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Questions and Answers
State the element in Period 3 that has the highest first ionisation energy.
State the element in Period 3 that has the highest first ionisation energy.
Argon / Ar
Explain why the TlCl2 + ion has the shape that you have drawn in part (f)(i).
Explain why the TlCl2 + ion has the shape that you have drawn in part (f)(i).
Two bonds (pairs of electrons) repel equally.
Explain why CF4 has a bond angle of 109.5°.
Explain why CF4 has a bond angle of 109.5°.
4 bonding pairs of electrons around carbon repel equally.
Explain how the electron pair repulsion theory can be used to deduce the shape of PF3.
Explain how the electron pair repulsion theory can be used to deduce the shape of PF3.
Explain why magnesium has a higher melting point than sodium.
Explain why magnesium has a higher melting point than sodium.
Write an equation for the reaction of sulfur(IV) oxide with water.
Write an equation for the reaction of sulfur(IV) oxide with water.
Write an equation for the reaction between phosphorus(V) oxide and magnesium oxide.
Write an equation for the reaction between phosphorus(V) oxide and magnesium oxide.
Write an equation for the reaction of magnesium with titanium(IV) chloride.
Write an equation for the reaction of magnesium with titanium(IV) chloride.
Explain why calcium has a higher melting point than strontium.
Explain why calcium has a higher melting point than strontium.
Write the simplest ionic equation for the reaction of acidified barium chloride with sulfate ions.
Write the simplest ionic equation for the reaction of acidified barium chloride with sulfate ions.
Write the equation for the reaction of sodium bromide with concentrated sulfuric acid and explain why bromide ions react differently from chloride ions.
Write the equation for the reaction of sodium bromide with concentrated sulfuric acid and explain why bromide ions react differently from chloride ions.
Discuss how to prepare a pure sample of silver bromide from a mixture of sodium chloride and sodium bromide.
Discuss how to prepare a pure sample of silver bromide from a mixture of sodium chloride and sodium bromide.
Write an ionic equation for the reaction between chlorine and cold dilute sodium hydroxide solution.
Write an ionic equation for the reaction between chlorine and cold dilute sodium hydroxide solution.
State how to test a sample of water for chloride ions.
State how to test a sample of water for chloride ions.
Deduce the half-equation for the formation of hydrogen sulfide from concentrated sulfuric acid.
Deduce the half-equation for the formation of hydrogen sulfide from concentrated sulfuric acid.
State why silver nitrate solution is acidified when testing for iodide ions.
State why silver nitrate solution is acidified when testing for iodide ions.
Explain why dilute hydrochloric acid is not used to acidify the silver nitrate solution.
Explain why dilute hydrochloric acid is not used to acidify the silver nitrate solution.
Describe the method to prepare a solution containing a known mass of MHCO3.
Describe the method to prepare a solution containing a known mass of MHCO3.
Explain how ions are accelerated, detected and their abundance determined in a TOF mass spectrometer.
Explain how ions are accelerated, detected and their abundance determined in a TOF mass spectrometer.
Write a half-equation for the reduction of chlorate(I) ions to chlorine in acidic conditions.
Write a half-equation for the reduction of chlorate(I) ions to chlorine in acidic conditions.
Write an overall equation for the redox reaction of chlorate(I) ions with hydrochloric acid.
Write an overall equation for the redox reaction of chlorate(I) ions with hydrochloric acid.
What is observed when sodium chlorate(l) is added to potassium iodide?
What is observed when sodium chlorate(l) is added to potassium iodide?
Give one reason why bond enthalpy from your calculations differs from literature values.
Give one reason why bond enthalpy from your calculations differs from literature values.
Suggest improvements to the method and analysis for more accurate enthalpy change determinations.
Suggest improvements to the method and analysis for more accurate enthalpy change determinations.
Write a half-equation for the conversion of NO2 − in an acidic solution into NO.
Write a half-equation for the conversion of NO2 − in an acidic solution into NO.
Write an overall ionic equation for the reaction of NO2 − in an acidic solution with I−.
Write an overall ionic equation for the reaction of NO2 − in an acidic solution with I−.
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Study Notes
Ionisation Energy
- Argon (Ar) in Period 3 has the highest first ionisation energy due to its large number of protons, resulting in a strong nuclear charge, while maintaining the same electron shielding as other elements in the period.
Molecular Shape and Repulsion
- The TlCl2+ ion exhibits a geometry where bond pairs of electrons repel equally to maximize distance between them.
- CF4 has a bond angle of 109.5° because it has four bonding pairs around carbon, which repel equally and are arranged as far apart as possible.
Electron Pair Repulsion Theory
- In PF3, phosphorus (P) has five outer shell electrons, leading to three bonding pairs and one lone pair, resulting in a trigonal pyramidal shape with a bond angle decreased to 107°.
- Lone pairs repel more strongly than bonding pairs.
Melting Points
- Magnesium (Mg) has a higher melting point than sodium (Na) due to Mg2+ having a greater charge compared to Na+, increasing the strength of electrostatic attraction.
- Calcium has a higher melting point than strontium (Sr) because it has delocalised electrons closer to cations, leading to stronger attraction between cations and delocalised electrons.
Reactions with Acids
- Sulfur(IV) oxide (SO2) reacts with water to form hydrogen ions and bisulfite ions: SO2 + H2O → H+ + HSO3-.
- Phosphorus(V) oxide reacts with magnesium oxide: P4O10 + 6MgO → 2Mg3(PO4)2.
- The reaction of magnesium with titanium(IV) chloride yields titanium and magnesium chloride: 2Mg + TiCl4 → 2MgCl2 + Ti.
Ionic Equations
- The simplest ionic equation for the reaction of barium chloride with sulfate ions is: Ba2+ + SO4 2- → BaSO4.
- The half-equation for the formation of hydrogen sulfide from sulfuric acid is: SO4 2− + 10H+ + 8e− → H2S + 4H2O.
Chloride Tests
- Testing for chloride ions involves adding silver nitrate (AgNO3) to yield a white precipitate: Ag+ + Cl− → AgCl.
- To test for iodide ions, silver nitrate is acidified to prevent interference from other ions: HCl adds a precipitate that complicates the test.
Iodide Reaction and Observations
- Sodium bromide reacts with sulfuric acid to form sodium sulfate, bromine, sulfur dioxide, and water: 2NaBr + 2H2SO4 → Na2SO4 + Br2 + SO2 + 2H2O. Bromide ions, larger than chloride ions, are oxidized more readily.
- A solution of sodium chlorate(I) added to potassium iodide turns brown due to the formation of iodine (I2) from the oxidation of iodide ions (I−).
Determining Enthalpy and Bond Enthalpy
- Mean bond enthalpy values can differ from calculated values because they are averaged from various compounds, not just a single type.
- To improve the accuracy of enthalpy measurements, methods can include better insulation, extended temperature recording prior to reaction, and extrapolating data for temperature corrections.
Half-Equations for Reactions
- Reduction of chlorate(I) ions in acidic conditions can be represented as: 2ClO− + 4H+ + 2e− → Cl2 + 2H2O.
- Overall ionic reaction of chlorate(I) ions with hydrochloric acid: ClO− + Cl− + 2H+ → Cl2 + H2O.
Ionic Reactions with NO2 −
- Conversion of nitrate ions (NO2−) in acidic solutions into nitric oxide (NO): NO2− + e− + 2H+ → NO + H2O.
- Overall ionic reaction of NO2− with iodide ions (I−) produces iodine, nitric oxide, and water: 2NO2− + 2I− + 4H+ → I2 + 2NO + 2H2O.
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