O-LevelChemistryStoichiometry5070/21 · May/June 2017 · Q710 Marks
Copper reacts with concentrated nitric acid. Cu(s) + 4HNO₃(aq) → Cu(NO₃)₂(aq) + 2NO₂(g) + 2H₂O(l)
- (a)Suggest what you would observe when copper reacts with concentrated nitric acid.[1]
- (b)(i)Suggest the name of the salt of formula Cu(NO₃)₂.[1]
- (b)(ii)Copper is oxidised when it reacts with concentrated nitric acid. Use the equation to explain that copper has been oxidised.[1]
- (c)An excess of copper is added to 25.0 cm³ of 16.0mol/dm³ HNO₃. Use this information, together with the equation above, to calculate the volume of NO₂ formed. The gas volume is measured at room temperature and pressure. volume of NO₂ = ................................................................[3]
- (d)When heated, Cu(NO₃)₂ decomposes to form CuO, NO₂ and O₂. Construct the equation for this reaction.[1]
- (e)(i)To a sample of Cu(NO₃)₂(aq), a student adds aqueous ammonia drop by drop until it is in excess. Describe what is observed.[2]
- (e)(ii)The student repeats the experiment but adds aqueous sodium hydroxide instead of aqueous ammonia. Describe what is observed.[1]
Mark scheme
Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.
- B7(a) Blue solution / brown gas / gas bubbles / metal disappears (1)
- B7(b)(i) Copper(II) nitrate (1)
- B7(b)(ii) Copper loses electron(s) (1)
- B7(c) Moles of acid = 0.025 × 16 OR 0.4 (1)
- Moles of NO2 = 0.2 (1)
- Volume of NO2 = 4.8 dm³/4800 cm³ (1)
- B7(d) 2Cu(NO3)2 2CuO + 4NO2 + O2 (1)
- B7(e)(i) Blue precipitate / blue solid (1)
- In excess becomes a dark blue solution (1)
- B7(e)(ii) Blue precipitate / blue solid (which does not redissolve) (1)
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