1)
2Al + 3H2SO4 = Al2(SO4)3 + 3H2↑
2Al + 6H[+] + 3SO4[2-] = 2Al[3+] +3SO4[2-] + 3H2↑
2Al + 6H[+]= 2Al[3+] + 3H2↑
2)
Al2O3 + 6HCl = 2AlCl3 + 3H2O
Al2O3 + 6H[+] + 6Cl[-] = 2Al[3+] + 6Cl[-] + 3H2O
Al2O3 + 6H[+]= 2Al[3+] + 3H2O
3)
Al2(SO4)3 + 3BaCl2 = 3BaSO4↓ + 2AlCl3
Al[3+] + 3SO4[2-] + 3Ba[2+] + 6Cl[-] = 3BaSO4↓ + 2Al[3+] + 6Cl[-]
3Ba[2+] + 3SO4[2-] = 3BaSO4↓
4)
Al(OH)3 + 3HNO3 = Al(NO3)3 + 3H2O
Al(OH)3 + 3H[+] + 3NO3[-] = Al[3+] + 3NO3[-] + 3H2O
Al(OH)3 + 3H[+] = Al[3+] + 3H2O