Chemistry questions I got wrong

• Chlorine has a low boiling point because the forces between the molecules are weak.

  Explain how these forces arise between molecules of chlorine.

  (Random) Movement of electrons in one molecule (creates a dipole).

  Induces dipole in a neighbouring molecule.

  (These) Temporary dipoles attract
• Describe the structure and bonding in magnesium

  Giant lattice of Mg atoms

  Electrostatic attractions between nuclei and delocalised electrons
• State the trend in atomic radius of the elements down group 2 from Mg to Ba.

  Give a reason for this trend

  Trend: atomic radius increases

  Reason: number of electron energy levels increases
• Give an equation, including state symbols for the reaction of magnesium with steam.

  State two observations for this reaction.

  Equation:

  Mg(s) + H2O(g) -> MgO(s) + H2

  Observation 1: bright white flame

  Observation 2: white powder
• Why do the electron pairs in CF4 repel each other?

  To be as far apart as possible
• How are the lone pairs arranged in XeF4?

  As far apart as possible
• What are the key differences in the shapes and bond angles of CF4 and XeF4?

  • CF4:
  • Shape: Tetrahedral
  • Bond angle: 109.5°
  • Four bonding pairs, no lone pairs
  • XeF4:
  • Shape: Square planar
  • Bond angle: 90°
  • Four bonding pairs, two lone pairs
• Explain why electronegativity of the halogens decreases down the group

  Larger atoms so weaker attraction between nucleus and bonding pair of electrons
• Concentrated sulfuric acid reacts with solid sodium chloride and with solid sodium bromide.

  State one similarity in, and one difference between these reactions.

  Similarity: misty White fumes are observed

  Difference: red-brown-orange fumes are observed with bromide
• Give a half equation to show the oxidation of iodide ions

  2I- —> I2 + 2e-
• Give a half equation to show the reduction of concentrated sulfuric acid to hydrogen sulfide

  H2SO4 + 8H+ + 8e- —> H2S + H2O
• State the meaning of the term electron impact ionisation

  High energy electrons are used to knock out an electron
• State how ions are detected, and how the abundance of each ion is measured in a TOF mass spectrometer

  How ions are detected: ions hit a detector and each ion gains an electron generating a current

  How abundance is measured: the abundance is proportional to the size of the current
• The temperature of a (forward exothermic) equilibrium mixture is decreased.

  Predict the effect on the value of Kc and give a reason.

  Prediction: Kc increases

  Reason: equilibrium shifts in the exothermic direction to increase the temperature
• Explain how the value of the Cl-Al-Cl bond angle in AlCl3 changes if at all on formation of the compound H3NAlCl3

  Aluminium is now surrounded by 4 pairs of electrons.

  Therefore Cl-Al-Cl bond angle decreases
• Give reason why the bond enthalpy you calculated is different from the mean bond enthalpy quoted in a data book (388jkmol-1)

  Data book value derived from different compounds
• Give the meaning of the term electronegativity

  Power of an atom to attract a pair of electrons
• Suggest two reasons why the sulfur dioxide by-product of this process is removed from the exhaust gases

  Causes acid rain

  Is toxic
• Give the oxidation state of nitrogen in the following species

  NO2-: +3

  NO: +2
• Write a half equation for the conversion of NO2- in an acidic solution into NO


  NO2-+ e- + 2 H+ —› NO + H2O
• Describe how the molecules are ionised using electrospray ionisation

  Molecules are dissolved in a volatile solvent then shot through a fi e hypodermic needle at a positive charge, molecules gain an electron
• Explain the patterns in the first ionisation energies of the elements from lithium to neon

  • 1st IE increases
  • More protons
  • Electrons in same energy level
  • No extra shielding
  • Stronger attraction between nucleus and outer e-
  • Be —> B
  • B lower than Be
  • Outer electron than in 2p
  • Higher energy than 2s
  • N —> O
  • O lower than N
  • 2 electrons in 2p need to pair
  • Pairing causes repulsion
• Give an equation for the reaction between titanium(IV) chloride and magnesium. State the role of magnesium.

  Equation: 2Mg + TiCl4 —> Ti + 2MgCl2

  Role of magnesium: reducing agent
• concentrated sulfuric acid reacts with solid sodium chloride and with solid sodium bromide. state one similarity in and one difference between these reactions

  similarity: Hydrogen halides formed difference: different hydrogen halides
• what are the four stages of a mass spectrometer


  1. ionisation 2. acceleration 3. deflection 4. detection
• define the term relative atomic mass

  relative atomic mass is the average mass of all isotopes of an element relative to 12C
• explain the term isotopes

  isotopes are variations of an element with different numbers of neutrons
• Predict the effect of increasing the temperature on the yield of propanoic acid

  effect on yield: decrease yield explanation: the forward reaction is exothermic so increasing the temperature would make the equilibrium shift to the left as it goes to the side with the lower temperature, therefore the yield decreases
• a second organic product, X, is formed in small quantities. The boiling point of X is 49°C. Identify X

  propanal
• explain why compound K is a major product in the reaction

  1. K formed from a more stable carbocation 2) Major product from tertiary carbocation 3) Stability from greater inductive groups
• Acidified potassium dichromate (VI) is used as the oxidising agent (added to propanoic acid) state the colour change in this reaction


  Orange ---> green
• although the C-Cl bond is polar, CCl4 is a non-polar molecule


  symmetrical molecule, so the dipoles cancel out
• there are van Der Waals forces between non-polar molecules. explain what causes these forces


  temporary dipoles are formed induces a dipole in another molecule temporary dipoles in different molecules attract between δ- and δ+ the atoms in different molecules
• explain why the C-Cl bond is polar 


  Cl is more electronegative than carbon making Cl δ+ and C δ- (electron density is uneven)
• Define electronegativity 


  relative ability to attract a pair of electrons in a covalent bond
• Explain in terms of oxidising ability why the observations from these reactions do not allow the student to identify the halide ion present in P and the halide ion present in R


  one is a better oxidising agent than the other, oxidizing ability is being able to remove an electron
• Identify the halide ion present in Q Give the ionic equation that occurs when bromine water is added to Q


  Halide Ion in Q: Iodide ionic equation: Br2 + 2I- + BrH -> IH + Br
• Give two features of a reaction in equilibria


  1. Forward and reverse reactions proceeding at equal rates
  2. concentrations remain constant
• The equilibrium mixture is compressed into a smaller volume.

  Deduce the effect of this change on the equilibrium yield of oxygen and the value of Kp 


  Effect on yield of oxygen: decrease yield

  Effect on Kp: no effect
• The equilibrium mixture is allowed to reach equilibrium at a lower temperature.

  Explain why the equilibrium yield of oxygen decreases


  The forward reaction is endothermic;

  equilibrium shifts in the direction to oppose the decrease in temperature