② Iron can replace copper in Cu(NO3)2 solution and generate ferrous nitrate at the same time. The chemical equation of this reaction is: Fe+Cu (NO3) 2 ═ Cu+Fe (NO3) 2.
(4) group a: let the mass of zinc be x.
Zn+2HCl═ZnCl2+H2↑
652
x？ 0.02 g
65x = 20.02g
Solution: x = 0.65g
So the mass fraction of copper is: 7.4g? 0.65g 7.4g× 100% = 9 1.2%
Group B: the mass fraction of copper is 6.66g7.4g× 100%=90%. % = 90%.
(5) Reflection and evaluation: According to the consulted data, the alloy has a compact structure, and only a part of zinc contained in it reacts with hydrochloric acid, so it can be judged that classmate A's scheme is unreasonable.
So the answer is: (2) Zn+2HCl ═ ZnCl2+H2 ↑;
②Fe+Cu(NO3)2═Cu+Fe(NO3)2.
(4)9 1.2%; 90%.
(5) a classmate; The alloy has a compact structure, in which only part of zinc reacts with hydrochloric acid.