2017 Chemistry. National 5. Finalised Marking Instructions

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National Qualifications 2017 2017 Chemistry National 5 Finalised Marking Instructions Scottish Qualifications Authity 2017 The infmation in this publication may be reproduced to suppt SQA

1 National Qualifications Chemistry National 5 Finalised Marking Instructions Scottish Qualifications Authity 2017 The infmation in this publication may be reproduced to suppt SQA qualifications only on a noncommercial basis. If it is reproduced, SQA should be clearly acknowledged as the source. If it is to be used f any other purpose, written permission must be obtained from permissions@sqa.g.uk. Where the publication includes materials from sources other than SQA (secondary copyright), this material should only be reproduced f the purposes of examination assessment. If it needs to be reproduced f any other purpose it is the centre s responsibility to obtain the necessary copyright clearance. SQA s NQ Assessment team may be able to direct you to the secondary sources. These ing instructions have been prepared by examination teams f use by SQA appointed ers when ing external course assessments. This publication must not be reproduced f commercial trade purposes.

2 General ing principles f National 5 Chemistry This infmation is provided to help you understand the general principles you must apply when ing candidate responses to questions in this Paper. These principles must be read in conjunction with the detailed ing instructions, which identify the key features required in candidate responses. (a) (b) Marks f each candidate response must always be assigned in line with these general ing principles and the specific Marking Instructions f this assessment. If a specific candidate response does not seem to be covered by either the principles detailed Marking Instructions, and you are uncertain how to assess it, you must seek guidance from your Team Leader. (c) Marking should always be positive. This means that, f each candidate response, s are accumulated f the demonstration of relevant skills, knowledge and understanding: they are not deducted from a maximum on the basis of errs omissions. A guiding principle in ing is to give credit f crect chemistry rather than to look f reasons not to award s. Example 1: The structure of a hydrocarbon found in petrol is shown below. Name the hydrocarbon. Although the punctuation is not crect, 3, methyl-hexane should gain the. (d) Example 2: A student measured the ph of four carboxylic acids to find out how their strength is related to the number of chline atoms in the molecule. The results are shown in the table Structural fmula ph CH 3COOH 1 65 CH 2ClCOOH 1 27 CHCl 2COOH 0 90 CCl 3COOH 0 51 State how the strength of the acids is related to the number of chline atoms in the molecule. Although not completely crect, an answer such as the me Cl 2, the stronger the acid should gain the. (e) (f) There are no half s awarded. Candidates must respond to the command wd as appropriate and may be required to write extended answers in der to communicate fully their knowledge and understanding. page 2

3 (g) Marks should be awarded f answers that have increct spelling loose language as long as the meaning of the wd(s) is conveyed. Example: Answers like distilling (f distillation ) and it gets hotter (f the temperature rises ) should be accepted. However the example below would not be given any credit, as an increct chemical term, which the candidate should know, has been given. Example: If the crect answer is ethene, and the candidate s answer is ethane, this should not be accepted. (h) A crect answer followed by a wrong answer should be treated as a cancelling err and no s should be awarded. Example: State what colour is seen when blue Fehling s solution is warmed with an aldehyde. The answer red, green gains no s. (i) If a crect answer is followed by additional infmation which does not conflict, the additional infmation should be igned, whether crect not. Example: State why the tube cannot be made of copper. If the crect answer is related to a low melting point, Copper has a low melting point and is coloured grey would not be treated as having a cancelling err. (j) (k) (l) (m) (n) (o) Unless a numerical question specifically requires evidence of wking to be shown, full s should be awarded f a crect final answer (including units if required) on its own. The partial s shown in the ing scheme are f use when wking is given but the final answer is increct. An exception is when candidates are asked to Find, by calculation, when full s cannot be awarded f the crect answer without wking. Where the ing instructions specifically allocate a f units in a calculation, this should not be awarded if the units are increct missing. Missing increct units at intermediate stages in a calculation should be igned. As a general rule, where a wrong numerical answer (already penalised) is carried fward to another step, credit will be given provided the result is used crectly. The exception to this rule is where the ing instructions f a numerical question assign separate concept s and an arithmetic. In such situations, the ing instructions will give clear guidance on the assignment of partial s. Igne the omission of one H atom from a full structural fmula provided the bond is shown one carbon to hydrogen bond missing provided the hydrogen is shown. A symbol crect fmula should be accepted in place of a name unless stated otherwise in the ing instructions. When fmulae of ionic compounds are given as answers it will only be necessary to show ion charges if these have been specifically asked f. However, if ion charges are shown, they must be crect. If increct charges are shown, no s should be awarded. page 3

4 (p) If an answer comes directly from the text of the question, no s should be awarded. Example: A student found that 0 05 mol of propane, C 3H 8 burned to give 82 4 kj of energy. C 3H 8(g) + 5O 2(g) 3CO 2(g) + 4H 2O(l) Name the type of enthalpy change which the student measured. No s should be awarded f 'burning' since the wd 'burned appears in the text. (q) Unless the question is clearly about a non-chemistry issue, eg costs in industrial chemical process, a non-chemical answer gains no s. Example: Suggest why the (catalytic) converter has a honeycomb structure. A response such as to make it wk may be crect but it is not a chemical answer and the should not be awarded. page 4

5 Marking Instructions f each question Section 1 Question Answer Mark 1. D 1 2. C 1 3. A 1 4. D 1 5. A 1 6. B 1 7. C 1 8. B 1 9. A A D C C B D C A B A C 1 page 5

6 Detailed ing instruction f each question Section 2 Question Answer Max 1. (a) Isotope(s) 1 (b) (c) Different numbers of neutrons the atoms have 18, neutrons 36 1 Award zero s f -different mass in the nucleus -different number of particles in the nucleus 1 Accept amu g if stated Ar 36 Ar page 6

7 2. (a) Carbon nanotube Nanotube 1 Award zero s f -carbon on its own -graphene nanotubes -graphite nanotubes (b) Lithium Li 1 (c) 20 5 with no wking (2) 2 Accept mol l -1 mol/l 21 with crect wking (2) Partial ing Demonstration of the crect use of the relationship concept. ie 41/2. (1) 41/1 = 41 (1) Wking must be shown Zero s awarded f - 41 without wking. page 7

8 2 Question Answer Max 3. (a) Must show all outer electrons 1 Accept cross dot e e- to represent electrons a mixture of these. Cl Cl Accept petal diagram. The non-bonding electrons in each chline atom must be shown but do not need to be together/shown as a pair. Bonding electrons MUST be on the line in the overlapping area. The example below is awarded zero s. If inner electrons are shown they must be crect ie 2,8 (b) Tetrahedral / tetrahedron 1 (c) Gains an electron (from sodium) 1 Accept - sodium gives an electron - chline takes an electron Indication that the electron arrangement increases by 1 eg electron arrangement goes from to 2.8.8, outer electron number goes from 7 to 8. Award zero s f - implying that chline gains me than one electron - a chlide ion gains an electron (d) low no 1 2 high no 1 1 f both crect properties f chlomethane gas 1 f both crect properties f solid sodium chlide page 8

9 4. (a) (i) 2 All 4 crect 2 s 2/3 crect 1 0/1 crect 0 s (ii) Iron would not melt/ be molten/liquid able to flow 1 Award zero s f: -it is the melting point of iron however, this does not negate a crect answer. Iron would be solid Iron needs to be molten/liquid/flowing (b) Fe 2+ Fe 3+ + e - Fe 2+ - e Fe 3+ 1 State symbols are not required however, if given they must be crect page 9

10 5. (a) (i) 14 (days) 1 No units required but no is awarded if wrong unit is given. (Wrong units are only penalised once in any paper). (ii) 42 (days) (2) 2 Allow follow through from part (a)(i) to allow the candidate to access both s Partial ing 3 half-lives (1) Crect number of days f an (1) increct number of half-liveswking must be shown. No units required but maximum of 1 is awarded if wrong unit is given. (Wrong units are only penalised once in any paper). (b) beta e 1 0 e - 1 page 10

11 6. 1 : The student has demonstrated a limited understanding of the chemistry involved. The candidate has made some statement(s) which is/are relevant to the situation, showing that at least a little of the chemistry within the problem is understood. 2 s: The student has demonstrated a reasonable understanding of the chemistry involved. The student makes some statement(s) which is/are relevant to the situation, showing that the problem is understood. 3 s: The maximum available would be awarded to a student who has demonstrated a good understanding of the chemistry involved. The student shows a good comprehension of the chemistry of the situation and has provided a logically crect answer to the question posed. This type of response might include a statement of the principles involved, a relationship an equation, and the application of these to respond to the problem. This does not mean the answer has to be what might be termed an excellent answer a complete one. 3 page 11

12 7. (a) Carboxyl 1 COOH (b) (i) Any acceptable structural fmula f butanoic acid eg CH 3CH 2CH 2COOH CH 3(CH 2) 2COOH 1 Accept mixture of shtened and full structural fmula Igne - the omission of one H atom (from a carbon atom) in full structural fmula provided the bond is shown - one carbon to hydrogen bond missing provided the hydrogen is shown. Award zero s f C 3H 7COOH page 12

13 7. (b) (ii) Butanoic acid it has bigger / stronger / me fces (of attraction) (1) 2 The term bond is only acceptable if it is specifically identified as between the molecules used with the term intermolecular. Between molecules mention of intermolecular attractions (1) Mention of breaking bonds /bonds within molecule chain / breaking carbon to carbon carbon to hydrogen bonds me bonds cannot gain the second but does not negate the first. Candidates can be awarded the full/partial s if they crectly explain why propanoic acid has a lower melting point but propanoic acid must be stated in their answer. If neither of these two points are given, a maximum of 1 can be awarded f - butanoic acid it is bigger has me carbons hydrogens atoms longer carbon chain Me bonds in the compound is not sufficient to imply a larger molecule but does not negate. page 13

14 8. (a) (i) Glowed brighter/me brightly than zinc 1 Glowed most brightly/very brightly/white light (ii) Faster/higher/speed up/increase 1 Award zero s f -takes less time on its own but does not negate crect answer. (b) Magnesium 1 Can be circled, highlighted etc Mg page 14

15 9. (a) They have the same general fmula AND 1 Award zero s f -molecular fmula -structural fmula -chemical fmula similar/same chemical properties Both required f 1 Award zero s f - physical properties in place of chemical properties however, it does not negate (b) Isomer(s) 1 (c) (i) Increasing carbon chain length/ number of carbons takes me time (longer, slower) 1 Decreasing carbon chain length/ number of carbons takes less time (faster, quicker) Straight chain takes me time (longer, slower) than branched chain Branched chain takes less time (faster, quicker) than straight chain (ii) Indication that the expected position occurs anywhere on the hizontal line between ethene and 2-methylpropane. 1 page 15

16 10. (a) (i) 1 Accept - copper sulfate instead of copper(ii) sulfate - name of solution without (aq) solution. ALL REQUIRED FOR 1 MARK (ii) 3Cu Al 3Cu + 2Al 3+ 1 Accept crect multiples Zero s awarded f -electrons shown in equation, unless clearly sced out. State symbols are not required however if given they must be crect page 16

17 10. (b) (%) (3) 3 Partial ing GFM = 342 (1) 54/342 x 100 (concept ) (1) This step on its own 2 s Calculation of final answer using the crect relationship (1) Maximum 2 s (wking must be shown) Increctly calculated GFMallow follow through using the mass of aluminium from wking Using mass of Al as 27-27/342 x 100 = Using atomic numbers- 26/170 x 100 = Candidate crectly calculates percentage of sulfur ( %) oxygen ( %) rather than aluminium Maximum of 1 - wking must be shown f value divided by 342 does not crespond to an element in the compound, award a maximum of 1. No units required but maximum of 2 s can be awarded if wrong unit is given. (Wrong units would only be penalised once in any paper) page 17

18 11. (a) ph of solution goes down / decreases / goes below 7 / goes to a value less than 7 from 7 because the H + ion / hydrogen ion concentration increases /goes up me H + than OH - / H + > OH (2) 2 Award zero s f - it gets me acidic - sulfur dioxide is a nonmetal /acidic oxide These two do not negate a crect answer. Award zero s f any mention of ph being above 7. Partial ing ph of solution goes down/ decreases/goes below 7/ goes to a value less than 7 from 7 (1) H + ion / hydrogen ion concentration increases/goes up / me H + than OH - / H + > OH - (1) If the candidate states the ph increases/goes up/goes above 7, the f the description of me H + cannot be awarded. (b) Decreases /goes down /gets lower 1 If the candidate mentions temperature and solubility in their answer the cause and effect must be given ie - as the temperature increases the solubility decreases the solubility decreases as the temperature increases Award zero s f - as the solubility decreases the temperature increases - the temperature increases as the solubility decreases page 18

19 12. (a) 1 Circling of either C=C OH. Award zero s f (b) Ester(s) 1 (c) 21 (g) (3) Partial s 1 f either: Both GFMs 3 No units required but a maximum of two s can be awarded if wrong unit is given. (Wrong units are only penalised once in any paper) ie 154 and 210 Moles of geraniol ie (15 4 / 154) = 0 1 mol 1 concept f either: GFM of ester 15 4 x GFM of geraniol ie 15.4 x (210 / 154) Moles of geraniol x GFM of ester ie 0 1 x 210 (Either of these two steps on their own with all crect substitutions 2 s) 1 f calculated final answer provided the concept has been awarded. page 19

20 13. (a) C n H 2n-2 1 Accept x etc in place of n C n H n2-2 C n H 2(n-1) (b) (i) Allow one end bond to be missing. (ii) Addition / additional 1 Award zero s f - add (c) (i) 1 Igne - the omission of one H atom (from a carbon atom) in full structural fmula provided the bond is shown - one carbon to hydrogen bond missing provided the hydrogen is shown. (ii) The two bromine atoms are not next to one another. The two bromines are separated by a hydrogen. The two bromine branches are not next to one another. 1 Award zero s f -bromide -bromine molecules. Accept wds/phrases that imply not together not next to each other. page 20

21 14. (a) (i) Any crect shtened full structural fmula f hexan-1-ol 1 Bond to the hydroxyl group must be to the O of the OH. Igne the omission of one H atom (from a carbon atom) in full structural fmula provided the bond is shown igne one carbon to hydrogen bond missing provided the hydrogen is shown. (ii) 188 (kj) 1 No units required but no is awarded if wrong unit is given. (Wrong units are only penalised once in any paper). (b) (kj kg -1 ºC -1 ) Partial ing (3) 3 No units required but a maximum of two s can be awarded if wrong unit is given. (Wrong units are only penalised once in any paper) Using the crect concept of c = Eh / m T with Eh = 13 3 (1) 0 1 and 34 (1) A further can be awarded f the candidate s calculated answer only if the f the concept has been awarded. (1) and 100 can be used if the calculation is carried out in J/g. (The final answer would be 3 9 and the unit is crect if given as J g -1 ºC -1. as kj kg -1 ºC -1 ) Alternatively and 0 1 can be used but the final answer should be 3912 J kg -1 ºC -1 (units must be shown and crect f 3 s to be awarded). If no unit, the unit given in question is used then 2 s are awarded as the f the final calculated answer is not awarded. Or alternatively - the answer, 3912, can be divided by 1000 to give the crect answer in kj kg -1 ºC -1. page 21

22 15. 1 : The student has demonstrated a limited understanding of the chemistry involved. The candidate has made some statement(s) which is/are relevant to the situation, showing that at least a little of the chemistry within the problem is understood. 2 s: The student has demonstrated a reasonable understanding of the chemistry involved. The student makes some statement(s) which is/are relevant to the situation, showing that the problem is understood. 3 s: The maximum available would be awarded to a student who has demonstrated a good understanding of the chemistry involved. The student shows a good comprehension of the chemistry of the situation and has provided a logically crect answer to the question posed. This type of response might include a statement of the principles involved, a relationship an equation, and the application of these to respond to the problem. This does not mean the answer has to be what might be termed an excellent answer a complete one. 3 [END OF MARKING INSTRUCTIONS] page 22

2016 Chemistry. National 5. Finalised Marking Instructions

2016 Chemistry. National 5. Finalised Marking Instructions National Qualifications 2016 2016 Chemistry National 5 Finalised ing Instructions The information in this publication may be reproduced to support SQA qualifications only on a non-commercial basis. If