2. Test for Cu2+,Ag+1,Zn2+ and Al3+ 6MHCl is added to a solution that may contain four ions (Cu2+,Ag+1,Zn2+ and Al3+). No precipitate forms. The addition of 6MNaOH until the solution is basic results in no formation of precipitate. Ions present: Ions absent: lons undetermined: 3. Test for Cu+2,Fe+3, and Al3+ 6MNaOH is added to a clear solution that may contain the three ions (Cu+2,Fe+3, and Al3+) until the solution is basic. A dark precipitate forms. The precipitate totally dissolves in 6M H2SO4. The addition of 6MNH3 to this acidic solution until it is basic results in a clear, colorless solution containing a dark precipitate. The dark precipitate completely dissolves in 6MHCl. Ions present: Ions absent: lons undetermined: Why are confirmatory tests necessary