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Which of the following does not have exactly 10 electrons?
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Comment on the fact that there is close agreement between the values for sodium chloride, NaCl.
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Chem unit 1 pastpap5
| Question | Answer |
|---|---|
| Which of the following does not have exactly 10 electrons? | à A molecule of nitrogen, N2 |
| Comment on the fact that there is close agreement between the values for sodium chloride, NaCl. | à (Bonding in NaCl) 100% ionic OR almost completely ionic OR no covalent character/(very) little covalent character. |
| Classify the type and mechanism of the reaction that occurs when myrcene reacts with bromine, Br2. | Electrophilic (1) addition |
| What colour change would you observe when bromine, dissolved in an organic solvent, is added to myrcene? --> | From: Red / brown / orange / yellow or combinations of these colour. To: colourless. |
| Suggest a reason why the alkanes are liquefied. à | Easier to transport / easier to store/ less space / less volume needed for storage / easier to handle / easier to transfer. |
| Liquefied petroleum gas (LPG) is a fuel sold as an alternative to petrol. | It is a mixture of liquefied C3 and C4 alkanes. |
| Which of the following statements correctly describes an environmental problem caused by the burning of hydrocarbon fuels? | --> The carbon dioxide produced absorbs heat radiated from the Earth and leads to global warming. |
| Explain, in terms of chemical bonding, why the experimental value for silver iodide, AgI, is more exothermic than the value calculated theoretically for the same compound.--> | AgI has (a degree of) covalent character (1) due to polarization or distortion (of the anion) |
| Suggest why the first ionization energies of the Group 1 elements decrease down the group. | (outermost) electron further from the nucleus/atoms get bigger/more shells • (outermost) electron more shielded (by inner shells of e-) • |
| Suggest why the first ionization energies of the Group 1 elements decrease down the group. à | (force of) attraction between nucleus and (outermost) electron decreases (down the Group) OR (outermost) electron held less strongly (down the Group) OR (outermost) electron becomes easier to remove (down the Group). |
| Explain why silicon has a much higher melting temperature than sulfur --> | Si : covalent bonds / many bonds/strong bonds (between atoms) (1) S : weak forces /van der Waals’ forces/London forces/dispersion forces/intermolecular forces/induced-dipole forces (1) (need to be overcome). |
| Explain why the melting temperature increases from sodium to aluminium.--> | Cations/ions decrease in size (from Na+ to Al3+) OR charge increases/charge density on (cat)ions increases/ “effective nuclear charge” increases (from Na+to Al3+) (1) more e– (per atom in ‘sea’ of delocalized electrons) / more delocalized electrons |
| Explain why the melting temperature increases from sodium to aluminium.--> | (force of) attraction between (cat)ions/ (delocalised) electrons increases (from Na to Al) d) Magnesium forms the basic oxide, MgO. This oxide is almost insoluble in H20. On gentle warming + dilute H2S04, MgO reacts to form aqueous MgS04(aq) |
| Describe how you would use the above reaction to prepare a pure sample of magnesium sulfate | Add MgO to acid/react MgO with acid/dissolve MgO in acid/ Filter. Heat/boil filtrate /MgSO4 solution (until volume reduced by half). |
| Describe how you would use the above reaction to prepare a pure sample of magnesium sulfate | Leave to cool/leave to crystallise/evaporate slowly/leave to evaporate./(decant / filter / pick out crystals,then) Leave to dry/pat dry/dry between filter papers/put in an oven/put in a desiccator/dry the crystals. |
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