Al2O3+6HNO3=2Al(NO3)3+3H2O
m(HNO3)раствора=V*p=281*1.031=289.711
m(HNO3)вещества=m(HNO3)раствора*w=289.711*0.063=18.25
n(HNO3)=m/M=18.25/63=0.3
n(Al(NO3)3)=n(HNO3)/3=0.3/3=0.1
m(Al(NO3)3)=n*M=0.1*213=21.3
n(Al2O3)=n(HNO3)/6=0.3/6=0.05
m(Al2O3)=n*M=0.05*102=5.1
mраствора=m(HNO3)раствора+m(Al2O3)=289.711+5.1=294.8
w(Al(NO3)3)=m(Al(NO3)3)/mраствора=21.3/294.8=0.072 или 7,2%