CHEMISTRY HIGHER
Answer all questions. LEVEL
Answers must PAPER
be written within 2 boxes
the answer MAY 2021
provided.
1.a) Automobile air bags inflate by a rapid decomposition reaction. One typical
compound used is guanidinium nitrate, C(NH2)3NO3, which decomposes very rapidly
to form nitrogen, water vapour and carbon. Deduce the equation for the
decomposition of guanidinium nitrate. [1]
. C(NH2)3NO3 (s) → 2N2 (g) + 3H2O (g) + C (s) ✔
b) Calculate the total number of moles of gas produced from the decomposition of
10.0 g of guanidinium nitrate.
[1]
10.0 g
moles of gas = « 5 × =¿ » 0.409 «mol» ✔
122.11 g mo l−1
c) Calculate the pressure, in kPa, of this gas in a 10.0 dm3 air bag at 127°C, assuming
no gas escapes. [1]
d) Suggest why water vapour deviates significantly from ideal behaviour when the
gases are cooled, while nitrogen does not.
[2]
Any two of:
nitrogen non-polar/London/dispersion forces AND water polar/H-
bonding ✔
water molecules attract/condense/occupy smaller volume «and
therefore deviate from ideal behaviour» ✔
Must mention the different type of intermolecular forces in water and nitrogen
e) Another airbag reactant produces nitrogen gas and sodium.
2
,Suggest, including an equation, why the products of this reactant present a safety
hazard. [2]
2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g) ✔
hydrogen explosive
OR
highly exothermic reaction
OR
sodium reacts violently with water
OR
forms strong alkali ✔
NOTE: Accept the equation of combustion of hydrogen.
Do not accept just “sodium is reactive/dangerous
2. a) Compound A is in equilibrium with compound B.
Predict the electron domain and molecular geometries around the oxygen atom of
molecule A using VSEPR.
[2]
Electron domain geometry: tetrahedral ✔
Molecular geometry: bent/V-shaped ✔
b) The equilibrium constant, Kc, for the conversion of A to B is 1.0×108 in water
at 298K.
Deduce, giving a reason, which compound, A or B, is present in greater
concentration when equilibrium is reached.
[1]
B AND Kc is greater than 11/large ✔
3a) Hydrochloric acid reacts with manganese dioxide to release chlorine gas.
3
, State the full electronic configuration of Manganese atom.
[1]
Mn: 1s22s22p63s23p64s23d5
b) State, giving a reason, whether the chlorine atom or the chloride ion has a larger
radius. [1]
−¿¿
Cl AND more «electron–electron» repulsion ✔
c) Outline why the chlorine atom has a smaller atomic radius than the sulfur atom.
[2]
Cl has a greater nuclear charge/number of protons/ Z eff «causing a stronger pull on the
outer electrons» ✔
same number of shells
OR
same «outer» energy level
OR
similar shielding ✔
d) The mass spectrum of chlorine is shown
4
Answer all questions. LEVEL
Answers must PAPER
be written within 2 boxes
the answer MAY 2021
provided.
1.a) Automobile air bags inflate by a rapid decomposition reaction. One typical
compound used is guanidinium nitrate, C(NH2)3NO3, which decomposes very rapidly
to form nitrogen, water vapour and carbon. Deduce the equation for the
decomposition of guanidinium nitrate. [1]
. C(NH2)3NO3 (s) → 2N2 (g) + 3H2O (g) + C (s) ✔
b) Calculate the total number of moles of gas produced from the decomposition of
10.0 g of guanidinium nitrate.
[1]
10.0 g
moles of gas = « 5 × =¿ » 0.409 «mol» ✔
122.11 g mo l−1
c) Calculate the pressure, in kPa, of this gas in a 10.0 dm3 air bag at 127°C, assuming
no gas escapes. [1]
d) Suggest why water vapour deviates significantly from ideal behaviour when the
gases are cooled, while nitrogen does not.
[2]
Any two of:
nitrogen non-polar/London/dispersion forces AND water polar/H-
bonding ✔
water molecules attract/condense/occupy smaller volume «and
therefore deviate from ideal behaviour» ✔
Must mention the different type of intermolecular forces in water and nitrogen
e) Another airbag reactant produces nitrogen gas and sodium.
2
,Suggest, including an equation, why the products of this reactant present a safety
hazard. [2]
2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g) ✔
hydrogen explosive
OR
highly exothermic reaction
OR
sodium reacts violently with water
OR
forms strong alkali ✔
NOTE: Accept the equation of combustion of hydrogen.
Do not accept just “sodium is reactive/dangerous
2. a) Compound A is in equilibrium with compound B.
Predict the electron domain and molecular geometries around the oxygen atom of
molecule A using VSEPR.
[2]
Electron domain geometry: tetrahedral ✔
Molecular geometry: bent/V-shaped ✔
b) The equilibrium constant, Kc, for the conversion of A to B is 1.0×108 in water
at 298K.
Deduce, giving a reason, which compound, A or B, is present in greater
concentration when equilibrium is reached.
[1]
B AND Kc is greater than 11/large ✔
3a) Hydrochloric acid reacts with manganese dioxide to release chlorine gas.
3
, State the full electronic configuration of Manganese atom.
[1]
Mn: 1s22s22p63s23p64s23d5
b) State, giving a reason, whether the chlorine atom or the chloride ion has a larger
radius. [1]
−¿¿
Cl AND more «electron–electron» repulsion ✔
c) Outline why the chlorine atom has a smaller atomic radius than the sulfur atom.
[2]
Cl has a greater nuclear charge/number of protons/ Z eff «causing a stronger pull on the
outer electrons» ✔
same number of shells
OR
same «outer» energy level
OR
similar shielding ✔
d) The mass spectrum of chlorine is shown
4
