Edexcel Jan 2017 (IAL) Paper 1 Q24 (with explained solutions) |

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Edexcel Jan 2017 (IAL) Paper 1 Q24

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24 This question is about the alkali metal potassium and the salt potassium chloride. (a) (i) A sample of potassium is known to consist of isotopes with mass numbers 39 and 41. For each isotope, complete the table below to show the numbers of protons, neutrons and electrons. Isotope mass number Number of protons Number of neutrons Number of electrons 39 41 A E R A S I H T N I E T I R W T O N O D (ii) Explain the meaning of the term isotope, using the information from the table in (a)(i). (2) (1) A E R A S I H T N I E T I R W T O N O D(iii) The relative atomic mass of this sample of potassium is 39.1. Calculate the percentage abundance of each isotope. (2) A E R A S I H T N I E T I R W T O N O D *P48367A01924* 19 Turn over<br />
(b) The chart below shows the successive ionisation energies of potassium. ) 1l o m J k E I ( g o 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 Successive ionisation energies of potassium Z = 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Ionisation number (i) Estimate the 1st ionisation energy and the 19th ionisation energy of potassium. Use data from the graph and your calculator. (ii) Explain why the logarithm of the ionisation energy is used in plotting this graph rather than the ionisation energy. (1) (1)20 *P48367A02024* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br />
(iii) Write the equation for the first ionisation energy of potassium. *(iv) Explain why there is a general rise in the value of the successive ionisation energies. (2) (2) A E R A S I H T N I E T I R W T O N O DA E R A S I H T N I E T I R W T O N O D*(v) Explain each of the three sharp rises in the graph. You should include details of the subshell from which the electron is removed at each sharp rise. (3)A E R A S I H T N I E T I R W T O N O D *P48367A02124* 21 Turn over<br />
(c) (i) Draw a dot and cross diagram for potassium chloride. Only show the electrons in the outer shell of both ions. (2) (ii) Compare the electrical conductivity of potassium metal and potassium chloride. (2)(iii) Describe two similarities in the structure and bonding of potassium metal and potassium chloride. (2)(iv) Give one difference between the structures of potassium metal and potassium chloride. (1)(Total for Question 24 = 21 marks) TOTAL FOR SECTION B = 60 MARKS TOTAL FOR PAPER = 80 MARKS 22 *P48367A02224* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br />

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Question Number 24(a)(i) Question Number 24(a)(ii) Acceptable Answers Isotope mass number 39 41 Each correct row (1) Number of protons Number of neutrons Number of electrons 19 19 20 22 19 19 Reject Mark Acceptable Answers Isotopes OR atoms OR they OR elements OR species that have the same numbers of protons (and electrons) / 19 protons but different numbers of neutrons / 20 and 22 neutrons Must mention both protons and neutrons Reject Mark Reject Mark Acceptable Answers Question Number 24(a)(iii) 39x + 41(100 - x) = 39.1 100 ALLOW 39x + 41y = 39.1 (1) 100 -2x = 3 910 -4 100 = - 190 x = 95 3995% 415% (1) Both correct with no working 2<br />
Reject Mark Acceptable Answers 102.6 = 39840 (kJ mol-1) ALLOW Any value between 250 - 550 (kJ mol-1) OR 105.7 = 501 00050 000 (kJ mol-1) ALLOW Any value between 250,000760,000 (kJ mol-1) IGNORE units even if incorrect e2.6 etc Reject Mark Acceptable Answers Question Number 24(b)(ii) The large range (of numbers from 398 to 500 000 is too big a range to plot directly) OR to fit numbers onto graph OR (Taking logarithms) makes the numbers manageable to plot ALLOW Ionisation energies too large Question Number 24(b)(i)<br />
Acceptable Answers Question Number 24(b)(iii) K(g) - e()K+(g) Reject Mark OR K(g)K+(g) + e() States, dependent on correct electron transfer (1) Rest of the equation correct (1) Acceptable Answers Question Number 24*(b)(iv) Any two from Electrons removed from (more) positive ion each time / proton : electron ratio increases ALLOW greater effective nuclear charge (1) So the ion is smaller / has less electrons / has less electron repulsion / electron (to be removed) is closer to nucleus (1) so greater electrostatic attraction / greater attraction between nucleus and electron (1) IGNORE Shielding increasing Nuclear charge increasing Reject Mark<br />
Acceptable Answers Question Number 24*(b)(v) Any three from Reject MarkEach rise is caused by removing an electron from an inner (quantum) shell / energy level OR shell / energy level which is closer to the nucleusThe first sharp increase is when a 3p electron is removed (for the first time / rather than a 4s electron)The second sharp increase is when a 2p electron is removed (for the first time / rather than a 3s electron)The third sharp increase is when a 1s electron is removed (for the first time / rather than a 2s electron) Acceptable Answers Question Number 24(c)(i) Reject Mark (1) (1) OR No electrons around the potassium ion IGNORE the absence of empty ring around the potassium IGNORE inner electrons ALLOW 1 for two correct electronic structures with no charges<br />
Reject Mark Acceptable Answers Question Number 24(c)(ii) Potassium conducts when solid (or molten) ALLOW potassium conducts in all states (1) Whereas potassium chloride (only) conducts when molten / in (aqueous) solution (1) Question Number 24(c)(iii)* Both solids are held together by forces of (electrostatic) attraction OR Both have positive and negative particles (1) (In both solids positive ions) are in fixed positions / in a lattice / regular arrangement OR both have regular 3D shape / arrangement OR lattice structures IGNORE Giant structures (1) Reject Mark Both have positive and negative ions<br />
Reject Mark Acceptable Answers Question Number 24(c)(iv)* In metal electrons are free to move / delocalised electrons OR In KCl electrons are not free to move / not delocalised OR In ionic solid negative ions are in fixed positions OR KCl contains anions and cations and (only) cations in K / K does not contain anions (TOTAL FOR QUESTION 24) =21 MARKS TOTAL FOR PAPER = 80 MARKS<br />

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