Question
State the condensed electron configurations for Cr and Cr3+. [2]
Cr:
Cr3+:
Answer/Explanation
Ans:
Cr: [Ar] 4s13d5
Cr3+: [Ar] 3d3
Accept “[Ar] 3d54s1 ”.
Accept “[Ar] 3d34s0 ”. A
ward [1 max] for two correct full electron configurations “1s22s22p63s23p64s13d5 AND 1s22s22p63s23p63d3 ”. Award [1 max] for 4s13d5 AND 3d3
Question
Draw and label an energy level diagram for the hydrogen atom. In your diagram show how the series of lines in the ultraviolet and visible regions of its emission spectrum are produced, clearly labelling each series.
Answer/Explanation
Markscheme
showing y-axis labelled as energy/E / labelling at least two energy levels;
showing a minimum of four energy levels/lines with convergence;
showing jumps to n = 1 for ultraviolet series;
showing jumps to n = 2 for visible light series;
Must show at least two vertical lines per series to score M3 and M4 but penalize once only.
For M3, M4 if transition not shown from higher to lower energy level penalize only once.
Examiners report
Although this generally proved to be the second most difficult question in Section A there were some excellent diagrams with some even linking a correct energy level diagram with a correct line emission spectrum. Candidates in some schools, however, appeared not to have encountered these ideas at all. Common errors were to label the first energy level as n = 0 rather than n = 1 and to only include one transition for each series. Sometimes the arrows showed the absorption rather than the required emission transition.
Question
Titanium is a transition metal.
TiCl4 reacts with water and the resulting titanium(IV) oxide can be used as a smoke screen.
Describe the bonding in metals.
Titanium exists as several isotopes. The mass spectrum of a sample of titanium gave the following data:
Calculate the relative atomic mass of titanium to two decimal places.
State the number of protons, neutrons and electrons in the \({}_{22}^{48}{\text{Ti}}\) atom.
State the full electron configuration of the \({}_{22}^{48}{\text{Ti}}\)2+ ion.
Explain why an aluminium-titanium alloy is harder than pure aluminium.
State the type of bonding in potassium chloride which melts at 1043 K.
A chloride of titanium, TiCl4, melts at 248 K. Suggest why the melting point is so much lower than that of KCl.
Formulate an equation for this reaction.
Suggest one disadvantage of using this smoke in an enclosed space.
Answer/Explanation
Markscheme
electrostatic attraction
between «a lattice of» metal/positive ions/cations AND «a sea of» delocalized electrons
Accept mobile electrons.
Do not accept “metal atoms/nuclei”.
[2 marks]
\(\frac{{(46 \times 7.98) + (47 \times 7.32) + (48 \times 73.99) + (49 \times 5.46) + (50 \times 5.25)}}{{100}}\)
= 47.93
Answer must have two decimal places with a value from 47.90 to 48.00.
Award [2] for correct final answer.
Award [0] for 47.87 (data booklet value).
[2 marks]
Protons: 22 AND Neutrons: 26 AND Electrons: 22
[1 mark]
1s22s22p63s23p63d2
[1 mark]
titanium atoms/ions distort the regular arrangement of atoms/ions
OR
titanium atoms/ions are a different size to aluminium «atoms/ions»
prevent layers sliding over each other
Accept diagram showing different sizes of atoms/ions.
[2 marks]
ionic
OR
«electrostatic» attraction between oppositely charged ions
[1 mark]
«simple» molecular structure
OR
weak«er» intermolecular bonds
OR
weak«er» bonds between molecules
Accept specific examples of weak bonds such as London/dispersion and van der Waals.
Do not accept “covalent”.
[1 mark]
TiCl4(l) + 2H2O(l) → TiO2(s) + 4HCl(aq)
correct products
correct balancing
Accept ionic equation.
Award M2 if products are HCl and a compound of Ti and O.
[2 marks]
HCl causes breathing/respiratory problems
OR
HCl is an irritant
OR
HCl is toxic
OR
HCl has acidic vapour
OR
HCl is corrosive
Accept “TiO2 causes breathing problems/is an irritant”.
Accept “harmful” for both HCl and TiO2.
Accept “smoke is asphyxiant”.
[1 mark]