What substances will increase the molar solubility of nickel(II) phosphate in a saturated solution?

To determine the substances that can increase the molar solubility of nickel(II) phosphate in a saturated solution, we need to consider the common ion effect and the pH of the solution.

The molar solubility of a compound can be increased by adding a substance that either forms a complex with the metal ion or has a common ion with one of the ions in the compound.

In the case of nickel(II) phosphate (Ni3(PO4)2), it dissociates into Ni2+ ions and PO43- ions in water.

To increase the molar solubility of nickel(II) phosphate, we can do the following:

1. Complex-forming agents: Adding substances that can form complex ions with the Ni2+ ions can increase the solubility. For example, adding ammonia (NH3) as a complexing agent can form the ammine complex of nickel [Ni(NH3)6]2+, which increases the solubility of nickel ions.

2. Acidic conditions: Adjusting the pH of the solution can also affect the solubility of nickel(II) phosphate. Since nickel(II) phosphate contains phosphate ions (PO43-), which are basic, decreasing the pH of the solution by adding an acid like hydrochloric acid (HCl) can protonate the PO43- ions, forming HPO42- or H2PO4- ions. These protonated forms are more soluble than the original phosphate ions, leading to an increase in the overall solubility.

It is important to note that adding too much of these substances may also cause precipitation or the formation of new solid compounds, so the concentrations and stoichiometric ratios should be carefully considered to ensure increased solubility without unwanted side reactions.

In summary, adding complex-forming agents like ammonia or adjusting the pH of the solution using an acid can increase the molar solubility of nickel(II) phosphate.