City College Manchester 1 1. This question concerns the chemistry of the Group II metals Mg to Ba. An aqueous solution of a Group II metal chloride, XCl 2 , forms a white precipitate when dilute aqueous sodium hydroxide is added. A separate sample of the solution of XCl 2 does not form a precipitate when dilute aqueous sodium sulphate is added. An aqueous solution of a different Group II metal chloride, YCl 2 , does not form a precipitate when dilute aqueous sodium hydroxide is added. A separate sample of the solution of YCl 2 forms a white precipitate when dilute aqueous sodium sulphate is added. Suggest identities for the Group II metals X and Y. Write equations, including state symbols, for the reactions which occur. (Total 6 marks)
Transcript
City College Manchester 1
1. This question concerns the chemistry of the Group II metals Mg to Ba. An aqueous solution of a Group II metal chloride, XCl2, forms a white precipitate when dilute aqueous sodium hydroxide is added. A separate sample of the solution of XCl2 does not form a precipitate when dilute aqueous sodium sulphate is added.
An aqueous solution of a different Group II metal chloride, YCl2, does not form a precipitate when dilute aqueous sodium hydroxide is added. A separate sample of the solution of YCl2 forms a white precipitate when dilute aqueous sodium sulphate is added.
Suggest identities for the Group II metals X and Y. Write equations, including state symbols, for the reactions which occur.
(c) A sample of copper contains the two isotopes 63Cu and 65Cu only. It has a relative atomic mass, Ar, less than 64. The mass spectrum of this sample shows major peaks with m/z values of 63 and 65, respectively.
(i) Explain why the Ar of this sample is less than 64.
........................................................................................…............................... (iii) In addition to the major peaks at m/z = 63 and 65, much smaller peaks at m/z = 31.5
and 32.5 are also present in the mass spectrum. Identify the ion responsible for the peak at m/z = 31.5 in the mass spectrum. Explain why your chosen ion has this m/z value and suggest one reason why this peak is very small.
Identity of the ion .............................................................................................
Explanation for m/z value ................................................................................
3. (a) There is a trend in the reactivity of the Group II metals, Be–Ba, with water. State this trend and give the conditions under which magnesium reacts rapidly with water. Write an equation to represent this reaction.
Trend Be to Ba ………...................................................................................………..
(b) Describe what you would observe when a few drops of aqueous sodium hydroxide are added to aqueous beryllium chloride, followed by a large excess of aqueous sodium hydroxide. Write equations for the two reactions which occur.
Observation when a few drops are added ....................................................…………
4. (a) Iodine and graphite crystals both contain covalent bonds and yet the physical properties of their crystals are very different. For iodine and graphite, state and explain the differences in their melting points and in their electrical conductivities.
(9) (b) Draw the shape of the BeCl2 molecule and explain why it has this shape.
State and explain the effect that an isolated Be2+ ion would have on an isolated Cl– ion and explain how this effect would lead to the formation of a covalent bond. Give one chemical property of Be(OH)2 which is atypical of the chemistry of Group II hydroxides.
(6) (Total 15 marks)
City College Manchester 5
5. The diagram below shows the values of the first ionisation energies of some of the elements in Period 3.
First ionisationenergy/kJ mol –1
1600
1400
1200
1000
800
600
400
200
0Na Mg Al Si P S Cl Ar
(a) On the above diagram, use crosses to mark the approximate positions of the values of the first ionisation energies for the elements Na, P and S. Complete the diagram by joining the crosses.
(3)
(b) Explain the general increase in the values of the first ionisation energies of the elements Na–Ar.
(d) The mass spectrum of a sample of chromium shows four peaks. Use the data below to calculate the relative atomic mass of chromium in the sample. Give your answer to two decimal places.
7. Diamond and graphite are both forms of carbon. Diamond is able to scratch almost all other substances, whereas graphite may be used as a lubricant. Diamond and graphite both have high melting points.
Explain each of these properties of diamond and graphite in terms of structure and bonding. Give one other difference in the properties of diamond and graphite.
(Total 9 marks)
City College Manchester 7
8. (a) Define the term electronegativity and explain why the electronegativity values of the Group II elements Be–Ba decrease down the group.
(4)
(b) Name the strongest type of intermolecular force between hydrogen fluoride molecules and draw a diagram to illustrate how two molecules of HF are attracted to each other. In your diagram show all lone pairs of electrons and any partial charges. Explain the origin of these charges. Suggest why this strong intermolecular force is not present between HI molecules.
(7)
(c) Crystals of sodium chloride and of diamond both have giant structures. Their melting points are 1074 K and 3827 K, respectively. State the type of structure present in each case and explain why the melting point of diamond is so high.
(4) (Total 15 marks)
City College Manchester 8
9. (a) Ammonium sulphate reacts with aqueous sodium hydroxide as shown by the equation
below.
(NH4)2SO4 + 2NaOH → 2NH3 + Na2SO4 + 2H2O
A sample of ammonium sulphate was heated with 100 cm3 of 0.500 mol dm–3 aqueous sodium hydroxide. To ensure that all the ammonium sulphate reacted, an excess of sodium hydroxide was used. Heating was continued until all of the ammonia had been driven off as a gas. The unreacted sodium hydroxide remaining in the solution required 27.3 cm3 of 0.600 mol dm–3 hydrochloric acid for neutralisation.
(i) Calculate the original number of moles of NaOH in 100 cm3 of 0.500 mol dm–3 aqueous sodium hydroxide.
(v) Use your answer in part (a) (iv) to calculate the number of moles and the mass of ammonium sulphate in the sample. (If you have been unable to obtain an answer to part (a) (iv), you may assume that the number of moles of NaOH which reacted with ammonium sulphate equals 2.78 × 10–2 mol. This is not the correct answer.)
Moles of ammonium sulphate ...........................................................................
10. Lithium hydride, LiH, is an ionic compound containing the hydride ion, H– The reaction between LiH and aluminium chloride, AlCl3, produces the ionic compound LiAlH4
(a) Balance the equation below which represents the reaction between LiH and AlCl3
LiH + AlCl3 → LiAlH4 + LiCl (1)
(b) Give the electronic configuration of the hydride ion, H–
........................................................................................…............................... (ii) Why is a chloride ion polarised more by an aluminium ion than by a magnesium
13. (a) Iodine and diamond are both crystalline solids at room temperature. Identify one
similarity in the bonding, and one difference in the structures, of these two solids. Explain why these two solids have very different melting points.
(6)
(b) (i) For the elements Mg–Ba, state how the solubilities of the hydroxides and the solubilities of the sulphates change down Group II.
(ii) Describe a test to show the presence of sulphate ions in an aqueous solution. Give the results of this test when performed on separate aqueous solutions of magnesium chloride and magnesium sulphate. Write equations for any reactions occurring.
(iii) State the trend in the reactivity of the Group II elements Mg–Ba with water.
Write an equation for the reaction of barium with water. (9)
(b) Draw the shapes, including any lone pairs of electrons, of a phosphine molecule and of a phosphonium ion. Give the name of the shape of the phosphine molecule and state the bond angle found in the phosphonium ion.
PH3 +4PH
Shape of PH3 ……………………… Bond angle in ……………...... +4PH
(4) (Total 7 marks)
City College Manchester 16
15. (a) Sodium carbonate forms a number of hydrates of general formula Na2CO3.xH2O
A 3.01 g sample of one of these hydrates was dissolved in water and the solution made up to 250 cm3. In a titration, a 25.0 cm3 portion of this solution required 24.3 cm3 of 0.200 mol–1 dm–3 hydrochloric acid for complete reaction.
The equation for this reaction is shown below.
Na2CO3 + 2HCl → 2NaCl + H2O + CO2
(i) Calculate the number of moles of HCl in 24.3 cm3 of 0.200 mol dm–3 hydrochloric acid.
...........………………………………………………………………………….
(ii) Deduce the number of moles of Na2CO3 in 25.0 cm3 of the Na2CO3 solution.
...........………………………………………………………………………….
(iii) Hence deduce the number of moles of Na2CO3 in the original 250 cm3 of solution.
...........………………………………………………………………………….
(iv) Calculate the Mr of the hydrated sodium carbonate.
...........………………………………………………………………………….
...........…………………………………………………………………………. (5)
(b) In an experiment, the Mr of a different hydrated sodium carbonate was found to be 250. Use this value to calculate the number of molecules of water of crystallisation, x, in this hydrated sodium carbonate, Na2CO3.xH2O
(c) A gas cylinder, of volume 5.00 × 10–3 m3, contains 325 g of argon gas.
(i) Give the ideal gas equation.
...........………………………………………………………………………….
(ii) Use the ideal gas equation to calculate the pressure of the argon gas in the cylinder at a temperature of 298 K. (The gas constant R = 8.31 J K–1 mol–1)
...........………………………………………………………………………….
...........………………………………………………………………………….
...........………………………………………………………………………….
...........…………………………………………………………………………. (4)
(Total 12 marks)
City College Manchester 18
16. (a) Methanol has the structure
H
C O
H
H H
Explain why the O–H bond in a methanol molecule is polar.
(b) The boiling point of methanol is +65 °C; the boiling point of oxygen is –183 °C. Methanol and oxygen each have an Mr value of 32. Explain, in terms of the intermolecular forces present in each case, why the boiling point of methanol is much higher than that of oxygen.
18. A sample of iron from a meteorite was found to contain the isotopes 54Fe, 56Fe and 57Fe.
(a) The relative abundances of these isotopes can be determined using a mass spectrometer. In the mass spectrometer, the sample is first vaporised and then ionised.
........................................................................................................................... (iii) State the difference, if any, in the chemical properties of isotopes of the same
19. (a) Lead(II) nitrate may be produced by the reaction between nitric acid and lead(II) oxide as shown by the equation below.
PbO + 2HNO3 → Pb(NO3)2 + H2O
An excess of lead(II) oxide was allowed to react with 175 cm3 of 1.50 mol dm–3 nitric acid. Calculate the maximum mass of lead(II) nitrate which could be obtained from this reaction.
(b) An equation representing the thermal decomposition of lead(II) nitrate is shown below.
2Pb(NO3)2(s) → 2PbO(s) + 4NO2(g) + O2(g)
A sample of lead(II) nitrate was heated until the decomposition was complete. At a temperature of 500 K and a pressure of 100 kPa, the total volume of the gaseous mixture produced was found to be 1.50 × 10–4 m3.
(i) State the ideal gas equation and use it to calculate the total number of moles of gas produced in this decomposition. (The gas constant R = 8.31 J K–1 mol–1)
Ideal gas equation .........................................................................................
Total number of moles of gas ............................................................................
............................................................................................................................ (ii) Deduce the number of moles, and the mass, of NO2 present in this gaseous mixture.
(If you have been unable to calculate the total number of moles of gas in part (b)(i), you should assume this to be 2.23 × 10–3 mol. This is not the correct answer.)
Number of moles of NO2 ..................................................................................
