Empirical & Molecular formula.pdf

Size: px

Start display at page:

Download "Empirical & Molecular formula.pdf"

Domenic Payne
5 years ago
Views:

1 ...4 Empirical & Molecular formula.pdf 76 minutes 7 marks Page of 0

2 M. (a) Ideal gas equation law () (b) Moles of X: n = () = = () 6.5 to 6.6 0, min sig figs If write n = zero here, but can score M r Relative molecular mass of X: M r = () 6.5 to 6.5 = 6 () 4 (c) % oxygen = 5.6 () C =8.7 / H = 9.68 / O = 57.6() / 6 () =. = 9.68 =. : : CH O () If no % O or if wrong A r used then max Correct empirical formula earns all three marks (d) ( CH O) = C H 6 O () [9] M. (a) Relative charge () Relative mass /800 or () Accept zero / negligible (b) (i) Protons = 4 () (ii) Neutrons = 8 () (iii) Need (relative) abundance or peak height or intensity / amount / number / % / fraction of each element () Not: ratio of each isotope Page of 0

3 (c) (i) Reason : To allow particles to be accelerated / deflected / detected or to count Reason : Charged particles or to generate a current in the detector Any () Not: to allow m/z to be measured (ii) Magnetic field or electric field or electromagnet () (iii) Deflection depends on mass or m/z () 4 (d) (i) (simplest) ratio of atoms of each element in compound () (ii) % oxygen = 9.5% () Na 8.4/ Cr./5 O 9.5/6 () =. = 0.67 =.47 (::4) so empirical formula = Na CrO 4 () If % oxygen not calculated, only M available; if A r values wrong, only M available 4 [] M. (a) (i) = (mol) () accept 0.07 or 0.08 (ii) = (mol) () accept 0.0 If both (i) and (ii) answers wrong, allow ONE process mark for both correct processes (iii) = (mol) () Not conseq must use figures shown Page of 0

4 (iv) Moles of MgCO = 0.067/ = 0.05 (mol) () allow Mass of MgCO = () allow 84 mark conseq on moles MgCO accept.g mark conseq =.5g () Percentage MgCO =.5/.5 00 () mark conseq (check for inversion) mark conseq = 90% () range = % If % expression inverted, lose M4 and M5 8 (b) (i) % oxygen = 8.0 () Na = 6.5/ S = 5.5/(.) O = 8.0/6 () =.587 = =.75 = :: () If no % of oxygen Max (allow M only) If % for Na and S transposed, or atomic numbers used, M only available (ii) Na SO + HCl NaCl + H O + SO () allow multiples allow SO + H + H O + SO 4 [] M4. (a) 4LiH + AlCl LiAlH 4 + LiCl (b) H = s or s Page 4 of 0

5 (c) Tetrahedral or diagram (Not distorted tetrahedral) (Equal) repulsion between four bonding pairs / bonds (Not repulsion between H atoms loses M and M) (Not separate as far as possible ) ( 4 may be inferred from a correct diagram) (d) Dative (covalent) or coordinate Lone pair or non-bonding pair of electron or both e QoL Donated from H to Al or shared between H and Al (tied to M) (Not from H atom ) (Not to Al ion ) (Not e s transferred ) [8] M5. (a) (i) Na + NH NaNH + H (or multiples) (ii) (Missing H penalise once only) [NOT dot-and-cross diagrams] [NOT 90 / 80 angles] (need lp & bent shape) (iii) 07 (iv) More lone pairs on NH, than on NH Lone pairs repel more than bonding pairs Must be comparison (Mark separately) [NOT repulsion between atoms or between bonds] Page 5 of 0

6 (b) (i) Simplest ratio of atoms of each element in a compound / substance / species / entity / molecule (ii) Mg N O (0.675) MgN O 6 (Mark M first. If any wrong A r used = CE = 0) (Accept Mg(NO ) for M if above working shown) [9] M6. (penalty for sig fig error =mark per question) (a) (i) moles KNO =.00/0. = (mol) (ii) pv = nrt or n = pv/rt moles O = n = = () () = (mol) (mark answer first check back if wrong) (transcription error lose M, mark M4 conseq on error) (if untraceable figures used M=M4=0) (if wrong temp conversion lose M conseq M4) (if n = RT/pV CE, lose M and M4) Page 6 of 0

7 (b) (i) simplest/lowest ratio of atoms of each / element/s in a compound / substance / species / entity / molecule (ii) K N O () () KNO () (M tied to M), (M can be transferred from equation if ratio correct but EF not given) (if calc inverted, lose M and M), (if used At N / wrong No for Ar then CE, lose M and M) (if % of O missing, award M only) (c) KNO KNO + O or fractions/multiples (accept KNO K N O 4 + O ) (do NOT accept Y in equation) [0] M7. (a) [Diagrams must be complete and accurate] (b) (i) Attraction /electrostatic forces/bonds/attractions between (positive) ions/lattice and delocalised/free electrons/sea of electrons. [Not metallic bonding] [Not just forces ] (ii) Electrostatic attractions/forces between ions or attractions between (oppositely charged) ions/ Na + & Cl [Not ionic bonding] Page 7 of 0

8 (iii) (Here) the ionic bonding in NaCl is stronger/requires more energy to break than the metallic bonding in Na QoL Accept bonding/forces of attraction in NaCl is stronger than in Na [If IMF/molecules/van der Waals /dipole dipole mentioned in parts(i) or (ii), then CE = 0 for parts (i) and/or(ii) and CE = 0 for part(iii)] (c) Comparison: Sodium conducts and sodium chloride does NOT conduct Allow only Na conducts Accept Na conducts, NaCl only conducts when molten [Do not accept sodium conducts better than sodium chloride etc.] Explanation: (Delocalised) electrons flow though the metal Allow e move/carry current/are charge carriers/transfer charge. [Not electrons carry electricity ] [Not NaCl has no free charged particles ] Ions can t move in solid salt (d) Layers can slide over each other idea that ions/atoms/particles move [Not molecules] [Not layers separate] (e) (i) Na Cl O 0.9(9) 0.9(8).8() Hence: Accept backwards calculation, i.e. from formula to % composition, and also accept route via M r to ; 5.5; 48, and then to :: [If % values incorrectly copied, allow M only] [If any wrong A r values/atomic numbers used = CE = 0] (ii) Cl + 6NaOH 5NaCl + NaClO + H O [] Page 8 of 0

9 =.86: 4.6 = :.5 therefore formula is N O 5 M8. (a) (i) Moles of gas produced = PV = nrt V = nrt/p = 8. 98/00000 = m (ii) /98 = 0.49 m (b) (i) any two from: exhaust gases hot so would boil the solution away solution would splash reaction might be too slow would need continuous supply of solution and/or replacement of products (ii) Commercial advantage could sell chlorine and/or hydrogen environmental disadvantage generation of electricity likely to lead to release of CO (or chlorine toxic) (c) % O = 74% N:O = 6/4:74/6 (d) N O N + O (e) Proportion of O increased leading to higher T (or more complete combustion) [4] Page 9 of 0

10 M9. (a) (i) 0.000/.0 0 ; Penalise < sf in (a)(i); Allow (for candidates who have used Mg as 4) (ii) Allow correct answer a(i). (iii) / ; Allow / (iv) moles; Allow range to Allow (a)(iii) (a)(ii) (must be positive). (b) PV = nrt; Allow all capitals/ lower case. V = ; M Mark is for all numbers correct. If units in answer are in dm allow this expression with 96 in denominator. 0.0 m /. dm ; M Must have correct units/ allow 00 cm. Allow min sig figs in answer. Page 0 of 0

11 (c) O = 69.6 (%);.7 : 4.5 Use of 7/8 CE then M only. ( : ) NO Mark for formula not ratio. If NO and no working shown then allow mark. If 69.6% + NO only =. Need to see evidence of M working. Allow M conseq on the wrong M (ie max ). [0] M0. (a) O = 74.% N O 5 If atomic numbers or molecular masses are used lose M This ratio alone will not score the final mark. (It would get ) Allow marks for N O 5 (b) Toxic/poisonous/forms an acidic gas/forms NO which is acidic/ respiratory irritant/forms HNO when NO reacts with water and oxygen/ triggers asthma attacks/greenhouse gas/photochemical smog/ contributes to global warming/formation of acid rain ignore NO is an acidic gas or NO is acidic in water Not references to ozone layer (c) NO + O NO Accept multiples or fractions of equation Ignore wrong state symbols Page of 0

12 (d) Nitrogen/N and oxygen/o combine/react QWC (not N and O combine) Not nitrogen in fuel Allow N + O NO for M only spark/high temperature/ C (e) NO + CO N + CO OR NO N + O Accept multiples or fractions of equation Ignore wrong state symbols Allow C 8 H 8 + 5NO 8CO +.5N + 9H O [8] M. (a) N - / N (b) F / fluoride Ignore fluorine/f Penalise Fl (c) Li N / NLi (d) M for correct fractions (=.0 =.5).5 or : M for correct ratio Ca N If Ca N shown and with no working award marks If Ca N obtained by using atomic numbers then lose M Page of 0

13 (e) Si + N Si N 4 Accept multiples [7] M. (a) (i) Crude oil / oil / petroleum Do not allow petrol (ii) Fractional distillation / fractionation / fractionating Not distillation alone (b) (i) 5 Allow five / V (ii) Chain (isomerism) Allow branched chain / chain branched / side chain (isomerism) Ignore position (isomerism) Do not allow straight chain / geometric / branched / function (c) (i) C H 6 / H 6 C Only (ii) Thermal cracking If not thermal cracking, CE = 0/ If blank mark on High temperature Allow high heat for high temperature (400 C < T < 900 C) or (650 K < T < 00 K) Not heat alone If no T, units must be and High pressure (> 0 atm, > MPa, >000 kpa) (iii) To produce substances which are (more) in demand / produce products with a high value / products worth more Ignore to make more useful substances (d) (i) Corrosive or diagram to show this hazard symbol Ignore irritant, acidic, toxic, harmful Page of 0

14 (ii) ( ) ( ) =76.75(%) or 76.8(%) Allow answers > sig figs (e),-dichloro- methylpentane Ignore punctuation Any order C H 6 Cl [] M. (a) P = (Pa) and V = 5.00 x 0 (m ) M is for correctly converting P and V in any expression or list Allow 00 (kpa) and 5 (dm ) for M. M is correct rearrangement of PV = nrt = 0.0 moles (of gas produced) This would score M and M. Therefore = moles B O M is for their answer divided by 5 Mass of B O = x 69.6 M4 is for their answer to M x 69.6 =.8 (g) M5 is for their answer to sig figures..8 (g) gets 5 marks. (b) B +.5 Cl BCl Accept multiples. bonds Page 4 of 0

15 Pairs repel equally/ by the same amount Do not allow any lone pairs if a diagram is shown. (c) (i) 4./7. (= 0.68 moles BCl ) 0.68 x (=.05 moles HCl) Allow their BCl moles x Conc HCl = Allow moles of HCl 000 / 500 =.0 to. mol dm Allow. Allow significant figures or more (ii) H BO + NaOH Na BO + H O Allow alternative balanced equations to form acid salts. Allow H BO + NaOH NaBO + H O (d) Mark is for both M r values correctly as numerator and denominator. 8.98(%) Allow 9(%). Sell the HCl (e) Alternative method Cl = 86.8% Cl = 4 g B Cl B Cl Page 5 of 0

16 ..45 or ratio : or BCl :4 ratio BCl has M r of 8.8 so 8.8 x = 6.6 Formula = B Cl 4 B Cl 4 Allow 4 marks for correct answer with working shown. Do not allow (BCl ) [0] M4. (a) (i) The power of an atom or nucleus to withdraw or attract electrons OR electron density OR a pair of electrons (towards itself) Ignore retain In a covalent bond (ii) More protons / bigger nuclear charge Same or similar shielding / electrons in the same shell or principal energy level / atoms get smaller Not same sub shell Ignore more electrons (b) Ionic If not ionic then CE = 0 / If blank lose M and mark on Strong or many or lots of (electrostatic) attractions (between ions) If molecules / IMF / metallic / atoms lose M + M, penalise incorrect ions by mark Between + and ions / between Li + and F ions / oppositely charged ions Allow strong (ionic) bonds for max out of M and M (c) Small electronegativity difference / difference = 0.5 Must be comparative Allow non-metals Page 6 of 0

17 MF (= 70.0 / 5) = O F or F O (d) (i) (simple) molecular Ignore simple covalent (ii) OF + H O O + HF Ignore state symbols Allow multiples Allow OF written as F O (iii) 45.7% O ( O F ) ( ) ( 6 9 ) If students get M upside down lose M + M Check that students who get correct answer divide by 6 and 9 (not 8 and 9). If dividing by 8 and 9 lose M and M but could allocate M4 ie max (.85.85) ( ) EF = OF or FO Calculation of OF by other correct method = marks Penalise Fl by mark [4] Page 7 of 0

18 M5. (a) Method Method Mass of H O = Percentage of H O = 44% (=.9 g) If there is an AE in M then can score M and M If M r incorrect can only score M ZnSO 4 H O ZnSO4 HO ( ) ( : 7 ) ( ) ( : 7 ) x = 7 x = 7 If x = 7 with working then award marks. Allow alternative methods. If M incorrect due to AE, M must be an integer. (b) Moles HCl = 0.(0) mol ZnCl = 0.06(0) OR 0. / If M incorrect then CE and cannot score M, M and M4. mass ZnCl = Allow ( 5.5) for 6.4 = 8.8(4) (g) OR 8. (g) Must be to significant figures or more. Ignore units. (c) Moles ZnCl = (= ) OR moles Zn = Mass Zn reacting = = (5. g) M is for their M 65.4 Page 8 of 0

19 M is M 00 / 5.68 provided M is < 5.68 = 90.% OR 90.% Allow alternative methods. M = Moles ZnCl = 0.7 (= ) 6.4 M = Theoretical moles Zn = 5.68 (= ) 65.4 M = M 00 / M = ( / ) M4 = 90.% OR 90.% (d) Ionic If not ionic CE = 0/ Strong (electrostatic) attraction (between ions) between oppositely charged ions / + and ions / F and Zn + ions If IMF, molecules, metallic bonding implied CE = 0/ [4] Page 9 of 0

20 Page 0 of 0

Page 1 M1.A [1] M2.C [1] M3.C [1] M4.B [1] M5.A [1] M6.A [1] M7.C [1]

Page 1 M1.A [1] M2.C [1] M3.C [1] M4.B [1] M5.A [1] M6.A [1] M7.C [1] AS Paper and Bonding MARK SCHEME M.A [] M.C [] M3.C [] M4.B [] M5.A [] M6.A [] M7.C [] M8. (a) (i) positive ions () (attract) delocalised electrons () (or sea of or free or mobile) () Confusion with ve