A student adds sodium hydroxide, a little at a time and then in excess, to nine different solutions…

Contributed by StemPy Lab

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

A student adds sodium hydroxide, a little at a time and then in excess, to nine different solutions of the cations lead(II), copper(II), aluminium, iron(III), zinc, nickel(II), cobalt(II), manganese(II) and magnesium. Every one gives a precipitate first. The student then repeats the experiment with ammonium hydroxide. Use the facts in the reminder. Count five numbers. First, the precipitates that dissolve in excess sodium hydroxide. Second, those that dissolve in excess ammonium hydroxide. Third, those that do both. Fourth, those that do either. Fifth, those that do neither.

Need a reminder? The key ideaShow

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

← All Problems

← A solution holds seven cations at once: lead(II), copper(II), iron(III), zinc, nickel(II), barium…A solution holds 0.0200 mol of iron(III) ions… →

More onPrinciples Related to Practical Chemistry

Discussion (0)

Loading…

The group scheme is: zero $\text{NH}_4^+$ ; I $\text{Pb}^{2+}$ ; II $\text{Cu}^{2+}$ ; III $\text{Fe}^{3+}$ , $\text{Al}^{3+}$ ; IV $\text{Zn}^{2+}$ , $\text{Ni}^{2+}$ , $\text{Co}^{2+}$ , $\text{Mn}^{2+}$ ; V $\text{Ca}^{2+}$ , $\text{Ba}^{2+}$ ; VI $\text{Mg}^{2+}$ . Zinc, aluminium and lead hydroxides dissolve in excess sodium hydroxide. Copper, nickel, zinc and cobalt hydroxides dissolve in excess ammonium hydroxide as ammines. Iron(III) and hexacyanoferrate(II) make Prussian blue: $4\ \text{Fe}^{3+} + 3\ [\text{Fe(CN)}_6]^{4-} \rightarrow \text{Fe}_4[\text{Fe(CN)}_6]_3$ .