OCR A Jun 2016 Paper 1 Q3 (with explained solutions) |

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OCR A Jun 2016 Paper 1 Q3

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The elements of Period 2 and Period 3 of the Periodic Table are shown in Table 3.1. Group Period 2 Period 3 Li Na Be Mg Al Si Cl Ne Ar Table 3.1 (a) The elements in these two periods show a repeating pattern in chemical and physical properties. What is the name given to this repeating pattern of properties?[1] (b) State the element in Table 3.1 with: the lowest first ionisation energythe lowest fourth ionisation energythe lowest boiling point[3] (c) Gallium, atomic number 31, is in Period 4 of the Periodic Table. Gallium is a Group 3 element. Predict the formula of a gallium ion.[1]OCR 2016<br />
(d) The melting points of the Period 3 metals sodium and magnesium are shown below. Metal sodium magnesium Melting point / C 98 649 Explain the differences in the melting points of sodium and magnesium, using the model of metallic bonding. In your answer you should use appropriate technical terms spelled correctly.[3] (e) When magnesium nitrate, Mg(NO3)2, is heated, it decomposes as shown. 2Mg(NO3)2(s) 2MgO(s) + 4NO2(g) + O2(g) A student heats 2.966 g of Mg(NO3)2, which decomposes as above. Calculate the total volume of gas formed, in cm3, at room temperature and pressure, RTP. total volume of gas formed =cm3 [3]OCR 2016 Turn over<br />
(f) Fluorine forms several compounds with sulfur and with oxygen. (i) Give the formula and the name of the compound formed between fluorine and sulfur which has octahedral molecules. FormulaName[1] (ii) Fluorine reacts with aqueous sodium hydroxide to form the oxide F2O. Two other products are also formed. One product is an ionic compound with a relative formula mass of 42.0. Construct a balanced equation for this reaction.[2] (g) (i) Fluorine is the most electronegative element. Indicate any dipoles on the molecule of F2O below using partial charges. (ii) Suggest the shape of the F2O molecule and the FOF bond angle. ShapeBond angle(iii) What is the oxidation number of oxygen in F2O? Include the sign in your answer. [1] [1][1] [Total: 17]OCR 2016<br />
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F321 Question 3 3 (a) (b) 3 3 (c) (d) Ga3+ (cid:51) Answer Periodicity (cid:51) Sodium OR Na (cid:51) Silicon OR Si (cid:51) Neon OR Ne (cid:51) M1 Number of bonding electrons mark Magnesium has more outer OR bonding electrons (cid:51) M2 Ionic charge mark Magnesium ions have a greater (positive) charge (density) (cid:51) M3 Attraction mark Magnesium has a greater attraction between ions and delocalised electrons (cid:51) Mark Scheme June 2016 Mark 1 3 Guidance ALLOW reverse argument throughout ALLOW more delocalised electrons for more outer electrons DO NOT ALLOW Magnesium molecules for M1 ALLOW Mg2+ ion OR Mg ion for magnesium ion ALLOW Mg2+ and Na+ for M2 (may be seen in a diagram) IGNORE magnesium has a greater charge but ALLOW magnesium has a greater ionic charge IGNORE nuclear charge DO NOT ALLOW atoms or molecules having a greater charge for M2 ALLOW stronger metallic bonds only when a clear description of metallic bonding is given. Eg The attraction of positive (metal) ions to delocalised electrons QWC delocalised/delocalized spelled correctly at least once in context of M3 (may be seen in M1 but used in M3) delocalised need not be directly next to electrons eg Mg has more delocalised electrons and the ions have a greater attraction to these electrons would secure M3 10<br />
F321 Question 3 (e) Mark Scheme June 2016 Mark Answer First check the answer line. If answer = 1200 cm3 award 3 marks. Mol of Mg(NO3)2 = 2.966 = 2(.00) x 102 OR 0.02(00) mol(cid:51) 148.3 Mol of gas = 2(.00) x 102 x 5/2 = 5(.00) x 102 OR 0.05(00) mol (cid:51) Vol of Gas = 0.05 x 24 000 = 1200 cm3 (cid:51) (f) (g) (i) SF6 AND Sulfur(VI) fluoride OR Sulfur hexafluoride (cid:51) (ii) 2F2 + 2NaOH (cid:198) F2O + 2NaF + H2O M1 F2O AND NaF (cid:51) M2 Rest of equation (including balance) (cid:51) (i)on each F AND + on O (cid:51) (ii) Shape: non-linear AND Bond angle: 104.5 o (cid:51) (iii) +2 (cid:51) 1 17 Total 11 Guidance If answer = 960 cm3 award 2 marks. If answer = 240 cm3 award 2 marks. ALLOW ECF for answers to at least two significant figures up to calculator value, correctly rounded ALLOW separate numbers of mol of each gas for M2 (0.04(00) mol NO2 and 0.0100 mol O2) ALLOW a second mark if only volume of O2 (240 cm3) OR only volume of NO2 (960 cm3) is calculated IGNORE sulfur fluoride ALLOW multiples IGNORE state symbol ALLOW OF2 for F2O AND FNa for NaF ALLOW both marks for alternative equations which have both F2O and NaF AND three products Eg 3F2 + 2NaOH (cid:198) 2F2O + 2NaF + H2 Eg 2F2 + NaOH (cid:198) F2O + NaF + HF ALLOW 2+ OR + + on O For shape ALLOW alternative words eg V-shaped bent angular. In the absence of words allow a diagram with a non-linear shape FOF bond angle > 90o. For bond angle ALLOW 106> bond angle 102 (Actual = 102o) ALLOW 2+<br />

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