m(Cu)=19.2=>n(Cu)=0.03mol
Cu~Cu(NO3)2·xH2O
0.03
m[Cu(NO3)2·xH2O]=56.4+5.4x
x=0,m=56.4
x=1,m=61.8
x=2,m=67.2
x=3,m=72.6
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x=n,m=56.4+5.4n(n是正整数)