please answer all 4 questions. I need brief and correct answers. thank you in advance.
1. Why is it important to mix the solutions after adding the reagents? How is mixing done in this experiment?
2. What is the reason for rinsing the precipitates before further testing?
3. What two things are extremely important to remember when centrifuging?
4. Why is it possible to separate Cu+2 from Al+3 and Fe+3 with NH4OH but not with NaOH? (Hint, consider solubility properties.)
1. Mixing of solutions after adding reagents is done to ensure homogeneity. The reaction must proceed under kinetic control with no major issues related to mixing.
2. The settling precipitate attracts ions and some dissociated compounds to its surface by Vanderwaal's and other forces. Rinsing the precipitate with water or other low ionicity solvent removes the ions or impurities from its surface.
a) The work surface must be level and firm.
b) Balance the tubes in the rotor by putting additional tube with same mass of water in the opposing hole on the rotor.
4. Addition of NH4OH at first produces Cu(OH)2(s), Al(OH)3(s), and Fe(OH)3(s). Further addition of NH4OH produces water soluble Cu(NH3)42+ but does not dissolve the other two hydroxides. Addition of NaOH produces the three hydroxides and further addition of NaOH would produce soluble NaAl(OH)4(aq), but would leave Cu(OH)2(s) and Fe(OH)3(s) together in the solution.