference to chemical reactions/anomalous results/decreased speed of ions/ wrong percentage abundance given

4 11(b)(ii) No effect / unaffected / they would not be accelerated/only affects charged particles 1 IGNE Reference to detection/deflection/magnetic field 11(b)(iii) Any one correct statement scores Three correct statements scores () Reference to peaks at 3,34,36 or both oxygen atoms from the manganate(vii) ion gives a (molecular / parent ion) peak at or 65 one oxygen atom from the manganate(vii) ion / one from water gives a (molecular / parent ion) peak at 64 both oxygen atoms from the water gives a (molecular / parent ion) peak at 6 IGNE 18 O peak Both oxygen atoms from the magnagate(vii) ion gives a (molecular/parent ion) peak four more 11(c)(i) (Error 1) peaks at 35 and 37 should be in 3:1 ratio/the peak at 35 should be three times the height of the peak at 37 Reference to the height of the peak at 35 being at 75% compared to the height of the peak at 37 being at 5% Just greater (Error ) there should be a peak at 7 IGNE Reference to the height/intensity of the peak at 7

5 11(c)(ii) ( 37 Cl 37 Cl) + [ 37 Cl 37 Cl] + ( 37 Cl 37 Cl) + Cl 37 Cl + + Cl ( 37 Cl+ 37 Cl) + 37 Cl + 1 (Total for 11 = 1 marks)

6 1(a)(i) (i) t mark Weighted mean mass average weight 3 (Weighted) average (atomic) mass Second mark (Mass) of atom(s) (of an element) (Mass of all) the isotopes (of an element) Third mark Divided by / compared with 1/1th the mass of (an atom of) 1 C / C-1 On a scale in which 1 C / C-1 = 1 (g) atom of an isotope Mole(s) of atoms 1(a)(ii) (Beam of) high energy electrons / accelerated electrons / electrons from electron gun / high speed electrons / Just electron gun / electron(s) Electron beam Electrons bombard / hit / blast the (gaseous) atoms Electrons are fired at the (gaseous) atoms Knock off / liberates an electron(s) / leads to loss/removal of electron(s) (from the gaseous atoms) highly charged electrons Just takes an electron(s) IGNE References to ionising / forming (positive) ions / just an equation e.g. M(g) M + (g) + e

7 1(a)(iii) Correct answer with or without working scores both marks ((84.0 x 0.56) + (86.0 x 9.86) + (87.0 x 7.0) +(88.0 x 8.56))/100 = 87.7 (must be to 3 SF) NOTE 87.71/ / score with or without working IGNE g or g mol -1, but wrong units, eg %, lose the second mark 1(b) 1(c) s (block) S (block) IGNE group / period 5 Any number in front of the s e.g. 4s Any other group number / period number covalent bonding (0) 1 First mark Correct dot and cross diagrams with + charge on Sr and charge on Cl no electrons or 8 electrons on outer shell of Sr dots or crosses for electrons diagrams without square brackets Second mark Ratio of 1 strontium and chloride (ions) this shown as in front of a chloride ion or subscript after the ion IGNE any inner shell electrons max 1 for incorrect symbol(s)

8 1(d) SrO(s) + HNO 3 (aq) Sr(NO 3 ) (aq) + H O(l) H scores (0) SrO(s) + H + (aq) Sr + (aq) + H O(l) Correct formulae and balancing multiples State symbols If no other mark awarded, Ionic equation given as O - (s) + H + (aq) H O(l) 1(e) SrC O 4 with or without working scores 3 marks Sr C O % A r divide by smaller ratio 1 (.004) 4/3.993 If all A r /%, scores (0) overall If all %/atomic number, scores (0) overall 3 empirical formula SrC O 4 symbols in any order use of 87.7 instead of 87.6 Incorrect symbol(s) TE for MP and 3, if one slip in MP1 or MP (Total for 1 = 15 marks)

9 13(a) (Subatomic particle) (Relative mass) (Relative charge) (proton) 1 +1/1+ Just + for proton charge 3 (neutron) 1 0 Just neutral for neutron charge (electron) 1/000 to 1/1800 or negligible or to /1 Just for electron charge Zero / 0 for mass of an electron for each correct row MAX if only one COLUMN correct IGNE any masses in g or kg IGNE any charges in coulombs 13(b) Atoms with the same number of protons IGNE same number of electrons Element(s) with the same number of protons (but) different numbers of neutrons IGNE References to atomic number / mass number / nucleons / JUST atoms of the same element 13(c)(i) Electron gun / high-speed electrons / high-energy electrons / fast-moving electrons / bombardment with electrons Just electrons / Highly-charged electrons Knock-out / remove electron(s) IGNE References to ionizing / forming ions / just equations such as Rb(g) Rb + (g) + e / other stages in the process of mass spectrometry

10 13(c)(ii) [FIRST, check the answer on the answer line IF answer = 85.6 award (3) marks] 3 1st mark: 85 x x 1 85 x x 8.6 nd mark: 3.5 (can 7 if ratio given as 5:) 100 TE using incorrect % abundances or ratios 3rd mark stand alone for correct rounding (TE only if value calculated is between 85 and 87) (= 85.57, but accurate answer depends on rounding) Final answer rounded to 85.6 (ie 1 dp) Ignore units even if incorrect. NOTE 85.5 without working scores (0) 13(d) (Left-hand box) Delocalised electron(s) BOTH these words needed Just electrons Negativelycharged ions (Right-hand box) Positive ion(s) / cation(s) / Rb + metal ion(s) nuclei / nucleus / positive atoms positively-charged lattice (Total for 13 = 1 marks)

Formulae, Equations & Amount of Substance

Formulae, Equations & Amount of Substance Scheme Level Subject Exam Board Topic Sub Topic Booklet International A Level Chemistry Edexcel The Core Principles of Chemistry Formulae, Equations & Amount of