Practical work 4: the nitrogen subgroup
Answers are for parents and teachers.
1
How many mol HNO₃ are needed for 80 g CuO (CuO + 2HNO₃ → Cu(NO₃)₂ + H₂O, M(CuO) = 80)?
2 mol
2
In NH₄Cl + NaOH → NaCl + NH₃ + H₂O, how many grams of NH₃ come from 2 mol NH₄Cl?
34 g
3
Write a plan to tell K₂SO₄, NH₄Cl and KNO₃ apart.
BaCl₂ → precipitate with K₂SO₄; NaOH + warming → NH₃ from NH₄Cl; the rest is KNO₃.
4
What are the precipitate colours when AgNO₃ is added to neutralized H₃PO₄ and to HCl?
H₃PO₄ — yellow Ag₃PO₄; HCl — white AgCl.
5
Why must barium salts never be swallowed in practical work?
Soluble barium salts are poisonous.