O-LevelChemistryRates of Reaction5070/21 · May/June 2021 · Q710 Marks
Aqueous ammonium nitrite, NH4NO2(aq), decomposes when heated, as shown. NH4NO2(aq) → N2(g) + 2H2O(l)
- (a)A 25.0 cm³ sample of 0.150 mol/dm³ NH4NO2(aq) is heated. Calculate the maximum volume, in dm³, of nitrogen formed, measured at room temperature and pressure.[2]
- (b)The concentration of NH4NO2(aq) is decreased. The temperature of the reaction remains constant. State and explain how the rate of reaction changes.[3]
- (c)NH4NO2 contains the ammonium ion, NH4+, and the nitrite ion. A mixture of aqueous calcium hydroxide and NH4NO2(s) is warmed. Calcium nitrite, water and a gas are formed. The gas turns damp red litmus paper blue. Construct the equation for this reaction.[3]
- (d)NH4NO2(aq) is added to a sample of aqueous potassium iodide. A brown solution is formed.
- (d)(i)Name the brown solution.[1]
- (d)(ii)Name the type of reaction that causes this brown solution to form.[1]
Mark scheme
Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.
- 7(a) moles of NH4NO2 = 0.00375 (1)
- 7(a) volume = 0.09 (dm³) (1)
- 7(b) decreased (1)
- 7(b) less crowded particles / less particles per unit volume / greater space between particles (1)
- 7(b) collision frequency decreases / fewer collisions per second / decrease rate of collisions (1)
- 7(c) 2NH4NO2 + Ca(OH)2 → 2NH3 + Ca(NO2)2 + 2H2O
- 7(c) correct identification of ammonia as a product (1)
- 7(c) correct formula for calcium nitrite (1)
- 7(c) balanced equation (1)
- 7(d)(i) (aqueous) iodine
- 7(d)(ii) oxidation
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