Exampro questions ionic bonding, Exams of Chemistry

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3.1.3.1 Ionic bonding

Name: ________________________

Class: ________________________

Date: ________________________

Time: (^) 128 min. Marks: (^) 119 marks

Comments:

Q1. This question is about atomic structure. In the nineteenth century JJ Thomson discovered the electron. He suggested that negative electrons were found throughout an atom like ‘plums in a pudding of positive charge’. The diagram shows an atom of element R using the ‘plum pudding’ model. An atom of R contains seven electrons. (a) State two differences between the ‘plum pudding’ model and the model of atomic structure used today.

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(b) Deduce the full electron configuration of an atom of element R.

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(1) (c) Identify R and deduce the formula of the compound formed when R reacts with the Group 2 metal in the same period as R.

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(1) (Total 4 marks)

(d) Sodium reacts with ammonia to form the compound NaNH 2 that contains the NH 2 –^ ion. Draw the shape of the NH 2 –^ ion. Include any lone pairs of electrons that influence the shape. Predict the bond angle. Justify your prediction. Shape Bond angle ____________________ Justification _________________________________________________________

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(4) (Total 17 marks) Q3. Element Q forms a sulfate with formula QSO 4 Which of these could represent the electronic configuration of an atom of Q? A [Ne]3s^1 B [Ne]3s^2 C [Ne]3s^2 3p^1 D [Ne]3s^1 3p^2 (Total 1 mark)

Q4. What is the formula of calcium nitrate(V)? A CaNO 3 B Ca(NO 3 ) 2 C Ca 2 NO 2 D Ca(NO 2 ) 2 (Total 1 mark) Q5. Some airbags in cars contain sodium azide (NaN 3 ). (a) Sodium azide is made by reacting dinitrogen monoxide gas with sodium amide (NaNH 2 ) as shown by the equation. 2NaNH 2 + N 2 O NaN 3 + NaOH + NH 3 Calculate the mass of sodium amide needed to obtain 550 g of sodium azide, assuming there is a 95.0% yield of sodium azide. Give your answer to 3 significant figures.

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(5) (b) If a car is involved in a serious collision, the sodium azide decomposes to form sodium and nitrogen as shown in the equation. 2NaN 3 (s) 2Na(s) + 3N 2 (g) The nitrogen produced then inflates the airbag to a volume of 7.50 × 10−2^ m^3 at a pressure of 150 kPa and temperature of 35 °C. Calculate the minimum mass of sodium azide that must decompose.

Predict the type of bonding in a crystal of sodium azide. Suggest why its melting point is high. Type of bonding _____________________________________________________ Reason for high melting point ___________________________________________

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(3) (e) The azide ion has the formula N 3 − (i) The azide ion can be represented as N N − N− One of these bonds is a co−ordinate bond. On the following diagram, draw an arrowhead on one of the bonds to represent the direction of donation of the lone pair in the co−ordinate bond.

N N − N

− (1) (ii) Give the formula of a molecule that has the same number of electrons as the azide ion.

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(1) (iii) Which is the correct formula of magnesium azide? Tick (✓) one box. Mg 3 N

MgN MgN 6 Mg 3 N 2 (1) (Total 21 marks) Q6. Zinc forms many different salts including zinc sulfate, zinc chloride and zinc fluoride. (a) People who have a zinc deficiency can take hydrated zinc sulfate (ZnSO 4. x H 2 O) as a dietary supplement. A student heated 4.38 g of hydrated zinc sulfate and obtained 2.46 g of anhydrous zinc sulfate. Use these data to calculate the value of the integer x in ZnSO 4. x H 2 O Show your working.

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(4) (d) Predict the type of crystal structure in solid zinc fluoride and explain why its melting point is high.

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(3) (Total 14 marks) Q7. The table below shows the boiling points of some hydrogen compounds formed by Group 6 elements. H 2 O H 2 S H 2 Se H 2 Te Boiling point / K 373 212 232 271

(a) State the strongest type of intermolecular force in water and in hydrogen sulfide (H 2 S). Water _____________________________________________________________ Hydrogen sulfide _____________________________________________________

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(2) (b) Draw a diagram to show how two molecules of water are attracted to each other by the type of intermolecular force you stated in part (a). Include partial charges and all lone pairs of electrons in your diagram. (3) (c) Explain why the boiling point of water is much higher than the boiling point of hydrogen sulfide.

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(1) (d) Explain why the boiling points increase from H 2 S to H 2 Te

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(2) (e) When H+^ ions react with H 2 O molecules, H 3 O+^ ions are formed. Name the type of bond formed when H+^ ions react with H 2 O molecules.

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(4) (b) The isotopes of silver, when vaporised, can be separated in a mass spectrometer. Name the three processes that occur in a mass spectrometer before the vaporised isotopes can be detected. State how each process is achieved.

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(6) (c) State the type of bonding involved in silver. Draw a diagram to show how the particles are arranged in a silver lattice and show the charges on the particles.

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(3) (d) Silver reacts with fluorine to form silver fluoride (AgF). Silver fluoride has a high melting point and has a structure similar to that of sodium chloride. State the type of bonding involved in silver fluoride. Draw a diagram to show how the particles are arranged in a silver fluoride lattice and show the charges on the particles. Explain why the melting point of silver fluoride is high.

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(5) (Total 20 marks) Q9. At room temperature, both sodium metal and sodium chloride are crystalline solids which contain ions.

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(1) (e) Sodium chlorate(V), NaClO 3 , contains 21.6% by mass of sodium, 33.3% by mass of chlorine and 45.1% by mass of oxygen. (i) Use the above data to show that the empirical formula of sodium chlorate(V) is NaClO 3

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(ii) Sodium chlorate(V) may be prepared by passing chlorine into hot aqueous sodium hydroxide. Balance the equation for this reaction below. ....... Cl 2 + ....... NaOH → ....... NaCl + NaClO 3 + 3H 2 O (3) (Total 12 marks) Q10. (a) Complete the following table. Particle Relative charge Relative mass Proton Neutron Electron (3) (b) An atom of element Z has two more protons and two more neutrons than an atom of. Give the symbol, including mass number and atomic number, for this atom of Z.

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(2) (c) Complete the electronic configurations for the sulphur atom, S, and the sulphide ion, S2–.

S 1s^2 ___________________________________________________________ S2–^ 1s^2 ___________________________________________________________ (2) (d) State the block in the Periodic Table in which sulphur is placed and explain your answer. Block ______________________________________________________________ Explanation _________________________________________________________ (2) (e) Sodium sulphide, Na 2 S, is a high melting point solid which conducts electricity when molten. Carbon disulphide, CS 2 , is a liquid which does not conduct electricity. (i) Deduce the type of bonding present in Na 2 S and that present in CS 2 Bonding in Na 2 S ________________________________________________ Bonding in CS 2 _________________________________________________ (ii) By reference to all the atoms involved explain, in terms of electrons, how Na 2 S is formed from its atoms.

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(iii) Draw a diagram, including all the outer electrons, to represent the bonding present in CS 2 (iv) When heated with steam, CS 2 reacts to form hydrogen sulphide, H 2 S, and carbon dioxide. Write an equation for this reaction.

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Mark schemes Q1. (a) Assume current model unless otherwise stated. Statement about the nucleus: (Central) nucleus contains protons and neutrons. Allow “protons and neutrons are in the centre of the atom” 1 Statement about electrons Electrons are now arranged in energy levels/shells/orbitals Ignore “mostly empty space” Ignore electrons surround / orbit nucleus Allow additional statement about neutrons but must be separate from statement about nucleus to score e.g. no neutrons in plum pudding / neutrons now recognised 1 (b) 1s^2 2s^2 2p^3 Ignore commas, capitals and subscripts Allow 1s^2 2s^2 2px^1 2py^1 2pz^1 1 (c) (R is N (nitrogen)) Formula Be 3 N 2 Accept Be 3 R 2 only if stated R = nitrogen Accept N 2 Be 3 1 [4] Q2. This question is marked using Levels of Response. Examiners should apply a ‘best-fit’ approach to the marking. Level 3 5- marks All stages are covered and the explanation of each stage is generally correct and virtually complete. Answer is communicated coherently and shows a logical progression from stage 1 to stage 2 and then

stage 3. Coherent communication requires that there is a comparison between the types of bonding and that the bonding is correct for each substance. Level 2 3- marks All stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies OR two stages are covered and the explanations are generally correct and virtually complete. Answer is mainly coherent and shows some progression from stage 1 to stage 2 and then stage 3. Level 1 1- marks Two stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies OR only one stage is covered but the explanation is generally correct and virtually complete. Answer shows some progression between two stages Level 0 0 marks Insufficient correct chemistry to gain a mark. Indicative chemistry content. Contradictions (eg molecules, IMFs, covalent bonding,) negate statements. Stage 1 - Na 1a) Na has metallic bonding 1b) there is attraction/ bonding between the positive nucleus/ ion and the delocalised electrons in Na 1c) Na has a giant/lattice structure Stage 2 – NaBr or NaI 2a) Ionic bonding in NaBr and/or NaI 2b) There is attraction/ bonding between the + and – ions in NaBr and/or NaI 2c) NaBr and/or NaI have a giant/lattice structure Stage 2 – comparison of bonding 3a) The ionic bonds are stronger (or wtte) than the metallic bonds 3b) there is stronger attraction (or wtte) between the + and – ions in NaBr than in NaI 3c) since the Br–^ ion is smaller than the I– ion 6 (b) M1 Na + H 2 O → NaOH + ½ H 2 Allow multiples 1 M2 (Mass Na = 0.250 g so moles Na = 0.250/23.0) = 0.