Problem: For which salt in each of the following groups will the solubility depend on pH?i) NaF, NaBrii) Ba(ClO4)2 , Ba(ClO2)2iii) Ca(OH)2, CaI2iv) Fe(NO3)2, Fe(CN)2

FREE Expert Solution

We are asked which of the following salts in each pair would the solubility depend on pH?

The salt will only depend on the pH if it has an ion that is a conjugate base of a weak acid or a conjugate acid of a weak base.


Recall:

A conjugate base is simply the part of the molecule left after removing an H+.

A conjugate acid is simply the molecule after adding an H+.


Weak acids are weak electrolytes that don’t completely ionize but instead reach a state of equilibrium. 


However, it’s easier to identify strong acids than familiarize yourself with all the weak acids (since the common strong acids have rules and are relatively fewer).


Strong acids are considered strong electrolytes. They completely dissociate into ions when dissolved in water.

Strong binary acids – paired with a highly electronegative atom

Strong binary acids are:              HCl, HBr, and HI

Strong oxyacids (or oxoacids) - have 2 or more oxygens than hydrogens

Oxyacids → possess H+ ion, connected to nonmetal and oxygen

Common strong oxyacids are:                  HNO3, HClO3, HClO4, H2SO4

Exceptions to the rule are:                            Oxalic acid (H2C2O4and Iodic acid (HIO3)

▪ both have 2 more O than H but are weak acids because carbon and iodine have low electronegativity


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Problem Details

For which salt in each of the following groups will the solubility depend on pH?

i) NaF, NaBr

ii) Ba(ClO4)2 , Ba(ClO2)2

iii) Ca(OH)2, CaI2

iv) Fe(NO3)2, Fe(CN)2

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