Which of the following anions would precipitate the most in the reaction of sodium salts with magnesium chloride? What could be done to increase the solubility of the precipitate?

#a)# #"SO"_4^(2-)#
#b)# #"HCO"_3^(-)#
#c)# #"CO"_3^(2-)#
#d)# #"NO"_3^(-)#

Question

#a)# #"SO"_4^(2-)#
#b)# #"HCO"_3^(-)#
#c)# #"CO"_3^(2-)#
#d)# #"NO"_3^(-)#

Naomi Aronson · Accepted Answer

Most likely sulfate, but you would need to conduct your own experiment to be sure.

And the source of this response is...

#"Na"_2"SO"_4(aq) + "MgCl"_2(aq) -> "NaCl"(aq) + "MgSO"_4(s)#

#s_(MgSO_4) ~~ "35.1 g/100 mL water"# at #25^@ "C"#

which is fairly high. However, in contrast to popular belief, the solubility decreases upon boiling.

One of the few examples that I can think of that becomes less soluble at higher temperatures is magnesium sulfate. You can read more about this here, but in summary...

Increasing the temperature for #"MgSO"_4(aq)# shifts the equilibrium between crystallization and [dissolution + solvation], towards crystallization, because its dissolution process is exothermic. #DeltaH ~~ -"91.2 kJ/mol"#.

Regarding the others...

#s_(Mg(HCO_3)_2) = "0.077 g/100 mL water"# at #25^@ "C"#

#s_(MgCO_3) = "0.0139 g/100 mL water"# at #25^@ "C"#

#s_(Mg(NO_3)_2) = "large"# at #25^@ "C"#

And it's evident that the first two precipitate at room temperature and pressure. Where did I find this information on Wikipedia?

Ellie Andrews · Answer

undefined Sulfate. Increase temperature or add a more soluble cation.

Which of the following anions would precipitate the most in the reaction of sodium salts with magnesium chloride? What could be done to increase the solubility of the precipitate?

#a)# #"SO"_4^(2-)# #b)# #"HCO"_3^(-)# #c)# #"CO"_3^(2-)# #d)# #"NO"_3^(-)#

#a)# #"SO"_4^(2-)#
#b)# #"HCO"_3^(-)#
#c)# #"CO"_3^(2-)#
#d)# #"NO"_3^(-)#